Microdetermination of Sulfur by Hydrogenation and Gas Chromatography I. OKUNO, J. C. MORRIS, a n d W. E. HAINES laramie Petroleum Research Cenfer, Bureau of Mines,
b A method combining hydrogenation and gas chromatographic techniques has been developed for r a p i d determinations of sulfur in microsamples of volatile organic materials. Two modifications of the method a r e d e scribed. O n e permits estimation of sulfur in samples of such small size that a sulfur determination i s otherwise difficult a n d time-consuming. The other gives better accuracy but the sample to 10 mg. requirements a r e larger-5 Either procedure can b e completed in 30 minutes.
A
has been developed for measuring the sulfur content of samples obtained by microtechniques such as gas chromatogrrtphy. This method is based on catalytic hydrogenaMETHOD
Helium
6
U. S.
Department o f the Inferior, Laramie, Wyo.
ucts must be trapped and measured quantitatively so that the original sample weight can be estimated. Gas chromatography was selected as the most appropriate analytical tool available because it offered a rapid, sensitive, and convenient means of accomplishing this type of analysis. The method developed may be applied in two ways, the choice depending on the accuracy desired and the size of the sample: as an estimative procedure for samples too small to be weighed conveniently or as a truly quantitative procedure for samples from 5 to 10 mg. The procedure for larger samples was developed after it was found, in the course of the work on the estimative procedure, that as little as 5 mg. of sulfur could be quantitatively determined. The general method is the same for both procedures and consists of three steps-catalytic hydrogenation of the
tion followed by gas chromatographic analysis of the products. Catalytic hydrogenation of sulfur compounds has been used as an analytical tool for many years, both qualitatively-to identify such compounds through identification of the compounds resulting from hydrogenation (,$)--and quantitatively-to determine sulfur as hydrogen sulfide. All of the quantitative methods, from the early work of ter Meulen (3) to the recent work of Schluter (2), require that the sample be weighed. Weighing small samples, such as those obtained from gas chromatography, is inconvenient and often impractical. Problems of weighing are caused not only by the small quantities, but also by moisture condensation during handling so that, unless extreme precautions are taken, sample weights will include a high proportion of water. To determine the per cent of sulfur in unweighed samples, all of the hydrogenation prod-
+
Ii
c
+
Hydrogen
-1
Hrdroaenation . unit Figure 1. A.
-[_ Trappinq 4Unit
I
Chromatographic Unit
4 I
Schematic diagram o f hydrogenation-gas chromatograph apparatus
Flowmeter U-tube mercury manometer C. Pretrap (4 inches o f coiled 1/4inch glass tubing packed with 40- to 60-mesh Linde 5A Molecular Sieves) 0. Sample injection port fitted with a rubber serum cap E. Sample reservoir, borosilicate glass F. Quartz reaction tube (1 8 X '/2 inch 0.d. with 28/15 ball ioints)
B.
1
G.
1.5-inch catalyst zone (platinum gauze, 45-mesh, tightly rolled and pioced midway in reaction tube) H. Trap (coil made of 6 inches of 12-goge stainless steel hypodermic needle tubing packed with stainless steel helices) J. Trap (some as item H except packed with 40- to 60-mesh Linde 5 A Molecular Sieves) K. Column (same as item H except packed with 14- to
30-mesh Linde 4A Molecular Sieves) I. Chromatographic injection port M. Reference detector N. Chromatographic column ( 6 X 1/4 inch column o f 40to 60-mesh Davidson silica eel1 0. Sample sensing detector P. Variable transformer Nos. 1 to 6. Two-way stopcocks
VOL. 34, NO. 11, OCTOBER 1962
1427
sample to produce hydrogen sulfide and methane as the only significant products, trapping of the hydrogenation products, and measurement of the products by gas chromatography-all in a continuous system. The two procedures differ in the last two steps. I n the estimative procedure. the hydrogenation products are trapped and analyzed, and per cent sulfur is estimated from the ratio of the area or height of the hydrogen sulfide peak to the sum of the areas or heights of the hydrogen sulfide and methane peaks. I n the quantitative procedure, a sample weight is obtained, the area of the hydrogen sulfide peak is measured, and the weight of sulfur is obtained from a calibration curve. EXPERIMENTAL
