ARRANGEMENT AT A GAS FLOW THROUGH CELL FOR SPECTROPHOTOMETRIC ANALYSIS OF CHEMICAL COMPOUNDS

Abstract: A gas flow cell for spectrophotometric analysis of chemical compounds, consisting of a longish preferably cylindrical body (1) with a longitudinal central channel (2) which at the ends of the body (1) is limited by mutually parallel windows (3, 4) which are tightfitting against the channel (2) and transparent for the radiation used at the analysis. The channel (2) communicates at one end with connections (7, 8) for carrier gas and for injection of compounds and has at the other end an outlet (10) for the compounds and the carrier gas. Significant for the invention is that parallel with and at a distance from the mentioned channel (2) runs a second channel (11) serving for separation and connected between the connections (7, 8) and said end of the first mentioned channel (2). In this channel (11) there is a replaceable column tube (12) with filling of known composition.

Description: Arrangement at a gas flow through cell for spectrophotometric analysis of chemical compounds The present invention relates to an arrangement at a gas flow cell for spectrophotometric analysis of chemical compounds in the gas phase consisting of a longitudinal preferably cylindrical body with a longitudinal central channel which at both ends of the body is limited by two mutually parallel windows which are tightf itting against the channel and transparent for the radiation used at the analysis, which channel communicates at one end with connections for a carrier gas and for injecting compounds and at the other end has an outlet for the compounds and the carrier gas. Background of the invention That part of analytical chemistry which is dealing with separation and detection of organic compounds in mixtures has ever since in the sixties been dominated by gas chromatography where the detection normally is obtained by an unspecific detector. More recently the technique has developed towards combinations of gas chromatography (GC) with qualitative analytical methods like mass spectroscopy (MS), IR-spectrophotometry (IR) or UV-spectrophotometry (UV). The advantage with these combinations is first of all that it gives possibilities for identification of compounds which are separated on the gas chromatograph. Further on it gives the possibility to achieve selective detection for example by selecting a wavelength on the UV- or IR-detector where only aromato compounds gives a response. Drawbacks of known technique Gas chromatographs has in general a size and complexity which imply that the instrument must be permanently installed in one place. The injector, column and detector are further on individually heated and the possibilities for identification of an unknown compound is strongly restricted with conventionel instruments equipped with unspecific detectors. Additional drawbacks are lengthy start up times, occasionally relatively long analysis times and high instrument costs. Commersially available instrument combinations exist for GC/IR and for GC/MS but not for GC/UV. The commercial combination of instruments are very costly and have complicated connections between the gas chromatograph and the spectrophotometer which makes it considerably difficult for changing to other analytical techniques like IR-analysis of compounds in the liquid phase. The high costs and the complexity has led to that most analytical laboratories with a particularly quantitative direction will have restricted possibilities for identi¬ fication of compounds. Object of the invention A primary object of the invention in question is to achieve a gas flow cell by initially described kind, by which the combinations GC/UV and GC/IR as well as enrichment of compounds can be carried out. This is obtained according to the primary characteristic of the invention in that there is a second channel serving for separation connected between the connections and one of the ends of the first mentioned channel, in which channel there is replaceable column with column filling of a kind known per se. In that the body, according to a special characteristic of the invention, is of an electrically leading polymeric material of a temperature self-regulating quality and has electric connections so that the body can be heated by connection to a voltage supply is obtained that through utilization of the body as a resistor element with temperature self-regulating characteristic depending on increasing resistance with increasing temperature the cell can be heated in a way that a good separation of the compounds is achieved. Short description of the drawing In the following the invention will be further explained with reference to the ' attached drawing on which fig 1 in perspective shows a gas flow cell according to the present invention. Fig 2 shows a longitudinal section through the gas flow cell in fig 1 and fig 3 and 4 show one of the ends of the gas flow cell seen in axial direction respectively across this direction. Description of an embodiment On the drawing numeral I represents a longish preferably cylindrical body with a longitudinal central channel 2. The body 1 preferably has such dimensions that it fits in the cuvette housinq of a spertrnphnfnmefRr and owing to technical and constructive reasons is made in four parts la, lb, lc and Id which are kept together by screws 5 and, where so is necessary, are sealed with O-rings 6. Channel 2 is restricted at the both ends of the body 1 by mutually parallel windows "• ., h which arp kept in plner hy thn pnrts lc and Id and which are tightly f O PI__ connected to the channel 2. The windows 3, 4 are transparent for the radiation used at the analysis e.g. quartsglass at UV-detection and at IR-detection an IR- transparent material for example ZnSe. Channel 2 communicates partly with a connection channel 7 for carrier gas and partly with a connection channel 8 for injection the mixtures of compounds which are goinq to be analysed. In the connection channel 8 there is a sealing injection membrane 9 through which injection can be carried out by a syringe. The opposite end of the channel I communicates with an outlet channel 10 for the compounds and the carrier gas. On the outside of the body there are connection tubes 7a respectively 10a to the channels 7 and 10. According to the invention there is a channel 11 serving for separation and/or enrichment connected between the connections 7, 8 in which there are a replaceable column tube with a composition known to a man skilled in the art. Channel 2 and 11 communicate with each other at the both ends turned against the window 3 at the left hand side in fig 2. The channel 11 with the column tube 12 and its filling serves for separation of different compounds in a sample as will be explained in the followinq. As is known there is as a rule a requirement for a defined temperature increase in order to separate different compounds in a sample. According to the present invention for this reason the body is therefore marie of an electrically conducting material e.η. a carbon filled polymeriπ with self-requlatinn temperature characteristic and equipped with connections 13, 14, 15 which can be connected to controlled voltage supply either by parallel connection through 13 and 14 resp 14 and 1.5 or in a series connection i.e. through 13 and 15 so that different kinds of heating of the body can be carried out. The channel 8 for the injection of the sample which is analysed rjnes through the nonnr.ot.ion I . As ran be seen the πolumn tube 12 nf the instrument is extremely short. Tn order to obtain comparable separation capacity as for conventionally packed GC- columns the support material in the column tube 12 is of considerably smaller particle sizes. These support materials are commercially available as column filling materials for liquid chromatography. The liquid phase can be applied in a manner similar to what is usual for normal GC -supports. Description of an analysis example The gas flow cell is placed in a spectrophotometer and the connection tube 7a for the carrier gas is connected to a gas supply and the electrical connections 13-15 to a voltage supply, not thrown on th drawing. By applying a defined voltage over the poles 13-15, a defined temeprature is achieved in the body 1. The sample is injected through the injection membrane 9 and is shown out in the space just in front of the separation column 12. Injection of samples can be carried out either in the gas phase or in the liquid phase. The compound in the sample is separated in a known way in the column. When the separated compounds reach the channel 2, they are registered by the spectrophotometer and the absorbance (proportional against concentration) and signal from the detector of the spectrophotometer can be recorded on a recorder or treated by an integrator in an usual manner. Selective detection of compound groups are obtained by the selection of a suitable wavelength on the spectrophotometer. At identification of compounds the analysis procedure is somewhat depending on the characteristics of the spectrophotometer. Advanced spectrophotometers having fast scanning possibilities can deliver a complete wavelength spectra while the compound is passing through the qas flow cell. When simpler and slower sμoetroμholυmelι_rs are used Ll.e qas flow is stopped when the compound is in position in the qas cell and the spectra is reqistered from the captured compound whereupon the qas flow again is allowed to flow.

