US 3820660 A
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United States Patent .1191 Halasz et a1. 7 t
- 3,820,660 June 28, 1974 FLUID ANALYTICAL INSTRUMENT Inventors: Istvan Halasz, Kleeberstrabe 16,6
Frankfurt am Main; Hans Otto Gerlach, Im Kusler, 427 Altendorf-Ulfl-totte; Karl Friedrich Gutlich, Oppenheiner Strabc 45, 6 Frankfurt am Main; Peter Walkling, Dieckmann Weg 2, 216 Stade, all of Germany Filed: Feb. 2, 1973 Appl. No.: 329,142
Foreign Application Priority Data Feb. 15, l9 6 8 iern any 1675 313 7 R nes UISTApplica tin Data Continuation of Ser. No. 798,358, Feb. 11, 1969, abandoned.
US. Cl. 210/19 8 C, 55/386 Int. Cl B0ld /08 Field of Search /67, 197, 386; 210/31 C, 210/198, 198 C, 304, 322; /108-110; 138/42 References Cited UNITED STATES PATENTS 4/1929 LitIe,Jr....'..... .....;13fs/42 4/1950 Keyzeri... 65/108X 2,920,478 1/1950 ma 210/19sc 3,331,678 3,479,142 11/1969 Isree1ietal..... 138/42 x 3,493,497 2/1970 Pretoriusetal ..210/31c OTHER PUBLICATIONS nubreseem Lamps 61' Handrail "san tation";
Luke Thorington & Joel Shurgan. Sept. 24. 1961, paper.
Primary Examiner-Frank A. Spear lr.
Assistant Examiner-Robert H. Spitzer Attorney, Agent, or Firm-Gardiner, Sixbey, Bradford & Carlson 5 7 ABSTRACT A tubular element of non-circular cross section for conveying fluids gaseous orliquid for use in fluid ana- I lyzing apparatus where the composition of "the fluid more or less suddenly changes. The shape reduces overlapping of compositions. A tube of elliptical cross section is improved when major and minor axes of e1- lipse alternate along length of tube as by twisting the tube or providing offset pinches to a round tube. Additional efficiency is obtained when the tube with thealtemating positions of axes is wound into a helix of the order of 10 mm diameter.
7 5 Claims, 8 Drawing Figures 7/1967 Ireland 65/108 X Pmmmmza I914 3820.660 SHEET 2 [If 2 Fly. 5
A I Q 222 4 0 5'0 0'0 150 120 1Z0 1E0 150 200 Hams? 1 I FLUID ANALYTICAL INSTRUMENT This is a continuation, of applicationSer. No. 798,358,flled Feb. ll, l969 now abandoned.
BACKGROUND OF THE INVENTION 1. Field of the Invention A fluid analyzing instrument including a tube conduit having a cross section of non-circular shape and the tube being acutely contorted.
2. Description of the Prior Art Whenever there is a change in the composition of a fluid, gaseous or liquid, flowing through a conduit e.g. one composition following an other and both being transported by a carrier, there must not be unnecessary intermixing if the compositions are to be subsequently analysed. In column or conduit tubes for chromatographic instruments one of the objects-is that samples partitioned into sections following one another in the tube should, as much as possible, notbecome intermixed in the flowing media. That is to say, the partitioned fractions should be measured as having the same composition toward the end of the tubular conduit column as toward the beginning. This should be true either with respect to time or the amount eluted. Otherwise short time intervals to indicate true alteration in composition would be obscured by mixing action and not be detectable.
In many cases, especially when the composition alterations to be measured develop only slowly, for example over a period of minutes, this objection can be met by suitably proportioning the speed of flow relative to the diameter of the clean or uncoated tube. Often such measures are not suitable however, as when for minimizing time delay very high speeds are necessary.
