CA1050298A - Photometric system with conical flow cell - Google Patents
Photometric system with conical flow cellInfo
- Publication number
- CA1050298A CA1050298A CA226,424A CA226424A CA1050298A CA 1050298 A CA1050298 A CA 1050298A CA 226424 A CA226424 A CA 226424A CA 1050298 A CA1050298 A CA 1050298A
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- CA
- Canada
- Prior art keywords
- cell
- liquid
- flow
- sample
- photometer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000007788 liquid Substances 0.000 claims abstract description 68
- 230000000694 effects Effects 0.000 claims abstract description 19
- 230000005855 radiation Effects 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 11
- 230000006872 improvement Effects 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 8
- 230000003247 decreasing effect Effects 0.000 claims description 4
- 238000001514 detection method Methods 0.000 claims description 3
- 230000031700 light absorption Effects 0.000 claims description 2
- 238000005259 measurement Methods 0.000 claims description 2
- 238000010521 absorption reaction Methods 0.000 abstract description 5
- 210000004027 cell Anatomy 0.000 description 48
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 12
- 239000012530 fluid Substances 0.000 description 10
- 239000000243 solution Substances 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 6
- 238000002347 injection Methods 0.000 description 4
- 239000007924 injection Substances 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000004587 chromatography analysis Methods 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000011010 flushing procedure Methods 0.000 description 2
- GBMDVOWEEQVZKZ-UHFFFAOYSA-N methanol;hydrate Chemical compound O.OC GBMDVOWEEQVZKZ-UHFFFAOYSA-N 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000003643 water by type Substances 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000000149 argon plasma sintering Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000003339 best practice Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 210000002421 cell wall Anatomy 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000009850 completed effect Effects 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000011067 equilibration Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 238000004811 liquid chromatography Methods 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/85—Investigating moving fluids or granular solids
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Optical Measuring Cells (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Novel photometric apparatus having a conical shaped flow-cell comprising a light source proximate the narrow end and a photosensitive detector at the wider end of the cell. The flow-cell adequately compensates for or avoids a lens effect that has been discovered to be a substantial factor in electro-magnetic energy absorption studies on liquid streams.
Novel photometric apparatus having a conical shaped flow-cell comprising a light source proximate the narrow end and a photosensitive detector at the wider end of the cell. The flow-cell adequately compensates for or avoids a lens effect that has been discovered to be a substantial factor in electro-magnetic energy absorption studies on liquid streams.
Description
lOSOZ98 This invention relates to an improvement in photometric measuring systems.
In analysis of very small quantities of liquids, it has been recognized that the physical conditioning of the fluid must be done very carefully. Thus, ~or example, in the field of liquid chromatography wherein very small, continuously-flowing streams of liquid are measured, care is taken to minimize mechanical and thermal disturbance of the liquid stream between the chromatographic column and analytical apparatus in which the liquid stream from the column is to be continuously analyzed. The primary objective is to present, to a transparent sample cell, the precise sequence of changing liquid composition that leaves the chromatography column.
The rationale and particulars of such apparatus are described in the art. For example, see United States Patent 3,674,373 to Waters, Hutchins and Abrahams which involves a refractometer particularly well adapted to receive such a liquid stream. In general, the approach is to minimize the conduit path through which the liquid to be analyzed must travel and to provide a ~' .
maximum thermal-conditioning of the liquid within such a minimized path. This generally illustrates the art-recognized importance of careful handling of sample liquid between its point of origin and the sample cell in which it is to be 5 ' subjected to analysis, usually analysis which measures an effect of the sample liquid stream on some radiation directed into a flow-cell through which the stream passes.
Investigators have also realized that some attention must be given to the physical condition of the fluid even after it enters the flow-cell. Consequently, flow-cells have been made ever smaller to avoid mixing and peak-spreading effects and, in some cases, a positive thermal equilibration of the cell with the liquid has been sought in order to avoid ' light-shimmering effects along the cell walls. Moreover, the cells are usually positioned with outlets so placed that any entrained gas bubbles tend to be carried upwardly out of the cell. It is noted that U.S. Patent 3,666,941 to Watson describes a conical bifurcated cell wherein the , larger end of the cell faces the light source, thereby forming means to gather a maximum amount of fluorescence-exciting radiation. Applicant's discovery, to be detailed below, is based upon a major improvement in flow-cell construction which solves a problem quite different than that described by Watson but which, like Watson's apparatus, is 25 I particularly useful in combination with liquid chromotograhy applications.
'. I
.
., . _ !
1050~98 A recent patent, U.S. Patent 3,792,929, to Alpert, it has been noted, seems to disclose a conical sample-holding cell. I
The patent related to static-sample devices and in no way involves fluid lenses of any type; although the patent came to the atten- ¦
tion of the instant inventor after an error resulted in the word "field" appearing as "fluid" in the title of the Alpert patent.
Moreover, the apparent and relative dimensions of the Alpert cell would not allow its effective use in most continuous-flow 1 monitoring systems such as are encountered in liquid chromato-; graphic work and the like.
! SummarY of the Invention It is an object of present invention to provide an improved liquid chromatographic system of the type utilizing ¦
a photometric analytical means.
It is a further object of the invention to provide a means for operating a photometric process whereby it is possible ! to minimize the size of sample volume of a flow cell without unduly affecting the performance of the photometer.
