investigation of the Behavior of a Flame Ionization Detector Working under High Pressure Gilbert Blu and Flavien Lazarre S. N.P.A. Centre de Recherches de Pau, Laboratoire de Physique des Fluides, 64001, Pau, France
Georges Guiochon €cole Polytechnique, Laboratoire de Chimie Anaiytique Physique, 75, Paris, France
A flame ionization detector has been built for work under pressure up to 100 bars. The jet tip has 0.1-mm i.d. The distance between the jet and the collecting electrode is 4 mm and the collecting voltage is 300 volts. The pressure dependence of the response for methane, of the minimum amount of methane which can be detected and of the effect of the mass flow rates of hydrogen, carrier gas (nitrogen), and oxygen have been examined and found to be important. These flow rates should be carefully optimized especially at high pressure. The response of the FID is maximum for a pressure of about 3 bars and decreases with increasing pressure up to 100 bars. At the optimum hydrogen and nitrogen flow rates, the sensitivity of the FID for methane under pressure of 100 bars is about 5 x IO-' g/sec, Le., 500 times lower than at atmospheric pressure.
Whenever gases are compressed up to 1000 bars, their densities approach those of liquids and their solvent properties become progressively similar. The use of such compressed gases as mobile phases in chromatographic systems could induce a much larger rate of migration for species of high molecular weight, high polarity, and low volatility which have usually prohibitive retention times in conventional gas chromatographic systems a t moderate temperature and undergo decomposition a t higher temperatures. The numerous potential advantages of high pressure gas chromatography over the conventional technique have been outlined elsewhere (1, 2). The advantages over modern, high pressure liquid chromatography are the much larger diffusion coefficients in the mobile phases allowing greater efficiency to be obtained and the possibility of easily adjusting the partition coefficient in a wide range of values, just by changing the average pressure of the system. This method, however, also has important limitations. Apart from the difficulties of handling high pressure equipment, component detection is the most fundamental problem. A conventional detection system working under atmospheric pressure could not often be used because the species which had been induced to migrate under high pressure would stop moving as it reaches low pressure regions. It will clog the decompression system and will not reach the detector. Up to now, the detection problem has been tackled by converting the exiting stream of compressed gas into either a stream of dilute gas, by decompression (3, 4) or a L. McLaren, M . N . Myers, and J . C. Giddings, Science. 159, 197 (1968). G. W. Rjinders,
Chrornatographie sur colonne, "Proceedings of the 5th International Symposium on Separation Methods, Lausanne. 1969," E. Kovats, E d . , Sauerlander, Aarau, Switzerland, 1970, p
192. M . N.
Myers and J . C. Giddings. Separ. Sci.. 1 , 761
(1966)
stream of liquid, by cooling (2, 5, 6). Thus, the component detection is poor because the thermodynamic instability of the eluted species and, in the alternative technique by cooling, the small specific volume and diffusivity of liquid put severe requirements on detector dead volume and response time. Obviously, the ideal solution is to carry out detection a t the column outlet pressure. The use of a UV spectrophotometer similar to the one used in high pressure liquid chromatography is difficult. In addition to the limitation of its use to compounds absorbing UV light, its sensitivity a t moderate pressure (5-50 bars) would be small because of the low density of the mobile phase. This paper describes an experimental arrangement that makes it possible to use a flame ionization detector working under the column outlet pressure without employing a restriction between the column outlet and the detector. The flame ionization detector (FID) has an exceptionally high sensitivity, a wide dynamic range, an unusually small dead volume. Owing to these performances, the FID seems ready to be used in high pressure gas chromatography. A pioneering work has been published (7) concerning the ionizatioli efficiency of the FID between 1 and 25 bars. In order to estimate the direct influence of the total pressure and the mass flow rates of the three gas streams necessary to this detector on the performances of the FID, this paper gives further information on the signal-to-noise ratio and the response of the FID between 1 and 100 bars.
