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A simple gas chromatographic injection system
JOURNAL
OF
CHROMATOGRAPHY
609
Notes
CHROM.
4343
A simple
gas chromatographic
infection
system
In order to obtain optimum resolution in gas chromatographic analysis, it is necessary to inject the sample gas into a carrier gas flow in such a manner that the sample remains as nearly as possible as a disc or cylinder of gas sandwiched between the carrier. Conventional gas injection systems either use several stopcocks, which effectively divert the carrier through a sample holder tube, or are rather expensive. The cheaper systems suffer from the fact that several, stopcocks must be operated, resulting in a certain degree of spreading out or diffusing of the sample disc. This necessitates the use of a longer column that would otherwise suffice. We have for some time made use of a simple ‘home-made’ stopcock which we find minimizes the diffusion of the sample disc, and achieves good resolution wit11 columns up to 20 o/o shorter than have hitherto been necessary.
Fig. I, Vcrticnl
cross-section
Fig. 2. injection
stopcock.
through
barrel
of the
injection stopcock.
The stopcock key is shown in Fig. I. This key has two bores, one of which is a ‘straight-through bore which normally allows passage of the carrier gas from reslike a letter U -proervoir to chromatography column. The second bore -shaped vides the sample holder volume, which can be filled in the normal way. Our model had a sample volume of about 12 ml.
NOTES
610
The stopcock in position in a vacuum line is shown in Fig. 2. Once filled the key can be quickly turned so that the sample is compressed to a disc and carried directly to the chromatographic column. The improvement in peak shape that results from using this technique is shown in Fig. 3. The stopcock key was made by Mr. T. J. MAPLE (Chemistry Department, Queen Mary College) and the barrel was supplied and the grinding performed by ‘Clemwoods’, 20-24 Beaumont Road, Chiswick, IV. 4, of London for a mainOne of us (D. J.M.L.) wishes to thank the University tenance grant.
Fig. 3. Radio-chromatographic
traces of the separation of I-11’ (right-hantl peak) and CH,T
hand peak) on an activated silica gel column, under comparable conditions. Conventional proccdurcs were used for the top trace. The bottom trace was obtainecl using the injection clcscribecl in this note. The improvement in peak shape can bc seen quite clearly.
Mary College, University of Lodon, Dq5artment of Chemistry, .Vilc End Road, London, E.r (Great Britaiqt) Queen
Received
August 4th, Ig6g
J. Clrroruatog., .+4 (1969) bog-GIO
DAVID
(Icft-
injection stopcock
J. MALCOLME-LAWES DAVID S. URCH
OF
CHROMATOGRAPHY
609
Notes
CHROM.
4343
A simple
gas chromatographic
infection
system
In order to obtain optimum resolution in gas chromatographic analysis, it is necessary to inject the sample gas into a carrier gas flow in such a manner that the sample remains as nearly as possible as a disc or cylinder of gas sandwiched between the carrier. Conventional gas injection systems either use several stopcocks, which effectively divert the carrier through a sample holder tube, or are rather expensive. The cheaper systems suffer from the fact that several, stopcocks must be operated, resulting in a certain degree of spreading out or diffusing of the sample disc. This necessitates the use of a longer column that would otherwise suffice. We have for some time made use of a simple ‘home-made’ stopcock which we find minimizes the diffusion of the sample disc, and achieves good resolution wit11 columns up to 20 o/o shorter than have hitherto been necessary.
Fig. I, Vcrticnl
cross-section
Fig. 2. injection
stopcock.
through
barrel
of the
injection stopcock.
The stopcock key is shown in Fig. I. This key has two bores, one of which is a ‘straight-through bore which normally allows passage of the carrier gas from reslike a letter U -proervoir to chromatography column. The second bore -shaped vides the sample holder volume, which can be filled in the normal way. Our model had a sample volume of about 12 ml.
NOTES
610
The stopcock in position in a vacuum line is shown in Fig. 2. Once filled the key can be quickly turned so that the sample is compressed to a disc and carried directly to the chromatographic column. The improvement in peak shape that results from using this technique is shown in Fig. 3. The stopcock key was made by Mr. T. J. MAPLE (Chemistry Department, Queen Mary College) and the barrel was supplied and the grinding performed by ‘Clemwoods’, 20-24 Beaumont Road, Chiswick, IV. 4, of London for a mainOne of us (D. J.M.L.) wishes to thank the University tenance grant.
Fig. 3. Radio-chromatographic
traces of the separation of I-11’ (right-hantl peak) and CH,T
hand peak) on an activated silica gel column, under comparable conditions. Conventional proccdurcs were used for the top trace. The bottom trace was obtainecl using the injection clcscribecl in this note. The improvement in peak shape can bc seen quite clearly.
Mary College, University of Lodon, Dq5artment of Chemistry, .Vilc End Road, London, E.r (Great Britaiqt) Queen
Received
August 4th, Ig6g
J. Clrroruatog., .+4 (1969) bog-GIO
DAVID
(Icft-
injection stopcock
J. MALCOLME-LAWES DAVID S. URCH