Another object of the invention is to provide a novel process of analyzing liquid by photometric methods and a novel photometer for carrying out such analysis. I
Another object of the invention is to provide a novel and improved sample-receiving flow-cell.
Other objects of the invention will be obvious to ` those skilled in the art on reading the instant disclosure.
~ 42-041 ~050298 The above invention is based on the discovery that substantial spurious radiation signals are generated by a lens-type effect caused by laminar-flow patterns at the interface of compositions differing in refractive index; the effect is particularly troublesome in small cylindrical photometer sample-cells. These laminar flow patterns will sometimes be called "dynamic liquid lenses" in this description. In general the worst problems have been encountered in flow-cells in the microliter range, say flow-cells having a diameter of less than ~ about 2 millimeters. In the usual situation the flow path of an ultra violet absorptometer cell is selected to be one centimeter in length, and a flow cell of 2 millimeters maximum diameter will have a volume of less than about 32 microliters.
As the diameter increases the lens effect caused by a given rate of laminar-flow tends to decrease; but a mere increase in diameter of a cylindrical flow path to avoid the lens effect is not practical because the increased diameter would result in either (1) a large increase in the volume of the tube or (2) a substantial decrease in length of the tube.
A large increase in volume is untenable because the ability ;j of the apparatus to detect very small samples would be substantially limited by dilution factors. The length of the cell cannot be mar}cedly reduced without proportionately decreas-ing the magnitude of light absorbed by a given solution flowing through a cell. Still other conceivable tube configurations would give disadvantageous liquid flow patterns.
, _ 42-041 lOSOZ98 Because the problem of these dynamic fluid lenses is primarily encountered at the point of changing compositions, its solution has been found io enhance both the quantitative and ¦
qualitative analytical capabilities of liquid chromatographic systems and like analytical systems where constantly changing compositions are inherent in the method. However, the apparatus is useful in other lens-inducing situations encountered in the process industry; e.g., where the dynamic fluid lens may be induced by temperature change or other phenomena that result in ; formation of a refractive index gradient within the flow-cell.
On discovering the nature of the problem associated with such small flow-cells, applicant has devised a simple con-structional solution which substantially eliminates the problem:
I; he has provided a flow-cell whereby the lens effect is rapidly dissipated by a progressive increase in the crossectional area of the flow-cell along the flow path. Thus, the wall of the flow-cell advantageously forms a diverging surface of rotation whereby the walls form an angle of divergence of at least about one angular degree with the axis of the cell. An angle of about 1.5 or slightly greater provides sufficient widening to substantially dissipate the undesirable effect of the dynamic liquid lens formed at the interface of water and most organic solvents. The improvement is laxgely achieved by collecting refracted light, which would have otherwise been _ 5_ 4~-041 (~
lOSOZ98 absorbed on the wall of the cell, but it is also believed the reduction in velocity of the stream during its transit through the cell--usually a reduction of over 50%--causes a l! dissipation of the lens effect itself which reduces the amount 1 of refracted light directed against the walls of the cell.
Angles of divergence between the axis of the flowpath and the wall of the cell of 1 to 3 are most advantageous; larger angles only become problems because they usually dictate a larger Il cell size.
l, In liquid chromatographic applications, best results will be achieved if the apparatus to be used with the flow-cell is selected to achieve the most ideal flow pattern possible, i.e., the flow pattern most nearly achieving plug Il flow. This is true of all flow in a liquid chromatographic system: flow from sample injection to the column and flow between the column and the analytical component of the system.
Such apparatus is available: an injector advantageously used is that available under the trade description Model U6K Injector ~ by Waters Associates, Inc. A pumping system, advantageously 1 used to feed liquid into a high pressure column, is that available from the same source under the trade designation Model 6000 Solvent Delivery System~ However, as will be obvious to those skilled in the art, other such apparatus will be generally useful in many applications in which the ~ 1~ ~, 42-041 1050~98 ~ instant invention is advantageously used.
¦~ It will also be obvious to those skilled in the art ¦~ that a number of modifications can be made in the shape of the wall structure of the flow-cell. For example, further enlarge-ment of the cell conduit over that defined minimal conical shape will yield an operable cell that will avoid the effect of the dynamic liquid lens but will also be larger in size and therefore less favorable for many applications. Such enlargement is nonfunctional with respect to the present invention. However other such shapes including such as catenoidal horns, hyperbolic horns, parabolic and hyperbolic suraces as well as similar surfaces of revolution are all intended to be covered by the term "generally truncated cone" as used in this application. Such shapes may on some occasions be favorable in view of effects caused by special flow properties of the fluid components which form the dynamic lens, temperature profiles across the cell, friction effects along the surface of the wall or the like.
"Generally conical", therefore, is meant to include any flow-cell wherein the inlet port is smaller than the outlet port and the cross section of the cell is progressively larger as measured closer to the outlet port.
¦ It is to be realized that the most important structura:
aspect of the invention relates to the relationship of the con-¦ ical cell to the direction of the lightpath: the larger end of the cone must be toward the detector. It is possible, however, lOSOZ98 to reverse the direction of flow of the liquid to be analyzed through the ce]l. Best practice is to avoid this situation or, if for some reason it is desirable, to arrange the attitude of the cell so that any minute gas bubbles can be displaced upwardly toward the outlet port of the cell.