EXPERIMENTAL Design of the High Pressure FID. Various designs have been realized. The scheme of the one which gave the best results and is discussed here is illustrated in Figure 1. The setup of the detector demands classical high pressure technology, especially metalmetal sealings for tubing connections. Detector Cell. The body of the detector is made up of a stainless steel cylinder 500 m m long, 80-mm i.d. The use of stainless steel is necessary since under high pressure, mixtures of steam and oxygen are very corrosive. This cell is heated while steam produced by hydrogen combustion is condensed under pressure by passing the gas stream through a second cell identical to the detector cell. The desired pressure is kept in the detector cell by a needle valve controlling the gas outlet from this second cell. Coliecting Electrode a n d B u r n e r A r r a n g e m e n t . The arrangement of the collecting electrode and the burner is unusual. As can be seen in Figure 2, the collecting electrode is made from a porous disk 40-mm i.d., of sintered stainless steel particles (50 p ) through which the oxygen flow stream feeds the hydrogen flame. The burner is made of a stainless steel tube 40 m m long and about 0.1-mm i.d. The burner is set parallel with the collecting electrode and its tip is approximatively at the center of the porous disk. The distance between the collecting electrode and the burner can be adjusted when the detector is under pressure. It is usually 4 m m . This arrangement offers a satisfactory solution to ( 4 ) J. C. Giddings, M. N . Myers, L. McLaren, and A. Keller, Science. 162, 67 (1968). ( 5 ) S. T. Sie and G . W. A . Rjinders, Separ. Sci., 2, 699 (1967). (6) S. T. Sie and G . W. A. Rjinders, Ana/. Chim. Acta. 38, 31 (1967). (7) P. Bocek, J . Novak, and J . Janak,J. Chrornatogr. 48, 412 (1970).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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0
'
r - -- - ----
Figure 1. Diagram of the high pressure flame ionization detector electrical and pneumatic system 1 . Recorder; 2, Electrometer; 3, High impedance isolated battery; 4, Pressure gauge; 5. Auxiliary oxygen tank; 6, Oxygen tank; 7, Flow meters; 8, High pressure controllers; 9, Needle valves; 10, Sampling valve; 1 1 ,' Restrictor: 12, Burner; 13, Steam condensation vessel; 14, Restricting outlet needle valve; 15, Mobile ignitor; 16, Mobile collecting electrode; 17, Alumina piston: 18, Thermostated FID cell; 19, Quartz window; 20, High voltage generator
Figure 2. Diagram of the collecting electrode and the oxygen feed to the hydrogen flame 1 , F I D cell; 2, Collecting electrode; 3, O-ring; 4, PTFE piston; 5, Hole: 6, 02 inlet tubing; 7 , PTFE sheet: 8, Quartz disk; 9. Mobile piston; 10. Gland nut: 1 1 , Plug seal: 1 2 , Steel body: 13, PTFE disk; 14, Screw; 15.
Terminal the difficult problem of the electric connection between the collecting electrode and the electrometer. Connection b e t u e e n the Collecting Electrode and t h e Electrom e t e r . The burner is grounded so the impedance of the electrode insulator has to be above l O I 4 R. In connection with this oroblem. it should be emphasized that the classical and commonly used insulator materials lose most of either their resistivity (quartz, a h mina) or their mechanical resistance (PTFE) a t moderate tem1376
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
perature 18). For instance, the resistivity of pure alumina is about one tenth as high as 100 "C as a t 25 "C. Thus, this electric connection is very difficult to design and build. As shown in Figure 2, the system is designed so that the electric connection through the cell wall is in a cold zone of the FID which is scavenged by a dry stream of oxygen flowing through the collecting electrode as just described above. The electric connection itself is made by means of a quartz insulating disk, 5 m m thick, tightened between a stainless steel piston and a ring sandwich whose faces have been polished. The possible surface irregularities of the disk have been compensated by a P T F E sheet 0.05 m m thick. The pressure inside the cell and the mechanical tightening cause the PTFE rings to flow, providing a positive seal. Ignitor. A cell window permits one either to watch the hydrogen flame or to check ignition. The flame is ignited by a n electrical spark generator. The ignition by a glowing spiral would be possible but previous experience shows that the spiral is very shortlived. A 1000-Hz oscillator supplies about 5000 V to the secondary coil of a transformer. This voltage is multiplied by a succession of double voltage cells. As shown in Figure 1, the ignitor electrode can slide through a tube sealed in a n insulating piston, 50-mm i.d., which permits us to choose the distance from the jet tip of the burner. The distance required to ignite the flame under high pressure is shorter than 1 m m ; the igniting electrode can then be withdrawn to a distance of 40 m m . At 100 bars, a voltage of 50,000 volts is required to produce a spark hot enough to ignite the hydrogen-oxygen flame. Fluid Flou S>stem. There are three flows of gases to the detector (Hz, 0 2 : and Sz carrier gas) which have to be controlled. Fluid sources are stored in a thermostated room. Thus pressure fluctuations due to temperature variations are negligible compared to the fall of pressure due to the consumption of the detector which is less than 0.17~per minute. The principle of the flow control is to measure the pressure drop across a capillary tube by means of pressure tranducers (ACB - 440 Hd, Ateliers de Construction Beaudoin, Paris. France). There is no equipment available to measure mass flow rates under changing pressure. So we measure and control the gas flow rate under constant pressure (100 bars) and then we adjust the pressure to the desired \ralue, For a better understanding of Figure 1, one may describe a flow line as follows: Nitrogen flows from a 80-1. storage tank under pressure successively ihrough a closing valve (Autoclave), a flow meter (ACB 440 HD), a high pressure controller (ApCo 1342), a needle valve (KUPRO) to adjust the nitrogen flow rate, a restrictor, and then to the burner, In the following, all the flow are expressed in cm3! (8) E. Ryshkewitch, "Oxide Ceramics. Physical Chemistry and Technology," Academic Press, New York, N.Y., 1960, p 472.
