To Saporating COLUMN
ACID
111
65
Mt J
M
Figure 1. Apparatus for rapid determination of carbonate b y gas chromatography
V S and V Min Figure 1 were evacuated to less than 0.1 mm. of Hg. At the conclusion of stirring, the gas in the evolution flask was expanded into V , and V S . Volume V s was actually the sample inlet section of the gas phase chromatography apparatus. The analysis was then started by sweeping the gas contained in V s into the chromatography column with helium. The fraction of total gas that was removed for analysis is the ratio of V S to the sum V S V.! V F l?ss the volume of sample, acid, and stirring bar. The manometer is used in the initial calibration of this ratio by means of the ideal gas law. The volume V S &as 10.00 ml.; the total gas volume was about 160 ml., depending upon the size of sample and amount of acid.
+
Thus, in this equipment about l/&h of the carbon dioxide in the evolution flask was withdrawn for analysis. The gas to be analyzed contained air and water vapor in addition to carbon dioxide. Since water would quickly ruin the chromatographic column, it was removed (after aliquot V S was measured) by first passing the gas through a very small column of anhydrous magnesium perchlorate on the Kay to the separating column. The chromatographic separation (with helium as the carrier) was obtained on a column of silica gel 30 cm. long a t a superficial gas velocity of 4 cm. per second. A thermal conductivity detector constructed of thermistors (Western Electric 14B) and using a bridge current of 10 ma. provided a detection limit of about 0.01
Table I.
Accuracy and Precision of Determination
Substance Analyzed
Carbonate Found, mi44
+
XBS standard limestone sample la, certified analysis: 33.53y0 co2 Av.
% co2
33.37 33.10 33.09 33.19
pmole of carbon dioxide. This corresponded to a peak of 1% of full scale on a 1-mv. recorder. Only about I/&h of the gas evolved was measured, but as this might have come from a sample volume of 30 ml., a detection limit of about 0.005 m M carbonate in the original solution is estimated; for a 30-gram sample of solid this is about 0.2 p.p.m. of carbon dioxide. The time required per determination is about 10 minutes. This is governed primarily by the elution time of carbon dioxide through the gas chromatography apparatus. ACCURACY OF DETERMINATION
The above determination of carbonate is not absolute, because it relies upon a calibration of the detecting unit. However, the gas chromatography apparatus can be calibrated with pure carbon dioxide. This calibration does not involve in any way the evolution flask, acid, stirring, etc. The complete method was checked by the analysis of NBS standard limestone and also a standard solution of Na&Oa. The results are given in Table I. Both results show a precision of better than 1%, and both are about 1% low. For lowlevel determinations of carbon dioxide this is considered acceptable. RECEIVED for review July 26, 1961. Accepted October 13, 1961.
Analysis of Chlorophenols by Gas-Liquid Chromatography J.
A. BARRY,‘ R. C. VASISHTH,2 and F. J. SHELTON
Reichhold Chemicals, Inc., Seattle 24, Wash.
b Analysis of mixtures of chlorophenols has generally been performed b y infrared absorption spectrometry. A less expensive and equally effective method, based on gas-liquid chromatography (GLC), was worked out. Results obtained b y GLC and infrared spectrometry are compared briefly.