In chromatographic related analytical operations and other such operations which monitor microliter quantities of a flowing sample, the length-to-average diameter ratio of the flow cell is advantageously at least 5 to 1. It is primarily the monitoring of such small samples, rather than inherent optical considerations, which make angles of divergence greater than 3 undesirable for many applications.
One additional advantage of the apparatus disclosed herein is the fact that, for some applications, it allows the light source to be brought (physically, or by optical means) closer to the sample cell without undue losses of light by refraction and light scattering occuring primarily at the interfaces of gas-lens and liquid-lens interfaces.
Thus, in accordance with one broad aspect of the invention there is provided, in a photometer of the type utilizing a light source, a sample cell adapted to transmit a continuously-flowing liquid to be analyzed from an inlet port near one end thereof through a flowpath to an outlet port near the other end thereof, and a means for measuring the absorption of light in said sample cell, the improvement wherein said photometer comprises a light detector forming means to receive substantially all non-absorbed light trans-mitted from said sample cell, means for eliminating effects of liquid lenses comprising a generally conical sample cell, a smaller end of said sample ; cell being nearer said light source, such that there is substantially reduced loss of light refracted by said liquid lenses on walls of said sample cell.
`In accordance with another aspect of the invention there is provid-` ed, in a process for measuring the radiation absorptivity of a flowing liquid sample which comprises a plurality of sequential liquid compositions in a laminar flow mode, the improvement comprising substantially eliminating the interference of dynamic liquid lenses with said measuring by a) feeding sai.d liquid into a generally conical sample cell proximate a smaller cross-sectional end thereof, b) removing said liquid from said sample cell at a larger cross-sectional end thereof, c) and measuring the radiation absorptivity of said liquid through said cell, said measurement being carried out by detection at said larger end of said cell, substantially all of the non-absorbed radiation from a source proximate the smaller end of said cell.
In accordance with a further aspect of the invention there is provided a sample cell having an inlet port, an outlet port and a flowpath therebetween, said flowpath formed of a truncated, generally conical chamber forming means for overcoming refraction of radiation onto walls of said chamber during analysis of liquid passing therethrough, which cell has transparent end members adapting it to serve also as a path for transmitting light, said flowpath having a length-to-average diameter ratio of at least 5: 1.
; According to still another aspect of the invention there is provided, in a liquid chromatographic analytical apparatus of the type having a liquid chromatographic column adapted to emit a liquid stream comprising a series of sequentially-arranged liquid compositions, and means for conducting said stream to a photometer of the type comprising a sample flow-cell form-; ing a conduit for said liquid stream~ a means to provide a source of radiation, and a radiation detector arranged with respect to said conduit to form a radiation path therethrough~ the improvement including means for eliminating distortion of said radiation by dynamic liquid lens effects comprising a flow-cell which forms a truncated, generally conical, flowpath, a smaller end of said cone being nearer said radiation means, such that there is no substantial loss of refracted radiation on walls of said flow-cell.
-8a-lOSOZ98 Illustrative Example of the Invention In this application and accompanying drawings there is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but '' ;~
,., . .
~, :
:.~
:
~ 8b-.
l~ 42-041 j., I
i 1050298 it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it in a variety of forms, each as may be best suited in the condition of a particular case.
,,''"
" In the drawinqs:
¦ Figure l is a schematic diagram of an analytical, lO apparatus constructed according to the invention.
, Figure 2 is a section of a flow-cell constructed ; according to the invention.
Figure 3 is a graph illustrating the output signal "; of an ultra-violet absorption-measuring apparatus using a ~;' 15 ¦ conventional cylindrical flow-cell.
' Figure 4 is a graph illustrating a chart similar to : .
that shown in Figure 3 but obtained utilizing a flow-cell constructed according to the invention.
~;, Figure 1 illustrates an analytical system 10 com-¦ promising a source 12 of a liquid to be analyzed, a liquid j chromatography column 14, and an ultra-violet absorbtometer ~:~
, . I
',~
~ 9_ ... '11 , !
lOSOZ98 16 comprising a light source 18, an interference filter 20, a lens system 22, front windows 23, main housing wall of a sample cell 24, a rear window 26 and photoelectric detector 28.
Signals from photo detector 28 and a reference detector 28a are processed according to known techniques to provide a suitable electronic signal which may be used as a control means or as is more frequent, to provide a visible recording on a recorder means 30.
The single novel feature in Figure 1 is the sample cell 24 which incorporates the conical flowpath 32. However, this innovation directly enhances the performance of the entire system by providing means to take the liquid output from chroma-tographic column 14 and process it in the ultra-violet absorption apparatus so that the resulting light reaching detector 28 is substantially free of detrimental loss of light due to the influence of dynamic liquid lenses.
In the apparatus of Figure 1, the light source is rated at 2.4 watts and has principal wave length of 253.7 nanometers.
The volume of the sample cell, best seen in Figure 2, is about 12.5 microliters: it is about 0.04 inches in diameter at the inlet end, about 0.06 inches in diameter at the outlet end and - ¦ about 0.394 inches in length. A reference flo~-cell 34 is posi-tioned within cell assembly 36, as is common in the photometric ¦l analysis of liquids. This cell may be empty, full of a stagnant - 25 ¦ liquid or have a flowing reference fluid therein.
., 11 ¦1 -9a-Il il 42-041 Il . 105(1 ;~98 ¦ Figure 3 illustrates graphically the type of detection problem which can be encountered in radiation-absorption I'lanalysis because of interference in ultra-violet transmittance ¦Iby dynamic liquid lens as they move through a thin cylindrical ~sample cell.
