US3056277A - Vapor fractometers - Google Patents

Description

Oct. 2, 1962 N. BRENNER 3,056,277

VAPOR FRACTOMETERS Filed March 5, 1959 FIG. l

| 26 i I 1 24 I2 I4 I I6 22 ID OXYGEN AND I NITROGEN l8 2 (SILICA GEL) 2I REE 28 30 sans l L. MEASURING 32 34 n NITROGEN 36 (SYNTHETIC ZEOLITE) CARBON DIOXIDE (SILICA GEL) F I G. 2 OXYGEN (SYNTHETIC ZEOLITE) START IN VEN TOR.

NATHAMEL BRENNER BY WK ATTORNEY United States Patent O 3,056,277 VAPOR FRACTOMETERS Nathaniel Brenner, South Norwalk, Conn., assignor to The Perkin-Elmer Corporation, Norwalk", Conn., a corporation of New York Filed Mar. 5, 1959, Ser. No. 797,370 2 Claims. (Cl. 73-23) This invention relates to vapor fractionation and more particularly to a unique vapor fractometer apparatus which produces improved analyses.

Vapor fractometry, also known as vapor fraction chromatography, is a well-known analytical method for the analysis of multi-component samples. Two methods are most widely used for vapor fractometry. One of these is known as the clution-adsorption method, and the other is known as the elution-partition method of separation. In both methods a vapor sample is injected into a carrier gas, and the combination is then passed through a column containing a separating material. The material contained in the column slows the rate of progress of the different components of the sample by varying amounts, so that the carrier gas as it exits from the column contains bands of the various components of the sample. The columns which are used in chromatographic apparatus may be of several typesfor example, the well-known packed column and a newer coated column which comprises a tube having its internal surface coated with the separating material. The separating material may be either liquid or solid-alone, as in the coated tube, or in combination with various supporting materials.

Although vapor fractometry, as pointed out above, is a widely used and useful analytical procedure, there are certain problems which, up until the present time, have not been solved. One of these problems relates to the complete separation of all the components which may exist in a given sample. For example, many gas samples contain oxygen, nitrogen, and carbon dioxide and it is often desired to measure the concentration of each of these components in a sample. However, oxygen, nitrogen and carbon dioxide cannot be resolved in any system of single columns or columns in series unless highly cumbersome temperature programming systems o extremely long elution times are employed. The reason for this is that nitrogen and oxygen can be resolved only on powerful adsorbents which have excessive retention characteristics with respect to carbon dioxide. The only materials which separate oxygen from nitrogen conveniently at room temperature are synthetic zeolites of the type commercially known as Molecular Sieves. These materials, however, adsorb carbon dioxide irreversibly. Similarly, there are several adsorbents which will separate oxygen and nitrogen from carbon dioxide-silica-gel, for example.

Another problem which the apparatus of the prior art has failed to solve relates to the measurement of exact sample size. In vapor fractometry the small quantity of sample required makes the accurate metering of samples into the instrument quite ditficult. The size of the sample must be accurately known, however, in order to calculate percentages of components in the total sample. One approach to this problem which has been attempted is the development of accurate metering devices to inject precise amounts of sample. Such devices are complicated and expensive and must be precisely calibrated.

The primary object of this invention is to provide an apparatus capable of accurately separating and analyzing heretofore difiicultly separable components of a sample mixture. Another object is to provide a measurement system in the vapor fractometer itself which reflects the amount of sample injected by ordinary sampling methods.

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The above objects are achieved by providing a vapor fractometer for separating a sample into its constituents in accordance with their physical characteristics. The fractometer comprises a source of carrier gas and means for introducing the sample into the carrier gas. At least two columns are provided having a common inlet in series flow relationship with the carrier gas path. The columns define parallel paths for the How of carrier gas and sample and at least one of the columns contains material for which the components of the sample have different afiinities. In the embodiment herein described the detection means are then provided in series with the common outlet of the parallel columns for measuring the concentrations of the components present in the carrier gas. It is understood that the term parallel as used throughout this specification means functionally parallel and not necessarily physically parallel.

FIG. 1 is a drawing in schematic form of one embodiment of the present invention and FIG. 2 is a Fractogram of an example of an analysis employing the present invention.

The apparatus of the present invention will be more readily understood by reference to the drawing which shows in schematic form apparatus embodying the present invention. In the diagram a source 10 of carrier gas is illustrated in combination with a gas regulator 12 for providing gas to a conduit 14. Conduit 14 divides into two branch conduits 16 and 18. Conduit 18 conducts carrier gas to the reference side of detector 21. Conduit 16 conducts the carrier gas to parallel columns 20 and 22. A sample is injected into the carrier gas at sample injection point 24. Variable flow restriction elements 26 and 28 are provided in each of columns 20 and 22 for the proper apportionment of the gas flow therebetween. Thus, the rate of gas flow through column 20 is controlled by restriction element 26 independently of the rate of gas flow through column 22 controlled by element 28. As a result it is readily understood that the time relation of the eluted bands from columns 20 and 22 may be separately regulated and adjusted so that the bands of each can be time displaced in a predetermined order. This is considered to be a particularly novel feature of the present invention. The outlets of columns 20 and 2 are joined at point 30 and are connected by conduit 32 to the sensing cell of detector 21 and from there to an appropriate vent. A measuring circuit 34, such as a Wheatstone bridge, develops an output voltage which varies according to the difference in certain physical characteristics between the gases in the reference and sensing cells of detector 21. This difference is transmitted to recorder 36 where it is recorded as the percentage of a given component in the sampling mixture. By providing a vapor fractometer having at least two columns in parallel relationhip, it has been found possible to analyze quickly and accurately mixtures containing components which heretofore have been quite difficult to separate.