The problem outlined above is of special significance in chromatography, both gas and liquid, where a partitioningcolumn has a carrier medium flowing therethrough,into which medium a small slug of mixture is injected for separation into its components. The inner walls ofthe open tube are coated with a thin film acting as a stationary phase which reversibly interacts with the molecules ofthe mixture-under study e.g. by absorption and desorption. The several components of the mixture have different transit times through the interior of the column and hence are eluted from the column at different points of timefBecause the times of elution differ for the components, the latter can be determined by detectors based on heat conductivity or by differential refractometers. An important requirement for satisfactory measurement of the several components is that the different constituents ofthe mixture not overlap as they emerge or are eluted.
The ideal condition would be, that the length of the injected slug remained constant throughout the entire movement in the instrument, so that the individual components would emerge as slugs equally spaced one after the other. This has been found not to be the case however, but instead the slug undergoes a lengthening deformation which can lead to overlapping of the individual emerging slugs of the components to be determined in the mixture. In practice the lengthening increases with the flow-through speed dictated by the operating speed, which in turn is dictated by the duration of time in which an analysis must be made. The lengthening deformation is traceable to. mixing actions which occur at the separation between the slugs and the carrier medium upon its movement inside of round tubular conduits in apparatus having a column formed as an open tube.
SUMMARY OF THE INVENTION The invention shows a way to hold the above de scribed mixing action to an especially small amount in the longitudinal direction of the tube. It has been found if the clean cross section of the tube is not circular and the flow of the medium in the tube in the general direction of the tube is additionally altered or contorted or turned, the non-circular cross section and turning of the carrier flow each makes for greater efficiency and the two may be combined for still better results.
An effective and easily produced form of the invention is a tube having a substantially elliptical inner cross section that is additionally wound about an axis representing the direction of general flow through the tube. Results are better if the major axis of the ellipse lies in an approximate plane of a turn. The tube is preferably formed from conventional capillary tube for columns having an inner diameter of about 1 mm by partially flattening such a tube to give an elliptical cross section having major and-minor axes in the ratio 3:1. For supplying a contorted flow of the carrier medium the 1 mm tube is wound into a helix having a diameter of about 10 mm.
The contorted flow may be obtained by twisting an elliptical tube formed in the manner mentioned above to give a full twist every 25 mm, and then winding the twisted tube into a helix of 10 mm diameter.
Equally as satisfactory as the twisted tube is a form in'which successive sections of a round tube are partially flattened to elliptical cross sections and wherein alternate sections are at right angles to each other about the main longitudinal axis of the tube. If the sectional lengths are not more than 50 times the length of the major axis of the cross section the desired action is obtained. The resulting tube can be additionally woun'd helically to give even greater efficiency.
All of the mentioned tube forms can be produced very easily to give the advantageous increased effi' ciency.
BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows schematically a chromatographic apparatus including a source 1 of mobile phase or carrier medium, such as helium, providing a continuous stream of carrier gas. The source may be a storage tank provided with a regulating valve. At a zone 2 the carrier medium is supplied small amounts of the sample to be analysed-by a syringe 3 through a serum cap, so that a small injected slug of the sample starts off inside the transfer medium stream at zone 2. This slug migrates through the partitioning column 4 which is in the form of an open capillary tube whose inner walls are coated, the coating acting and reacting with components to be determoned in the sample. Owing to the different characteristic properties of the components to be separated, they undergo a differential separatory delay during passage through the column so as to leave the column serially, one component after another.
In the example shown, a detector 5, for example a measuring instrument based on heat conductivity, receives the separated fractions and indicates the amounts by registration on a recording chart 6. The composition may be determined by area-integration under the peaks of the chart curve in conventional manner after, for example, the column has been timecalibrated for operation of the system under fixed conditions. For good measurements it is essential that the peaks not overlap. They should be steep sided. This means that the slugs formed from the different components should not become so elongated inside the column that they may mix with each other. Since the column is of capillary dimensions and must be very long, the column is coiled helically to conserve space.