I In each of Figures 3 and 4, there is an initial peak ¦60 caused by a calibration fluid - a standard dichromate solution flowing through the cells at a rate of one milliliter per l minute. The next rise 61 in each curve, is merely an adjustment ¦ of the zero level of the recorder. At this point, each curve has a relatively flat reference level indicative of the low ultra-violet absorption of water.
This reference level is flat for the continuous feed ¦ in Figure 3 but interrupted by abrupt drops in light transmission 1 when injections of aqueous methanol solution are introduced into the column. These apparent increases absorptivity in absorption are caused by the refraction from dynamic fluid lens formed by the methanol-water interface and the interfaces of various Imixtures thereof. Once refracted, a substantial portion of light is absorbed on the parallel walls of the conventional flow-cell.
The valleys 64 of Figure 3 illustrate the effect caused ¦Iby a transition from water flow of .3 ml/minute to a flow of 1-3 ml per minute of a 10% aqueous solution of methanol. This ¦ solution is added through a sample loop over a period of about 3.3 minutes. Then, as water returns flushing the loop, there is an ¦lupward displacement 65 of the curve caused by the dynamic ~ 42-041 ,. . I, liquid lens ncw being formed of the water flush flowirg behind ¦ the methanol solution. After the flushing with water is com-pleted, fluid-lens induced displacement subsides until another I injection of water-methanol solution is started.
I Equivalent injections made in the same system, except for the use of a flow-cell as shown in Figure 2 result in no reduction in transmission, when methanol is added. Nor is there any substantial increase in transmission when the water ~ flush occurs. Such points are identified as 64a and 65a in Figure 4.
¦ It is stressed that it is intended to cover the appara-¦ tus of the invention, whether or not it exists in non-assembled parts, wherein some intrinsic or extrinsic system is so related ; ¦ to such parts that the system facilitates the collection of the¦ parts for assembly at a particular place or places. Such a system could include co-ordinated shipping instructions, a co-ordinated parts-packaging system, assemply instructions or any other system which facilitates assembly of apparatus into a ¦ functioning system as defined in claims explicitly relating to ¦ assembled systems.
It is to be understood that the following claims are intended to cover all of the generic and specific features of ; i the invention herein described and all statements of the scope of the invention which might be said to fall therebetween.
.1 1 ., ~
.,:, I ,
In analysis of very small quantities of liquids, it has been recognized that the physical conditioning of the fluid must be done very carefully. Thus, ~or example, in the field of liquid chromatography wherein very small, continuously-flowing streams of liquid are measured, care is taken to minimize mechanical and thermal disturbance of the liquid stream between the chromatographic column and analytical apparatus in which the liquid stream from the column is to be continuously analyzed. The primary objective is to present, to a transparent sample cell, the precise sequence of changing liquid composition that leaves the chromatography column.
The rationale and particulars of such apparatus are described in the art. For example, see United States Patent 3,674,373 to Waters, Hutchins and Abrahams which involves a refractometer particularly well adapted to receive such a liquid stream. In general, the approach is to minimize the conduit path through which the liquid to be analyzed must travel and to provide a ~' .
maximum thermal-conditioning of the liquid within such a minimized path. This generally illustrates the art-recognized importance of careful handling of sample liquid between its point of origin and the sample cell in which it is to be 5 ' subjected to analysis, usually analysis which measures an effect of the sample liquid stream on some radiation directed into a flow-cell through which the stream passes.
Investigators have also realized that some attention must be given to the physical condition of the fluid even after it enters the flow-cell. Consequently, flow-cells have been made ever smaller to avoid mixing and peak-spreading effects and, in some cases, a positive thermal equilibration of the cell with the liquid has been sought in order to avoid ' light-shimmering effects along the cell walls. Moreover, the cells are usually positioned with outlets so placed that any entrained gas bubbles tend to be carried upwardly out of the cell. It is noted that U.S. Patent 3,666,941 to Watson describes a conical bifurcated cell wherein the , larger end of the cell faces the light source, thereby forming means to gather a maximum amount of fluorescence-exciting radiation. Applicant's discovery, to be detailed below, is based upon a major improvement in flow-cell construction which solves a problem quite different than that described by Watson but which, like Watson's apparatus, is 25 I particularly useful in combination with liquid chromotograhy applications.
'. I
.
., . _ !
1050~98 A recent patent, U.S. Patent 3,792,929, to Alpert, it has been noted, seems to disclose a conical sample-holding cell. I
The patent related to static-sample devices and in no way involves fluid lenses of any type; although the patent came to the atten- ¦
tion of the instant inventor after an error resulted in the word "field" appearing as "fluid" in the title of the Alpert patent.
Moreover, the apparent and relative dimensions of the Alpert cell would not allow its effective use in most continuous-flow 1 monitoring systems such as are encountered in liquid chromato-; graphic work and the like.
! SummarY of the Invention It is an object of present invention to provide an improved liquid chromatographic system of the type utilizing ¦
a photometric analytical means.
It is a further object of the invention to provide a means for operating a photometric process whereby it is possible ! to minimize the size of sample volume of a flow cell without unduly affecting the performance of the photometer.
Another object of the invention is to provide a novel process of analyzing liquid by photometric methods and a novel photometer for carrying out such analysis. I
Another object of the invention is to provide a novel and improved sample-receiving flow-cell.