min a t a pressure of 1 bar and a temperature of 15 "C; the pressures are given in bars (1bar = 1.013 a t m = 14.51 psi). Procedure. Starting experiments with a high pressure FID is different from what is commonly done under atmospheric pressure (Figure 1)and so it needs to be described. The outlet needle valve of the FID being closed, the detector is filled by means of a n auxiliary source of oxygen until the pressure reaches the desired value: then the connections to the auxiliary oxygen supply are closed and the detector is supplied from the main oxygen line through which the flow rate can be controlled as described above. T h e total volume of the detector cell is about 2 liters and the oxygen flow rate is about 300 cm3/min, so that one has enough time to adjust the high pressure oxygen flow rate to the required value without creating a n excess of pressure in the detector, since the pressure is increasing at a rate of about 0.15 bar per min. Once this operation is done, the outlet needle valve of the detector cell is adjusted to keep constant the pressure in the detector. The oxygen flow rate being set, the nitrogen carrier gas line to the detector is opened. The carrier gas flow rate is about ten or twenty times smaller t h a n the oxygen one, so its contribution to the buildup of excess pressure in the detector is small and the setting of the oxygen flow rate does not have to be changed. After the pressure in the detector cell has been equilibrated, the valve of the high pressure hydrogen supply is opened. For understandable reasons, a pre-adjustment of the hydrogen flow rate is recommended before igniting the flame. This is done in the same way as the adjustment of the carrier gas flow rate. Then, the hydrogen supply is closed until the hydrogen concentration in the detector cell becomes lower than the limit of inflammability of oxygen-hydrogen mixtures. After that operation, the valve on the hydrogen line is reopened and the flame is ignited as explained above. Then the electometer. a Knick picoammeter P 24: is connected with the collecting electrode. The voltage applied across the collecting electrode and the burner is 300 V. Experimental determination of the voltage-intensity curves for various values of the total pressure and of the flow rate have shown that this voltage is sufficient to allow complete collection of the ions in the whole pressure range studied from 1 to 100 bars. In other words, at 300 V. the detector works in the plateau region of the voltage-intensity curve 19). The variation of the detector response to methane with the experimental conditions has been studied. T h e sample is introduced with a 10-fi1Microtech sampling valve (Series 1500) that has been modified in such a way that P T F E seals make it tight up to 150 bars. For this study, methane samples are introduced in the detector through a capillary tube 4 meters long, 0.25-mm i.d. Under normal conditions, i . e . , atmospheric pressure, the baseA and the maxiline noise of the detector is around 5 x m u m response around 70 mC/g for methane.
THEORETICAL The response of the flame ionization detector may be characterized by two factors: one factor, related t o its principle of operation, is the ionization yield R or the yield of the ionization reaction; the other factor is related to the chromatographic use of the detector, this is its sensitivity. Response of the FID-R. Although there has been considerable controversy regarding the possible mechanism of production of ions in flame and specially in the FID, it is generally accepted that in its usual application t o hydrocarbon analysis, the FID produces positive ions H 3 0 + by the following mechanism (20):
CHO+
+
e-
[H2"1.
co +
H ~ O + (1)
If a constant collecting voltage is applied across the flame when hydrocarbons or organic compounds are eluted from the chromatographic column, the H30+ ions are collected, (9) H. Bruderreck, I. Halasz, and W . Schneider, Anal. C'hem.. 36, 461 (1964). (10) P. Bocek and J. Janak, Chrornatogr. R e v . . 15, 111 (1971).