M
chlorophenols are produced commercially by the direct chlorination of molten phenol (7, 9). The mono- and dichlorophenols can be produced without the use of a catalyst, whereas a catalyst such as a metallic chloride (6,9)is needed to produce more highly chlorinated phenols. The reaction is similar to the chlorination of benzene (2, 4, 6, I O ) , various isomers being ASY
formed in large quantities depending upon the degree of chlorination and the catalyst used ( 2 , S , 5 ) . The distribution of isomers formed during the chlorination is of interest in studying the reaction from a fundamental standpoint. An accurate, rapid method of analysis is also needed for plant control in commercial production of chlorophenols ( 1 ) . Previous studies have utilized analytical techniques such as steam distillation (5) and infrared absorption spectrometry ( 1 ) . While distillation is a time-consuming process with limited accuracy, infrared spectrophotometers are expensive and not always accessible. It has been found that this analysis can be readily accomplished by GLC, utilizing a relatively inexpensive in-
strument. Appropriate conditions for this analysis along with typical results obtained by GLC and infrared spectrometry are presented here. EXPERIMENTAL PROCEDURE
The GLC analysis was performed using a Perkin-Elmer Vapor Fractometer, Model 154-C, equipped with a 1.0-mv. .recorder. Helium was used as a carrier gas. As a preliminary step various columns were tried to obtain suitable separation of known mixtures of chlorophenols expected in the reaction mixture. Three columns-a siliPresent address, University of Washington, Seattle 5, Wash. Present address, Reichhold Chemie, A. G., Hamburg, Germany. VOL. 34, NO. 1, JANUARY 1962
67
cone oil (Dow Corning No. 200), a silicone high vacuum grease, and a diisodecyl phthalate column-were selected for use and the operating conditions for optimum separation determined. Standard curves, concentration us. areas, were then obtained using specially purified chlorophenol samples. The areas were determined with a planimeter. Diisodecyl phthalate and silicone high vacuum grease columns were prepared by dissolving 5 grams of the material in methylene chloride, adding 25 grams of Teflon (Du Pont) powder; and evaporating the methylene chloride with gentle heat and stirring. A inch stainless steel column was filled with the Teflon powder so coated by applying a n electrical vibrator along the length of the column. The third
column was Perkin-Elmer column C. silicone oil 200. Solutions of samples to be analyzed vere prepared by dissolving 2 to 2.5 grams of the mixture in 25 ml. of benzene. Small amounts of this solution (0.010 to 0.050 ml.) were injected by a Hamilton microliter syringe. The same syringe was used for calibration and analysis, thus eliminating the necessity of syringe calibration. For comparison, sereral mixtures were analyzed by both GLC and infrared spectrometry. The infrared spectra mere obtained using a Beckman IR-5 double-beam spectrophotometer. The solutions of chlorophenols u-ere prepared in carbon disulfide and analyzed in 1-mm. matched cells with sodium chloride windows. Absorptivities were calculated from the spestra of pure chlo-
Procedure [ I ) Duso (125°C.) phenol
29-
e-
phenol
'u
,,,-
A ,A 2.6-
A ,
p-
>A
z phenol
0-
"-
28-
I,,I
5
IO
15
fin iime - minutes
Table 1.
Separations Obtained under Different Conditions
Mg./Sq. I n . hlinimum Compound Retention Time" Attenuator 1 Detectability Procedure 1. Diisodecyl phthalate column at 125" C., 51 inches. Eluting gas flow rate 200 ml./min. 8' 0,0667 0.15 Phenol 6' 0.0667 0.15 o-Chlorophenol Procedure 2 . Diisodecyl phthalate column a t 175' C., 51 inches. Eluting gas flow rate 100 ml./min. 2'40" Phenol 2/40" o-Chlorophenol 12' 0.0668 0.15 p-Chlorophenol 2,CDichlorophenol 7/20" 0.0664 0.1; 2,6-Dichlorophenol 7'20' 0,0664 0.15 2,4,6-Trichlorophenol 16'20" 0.0710 0.15 Procedure 3. Silicone 200 column a t 175" C., 72 inches. Eluting gas flow rate 30 ml./min. 3'10'' 0 0330 0 1 Phenol 3'50" 0 0270 0 05 o-Chlorophenol 7'10" 0 0340 0 1 p-Chlorophenol 2,4-Dichlorophenol 7/10" 0 0340 0 1 2,6-Dichlorophenol 8'10" 0 0340 0 1 2,4,6-TrichlorophenoI 14' 0 0332 0 1 Procedure 4. Silicone high vacuum column at 200" C., 72 inches. Eluting gas flow rate 75 ml./min. 2,4,6-Trichlorophenol 1' 0 2526 0 5 1'50" 0 2526 0 5 Tetrachlorophenol Pentachlorophenol 3'50" 0 2526 0 5 a Calculated from time of sample charge. Table II.