Other objects of the invention will be obvious to ` those skilled in the art on reading the instant disclosure.
~ 42-041 ~050298 The above invention is based on the discovery that substantial spurious radiation signals are generated by a lens-type effect caused by laminar-flow patterns at the interface of compositions differing in refractive index; the effect is particularly troublesome in small cylindrical photometer sample-cells. These laminar flow patterns will sometimes be called "dynamic liquid lenses" in this description. In general the worst problems have been encountered in flow-cells in the microliter range, say flow-cells having a diameter of less than ~ about 2 millimeters. In the usual situation the flow path of an ultra violet absorptometer cell is selected to be one centimeter in length, and a flow cell of 2 millimeters maximum diameter will have a volume of less than about 32 microliters.
As the diameter increases the lens effect caused by a given rate of laminar-flow tends to decrease; but a mere increase in diameter of a cylindrical flow path to avoid the lens effect is not practical because the increased diameter would result in either (1) a large increase in the volume of the tube or (2) a substantial decrease in length of the tube.
A large increase in volume is untenable because the ability ;j of the apparatus to detect very small samples would be substantially limited by dilution factors. The length of the cell cannot be mar}cedly reduced without proportionately decreas-ing the magnitude of light absorbed by a given solution flowing through a cell. Still other conceivable tube configurations would give disadvantageous liquid flow patterns.
, _ 42-041 lOSOZ98 Because the problem of these dynamic fluid lenses is primarily encountered at the point of changing compositions, its solution has been found io enhance both the quantitative and ¦
qualitative analytical capabilities of liquid chromatographic systems and like analytical systems where constantly changing compositions are inherent in the method. However, the apparatus is useful in other lens-inducing situations encountered in the process industry; e.g., where the dynamic fluid lens may be induced by temperature change or other phenomena that result in ; formation of a refractive index gradient within the flow-cell.
On discovering the nature of the problem associated with such small flow-cells, applicant has devised a simple con-structional solution which substantially eliminates the problem:
I; he has provided a flow-cell whereby the lens effect is rapidly dissipated by a progressive increase in the crossectional area of the flow-cell along the flow path. Thus, the wall of the flow-cell advantageously forms a diverging surface of rotation whereby the walls form an angle of divergence of at least about one angular degree with the axis of the cell. An angle of about 1.5 or slightly greater provides sufficient widening to substantially dissipate the undesirable effect of the dynamic liquid lens formed at the interface of water and most organic solvents. The improvement is laxgely achieved by collecting refracted light, which would have otherwise been _ 5_ 4~-041 (~
lOSOZ98 absorbed on the wall of the cell, but it is also believed the reduction in velocity of the stream during its transit through the cell--usually a reduction of over 50%--causes a l! dissipation of the lens effect itself which reduces the amount 1 of refracted light directed against the walls of the cell.
Angles of divergence between the axis of the flowpath and the wall of the cell of 1 to 3 are most advantageous; larger angles only become problems because they usually dictate a larger Il cell size.
l, In liquid chromatographic applications, best results will be achieved if the apparatus to be used with the flow-cell is selected to achieve the most ideal flow pattern possible, i.e., the flow pattern most nearly achieving plug Il flow. This is true of all flow in a liquid chromatographic system: flow from sample injection to the column and flow between the column and the analytical component of the system.
Such apparatus is available: an injector advantageously used is that available under the trade description Model U6K Injector ~ by Waters Associates, Inc. A pumping system, advantageously 1 used to feed liquid into a high pressure column, is that available from the same source under the trade designation Model 6000 Solvent Delivery System~ However, as will be obvious to those skilled in the art, other such apparatus will be generally useful in many applications in which the ~ 1~ ~, 42-041 1050~98 ~ instant invention is advantageously used.
¦~ It will also be obvious to those skilled in the art ¦~ that a number of modifications can be made in the shape of the wall structure of the flow-cell. For example, further enlarge-ment of the cell conduit over that defined minimal conical shape will yield an operable cell that will avoid the effect of the dynamic liquid lens but will also be larger in size and therefore less favorable for many applications. Such enlargement is nonfunctional with respect to the present invention. However other such shapes including such as catenoidal horns, hyperbolic horns, parabolic and hyperbolic suraces as well as similar surfaces of revolution are all intended to be covered by the term "generally truncated cone" as used in this application. Such shapes may on some occasions be favorable in view of effects caused by special flow properties of the fluid components which form the dynamic lens, temperature profiles across the cell, friction effects along the surface of the wall or the like.
"Generally conical", therefore, is meant to include any flow-cell wherein the inlet port is smaller than the outlet port and the cross section of the cell is progressively larger as measured closer to the outlet port.
¦ It is to be realized that the most important structura:
aspect of the invention relates to the relationship of the con-¦ ical cell to the direction of the lightpath: the larger end of the cone must be toward the detector. It is possible, however, lOSOZ98 to reverse the direction of flow of the liquid to be analyzed through the ce]l. Best practice is to avoid this situation or, if for some reason it is desirable, to arrange the attitude of the cell so that any minute gas bubbles can be displaced upwardly toward the outlet port of the cell.
In chromatographic related analytical operations and other such operations which monitor microliter quantities of a flowing sample, the length-to-average diameter ratio of the flow cell is advantageously at least 5 to 1. It is primarily the monitoring of such small samples, rather than inherent optical considerations, which make angles of divergence greater than 3 undesirable for many applications.