3 4
.
22
26
30
*
Figure 3. Variation of the mass efficiency R for CH4 vs. hydrogen mass flow rate. The figure on each curve gives the nitrogen mass flow-rate. Total pressure in the detector cell is 42 bars. The mass flow-rates are expressed in cm3/min at 1 bar and 15 "C
the ionization current I increases, and a positive signal is recorded. If the voltage is sufficiently large, all the ions are collected. The response of the FID is defined as the yield of the chemi-ionization reactions. Let Q (C) be the charge transferred between the burner and the collecting electrode during the introduction of M , (8) of the species to be detected. The mass iohization efficiency or the mass response will be:
Q is proportional to the peak areaA
tl and t 2 are the initial and final elution time of the peak and k is dependent on the signal amplifier system. R is a function of the flow rate of hydrogen and carrier gas, i . e , the gas velocity in the flame and the composition of the feed gas, of the oxygen flow rate and of the pressure. Sensitivity-S. The response of the FID must be associated with the noise level i which is usually given as 4 times the second moment of the detector signal. Thus, the minimum detectable signal will be defined as S = i/R
[gisec]
(4)
It should be noted that this sensitivity is a mass flow of sample. The minimum detectable amount of substance is a function of peak width as the peak area, determined by Equation 3, is a constant. So the sensitivity will be a function of both the carrier gas flow rate and the column efficiency. This problem will be discussed later.
RESULTS AND DISCUSSION The response of the FID depends on the flow rates of hydrogen and carrier gas to the flame, whereas usually the oxygen or air flow rate is much larger than stoichiometric and has no effect. In order to determine the pressure dependence of the detector response and sensitivity, it is necessary to carry out the optimization of the two flow rates a t various pressures in the range covered since, a t present, theory provides no relationship to estimate the effect of pressure on these optimum flow rates. Pressure Dependence of the FID Response. Figure 3 shows the variation, at a given pressure, of the detector response with hydrogen mass flow rate for various nitrogen mass flow rates. Such a graph allows derivation of the opANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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M A S S FLOW R A T E
Icm3 / m i " )
I Y
4 P (bar)
IO
0
i 2
3
s
20
;o'
?C13-
* +
Figure 4. Pressure dependence of the maximum mass ionization efficiency R, for CHI. Because of the lack of stability of the pressure controllers at low pressure, the noise is large at 2 , 3 could in fact be larger than reported here, and 5 bars and R, hence the dotted line. However R, cannot be lower
timum values of both flow rates. Similar graphs have been determined a t various pressures. The occurrence of a maximum in the FID response in all the pressure range has been evidenced by operating a t various H2 and N2 mass flow rates, from 0 to 150 cm3/min in thC low pressure range (1, 2, 3, 5 bars) and from 0 to 50 cm3/min in the high pressure range (22, 42, 82 bars). This maximum of response occurs a t H2 and N2 flow rates which varies slowly with the pressure. Figure 4 shows the plot of the maximum response R,,, us. pressure. This illustrates the pressure influence on the ionization yield. The response shows a maximum between 2 and 3 bars and then decreases with increasing pressure u p to 100 bars. Comments on the pressure dependence of R,,, are rather hazardous, owing to the lack of data concerning the type of flame used. However, it seems (11) that two chain reaction mechanisms are competing in this case. Usually, chain initiation and propagation steps are first- or second-order reactions in this type of flame, whereas chain stopping reactions are mainly of the third order. Consequently, the chain stopping step becomes predominent as the pressure increases which could explain the decrease of R,,, with increasing pressure, above 3-5 bars. For each experimental pressure and for various N2 mass flow rates, the FID responses have been plotted LIS. the Hz flow rate (Figure 3, for P = 42 bars). This set of curves shows the existence of ranges of H2 and N2 mass flow rates around the optimum values within which flow rate fluctuations have a rather weak influence on the FID response. However, it has been observed that these ranges are dependent on the pressure and decrease steadily with increasing pressure. For instance, the response of the FID remains larger than 0.90 R,,,, a t constant N2 mass flow rate (about 24 cm3/min) in an H2 flow rate range of 50-150 cm3/min a t 1 bar whereas a t 42 bars and 82 bars this (11) J. 0.Hirschfelder, C. F. Curtis, and R. B. Bird, "Molecular Theory of Gases and Liquids," Wiley, New York, N.Y., 1954, p 764.