As set forth above, a danger arises that such overlapping of the several components making up the mixture may occur inside the column with increasing speed of the medium through the column. A speed as high as possible is however desired in order to use the shortest possible time necessary for an analysis.
FIG. 2 shows a column in one form of the invention. As shown in cross section, a capillary cylindrical tube of about I mm inside diameter has been squeezed to produce one of elliptical cross section. The major and minor axes of the cross sections are about in the ratio 3:1 and are denoted a and b. The squeezing of the tube, if of metal, may be carried out between rollers, but it may be carried out in the same manner at softening temperatures if glass or plastic tubing is used. The tube is moreover coiled to form a relatively tightly wound helix of about 8 to 30 mm in diameter preferably about 10 mm, which is in the general course of the tube. The novel feature is then not as to the general loose coiling which is as shown in FIG. I in order to provide space for the long column 4, that heretofore used round tubes and was coiled into a helix of about 50 to 100 times the diameter ofthe tube. The invention provides much more efficiency than this coil, for the latter proved to be practically ineffective in the extension of the slugs.
The construction in FIG. 2 is thus a tight winding according to FIG. 2 incorporated in the further loose coiling shown in FIG. 1. In production, the conduit is first formed according to FIG. 2 and then the coiled tube is loosely wound according to FIG. I in order to reduce space requirements.
A modification of the invention is shown in FIG. 3. Here the same tube of elliptical cross section is used, but the tube is twisted so as to provide a full turn for each say, to 50 mm of length, preferably about mm, along its l ongitudinal axis. This twisting can be done by holding one end of a straight tube fast and turning the other about the tube axis. The lie of the different sectional portions is shown in FIG. 3a. Such a tube exhibits, in this very form, an increased effect in inhibition of overlapping. It can thus be coiled to conserve space as shown in FIG. I and used as a chromatographic column. An especially good effect is obtained if the twisted tube is first tightly wound as a helix similar to that in FIG. 2, and then the helical coil loosely looped in order to conserve space as shown in FIG. 1.
FIG. 4 shows another modification of the invention.
The results of the invention are shown by curves in FIGS. 5 and 6. The data of the curves were obtained by injecting a slug of sample having only one component into a carrier medium and after its passing through column, the height, h, equivalent to a theoretical plate, was determined as a measure for broadening of the bands. In chromatographic literature h 6 /L, that is, the varience (6 of the peaks of Gausian shape per unit of length of the column. I
This relation was applied to the various tube forms as follows:
A. A straight cylinder (1 mm diameter).
B. Cylindrical tube wound into helix of 10 mm diamplane of turn of helix of diameter l0 mm.)
D. Elliptical and wound (major axis lying in plane of turn of helix 10 mm in diameter, FIG. 2).
E. Elliptical and twisted and straight (a full turn per each 25 mm.)
F. Elliptical, twisted and wound (full turn per each 25 mm and wound into 10 mm diameter helix.
In the above examples straight denotes a coiling into loops with the loop diameter of at least 50 mm in diameter to save space.
Looping of the diameter was found to be essentially of the same effect as actually straight tubing.
All tubes of elliptical cross section'had about a 3:1 ratio of axes, and were made by squeezing a cylindrical tube of 1 mm clean inside diameter. All tubes were given, in known manner, an inner film of highly dispersed ferrite oxide of iron (above 30 sq. m/gram specific surface area uncoated) or coated with 10 percent by weight of polyethylene glycol (Mol. wt. 400 to 20,000). The thickness of the solid film was about I to 5 micrometers.
The total length of tubing used in a column was from I 20 to 30 meters for liquids and 45 meters for gas.
In FIGS. 5 and 6 the widening h of the slugs in cm is plotted against flow rate of the carrier medium in cm/sec. for the various forms of tubes A to F. FIG. 5 shows the results in the case of liquid chromatography. In all forms of the invention from C to F it is apparent that the values of h are less than those for the cylindrical tubing, whether tightly helically wound or not, at any given flow rate. It may be noted that the different forms vary in their effect. Especially noteworthy is the curve F for the elliptical, twisted, and then helically wound tube. This form of the tube gives a very low value for h and the action is nearly independent of flow rate.