Apparatus. T h e apparatus has three basic units: T h e hydrogenation unit, t h e trapping unit, and the chromatographic unit, as shown in the schematic diagram (Figure 1). All metal-to-glass connections were made with Swagelock fittings with Teflon seats. The hydrogenation unit includes flow regulating equipment, a trap, C, t o remove most of the nitrogen that occurs as an impurity in the hydrogen, a sample injection system, and the catalyst tube enclosed in a furnace. The system includes two additional traps, one cooled in liquid nitrogen, to collect the hydrogenation products except methane, and the second, packed with Molecular Sieves and cooled in a mixture of dry ice and ethylene trichloride, to collect the methane. These traps, made of stainless steel, are connected to a variable transformer so that they may be heated quickly b y passing a current through the tubing, which has sufficient resistance to function as a heater. The chromatographic unit is a modified Perkin-Elmer AIodel 154 Vapor Fractometer, equipped with a silica grl column. The chromatograph has been modified by bringing the helium rarrier gas from the injection port to the outside of the instrument and connecting it to the trapping system as shown. The helium, except during sampling of the traps, flows to the column and detector through bypass 1. Coil K is a part of the chromatographic unit in the estimative procedure, as it separates hydrogen, and also any nitrogen that pasjes trap C, from the methane. Estimative Procedure. -4 flow of approximately 20 cc. per minute of helium is directed through t h e quartz hydrogenation tube and into the atmosphere from stopcock 1, and the temperature of t h e furnace is raised to 1000" C. K h e n this temperature is reached, the helium is turned off and hydrogen is admitted a t a flow rate of approximately 50 cc. per minute for 15 minutes. T h e chromatographic unit is set a t a temperature of 80" C., and the helium carrier gas is
-
1428
ANALYTICAL CHEMISTRY
TIME, m i n
TIME, min.
Figure 2. Products from the hydrogenation of 2-methylthiacyclopentane (approximately 0.5-pI. sample)
routed through bypass 1 a t a flow rate of 140 cc. per minute. Trap C is immersed in liquid nitrogen. (This trap is brought to room temperature between runs to free it from nitrogen.) Stopcocks 1, 2, and 3 are positioned so that hydrogen is routed from the reaction tube through traps H and J and is vented through stopcock 4 (a hood is sugested as a safety precaution). With a continuous flow of hydrogen t o prevent a backward flow of air into the traps, trap H is immersed in liquid nitrogen and trap J in a dry iceethylene trichloride mixture. The hydrogen flow rate is appropriately adjusted before injecting the sample1 pl. or less-through the rubber serum cap, D . For the analysis of materials boiling below 100" C., the hydrogen flow is adjusted to 20 cc. per minute, and the sample is allowed to vaporize a t room temperature. After 10 minutes, the flow rate is increased t o 50 cc. per minute for an additional 5 minutes to sweep all reaction products into the traps. For samples boiling above 100' C., a hydrogen flow rate of 50 cc. per minute is maintained for 15 minutes, and the inlet port is heated during the last 5 minutes to ensure complete vaporization. When hydrogenation is complete, the stopcocks are positioned so t h a t the products, which consist principally of hydrogen sulfide in trap H and of methane in trap J , can be chromatographed. First the hydrogen from the reaction tube is vented through stopcock 1. The helium carrier gas from the chromatograph then is routed from stopcock 2 through trap H and back to the chromatograph through bypass 2 . K h e n the base line of the chromatograph recorder has stabilized, the liquid nitrogen bath is lowered from trap H and the variable transformer is simultaneously turned on (18 volts for 30 seconds for our equipment); the products from trap H are thus vaporized into the chromatographic unit. After the hydrogen sulfide peak has been recorded, the stop-
cocks are adjusted so that the currier gas, instead of being routed through bypass 2 , is routed through trap J and column K to the chromatograph. The products in trap J are vaporized into the chromatograph by loivering the cooling bath and passing current through the trap, and the methane peak is recorded. Typical chromatograms using this method are shown in Figure 2 . Per cent sulfur is calculated from the following equation as derived in Results and Discussion. Kt. 7 'sulfur
=
A I X -11X 32 X 100 (-SI X 111 X 3 2 ) (A, X
+
K)
where -11 is the area (or hcight) of hydrogen sulfide peak, i12 is the area (or height) of methane peak, and .If is the relative molar response (see Calibration). Quantitative Procedure. The procedure is the same as t h a t described above except t h a t the sample ( 5 t o 10 mg.) is weighed before hydrogenation, and the methane trap, J . is not used. T h e hydrogenation products in trap H are flash-vaporized into the chromatograph, and the area of the hydrogen sulfide peak is measured. Calculations are made as follows: Wt. % sulfur = ___ Tv x 100 W,