One additional advantage of the apparatus disclosed herein is the fact that, for some applications, it allows the light source to be brought (physically, or by optical means) closer to the sample cell without undue losses of light by refraction and light scattering occuring primarily at the interfaces of gas-lens and liquid-lens interfaces.
Thus, in accordance with one broad aspect of the invention there is provided, in a photometer of the type utilizing a light source, a sample cell adapted to transmit a continuously-flowing liquid to be analyzed from an inlet port near one end thereof through a flowpath to an outlet port near the other end thereof, and a means for measuring the absorption of light in said sample cell, the improvement wherein said photometer comprises a light detector forming means to receive substantially all non-absorbed light trans-mitted from said sample cell, means for eliminating effects of liquid lenses comprising a generally conical sample cell, a smaller end of said sample ; cell being nearer said light source, such that there is substantially reduced loss of light refracted by said liquid lenses on walls of said sample cell.
`In accordance with another aspect of the invention there is provid-` ed, in a process for measuring the radiation absorptivity of a flowing liquid sample which comprises a plurality of sequential liquid compositions in a laminar flow mode, the improvement comprising substantially eliminating the interference of dynamic liquid lenses with said measuring by a) feeding sai.d liquid into a generally conical sample cell proximate a smaller cross-sectional end thereof, b) removing said liquid from said sample cell at a larger cross-sectional end thereof, c) and measuring the radiation absorptivity of said liquid through said cell, said measurement being carried out by detection at said larger end of said cell, substantially all of the non-absorbed radiation from a source proximate the smaller end of said cell.
In accordance with a further aspect of the invention there is provided a sample cell having an inlet port, an outlet port and a flowpath therebetween, said flowpath formed of a truncated, generally conical chamber forming means for overcoming refraction of radiation onto walls of said chamber during analysis of liquid passing therethrough, which cell has transparent end members adapting it to serve also as a path for transmitting light, said flowpath having a length-to-average diameter ratio of at least 5: 1.
; According to still another aspect of the invention there is provided, in a liquid chromatographic analytical apparatus of the type having a liquid chromatographic column adapted to emit a liquid stream comprising a series of sequentially-arranged liquid compositions, and means for conducting said stream to a photometer of the type comprising a sample flow-cell form-; ing a conduit for said liquid stream~ a means to provide a source of radiation, and a radiation detector arranged with respect to said conduit to form a radiation path therethrough~ the improvement including means for eliminating distortion of said radiation by dynamic liquid lens effects comprising a flow-cell which forms a truncated, generally conical, flowpath, a smaller end of said cone being nearer said radiation means, such that there is no substantial loss of refracted radiation on walls of said flow-cell.
-8a-lOSOZ98 Illustrative Example of the Invention In this application and accompanying drawings there is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but '' ;~
,., . .
~, :
:.~
:
~ 8b-.
l~ 42-041 j., I
i 1050298 it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it in a variety of forms, each as may be best suited in the condition of a particular case.
,,''"
" In the drawinqs:
¦ Figure l is a schematic diagram of an analytical, lO apparatus constructed according to the invention.
, Figure 2 is a section of a flow-cell constructed ; according to the invention.
Figure 3 is a graph illustrating the output signal "; of an ultra-violet absorption-measuring apparatus using a ~;' 15 ¦ conventional cylindrical flow-cell.
' Figure 4 is a graph illustrating a chart similar to : .
that shown in Figure 3 but obtained utilizing a flow-cell constructed according to the invention.
~;, Figure 1 illustrates an analytical system 10 com-¦ promising a source 12 of a liquid to be analyzed, a liquid j chromatography column 14, and an ultra-violet absorbtometer ~:~
, . I
',~
~ 9_ ... '11 , !
lOSOZ98 16 comprising a light source 18, an interference filter 20, a lens system 22, front windows 23, main housing wall of a sample cell 24, a rear window 26 and photoelectric detector 28.
Signals from photo detector 28 and a reference detector 28a are processed according to known techniques to provide a suitable electronic signal which may be used as a control means or as is more frequent, to provide a visible recording on a recorder means 30.
The single novel feature in Figure 1 is the sample cell 24 which incorporates the conical flowpath 32. However, this innovation directly enhances the performance of the entire system by providing means to take the liquid output from chroma-tographic column 14 and process it in the ultra-violet absorption apparatus so that the resulting light reaching detector 28 is substantially free of detrimental loss of light due to the influence of dynamic liquid lenses.
In the apparatus of Figure 1, the light source is rated at 2.4 watts and has principal wave length of 253.7 nanometers.
The volume of the sample cell, best seen in Figure 2, is about 12.5 microliters: it is about 0.04 inches in diameter at the inlet end, about 0.06 inches in diameter at the outlet end and - ¦ about 0.394 inches in length. A reference flo~-cell 34 is posi-tioned within cell assembly 36, as is common in the photometric ¦l analysis of liquids. This cell may be empty, full of a stagnant - 25 ¦ liquid or have a flowing reference fluid therein.
., 11 ¦1 -9a-Il il 42-041 Il . 105(1 ;~98 ¦ Figure 3 illustrates graphically the type of detection problem which can be encountered in radiation-absorption I'lanalysis because of interference in ultra-violet transmittance ¦Iby dynamic liquid lens as they move through a thin cylindrical ~sample cell.
