the shorter leaching method and the more lengthy sodium carbonate fusion dissolution method. Since a large number of sample analyses were necessary to evaluate the extent of plutonium radioactivity in the Colorado area, commercial laboratories were asked to assist in this work. They were requested to analyze the soils by the nitric-hydrochloric acid leach and t o compare this method with their internal methods. The results of the intercomparison are shown in Table 111. The error term shown for all measurements is a single Poisson error due t o counting. Measurements from Laboratory A for the Colorado soils in two out of three cases show higher plutonium-239 240 results than the measurements at HASL. A systematic error was not found for this difference. The sample collected in Illinois is a glacial silt “black” soil and this type has been used in this laboratory as a reference soil. The New York soils, 1, 2, and 3, also silt loam, were collected at a different site than the experimental sample; soil 1 was collected in 1967 from 0-20 centimeters and soils 2 and 3 were collected
+
____
-
__
__--
in 1969 a t 5-20 and 0-5 centimeters, respectively. Except for New York sample 3 which was 50 grams, all soils in Table 111 were analyzed using 100 grams. From the plutonium 239 240 results shown, the leaching method is comparable to other methods for the determination of plutonium in soil containing fresh and aged fallout. Also, from these results, it was concluded that either of the methods tested would be adequate for plutonium soil analysis although the nitric-hydrochloric acid leach method required one third the analysis time as compared to the method of complete solution by sodium carbonate fusion. A more detailed interpretation of the results obtained from Colorado soils as well as the extent of plutonium contamination found in the Rocky Flats area has been made by Krey and Hardy (12).
+
RECEIVED for review September 1,1970. Accepted November 10,1970.
~
Isothermal Gas Chromatographic Separation of Carbon Dioxide, Carbon Oxysulfide, Hydrogen Sulfide, Carbon Disulfide, and Sulfur Dioxide Willis L. Thornsberry, Jr. Research and Deceloptnent Laboratory, Freeport Sulpliur Company, Belle C l i m e , La. 70037
THEREHAS BEEN a persistent need for a simple and rapid method for analyzing mixtures of CO,, HIS, SO,, COS, and CS2. The importance of such a method has been greatly magnified by the increased emphasis placed on monitoring the concentration of these components in waste gas streams. Although the procedure described here is not applicable t o concentrations below the 50-ppm concentration range, it is useful for the monitoring of gases emitted from sulfuric acid plants, Claus recovery units, and for various other process control and laboratory applications. Recent papers by Stevens et a/. ( I , 2) describe a gas chromatographic system for the analysis of some sulfur gases in the concentration range extending below 1 ppm using a 34-ft Teflon (Du Pont) column containing 40-60 mesh Teflon packing coated with polyphenyl ether and phosphoric acid. A sulfur selective flame photoluminescent detector was used in this study. In the past ten years, a number of papers have been published which are concerned with the development of gas chromatographic columns for the separation and analysis of sulfur gases. Several of these papers were discussed in a previous communication from this laboratory (3). Since that time other methods have been published. Brinkmann ( 4 ) discussed the development of a column for the separation of these five gases; however, the method is hampered by a tailing SO2 ____~~_____.____
peak and the fact that no base-line separation is obtained either between COSand the inert gases, or between H S and COS. The development of porous polymer beads has provided what is probably the best and most trouble-free method for separating these gases when carbon disulfide is not present (5, 6). A 6-ft x 1/An, aluminum column of Porapak Q-S was tested in this laboratory and COS, COS, H2S, and SOY were eluted within 6 minutes; however, a CSn peak was not observed until about 40 minutes after sample injection. The column temperature was 98 “C and the helium carrier gas flow rate was 5 5 cc/min. An earlier communication from this laboratory outlined an analytical procedure for the simultaneous, isothermal separation and analysis of CO,, COS, H2S, SO2, and CS? using a silica gel column (3). Since that time, numerous columns have been prepared from this same batch of silica gel. All of these columns have been used successfully both in the laboratory and (with the addition of a precut column to remove moisture) in process instruments for continuous analysis. However, attempts to reproduce these results with silica gel from other sources and even with different lots obtained from the same source have failed. Various methods of treating these silica gels have been tried, including silanizing ; acid washing, using conditions ranging from simple washing t o refluxing with concentrated hydrochloric acid for 2 to 3 hours; and conditioning the
( 1 ) R . K. Stevens e/ a/., E/iriro/i.Sri. Tec/ino/., 3, 652 (1969). (2) R . K. Stevens and A . E. O’Keeffe, ANAL.CHEM., 42, (2), 143A (1 970). (3) C. T. Hodges and R . F. Matson, ihid., 37, 1065 (1965). (4) H. Brinkmann, C/iem, T c ~ / i(Leipzig), . 17, 168 (1965).