where d is the area of hydrogen sulfide peak in sample, W is the g r a m of sulfur per unit area (see Calibration), and, W , is the weight of sample, grams. Calibration. T h e calculations for the estimative procedure require the relative molar response for hydrogen sulfide and methane under the conditions of t h e experiment. This is conveniently measured b y hydrogenating a standard sample, consisting of a pure known sulfur compound, and measuring the hydrogen sulfide and methane peaks. From these measurements, the relative response, 31, may be determined as follows:
M = area (or height) of methane peak area (or height) of hydrogen sulfide peak X ratio of carbon t o sulfur in standard sample
For the particular conditions used in these experiments, the M value was 1.6 using peak area, or 3.5 using peak height. The calculations for the quantitative procedure require the value, U7, the grams of sulfur per unit area of the hydrogen sulfide peak. This value is obtained b y injecting a known amount of hydrogen sulfide into the chromatograph under operating conditions using bypass 1 and measuring the peak area. The weight of sulfur injected as hydrogen sulfide is then divided by this peak The use of peak area to obtain .'TI area is preferred over height because, unlike calibrations using peak height, a linear relationship exists through the origin of a plot relating weight of sulfur with peak area. Thus, only one calibration point is adequate to check for day-to-day changes in detector response. DEVELOPMENT
Hydrogenation. Various catalysts were tested t o find one that would give complete hydrogenation to hydregen sulfide and methane. Palladium or platinum on alumina gave low recoveries of hydrogen sulfide even after prolonged periods at high temperatures. Quartz granules were satisfactory for most sulfur compounds but gave low yields of hydrogen sulfide with thiophene. Quantitative yields mere obtained using palladium, platinum, or nickel supported on quartz, but the activity of these supported catalysts decreased rapidly and was not completely restored upon regeneration. Catalysts were regenerated by passing air through the hot tube for 15 minutes. With platinum gauze, quantitative yields of hydrogen sulfide were obtained with 12 or more runs, and the catalyst could be efficiently regenerated. Trapping. T h e efficiency of t h e trapping system was evaluated b y collecting a known amount of gas in the cooled traps a t flow rates comparable t o actual operating conditions. T h e system was considered satisfactory if t h e trapped gas, upon vaporization, gave t h e same peak area as t h e same a m o u n t of gas when i t was routed directly through t h e heated traps and chromatographed. A liquid nitrogen-cooled trap, packed with stainless steel helices, was found t o be effective for retaining hydrogen sulfide and hydrocarbons except methane. Molecular Sieves cooled to dry ice temperatures retained the methane and gave quantitative recovery when the trap was warmed as described under Procedure. Thus, a quantitative separation of methane and hydrogen sulfide can be effected by using both traps. Chromatographic Analysis. I n t h e estimative procedure, the a m o u n t of methane, as well as t h e a m o u n t of hydrogen sulfide, must be measured. T h e methane, together with some nitrogen not removed b y t r a p C and t h u s introduced as a contaminant in t h e hydrogen, is retained i n t r a p J. A Molecular Sieves column, K , at room temperature, mas found t o give a satis-
12-11. s i l i c o n 8 plus 6-11. I r i c r e s y l p h o r p h o l e 40'C. He-90 cc/min.
v) W
z a. 0 v) W
a a W 0
a 0 u W a
9
8
7
6 5 4 TIME, min.
3
2
1
0
Figure 3. Products (except methane) from the hydrogenation of 2-methylthiacyclopentane (approximately 1 -ml. sample)
factory separation of these gases. The effluent from the Molecular Sieves column, K , is routed through the silica gel column in the chromatograph only for convenience of measurement. I n the developmental work on the estimative procedure, i t was necessary to chromatograph the contents of trap H using a column that would separate hydrogen sulfide from a Ride range of hydrocarbons so that the estent of hydrogenation of both the carbon and the sulfur could be observed. A 1/4-inch column made up of 12 feet of Chromosorb with 10% of Dow Corning 703 silicone, in series with 6 feet of Celite nith 30y0 of tricresylphosphate, was satisfactory because i t resolved hydrogen sulfide and all the Cz to Cs hydrocarbons in a conveniently short time. Figure 3 is typical of the chromatograms obtained when this column was used to separate the products from the hydrogenation of a 1-p1. sample. Small amounts of lowboiling hydrocarbons-emerging before the hydrogen sulfide peak-could be seen only when the sensitivity was in-
Table 1.