Procedure 1
2 d
4
Known Found
A 12.39 13.8
Analysis of Known Mixtures by B C D E
11.62 11.09
Known Found Known Found
3.0 3.1
Known Found
68
D. 2,CDichlorophenol Not separated.
ANALYTICAL CHEMISTRY
Chromatography
F
G
H
60.45 2.98 63. 41° 21.19 1.04 22.35s
A. Phenol B. o-Chlorophenol C. p-Chlorophenol
0
12.55 12.36
GL
94.6 95.6
1.4 1.5
55.38
55.78
22 39 r o t analyzed
1.0 0.7
15.45 84.55 15.10 84.81 E. 2,6-Dichlorophenol F. 2,4,6-Trichlorophenol G. 2,3,4,6-Tetrachlorophenol H. Pentachlorophenol
Figure 1. cedures
Separations by four pro-
rinated phenols. The calculations were performed by the base line technique, after ascertaining that Beer's law holds in the concentration ranges used. GLC ANALYSIS
Four different procedures were found useful in performing the analysis. For each of these, experimental conditions, retention times, and calibration data are presented in Table I and Figure 1. Calibration figures are an average of three separate determinations in which peak areas were reproduced nithin 1 0 . 0 5 sq. inch. Many mixtures of lower chlorophenols containing phenol, and mono-, di-, and trichlorophenol can be separated by using a diisodecyl phthalate column a t two temperatures, 125" and 175" C. Horrever, this column does not separate 2,4- and 2,6-dichlorophenol. Using a column with silicone oil 200 as substrate, a t 175" C., p-chloropheno1 and 2,4-dichlorophenol hare the same retention time but 2,6-dichlorophenol can be separated. Thus a complete analysis of mixtures containing p-chlorophenol, 2,4-dichlorophenolJ and 2,B-dichlorophenol requires the use of tn-o different columns. LIixtures of more highly chlorinated phenols-namely, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol-can be conveniently analyzed using a silicone high vacuum grease column a t 200" C. Based upon solubility and sample size considerations, the smallest detectable amount of a given compound was taken as the necessary amount contained in a 50-pl. sample of a IO'% solution of the misture to give an area of 0.1 sq. inch a t the maximum instrument sensitivity (attenuation 1). These calculated values are also given in Table I as weight per cent minimum detectability. The
retention times given were read from the time of sample introduction. Typical recoveries of known mixtures are given in Table 11. The per cent found represents an average of five separate determinations in which the per cent component found varied B-ithin =‘c0.5% of the average value. These results show that this analysis can be performed rapidly and accurately by GLC.
Table 111.
Comparison of Infrared and GLC Analysis
Mixture 1 (Known) o-Chlorophenol 2,4-Dichlorophenol 2,6-Dichlorophenol 2,4,6-Trichlorophenol Total Mixture 2 (Known) 2,3,4,6-Tetrachlorophenol Pentachlorophenol
Known, Wt. 70
27.95 53.57 3.2 15.28 100.00 8.9 91.1
Found, Wt. 70 IR GLC 25.6 28.2
8.6 91.4
8.8
91.1
INFRARED ANALYSIS
For pure compounds the absorptivities obtained during the present investigation were very close to those reported by Scheddel (8) and are therefore not presented here. Typical results of analyses of known mixtures are reported in Table 111. The per cent found by GLC represents a n average of five scparate determinations, in which the per cent component found was reproducible within +0.5% of the average value. The per cent found by infrared also represents five separate determinations. However, in the case of components present in small quantity, such as 2,6-
dichlorophenol, the per cent component found varied as much as =t4.5% from the average value. LITERATURE CITED
(1) Hawkes, , .J. C . , J .
Appl.
Chem.
