US 3714812 A
An electron capture identification apparatus for identifying labelling additives which comprises a revolving gas/liquid chromatographic tube magazine for receiving samples from the sampling mechanism and an electron capture detector for detecting a labelling additive separated in the magazine. The eluents of the individual tubes of the magazine are mixed in an after-column whose eluent is supplied to the detector so as to provide a constant background indication and to compensate for minor variations between individual tubes of the magazine.
Claims available in
Description (OCR text may contain errors)
United States Patent Drinkwater et al. 1 Feb. 6, 1973 15 ELECTRON CAPTURE 3,444,722 5/1969 Roof ..73/23.1 TI I N A AR TUS 3,550,429 12/1970 MacMurtrie et al. ..73/23.1 V V v 7 2,234,499 3/1941 McAlliSter ..73/23  Invent J Dmlkwaier, Chester; 3,363,447 1/1968 Severs ..73/23.l
Albert Evans, Wirral, both of England Primary ExaminerRichard C. Queisser Assistant ExaminerC. E. Snee, I11  Asslgnee' Company E Y -i Attorney-J. H. McCarthy and T. E. Bicber 2 F1 d: M 22 1970 [2 1 ay 57 ABSTRACT pp 39,602 An electron capture identification apparatus for identifying labelling additives which comprises a  Foreign Application Priority Data revolving gas/liquid chromatographic tube magazine I WW W I V I for receiving samples from the sampling mechanism May 22, 1969 Great Britain ..26,209/69 and an electron capture detector for detecting a labelling additive separated in the magazine. The  U.S. C1 ..73/23.l luent of the individual tubes of the magazine are  Int. Cl. ..G0ln 31/08 mixed in an after-column whose eluent is supplied to  Field Of Search .73/23.1, 61.1 C, 23; the detector so as to provide a constant background C; indication and to compensate for minor variations between individual tubes of the magazine.  References Cited 3 Claims, 6 Drawing Figures UNITED STATES PATENTS 3,199,274 8/1965 Norem et a1 ..73/23.l X
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FIG 4 IN JOHN W. D
ELECTRON CAPTURE IDENTIFICATION APPARATUS BACKGROUND OF THE INVENTION This invention relates to analytical apparatus.
Many analytical processes, whether involving merely the detection of one particular component in a mixture of substances or the complete separation and identification of a complex mixture of substances, make use of the well-known process of gas chromatography. Gas chromatographic separation is conventionally carried out in columns or tubes which are packed with a solid adsorbent material (in gas-solid chromatography) or with a solid supporting material impregnated with liquid (in gas-liquid chromatography).
SUMMARY OF THE INVENTION The present invention provides apparatus which is particularly applicable to the detection of one component of a mixture of substances, and more particularly applicable to the analysis of sequential samples of a mixture of substances.
The apparatus of the invention will be discussed in this specification in connection specifically with the detection of tracer substances employed to indicate the presence of an interface between two hydrocarbon liquids travelling in succession in a pipeline, but it will be apparent that its potential application is much wider than this. For example, the apparatus may be used for the detection of a conventional component of a mixture; or where a succession of single substances are passing in sequence through a pipeline, the apparatus may be employed to detect an interface where one of the materials shows a characteristic feature which is detectable by the apparatus and in which it differs from its BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the gas chromatographic device of this invention in its most general form;
FIG. 2 is a flow diagram illustratingthe operation of the invention;
FIG. 3 is a vertical section of the gas chromatographic device and of the after-column;
FIG. 4 is a horizontal section along line 4-4 of FIG. 3.
FIG. 5 is a plan view of the top plate of the device of FIG. 3 along line 5-5 of FIG. 3; and
FIG. 6 is a plan view of the bottom plate of the device of FIG. 3 along line 66 of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the accompanying drawings shows diagrammatically, in vertical section, one embodiment of the apparatus, which comprises a sampling valve 1, a series of six chromatographic columns 2, and a detection device 3. Provision is also made (4) for back flushing of the chromatographic columns with the carrier gas.
The means for transferring a sample of material to be analyzed to the chromatographic unit may be any suitable sampling device, such as a sampling valve, and we 1 have used with particular success sampling valves of the kind described in our copending British application Ser. No. 4476/69 filed Jan. 27, 1969 Such valves can be particularly useful when samples have to be taken from materials which are under high pressure.