I In each of Figures 3 and 4, there is an initial peak ¦60 caused by a calibration fluid - a standard dichromate solution flowing through the cells at a rate of one milliliter per l minute. The next rise 61 in each curve, is merely an adjustment ¦ of the zero level of the recorder. At this point, each curve has a relatively flat reference level indicative of the low ultra-violet absorption of water.
This reference level is flat for the continuous feed ¦ in Figure 3 but interrupted by abrupt drops in light transmission 1 when injections of aqueous methanol solution are introduced into the column. These apparent increases absorptivity in absorption are caused by the refraction from dynamic fluid lens formed by the methanol-water interface and the interfaces of various Imixtures thereof. Once refracted, a substantial portion of light is absorbed on the parallel walls of the conventional flow-cell.
The valleys 64 of Figure 3 illustrate the effect caused ¦Iby a transition from water flow of .3 ml/minute to a flow of 1-3 ml per minute of a 10% aqueous solution of methanol. This ¦ solution is added through a sample loop over a period of about 3.3 minutes. Then, as water returns flushing the loop, there is an ¦lupward displacement 65 of the curve caused by the dynamic ~ 42-041 ,. . I, liquid lens ncw being formed of the water flush flowirg behind ¦ the methanol solution. After the flushing with water is com-pleted, fluid-lens induced displacement subsides until another I injection of water-methanol solution is started.
I Equivalent injections made in the same system, except for the use of a flow-cell as shown in Figure 2 result in no reduction in transmission, when methanol is added. Nor is there any substantial increase in transmission when the water ~ flush occurs. Such points are identified as 64a and 65a in Figure 4.
¦ It is stressed that it is intended to cover the appara-¦ tus of the invention, whether or not it exists in non-assembled parts, wherein some intrinsic or extrinsic system is so related ; ¦ to such parts that the system facilitates the collection of the¦ parts for assembly at a particular place or places. Such a system could include co-ordinated shipping instructions, a co-ordinated parts-packaging system, assemply instructions or any other system which facilitates assembly of apparatus into a ¦ functioning system as defined in claims explicitly relating to ¦ assembled systems.
It is to be understood that the following claims are intended to cover all of the generic and specific features of ; i the invention herein described and all statements of the scope of the invention which might be said to fall therebetween.
.1 1 ., ~
.,:, I ,
Claims (22)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a photometer of the type utilizing a light source, a sample cell adapted to transmit a continuously-flowing liquid to be analyzed from an inlet port near one end thereof through a flowpath to an outlet port near the other end thereof, and a means for measuring the absorption of light in said sample cell, the improvement wherein said photometer comprises a light detector forming means to receive substantially all non-absorbed light transmitted from said sample cell, means for eliminating effects of liquid lenses comprising a generally conical sample cell, a smaller end of said sample cell being nearer said light source, such that there is substantially reduced loss of light refracted by said liquid lenses on walls of said sample cell.
2. A photometer as defined in claim 1 wherein said light source and said measuring means are so selected that said photometer is an ultra-violet absorbence detector.
3. A photometer as defined in claim 1 wherein said sample cell has a volume of less than 32 microliters and a maximum diameter of less than 2 millimeters.
4. A photometer as defined in claim 2 wherein said sample cell has a volume of less than 32 microliters and a maximum diameter of less than 2 millimeters.
5. A photometer as defined in claim 1 wherein an angle of divergence between an axis of said flowpath and the wall of said flow-cell is from 1°
to 3°.
to 3°.
6. A photometer as defined in claim 2 wherein an angle of divergence between an axis of said flowpath and the wall of said flow-cell is from 1°
to 3°.
to 3°.
7. A photometer as defined in claim 3 where an angle of divergence between an axis of said flowpath and the wall of said flow-cell is from 1°
to 3°.
to 3°.
8. A photometer as defined in claim 4 wherein an angle of divergence between an axis of said flowpath and the wall of said flow-cell is from 1°
to 3°.
to 3°.
9. In a process for measuring the radiation absorptivity of a flowing liquid sample which comprises a plurality of sequential liquid compositions in a laminar flow mode, the improvement comprising substantially eliminating the interference of dynamic liquid with said measuring by a) feeding said liquid into a generally conical sample cell proximate a smaller cross-sectional end thereof, b) removing said liquid from said sample cell at a larger cross-sectional end thereof, c) and measuring the radiation absorptivity of said liquid through said cell, said measurement being carried out by detection at said larger end of said cell, substantially all of the non-absorbed radiation from a source proximate the smaller end of said cell.
10. A process as defined in claim 9 wherein the volume of liquid sample in said flow-cell is maintained at less than about 32 microliters and wherein said maximum diameter of said cell is 2 millimeters.
11. A process as defined in claim 9 wherein the radiation being measured is ultra-violet light.
12. A process as defined in claim 9 wherein the velocity of the sample liquid is decreased by at least about 50% during its movement from the inlet end of said sample cell to the outlet end of said cell.
13. A process as defined in claim 10 wherein the velocity of the sample liquid is decreased by at least about 50% during its movement from the inlet end of said sample cell to the outlet end of said cell.
14. A process as defined in claim 11 wherein the velocity of the sample liquid is decreased by at least about 50% during its movement from the inlet end of said sample cell to the outlet end of said cell.