( 5 ) E. L. Obermiller and G. 0. Charlier, J . Gas Clzromatogr., 6 , 446, (1 968). (6) E. L. Obermiller and G. 0. Charlier, J . Chromatogr. Sci., 1, 580 (1969).
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ANALYTICAL CHEMISTRY, VOL. 43, NO. 3, MARCH 1971
Table I. Operating Characteristicsof Columna Separation Retention "Q" factor Concentration time factor, Component (Volume, %) R Q S Air balance 0.12 ... ... co2 3.00 0.66 3.47 0.82 cos 1.11 1.22 3.30 0.46 HzS 4.30 1.85 4.12 0.34 cs2 1.52 4.40 3.52 0.58 so2 4.10 6.85 3.70 0.36 Lot No. 795/10B acid washed 2 f t X a Operating conditions: Deactigel 60/80 mesh. cc/min. Using a 5-cc syringe sample, column in a stream of the sulfur gases. None of these procedures produced a n acceptable column. Tailing peaks, especially the SO2 peak, were always a problem. Variations among different batches of silica gel are not unusual and this problem has often been reported (3, 7). This work relates to the use of a treated silica gel, "Deactigel," supplied by Applied Science Laboratories, State College, Pa. Although significant batch to batch variations were observed with Deactigel, a simple acid wash treatment consistently produced a column material which gave very good separation.
Q Value: Q
=
retention time/peak width
Separation Factor: S
f A
-
Width, W
...
...
N
...
2.84 0.19 192 1.52 0.37 174 1.40 0.45 272 2.04 1.25 198 1.33 1.85 219 in. Al. Col. at 122 "C with a He flow rate of 55
,ir
90
cos
cs2
n
11
80
ro
w -l
a V
v)
An F and M model 720 dual-column, programmedtemperature chromatograph equipped with a Gow Mac W-2 thermal conductivity detector and a 1-mV Honeywell recorder was used for this work. Helium carrier gas was used throughout all tests. G a s mixtures for calibration were obtained from Matheson Corporation and other test mixtures were prepared in the laboratory. Acid washing of the Deactigel was done by placing 10 grams of the Deactigel in a Buchner funnel with a medium porosity glass frit bottom and washing with 30 ml of concentrated hydrochloric acid, 90 ml of distilled water, and 90 ml of acetone in that order at a rate of 5 cc/min. The Deactigel was then air dried. The columns were prepared and conditioned overnight in the gas chromatograph oven at 200 "C with a helium flow of 55 cc/min through the column. This column has been used for the analysis of these gases in the concentration ranges of 0.01 to 2 0 z by volume. A 5-cc sample, both syringe sample and a gas sampling loop, was used throughout this work. The chromatogram in Figure 1 shows the separation obtained using a 2-foot x inch column of acid washed Deactigel a t a temperature of 122 "C and a carrier gas flow rate of 5 5 cc/min. These conditions were found to produce the best separation. The data presented in Table I constitute a detailed analysis of the chromatogram including a tabulation of the column description, operating conditions and retention times, and peak widths obtained for each component on each column. In addition, a number of parameters normally used to express the efficiency of gas chromatographic columns are tabulated. These include the Q value, separation factor, resolution, and the number of theoretical plates. These various terms, as used in this paper, are defined as follows:
*/4
R
100
EXPERIMENTAL
RESULTS AND DISCUSSION
Resolution,
No. of theoretical plates,
b
60
$ 50
w v)
z
0
n
v)
W
40
a 0
30
a 0
V W
a
20
IO 0
I. I
Figure 1 , Separation of sulfur gases on a two-foot coliirnn of acid washed Deactigel where retention time of the preceding peak retention time of peak for which separation factor is being calculated Resolution: R = (Q) (S) Number of theoretical plates: N = 16(Q)* tA tB
= =
If water vapor is present, it may be desirable to make special provisions to handle this. Possible solutions have been previously discussed (3). However, water does not interfere with the analysis and unless an unusually high water concentration is present o r a large number of consecutive samples are being taken, as in a process instrument, this will present little o r no problem. Aluminum, glass, or stainless steel tubing may be used to prepare these columns.
fB
= ___ fB
(7) H. Hall, ANAL.CHEM., 34, 61 (1962).
RECEIVED for review August 14, 1970. Accepted November 12, 1970. ANALYTICAL CHEMISTRY, VOL. 43, NO. 3, MARCH 1971
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