The tube of FIG. 4 with the 90 offset sectionsshowed results analogous to those by the form in FIG. 3.
The action in the case of gases, as shown in FIG. 6, is not as great as for liquids. But even here there is an appreciable reduction in the broadening h at the higher rates of flow, especially in the form embodying the twists and subsequent tight winding.
The different characteristics in the case of gases are probably due to higher diffusion coefficients of the molecules of the slugs with gas as compared with liq- .uids owing to greater mobility of the gas. This aids in the explanation of why the values of 11 rise in' the lower flow-rate ranges, for apparently the broadening by diffusion action exceeds that resulting from flowing action.
It is not definitely known why the invention works as it does. At. first glance it might be supposed that a broadening of the sample slug would appear least in an undisturbed stream such as a stream in a relatively straight round tube. But this is not the case, because the laminar flow develops as a parabolic flow pattern. The flow rate at the axis of the tube reaches a maximum and the rate at or near the wall is zero The flow occurs only parallel to the axis of the tube. Because of this flow profile, the slugs are parabolically pulled apart. Without any self motivated movement of the molecules, that is,
without diffusion movement, which occurs transverse to the tube axis also, the molecules in the neighborhood of the tube walls would remain almost indefinitely in the tube and those at the axis rush through the tube with maximum speed. The slug would accordingly become mixed" or blended over the whole length of the tube. Under the influence of thermal motion of the molecules, a constant exchange of position occurs all the same in such a way that molecules from the wall cules. The effect of this transverse flow is analogous to the increasing of the diffusion coefficientsand in the same way to a minimizing of the elongation of the slug is shown in the values for h in FIGS. 5 and 6.
The action is independent from the action of the partitioning column. The slug lengthening is accordingly reduced when alternate action of the molecules does 1 not take place with the coating of the partitioning column. The result is that the invention can be employed with all types of tubular conduits wherein the sample is transported, for example the conduits ahead of and/or after thepartitioning column. For the same reason the invention can be used to advantage in all other types of instruments having a flowing medium in conduits wherein mixing action in the longitudinal direction'of the tubular conduits is to be suppressed.
This is ofspecial importance when for any reason there is an abruptchange in composition of contentsfed to the tube, such as by the switching of sources of fluid supplied to the tube, with or without injection of spacing slugs.
The invention claimed is defined in the following? 1. Chromatographic apparatus for examining fluids comprising a source of carrier fluid, means connected to said source adapted to define a stream for the carrier fluid, means for introducinga sample into a stream of the carrier fluid, a chromatographic column defining a path for the fluid stream following the point of introduction of the sample, a detector connected to said chromatographic column for measuring a characteristic parameter of the fluid stream emerging from said chromatographic column, said chromatographic column being formed of tubing which has been geometrically deformed along a substantial portion of its length so that the tubinghas a major and a minor diameter, said major and minor diameters being alternatively rotated along the deformed portion to produce a movement of the fluid transverse to the direction of flow, said major and minor diameters being of constant lengths throughout the length of said tubing whereby the volume of fluid flow is unchanged throughout the length of said tubing.
2. Chromatographic apparatus according to claim 1 wherein said tubing is formed by successively pinching the tubing at spaced invervals along the length thereof with alternate pinchings disposed at 90 to each other.
. 3. Chromatographic apparatus according to claim 1 wherein said tubing is formed by flattening said tubing so that it assumes an elliptical cross section and thereafter twisting said tubing.
4. Chromatographic apparatus according to claim 1 wherein said tubing is coated on the inner wall to provide a stationary phase.
5. Chromatographic apparatus according to claim 1 wherein said tubing is coiled into a helix.