123 (1957). (2) Huntress, E. H., “Organic Chlorine Compounds,” pp. 53, 70, 1403, Wiley, New York, 1948. (3) Kohn, M., Sussmann, S.,Monatsh. 46, 590-1, 594 (1925). (4) MacMullin, R. B., Chem. Eng. Progr. 44, 183 (1948). (5) Ohta, N., Tokyo KGgy& Shikensko 7,
Hdkohu 52, 142 (1957). (6) Ibid., p. 247. (7) Pray, B. O., Sukov, D. N. (to Columbia-Southern Chemical Corp. 1, U. S. Patent 2,759,981 (Aug. 21, 1956). (8) Scheddel, R. T., ANAL. CHEM. 29, 1553 (1957). (9) Stoesser, W. C. (to Dow Chemical Co.), U.S.Patent 2,131,259 (Sept. 27, 1988’). (10) Tioupe, R. A., Colner, J. J., ANAL. CHEM.30, 129 (19%).
RECEIVEDfor review August 10, 1960. Resubmitted July 3, 1961. .\ccepted October 16, 1961. Northwest Regional Meeting, ACS, Richland, Wash., 1960.
Determination of Low Level Hydrocyanic Acid in Solution Using Gas-Liquid Chromatography CARL R. SCHNEIDER and HARRY FREUND Department of Chemistry, Oregon Sfate University, Corvallis, Ore. ,Distribution of hydrogen cyanide between water and air and analysis of the vapor by gas liquid chromatography permit determination of hydrocyanic acid in water in the concentration range to 5 X 10-4M. Equilibria involving other cyanide species are not disturbed significantly, as less than 1% of the hydrocyanic acid i s removed for analysis. The required instrumental sensitivity i s attained through a 2000-fold concentration step employing a short chromatographic column cooled in dry iceacetone and amplification of the thermistor bridge detector output prior to strip chart readout. Equipment and techniques are described and calibration curves and data on synthetic unknowns are presented.
toxicity of waters polluted with these compounds required an independent measure of the concentration of hydrocyanic acid. The analytical method was not to displace appreciably the complex equilibria relating cyanide ion, hydrocyanic acid, and heavy metal cyanide complexes. A determination based upon solutioii-air distribution of H C N and analysis of the air promised to meet this condition. A number of investigators have studied this distribution and in some cases applied it to analysis (5,9,10). The results of Lewis and Keyes (9) and of Shirado (10) can be used to calculate the distribution coefficient a t 20’ C.:
D
As aqueous hydrocyanic acid levels as low as 0.025 mg. per liter were to be determined, measurements of 0.1 pg. of hydrogen cyanide per liter of air were required. Gas chromatography in conjunction with a concentrat’on step and voltage amplification prior to readout
(3) has presented indirect evidence t h a t the toxicity to fish of systems containing heavy metal cyanides is due primarily to rnolecular hydrocyanic acid. Studies directed towards a better understanding of this effect and prediction of the OUDOROFF
rng. of HCN per liter of gas mg. of HCN per liter of solution = approx. 3 X 10-3 (1)
K -
provides both adequate sensitivity and specificity. EXPERIMENTAL
The basic techniques of distribution and concentration are s h o m in Figure 1. Air at a precisely regulated flow rate is bubbled through the sample. The equilibrated air then passes into a line, where it is dried and then sampled. I n one position of the valve a sample tubing is purged with the air, and in the other position is put into series with the carrier gas stream of the chromatograph for readout of the H C N as a peak. Even with the maximum sample volume, HCK solutions in the range of interest would not give detectable peaks. Hydrogen cyanide, because of its high ionization potential, is not readily adaptable for detection with the recently developed ultrasensitive chromatograph detectors. Voltage amplification permits some sensitivity increase, however. To obtain the required increase in sensitivity, the sample volume tubing is replaced by a short chromatographic column cooled in dry ice-acetone, and VOL. 34, NO. 1, JANUARY 1962
69