1378
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
100
Figure 5. Variation with the cell pressure of the N2 and H2 mass flow rates giving the maximum response (mass flow rates in cm3/min at 1 bar and 15 "C). The vertical lines indicate the range of flow-rate in which the response is larger than 0.9 R,
range is respectively 8-11 and 10.5-13.5 cm3/min. The H2 mass flow rate corresponding to the maximum response shows a marked trend to decrease with increasing pressure whereas the corresponding N2 mass flow rate is practically independent of the pressure (Figure 5). From a practical point of view, one should bear in mind that nitrogen is not used primarily to increase the detector response, but serves as carrier gas. Consequently, there is an important practical problem since the column and the burner diameters cannot be changed easily. The burner diameter determines the velocity in the flame, and thus the optimum flow rates to the detector; the column diameter determines the carrier gas velocity, and thus the column efficiency. Now is it possible to find a nitrogen flow rate which will give practically the maximum FID response and the maximum column efficiency in a large range of pressure? In Figure 6, the FID response maximized with respect to the H2 mass flow rate has been plotted 1's the pressure for various nitrogen flow rates. In the high pressure range, for N2 mass flow rate varying between 0 and 30 cm3/min, the relative variation of the FID response is less than 50%. The carrier gas velocity corresponding to maximum column efficiency decreases with increasing average column pressure 1121, so that the optimum carrier gas mass flow rate does not change much in a large range of pressure. Therefore, when working a t constant carrier gas mass flow rate, as in our experiments, it is possible to reconcile the requirements for both detector response and column efficiency if the column and burner diameters are properly chosen. All the experiments have been carried out at a constant 0 2 mass flow rate (300 cm3/min, at 1 bar and 15 "C). In H2-02 diffusion flames of the type used here, 0 2 is always in excess, because of the very small ratio ot the volumes of the flame and the FID cell this excess increases with the pressure. As one knows that at atmospheric pressure, the 0 2 flow rate has negligible influence on the FID response. it seems that there is no reason to investigate this dependence in high pressure experiments. (12) J. C. Giddings, "Dynamics of Chromatography ( I ) , " M . Dekker, New York, N . Y . , 1965, p 265.
- - -,
,
'*-*,
i c m 3 / mi")
3
4
5
6
7
8
9
%
15
20
Figure 8. Variation of the FID sensitivity S for CH4 vs. hydrogen 2
3
10
20
30 40
Figure 6. Variation with the cell pressure of the FID response maximized with respect to H2 mass flow rate at various N2 mass flow rates
mass flow rate at various nitrogen mass flow rates. Total pressure is 42 bars S (g/secl 10- 7
10-12
H2 (cm3/rinl
Figure 7. Variation of the signal noise i vs. the hydrogen mass
flow rate at various nitrogen mass flow rates. Total pressure in the detector cell is 42 bars. The square point corresponds to conditions of maximum response Pressure Dependence of the Minimum Detectable Amount. As mentioned above, the sensitivity of the detector is defined as the ratio of the noise to the detector response. As the FID is a mass flow sensitive detector (13), the sensitivy is given in mass flow rate unit (g/sec). Thus the minimum detectable amount of any compound depends on the column used (peak width) and on the carrier gas flow rate. As the noise level depends also on the hydrogen and nitrogen flow rates, the conditions for maximum sensitivy are not necessarily those for maximum ionization yield. Figure 7 shows the variation of the signal noise with the hydrogen flow rate a t various nitrogen flow rates under a pressure of 42 bars. Figure 8 shows the variation of the detector sensitivity obtained for a hydrogen (13) I. Halasz, A n a / . Chem.. 36,1428 (1964)
5
10
20
30
50
!CC
Figure 9. Variation of the sensitivity for CHI vs. the hydrogen
mass flow rate under various pressures at constant nitrogen mass flow rate (24 cm3/min). The square points correspond to the conditions for maximum mass ionization efficiency flow rate of 5 cm3/min, and a nitrogen flow rate approximatively 15 cm3/min, conditions which are quite different from those for maximum response (Hz = 9 cm3/min, Nz = 26 cm3/min) as shown on Figure 3. The typical shape of the curves is quite remarkable. T o point out the peculiar dependence of S on the Hz mass flow rate and on the total pressure, we show on Figure 9 the variations of S with hydrogen flow rate a t constant r\;2 mass flow rate (Nz = 24 cm3/min) and a t various pressures. Each curve may be divided into two regions. In the first one, S is constant; in the second region, S increases sharply with the Hz flow rate. It can be noted that region I has a range approximately independent of pressure above 20 bars. We also observe that the maximum response is in the transition between region I and I1 (Figure 9). ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