creased to the maximum. Quantities were below 1% in all experiments. Products with emergence times greater than hydrogen sulfide were not observed even a t highest sensitivity. Thus it was shown t h a t hydrogenation was complete enough so that hydrocarbons other than methane could be ignored without introducing a significant error. As the higher molecular weight hydrocarbons were absent, a chromatographic column that ould resolve the hydrogen sulfide and the higher hydrocarbons was not necessary. A column of silica gel was later used to measure the hydrogen sulfide because such a column was necessary in the quantitative procedure and it mas convenient to use the same Polumn for both methods. I n the quantitative procedure, the chromatographic problem was different because larger samples n i t h lower sulfur content were used. K h e n such samples are hydrogenated, the amount of light hydrocarbons becomes larger and the hydrogen sulfide, smaller. Slthough only the hydrogen sulfide is measured, it must be separated cleanly from the light hydrocarbons so that an accurate peak area can be determined. The silicone-tricresylphosphate column used in the developmental work on the estimative procedure was unsatisfactory because it alloned overlap of the acetylene peak n i t h the small hydrogen sulfide peak. A column of silica gel gave clean separation of the hydrogen sulfide peak as shown in Figure 4. RESULTS AND DISCUSSION
Estimative Procedure. Table I shows the results obtained when this procedure was tested with 0.5- t o 1-PI. samples of nine pure sulfur compounds -a disulfide, three thiophenes, a cyclic and a straight-chain sulfide, two aromatic thiols, and one aliphatic thioland with two blends of sulfur compounds
Estimation of Sulfur in Samples of 1 Microliter or Less
2-Methylthiacyclopentane
2-Methyl-2-pentanethiol 2-Thiapentane Thiophene
Sulfur, wt. Found Actual Height Area 31.4 31.4 31 4 32 0 31 2 27 2 26 9 27 5 27 2 26.7 35 6 34 5 35.4 35 6 35.8 38.1 42.4 44.8 42.1
2-Methy lthiophene
32.7
3-Methylthiophene
32.7
Benzenethiol
29.1
Phenvlmethanethiol
25.8
3,PDithiahexane
52.5
2-Methylthiacyclopentane
4.1
2-Methylthiacyclopentane in isGoctane
16.5
in iso-octane
31.2 31.1 29.1 36.3 28.8 29.1 24 8
41.9 31 3
26.0 46.6
23.7 51.6
44.9
48.1 ~.
4 5
4.6 15.2 15.8
4.2 4.3 16.7 15.9
Sulfur recovery, yo Height Area 100 100 102 S9 99
100 98
100 111 111
101
98 99
101 118
110 96
101
92 98 92
89 86 110 112
102 105
96
96
92
VOL. 34, NO. 1 1 , OCTOBER 1962
101
1429
Table II.
8.3
0.58
8.1
0.60
8.1
8.3 8.6 8.3 8.3 8.3
1-Hexanethiol Thiophene In iso-octane Thiophene
2-Thiapentane I-Hexanethiol Thiophene 9-Methylthiacyclopentane
Quantitative Determination of Sulfur in Naphthas
B
0.30
0.53 0.058
6.5 6.6 6.4 6.6 6 5 6.5 6.4 6.6 6.5 6.5 6.5 6.5
2-Methylthiacyclopentane
A
Hydrogenation method, wt. % 0 46 0.53 0.52 0.27
0.33 0.33
0.79 0.73 0.69 0.056 0.057
W v)
z
=
diluted with iso-octane. This procedure gives results with uncertainties of about 10% and thus is satisfactory for the ~ t o r k for which it was designedchecking a trapped peak from a gas liquid chromatographic (GLC) analysis to determine whether a sulfur compound i q the major component and to estimate the concentration of the compound. Results for one compound-thiophene-were consistently poor. This compound is particularly resistant to complete hydrogenation. The sulfur is recovered quantitatively as hydrogen sulfide, but methane recovery is low, probably because of some loss of carbon through coking, so that high sulfur percentages are obtained. Table I gives results calculated on the basis of both peak height and peak area. Better accuracy generally is obtsined using peak area, but use of peak height is often preferable because the method is designed for use on samples of unknown size and sulfur content. Under ANALYTICAL CHEMISTRY
103
W v)
a a
98 100
w
107 105
n
a 0 u
107
W
93 104
a
100
95 1
99
100 98
wt. C 12n
96 102 97
Substituting for n and
++ wt. H + wt. S 2n + 32m 14n + 32m
32m 14n 32m
+
x
100 (2)
But, because hydrogen sulfide and methane do not have equal molar responses in the chromatograph, i t is necessary t o introduce a correction factor for their relative response, M, where response per mole of methane di = response per mole of hydrogen sulfide or M=
response per gram-atom of C - A2/n response per gram-atom of S A l / m
Considering the response for carbon as the reference, then An/n = 1 or n = A2 and m = MA1
2
0
96
and =
8 6 4 TIME, min.