As an example of the present invntion, a one meter column was packed with silica-gel, a two meter column was packed with a synthetic zeolite and the two columns placed in parallel in a standard vapor fractometer. A gaseous sample comprising oxygen, nitrogen, and carbon dioxide was injected into the inert carrier gas. That part of the sample which passed through the column containing silica-gel was separated into two parts-oxygen and nitrogen appearing as one band and carbon dioxide as the second. That portion of the sample which passed through the column containing the synthetic zeolite was separated to yield an oxygen band and a nitrogen band. The carbon dioxide was irreversibly held by the latter column. An excellent analysis was obtained wherein separate, distinct peaks were recorded for carbon dioxide and nitrogen without the necessity of complex switching 3 arrangements. The particular time relationship of the bands passing to the detection apparatus is controlled by flow restrictors 26 and 28 to avoid any undesirable overlap and confusion of the bands. The resu ts of the above example are illustrated in FIG. 2. Any other combination of adsorption and partitioning agents may also be used in the columns of such a parallel system. 'For example, a separation of oxygen, nitrogen, carbon monoxide, methane, and higher hydrocarbons up to C, may be etfected in one sample run by placing a synthetic zeolite for the separation of oxygen, nitrogen, methane and carbon monoxide in parallel with a standard partition column containing dimethylsulfonane for the separation of the C; to C, fractions. Quantitative measurements of the foregoing analyses are obtained by calibration using known standards under identical conditions.

This invention is also suited for the analysis of gaseous samples when employing the small-diameter internallycoated columns known to the art as capillary columns. Columns of this type are described by Marcel J. E. Golay in an article entitled, Theory and Practice of Gas-Liquid Partition Chromatography With Coated Capillaries," appearing in the book Gas Chromatography published in 1958 by Academic Press Incorporated. Such a column may be used in this invention either in parallel with a similar column, or with a standard packed column.

As an example of yet another feature of the parallel column invention, a separation column may be provided in parallel with a non-separating column. The non-separating column would thereby provide a single peak readout having an area proportional to a fixed percentage of the total sample. This area could then be used as the basis for internal normalization calculation. Thus a standard sampling method may be utilized, although only a very small portion of the sample taken would be actually passed through the adsorption column.

It will be apparent to those skilled in the art that the invention as described herein has wide applicability in vapor fractomeu'y. Although only two analyses have been described, it will be understood that the parallel column system is practically unlimited in usefulness and, by proper selection of adsorbents, many different sample mixtures may be quickly and accurately analyzed.

It is of course understood that the embodiment above described and illustrated in the drawings is by way of example and various modifications could be made without departing from the spirit and scope of the present invention. For example, various arrangements of detection apparatus could be connected to the outlet ends of the columns.

I claim:

1. A vapor fraetometer for separating a sample into its constituents in accordance with their physical characteristics comprising a source of carrier gas; means defining a path for said carrier gas; means for introducing a sin gle sample into said carrier gas; at least two columns having a common inlet in series flow relationship with said path defining means, said columns defining parallel paths for the simultaneous flow of said carrier gas and sample, eachof said columns containing a diflferent material for which the components of the sample have different afiinities; flow control means adapted to control the relative flow rates between said columns; and detection means in series flow relationship with the outlets of said parallel columns for measuring the concentrations of said components in said carrier gas.

2. A vapor fractometer for separating a sample into its constituents in accordance with their physical characeristics comprising a source of carrier gas; means defining a path for said carrier gas; means for introducing a single sample into said carrier gas; at least two chromatographic separating columns having a common inlet in series flow relationship with said path defining means, said columns defining parallel paths for the simultaneous flow of said carrier gas and sample, each one of said columns comprising a tube internally coated with a different substance for which the components of the sample have different afiinities; flow control means adapted to control the relative flow rates between said columns; and detection means in series flow relationship with the common outlet of said parallel columns for measuring the concentrations of said components in said carrier gas.

References Cited in the file of this patent UNITED STATES PATENTS 2,728,219 Martin Dec. 27, 1955 2,868,011 Coggeshall Jan. 13, 1959 FOREIGN PATENTS 1,170,329 France Jan. 13, 1959 OTHER REFERENCES A publication entitled, Vapor Fractometry (Gas- Chromatography), by H. H. Hausdorff of the Perkin- Elmer Corporation, published in June, 1955.

An article entitled, Design Considerations of a Gas Chromatography System Employing High Efliciency Golay Columns by Richard D, Condon in Analytical Chemistry, vol. 31, No. 10, October, 1959, only page 1717 applied and referring to Golay, Symposium on Gas Chromatography, Amsterdam, Holland, 1958.

An article entitled Two-Stage Gas-Liquid Chromatography by Simmons et al. in Analytical Chemistry, vol. 30, No. 1, January, 1958, pp. 32-35.

The text entitled, Vapour Phase Chromatography" by D. H. Desty, 1957, Pp. 332-333.

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