The chromatographic unit conveniently consists of a plurality of chromatographic columns arranged with their long axes parallel to and equidistant from a common axis around which the columns rotate, suitably driven, so that they may be brought in succession to a sample injection station. In the apparatus shown in the accompanying drawings, for convenience the series of chromatographic columns consist essentially of tubes in a cylindrical piece of metal or other suitable material which is rotatable on its axis. Alternatively, of course, conventional columns of glass, metal or other suitable material could be supported in a suitable fashion so that they could be moved to the various stations as necessary. The actual dimensions of the chromatographic columns will, of course, be chosen with regard to their particular purpose and in accordance with known chromatographic principles. The apparatus illustrated is provided with means for back-flushing the columns, which allows for speedier analysis.
The detection device may be any convenient device capable of detecting, with appropriate accuracy and speed, the required substance. Such a detector may be capable, for example, of detecting electron absorbing materials.
Such electron capture detection devices have been described in the literature and are already well known in chromatography technology, having high sensitivity for certain halogenated compounds.
The apparatus of the invention, as has already been mentioned, has been employed in the direction of the interface between two different liquid hydrocarbons travelling in succession in a pipeline, by the incorporation into one of the liquids, at the interface, of an appropriate quantity of a suitable tracer substance.
Asthe tracer we have used a suitably volatile compound which can be detected by electron capture techniques. Several such tracers are known and have been described in the literature. They must have high electron affinity, should be suitably stable under conditions of use, and they should not adversely affect the materials and equipment which they contact in use. Polyfluorinated compounds have found application in the use of the apparatus of the invention, since the amounts of fluorine compound used is usually so small that any harmful effects are negligible and sulphur hexafluoride has proved particularly valuable as an interface indicator.
In use, the electron capture detection device responds unselectively, that is to say, it detects not only the particular tracer substances employed but also the presence of other electron absorbing materials which may be present in the eluate from the columns; this continues, of course, even when no tracer substance is present.
Thus the electron capture detector responds to the presence of, say, oxygen, so that even when the tracer substance is not present in the material being sampled the detector indicates the presence of a material having electron affinity. There is therefore, in effect, a continuous record of electron absorbing material passing through the detector, representing an electron absorbing background material, to which is added occasional peaks indicating the detection of an amount of a tracer substance. This constant recording of a background material is useful in that it is an indication that the detection device is operating satisfactorily. We have found, however, that the baseline which represents the background electron absorbing material is uneven, due apparently to variation in the retention of detectable materials on the different columns of the multi-column chromatography unit.
A substantially even baseline has been obtained by passing the eluate from all the columns of the chromatographic unit through a further, common, column which retains the various detectable materials contributing to the baseline reading and releases them at a substantially constant rate, in effect smoothing out the variations in individual column characteristics and producing a much more even baseline against which the detection of tracer substances can be observed.
In a further embodiment of the invention, then, there is provided a common after-column into which eluate from the different chromatography columns passes before it enters the detector. The after-column may be packed with any suitable material to constitute the stationary phase. Generally the packing material will be similar to that in the main columns. No repeated backflushing of this common column occurs, except on occasion when it may be desirable for periodic cleaning, since it operates continuously while-chromatography through any of the columns is going on.
FIG. 2 is a diagram showing the flow of a tracer substance after its transfer to an analysis apparatus comprising the after-column. In this Figure, 11 is a nitrogen supply, the nitrogen serving as the carrier and flushing gas, 12 is a molecular sieve purifier to remove electron absorbing materials from the nitrogen, 1 is the sampling valve, 2 is the chromatographic unit, 13 is the aftercolumn, 3 is the detector; 14 and 15 are the nitrogen lines for chromatography and backflush respectively.
. FIG. 3 is a vertical section through an embodiment of a valve/chromatographic unit comprising an aftercolumn and FIG. 4 is a section along the line 4-4 in FIG. 3. The sampling valve 1 is a valve as described in our copending British application Ser. No. 4476/69 filed Jan. 27, 1969.