yo
(1)
Wt. % sulfur
0
Figure 4. Products (except methane) from the hydrogenation of thiophene in sulfur) benzene (0.05 weight
104 99 104 94 99
these conditions, i t is difficult to preset the recorder attenuation so that an accurate area measurement can be obtained. The estimative procedure involves the estimation of the weight of the original sample from the amount of carbon and sulfur recovered as methane and hydrogen sulfide. Estimation of the sample weight is based on the assumptions that the sample is composed of carbon, hydrogen, and sulfur, and may be represented as C,H2,S, where n is the number of gram-atoms of carbon and m is the number of gram-atoms of sulfur. Then =
e
%
0.78 0.79 0.55 0.58 0.72 0.76 0.65 0.68 0.054 0.054 0.058 0.055
0.56
Wt. of sample
1430
Sulfur recovery,
0.60 0.57 0.45 0.48 0.63 0.64 0.49 0.55 0.058 0.055
0.45
8.2 8.2
2-Thiapentane
Lamp method, wt. yo 0.50
80°C. He-I40 c c / m i n .
0 LL
2-Methylthiacyclopentane
Naphtha
Sulfur, wt. yo Actual Found
Sample size, mg.
Material In benzene Thiophene
Table 111.
6-ft. s i l i c a p e l
Quantitative Determination of Sulfur in Test Solutions
rtt
in Equation 2,
Wt. % sulfur = 32 X M X A I (14 X Az) (32 X $1 X A I )
+
x 100
(3)
The presence of elements other than carbon, hydrogen, and sulfur would cause errors in the calculations unless corrections are made. The assumption of two hydrogen atoms for each carbon introduces some errors: I n the Ce sulfui compounds, perfpct recovery would give answers of 102% for aliphatics 100% for cyclics, and 95% for aromatics. These errors may be compensated for in the calculation if the typt> of compound is known, but in general the accuracy of the method does not justify such exacting calculations. Quantitative Procedure. Samples (IO-pl.) of benzene and iso-octane solutions of pure sulfur compounds, weighed t o the nearest 0.1 mg. were used for testing the quantitative procedure. Table I1 shows the results obtained with these samples. The procedure also was tested by applying i t to lO-,ul. samples of naphthas whose sulfur contents had been previously determined using the ASTM lamp method (1). The results, shown in Table 111, show favorable agreement between the two methods. Quantitative measurement of sulfur a t concentrations as low as 0.05% was accomplished without difficulty. However, application of the method to samples containing less than this amount of sulfur was not entirely satisfactory because of the difficulty of separating the hydrocarbon fragments and the hydrogen sulfide formed in the hydrogenation step. The principal problem, as illustrated in Figure 4, is the separation of the hydrogen sulfide from the acetylene that is produced. With additional hydrogenation efficiency to reduce the amount of acetylene, or with increased separation efficiency so that larger sam-
plcs could be used, the llletllod 1dgllt bc extended t o the determination of sulfur in the parts per lnillion might be accomplished by increasing the length of the catalyst zone or by lengthcning the chromatographic column. LITERATURE CITED
(1) Am. Soc. Testing Materials, “Tenta-
tive Method of Test for Sulfur in Petroleum Products and Liquefied Petroleum Gases, by C02-02 Lamp Method,” D 1266-55T.