15. In a liquid chromatographic analytical apparatus of the type having a liquid chromatographic column adapted to emit a liquid stream comprising a series of sequentially-arranged liquid compositions, and means for conducting said stream to a photometer of the type comprising a sample flow-cell forming a conduit for said liquid stream, a means to provide a source of radiation, and a radiation detector arranged with respect to said conduit to form a radiation path therethrough;
the improvement including means for eliminating distortion of said radiation by dynamic liquid lens effects comprising a flow-cell which forms a truncated, generally conical, flowpath, a smaller end of said cone being nearer said radiation means, such that there is no substantial loss of refracted radiation on walls of said flow cell.
the improvement including means for eliminating distortion of said radiation by dynamic liquid lens effects comprising a flow-cell which forms a truncated, generally conical, flowpath, a smaller end of said cone being nearer said radiation means, such that there is no substantial loss of refracted radiation on walls of said flow cell.
16. A chromatographic system as defined in claim 15 wherein said light source and said detecting means are so selected that said radiation detector is an ultra-violet radiation detector.
17. A chromatographic system as defined in claim 15 wherein said flow-cell has a maximum diameter of 2 millimeters.
18. A chromatographic system as defined in claim 16 wherein said flow-cell has a maximum diameter of 2 millimeters.
19. A chromatographic system as defined in claim 15 wherein the angle of divergence between the conical wall and axis of said flowpath is from 1° to 3°.
20. A chromatographic system as defined in claim 18 wherein the angle of divergence between the conical wall and axis of said flowpath is from 1° to 3°.
21. A system as defined in claim 20 wherein said flowpath has a length-to-average diameter ratio of at least 5:1.
22. A photometer as defined in claim 5 wherein the length-to-average diameter ratio of the flowpath is at least 5:1.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47007674A | 1974-05-15 | 1974-05-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1050298A true CA1050298A (en) | 1979-03-13 |
Family
ID=23866181
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA226,424A Expired CA1050298A (en) | 1974-05-15 | 1975-05-06 | Photometric system with conical flow cell |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5433871B2 (en) |
| CA (1) | CA1050298A (en) |
| DE (1) | DE2521453A1 (en) |
| FR (1) | FR2271566B1 (en) |
| GB (1) | GB1515023A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2927191A1 (en) * | 1979-07-05 | 1981-01-15 | Rush Presbyterian St Luke | Preparation of slide mounted blood sample - including exposure to fixing agent to maintain cell morphology |
| US4468124A (en) * | 1981-02-17 | 1984-08-28 | Beckman Instruments, Inc. | Double beam photometer for measuring fluid samples |
| JPS58500183A (en) * | 1981-02-17 | 1983-02-03 | ベツクマン インスツルメンツ インコ−ポレ−テツド | Double beam photometer for measurement of fluid samples |
| DE3688679T2 (en) * | 1985-09-09 | 1993-10-14 | Commw Scient Ind Res Org | FLOW CELL FOR ANALYZING SUBSTANCES. |
| JPS6329235A (en) * | 1986-07-23 | 1988-02-06 | Toutsuu Denshi Service Kk | Measuring instrument for degree of contamination of fluid |
| DE3700580A1 (en) * | 1987-01-10 | 1988-07-21 | Leybold Ag | Cell for gas analysers |
| GB8718151D0 (en) * | 1987-07-31 | 1987-09-09 | Sieger Ltd | Gas analyser |
| EP1385006A3 (en) * | 2002-07-24 | 2004-09-01 | F. Hoffmann-La Roche Ag | System and cartridge for processing a biological sample |
| JP5854621B2 (en) * | 2011-04-07 | 2016-02-09 | 株式会社日立ハイテクノロジーズ | Long optical path length flow cell |
| CN104833747B (en) * | 2015-05-06 | 2016-08-24 | 华东理工大学 | A kind of preparative hplc UV-detector using deep ultraviolet LED light source |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1840629U (en) * | 1960-03-24 | 1961-11-02 | Ados G M B H | THROUGH FLOW CUVETTE. |
| US3345910A (en) * | 1962-05-03 | 1967-10-10 | Technicon Corp | Colorimeter flow cell |
| US3614243A (en) * | 1969-08-01 | 1971-10-19 | Reno A Del Ben | Variable path-length gas cell |
| US3666941A (en) * | 1970-09-28 | 1972-05-30 | Lab Data Control Inc | Differential filter fluorimeter |
| CH542437A (en) * | 1971-08-27 | 1973-09-30 | Micromedic Systems Inc | Optical cuvette and method for its manufacture |
| JPS4890297A (en) * | 1972-02-29 | 1973-11-24 | ||
| JPS4938470A (en) * | 1972-08-17 | 1974-04-10 |
-
1975
- 1975-05-06 CA CA226,424A patent/CA1050298A/en not_active Expired
- 1975-05-13 FR FR7514863A patent/FR2271566B1/fr not_active Expired
- 1975-05-14 DE DE19752521453 patent/DE2521453A1/en active Granted
- 1975-05-15 GB GB2061275A patent/GB1515023A/en not_active Expired
- 1975-05-15 JP JP5791375A patent/JPS5433871B2/ja not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2521453A1 (en) | 1975-11-27 |
| JPS5433871B2 (en) | 1979-10-23 |
| FR2271566A1 (en) | 1975-12-12 |
| JPS50159775A (en) | 1975-12-24 |
| GB1515023A (en) | 1978-06-21 |
| FR2271566B1 (en) | 1979-01-19 |
| DE2521453C2 (en) | 1987-08-13 |
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