The chromatographic device consists of a cylindrical block of Duralumin rotatable about its axis, in which are drilled six columns, each 10 cm. long and 5 mm. in diameter. These are packed with a' suitable adsorbent material 21; the choice of material will present no difficulty to the skilled man. As an example, we have satisfactorily employed 25 percent squalene on Celite 545 for the separation of volatiles from hydrocarbons. In each column the packing is retained by a 3 mm. thick press-fit disc, 22, of sintered stainless steel (40 microns porosity). Grooves 27, 28, 29, 30 in the stationary end plates 23, 26 of the cylinder direct the gas flow as required, allowing a 10 second analysis of the vapor fraction from the sampling valve 1 (grooves 27, 29) and 20 seconds back flushing time (grooves 28, 30). The column is heated by an 85 watt cartridge element 24, in the bottom center of the unit. The cylinder rotates on its spindle 25, driven by an electric motor (not shown) synchronously with the sampling valve.
The following sequence has been employed in the detection of sulphur hexafluoride tracer in mineral oil: the sampling valve 1 delivers, at 10 second intervals, 2 microlitres of the oil sample, and the volatiles including the SP are carried with the nitrogen, which is delivered at 25 ml/min, into the chromatography column 2 which at that time is in the sample inlet position. The column is packed with 25 percent squalene on Celite 545 carrier. Chromatographic separation occurs in the column as it rotates, and after 10 seconds, during which time the SP will have passed through the column and into the after-column 13, the column reaches the backflushing position where the nitrogen stream is reversed so that materials retained in the columns are swept out. The column temperature is maintained at 50C.
The eluate from the column 2 enters the aftercolumn 13 which is packed with the same material as the main columns. The after-column 13 is a stainless steel tube 5 cm. long and 4 mm. in diameter. Variations in composition of the eluate, due for example to the differences in packing, etc. of the different columns, are smoothed out so that the eluate from the after-column 13 is substantially constant in its background component. This eluate then passes to the electron capture detector where the presence of electron absorbing material is detected and registered electronically. The detection of a tracer substance can be used in conventional apparatus (not shown) to control automatic switching of hydrocarbon or liquids when the tracer has been used as an interface indicator. In such applications the importance of an even baseline against which the tracer peak can be detected with certainty will be apparent.
In the apparatus described and illustrated, rotation of I the cylinder is continuous, direction and duration of gas flow through the columns being controlled by the grooves 27, 28, 29, 30 shown in FIGS. 5 and 6 which represent, respectively, the fixed end plates 23 and 26 located at the sample inlet and outlet ends of the cylinder. Alternatively, the cylinder could be made to rotate intermittently, so that the cylinder is stationary during the injection of the sample, although this arrangement is not preferred.
Apparatus as described above was used for the determination of the position of an interface between two different hydrocarbon oils travelling in contact in succession through a 50 cm. diameter pipeline. The tracer substance was 25 ml of trichlorofluoromethane and the distance travelled before analysis was 190 Km. Samples means for continuously revolving said chromatographic device at a substantially constant speed in timed sequence with the withdrawal of said sample by said sampling valve;
a source of carrier gas, said source being in fluid communication with said sampling valve, said source also being in fluid communication with said chromatographic device;
a detector device for detecting the presence of said tracer material in the eluent from said chromatographic device, said detector device being in fluid communication with said chromatographic device;
said chromatographic device including a stationary lower plate provided with first and second grooves, said first groove being in fluid communication with said sampling valve for introduction of said sample into said chromatographic columns;
a stationary upper plate having first and second grooves similar to said first and second grooves in said lower plate, said second groove being in fluid communication with said carrier gas source for backflushing said chromatographic columns;
a cylindrical shaped member rotatable about its axis,
said member being positioned between said upper and lower stationary plates, said member having a plurality of chromatographic columns spaced equal distance from the longitudinal axis of said cylindrical member, said first and second grooves in said upper and lower stationary plates being arranged such that any one of said chromatography columns is in fluid communication with said second groove for substantially twice as long as any of said chromatographic columns is in fluid communication with said first groove.
2. The apparatus of claim 1 further including an after-column between said chromatographic device and said detector device.
3. The apparatus of claim 1 wherein said detector is an electron capture detector.