( 2 ) Schluter, E. C., Jr., l’itrry, IC. l’., Matsuyama, G., ANAL. CHEX 32, 413 (1960). (3) Scott, W. W., “Scott’s Stmdard
tion performed as part of the Ainerican Petroleum Institute Research Project 48A on the Synthesis, Properties, and Isolation of Sulfur Compounds in Petroleum, Methods of Chemical Arialysis,” 5th carried out by the Bureau of Mines a t ed., p. 2509, Van Nostrand, New York, Laramie, Wyo., and Bartlesville, Okla. Work was done under cooperative agree1939. (4) Thoin son, C. J., Colemaii, 11. J., ments among the Bureau of Mines, U. S. Ward, C., Rall, H. T., A N ~ LC. ~ M . Department of the Interior, the American 32, 424 (1960). Petroleum Institute, and the University of Wyoming, Reference to specific comRECEIVED for review June 18, 1962. Acmercial materials or models of equipment cepted August 6, 1962. Division of Anis made to facilitate understanding and :tl tical Chemistry, 140th Meeting, ACS, does not imply endorsement by the Bureau C&cago, Ill., September 1961. Invcstigaof Mines.
8.
Quantitative Reproducibility of a Programmed Temperature Gas Chromatographic System with Constant Pressure Drop Using Packed and Golay Columns L. S. ETTRE and F. J. KABOT The Perkin-Elmer Corp., Norwalk, Conn.
b The advantages of a programmed temperature gas chromatographic system with flame ionization detector utilizing constant inlet pressure during operation were discussed by Golay et a / . (7) for qualitative analysis. This paper proves its accuracy and reproducibility for quantitative analysis.
I
prograninied teml)er:tturc gas chromatographs, the carrier gas flow is kept constant during operation. The outlet pressure of thc gas is constant (equal to atmospheric pressure) ; because the gas viscosity changes with temperature, n coiitinuous adjustment of thc carrier gas inlet pressure (using :tutom:ttic flon coiitrollers) is necess iry to maintain a constant flow during programmed temperature operation. ITon evcr, 1)). continuously changing the inlet pi essurc, thc pressure drop along the column 11 ill nlso change continuously. ‘This tcclinique \ins chosen because thc thermal conductivity detectors used in such units nere sensitive to the carrim gas flow and any change in the flow rate would result in n drift of the base line. The result of this mode of operation is that both the gas vclocity and the pressure drop along the column are changing and this complicates the mathematical treatment of retention times. On the other hand, the quantitatibe accuracy of such systems was ~ r o v e t l(4) and by using thermal conductir ity detectors, neither the relative peak are:t values nor the relatile reN MOST
sponse factors were affected by the different program rates relnt,i\,e to isothermal opera.tion. I n certain cascs--e.g., using flow sensitive detect,ors or dual columns where the flow rates through the respective columiis have to be mntchedflow regulation cannot he avoided. From a theoretical point of view, however, a system where both the coluinn inlet and outlet pressures are kept constant is more desirable. Specifically, in this case, the pressure drop along the column is independent of temperature as long as the entire column is uniformly heated and only the average velocity is a function of column teniperature. This simplification permits a relatively simple mathematical treatment of retention times which is discussed in detail separately (7’j. A recent’lydesigned programmed t,emperature gas chromatograph incorporates a flame ionization detector with both packed and Golay columns (6). Because the flame ionization detector is relatively insensitive to changes in the carrier gas flow rate (1, 2, 5 , a),the inlet pressure rat,her than the flow rate at column outlet is maintained constant during temperature programming; thus, the utilization of t,he quoted mathematical treatment for practical work became possible. While this treatment is related only to qualitative analysis, n gas chromatograph must also perform properly for quantitative analysis, with sufficient accuracy and reproducibility. Therefore, the quantitative results obtained with programmed temperature
operation must not differ from those determined under isothermal conditions. Because a flame ionization detector had not previously been used with continuously changing carrier gas flow rate, the quantitative reproducibility of the data obtained nith temperature programming under such conditions relative to the isothermal values from constant flow operation was as yet unproved. I n this respect, the first question is related to detector response. It is known that the response of the flame ionization detector is dependent upon the amount of sample component arriving in unit time at the detector. As the flow rate changes during a run, this value nil1 not be constant; i t is, therefore, necessary to demonstrate that the integral oC the resp0nse-i.e. the response for the total amount of sample component-1s ill still remain uiichanged. Because the carrier gas flow rate changes during operation, the ratio of hydrogen flow rate (which is constant) to carrier gas flow rate also varies during temperature programming; therefore, it is important to determine whether this will affect the quantitatisre results. Finally, a third problem arises if Golay columns are utilized in a gas chromatographic system: the question of split linwrity. I n a previous paper ( 3 ) this question was discussed in detail; because in the present system, the construction of the splitting device was similar to that described pre\ iously and the flow rate during splitting v a s VOL. 34, NO. 1 1 , OCTOBER 1962
1431