1379
Figure 10. Variation of S with pressure. The hatched zone corresponds to region I (Figure 9 ) and nitrogen flow rate between 10 and 30 crn3/rnin
From a practical point of view, it seems obvious that one should pick region I as the working range. In this region, S does not vary too much with pressure for iXz flow rate between 10 and 30 cm3/min (1 to 2 orders of magnitude, see on Figure 10). It can be observed also on this figure that for a N P mass flow rate of 24 cm3/min, S is 500 times as high a t 100 bars as a t 1 bar, whereas Figure 4 shows that the response factor decreases by a factor of 500 in this pressure range. This comes from the fact that in certain Hz and Nz mass flow rate ranges, the noise does not depend on the pressure and can be kept a t less than l O - I 3 A from 1 to 100 bars.
The setting of the flow rate to the detector, especially the one of the hydrogen flow rate, is critical at high pressures and moderate deviations from the optimum conditions can lead to an increase of the noise level by one to two orders of magnitude which makes the detector increasingly difficult to use a t high pressures. This is probably the reason why previous workers (7) found it impoasible to operate a FID above 25 bars. Our experimental design allows us to observe the flame (Figure l). In contradiction with what has been claimed to be the reason for a large amount of noise under high pressure, we never observed that the flame becomes thinner and higher with increasing pressure. In fact, the flame becomes smaller and can never touch the wall. It was also observed that the flame color changes from blue to white as the pressure increases. Moreover the flame turns to pink upon introduction of methane into it. Some exploratory experiments with an inversed system, i e . , oxygen flowing through the burner into a hydrogen medium, have led to the following observation: while a t atmospheric pressure, the oxygen flame could not be ignited (in all experimental flow conditions), the FID response and sensitivity a t higher pressures, from 2 up to 10 bars, are of the same order of magnitude as those of the conventional hydrogen flame. Finally, with the conventional hydrogen flame, in the pressure range below 100 bars, the detector is relatively easy to use and allows one to investigate the behavior of non-ideal gas mixtures under pressure and the conditions of application to analytical problems of high pressure gas chromatography.
ACKNOWLEDGMENT It is a pleasure to thank J. L. Joseph who carried out most of the experimental work. Received for review September 28, 1972. Accepted December l l , 1972.
Isolation of Column Phenomena in Gas Chromatography R . W. Dwyer, Jr. Philip Morris, U . S . A . ,Research Center, Richmond, Va. 23206
The method of Fourier transforms has been used to deconvolute experimental gas-chromatographic elution curves. This technique is suitable for isolating column phenomena and separating column processes. The greatest advantage of the Fourier deconvolution method is that it gives not only peak widths but also shapes. Examples of the utility of this method for diffusion and adsorption behavior are included.
In physicochemical studies using gas chromatography, one is interested in the molecular processes occurring in the column. The column is that part of the system in which both the physical and chemical characteristics of the molecular interactions can be varied. In pulse chromatography, the sample is introduced into the system a t 1380
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 8, JULY 1973
the injection port and passes through the end connections and column and into the detector. The resulting elution curve sensed by the detector is dependent on all of the zone-broadening processes occurring from the injection port to the point of detection. In order to isolate the effects of column phenomena from the total elution curve, one must correct for all of the extra-column band-broadening processes. In most applications of GC, the timeconcentration curve recorded by the detector is considered to be the distribution arising solely from the column. In accurate studies, the system is usually designed to minimize perturbing influences such as broadening effects in the ends, but these effects are seldom accounted for exactly. The purpose of this paper is to present a technique for isolating the time-concentration distribution arising solely from column phenomena and, further, to resolve the col-