Claims: Claims 1. Arrangement at a gas flow cell for spectrophotometric analysis of chemical compounds in the gas phase comprizing a longish preferably cylindrical body (1) having a longitudinal central channel (2) which at both ends of the body is limited by two against the channel (2) mutually parallel windows (3, 4) which are tightfitting and are transparent for the radiation used at the analysis which channel (2) communicates at one end with connections (7, 8) for a carrier gas and for injecting compounds and at the other end has an outlet (10) for the compounds and the carrier gas oha raot eri 7ed in that, there is a channel (11) serving for separation and/or enrichment connected between the connections (7, 8) and said one end of the first mentioned channel (2) in which channel (11) there is a replaceable column tube (12) with column filling of a kind known per se. 2. Arrangement according to claim 1, c h a r a c t eri zed in that, the body is made of an electrically conducting material preferably a polymeric material which has a temperature self-regulating characteristic by increas¬ ing resistance at increasing temperature. OMPI BAD ORIGINA 5 v ' °

Inventors: LAGESSON VERNER, LAGESSON-ANDRASKO LUDMILA, LAGESSON, VERNER, LAGESSON-ANDRASKO, LUDMILA
Applicants: INSCAN HB, HB INSCAN
Application year: 1984
Main classification: G01N21
IPC codes: G01N21, G01N30