and the percentages of each component are computed, taking into account the impurities (C1F and ClJ which may be present in the chlorine trifluoride. The esperimental results obtained are presented in Table I. CONCLUSION
Satisfactory results were obtained with the equipment used. Qualitative and quantitative analysis of corrosive mixtures of gases such as HF, Cl,, ClF3, or even TFa, may be successfully performed using the assembly described above. The system is extremely simple, and requires little care from the operator.
It may readily be adapted to programmed schedule of introduction. The inlet valve proved to have the necessary precision characteristics, tightness, and corrosion resistance. The detection cell has a high sensitivity and a stable signal all the time. The sensitive components, being protected from the gaseous flow, are not likely to have varying characteristics. ACKNOWLEDGMENT
Our appreciation is extended to Jacques P. Robin, Sational Institute of Applied Sciences, ISSX, for his technical help and guidance during this study.
LITERATURE CITED
(1) Chandenson, P. (to Ugine Society), U. S. Patent 3,007,333(July 11, 1961). ( 2 ) Ellis, J. F., Forrest, C. W., iillen, P. L., Anal. Chim. Acta 22, 27-33 (1960). (3) Ellis, J. F., I v e y , G., “Gas Chromatography 1958, D. H. Desty, ed., pp. 300-9, Butterworths, London, 1959. (4) Iveson, G., Hamlin, A. G., “Gas Chromatography 1960,” R. P. W. Scott, ed., pp. 333-43, Butterworths, London, 1961. (5) Lysyj, Ihor, h’ewton, Peter, ANAL. CHEM.35, 90-2 (1963). (6) Phillips, T. R., Owens, D. R., “Gas Chromatography 1960”, R. P. W. Scott, ed. , pp. 308-15, Butterworths, London, 1961. RECEIVEDfor review August 1, 1963. Accepted Xovember 4, 1963.
Determination of Organic Compounds in Dilute Aqueous Solution by Gas Liquid Chromatography JOSEPH J. CINCOTTA and RAYMOND FEINLAND Central Research Division, American Cyanamid Co., Stamford, Conn.
b The determination of organic compounds in dilute aqueous solution by gas chromatography has been a difficult problem when these compounds elute immediately after the crest of the water peak. A study has been made indicating that many such compounds can be determined with satisfactory precision and accuracy if a flame ionization detector is employed. Compounds studied include ketones, esters, and alcohols that elute in less than 1 to 7 minutes after the crest of the water peak. The relative responses of these compounds when present in nonaqueous solution and in dilute aqueous solution, in concentrations of less than 0.1% are compared. As a typical example, a rapid and direct quantitative method for determining ethyl acrylate monomer in aqueous polymeric emulsions is described.
M
have gas chromatographically analyzed organic compounds in aqueous solution using thermal conductivity detectors. One technique frequently employed is to choose a column that allows water to elute after or well ahead of the compounds to be determined (1, 7 , IO). This procedure, however, is not useful when the substances elute immediately after mater because the large tailing water peak partially or completely masks them. To circumvent this problem, Kung, Tl‘hitney, and Cavagnol (4) employed a heated precolumn of 488
A X Y AUTHORS
0
ANALYTICAL CHEMISTRY
calcium carbide ahead of their chromatographic column and thermal conductivity detector. When aqueous mixtures of alcohols, aldehydes, and esters containing up to 90% water mere injected, quantitative results were obtained because the water was converted to acetylene before entering the column. Swoboda (8) reported that alcohols in aqueous solution can be quantitatively determined if a n argon ionization detector and a dual column system are employed. He found that while such a detector gives practically no response for water, a one-column system was not suitable because the water in the argon passing through the detector greatly reduced its sensitivity to alcohols. Using a dual-column system he retained the mater on the first column and back flushed it to the atmosphere while separating the alcohol components on the second column. Emery and Koerner ( 2 ) determined lower carboxylic acids that elute after water in dilute aqueous solution employing one column and a flame ionization detector. They found, however, that compounds that elute very close to water could not be determined because the elution of large quantities of water extinguished their hydrogen flame for about two minutes. X’elsen, Eggertsen, and Holst (6) have reported a method for determining total volatile hydrocarbons in aqueous polymeric emulsions. They avoided water interference by oxidizing all the organic compounds that eluted from their column to carbon dioxide and
water. The water was then removed b a calcium sulfate tube ahead of t h thermal conductivity detector used to measure the carbon dioxide formed. A similar technique was described by Hunter, Ortegren, and Pence (3) for determining carboxylic acids in aqueous solution. Two other methods for determining residual monomers in latexes have recently appeared in the literature. Tweet and Niller (9) devised a procedure, by combining distillation and gas chromatography, for monomers that can be extracted readily from water. The monomer was first separated from the aqueous emulsion by a n extractive distillation in the presence of a suitable organic solvent. The organic fraction containing the residual monomer was then gas chromatographically analyzed. Shapras and Claver (6) detected some monomers in aqueous emulsions of interpolymers directly using flame ionization detection but discussed the quantitative aspects of the determination only briefly. Our objective was to explore further the possibility of using a one-column gas chromatographic system and a flame ionization detector to quantitatively determine organic compounds in dilute aqueous solution when they elute immediately after water. I n this paper, the results of our study using two such systems, one incorporating a nonpolar silicone grease column and the other a polar polyethylene glycol column are given. -1rapid and direct quantitative method for determining ethyl acrylate
monomer in aqueous polymeric emulsions or latexes is also described to demonstrate the applicability of the first system. EXPERIMENTAL
Apparatus and Corditions. I n t h e s t u d y of t h e silicone grease columnflame ionization syt,tem a BarberColman Model 20 gas chromatograph, equipped with a flame ionization detector made i n our laboratories, was employed. T h e instiwment was connected t o a 5-mv. M'heelco recorder. T h e column was preFared by packing a 9.5-foot length of 1/4-inch 0.d. stainless steel tubing with 20y0 by weight high vacuum ~ilicone grease (Daw Corning Corp.) on 60- to 80-mesh Chromosorb IT' dia omaceous silica solid support. Operating conditions were as follows: column temperature, 83' C.; vaporizer temperature, 134' C.: detector temperature, 102' C. ; helium flow rate, 2 c u i c feet per hour; detector voltage. 200 bolts. The polvethylene ~1wol-flame ionization svstem was studkd using an F&II Model 1609 gas chromatograph and a I-mv. Leeds and S o r t h r u p recorder. The column was Tire1 ared by packing a %foot length of 1/4-inch 0.d. stainless steel tubing with 2!0% by weight Polvglrcol 400 (Don Chemical Co.) on 60-80 mesh Celite 545 diatomaceous silica solid support. Operating condition. mere as follows: column temperature, 91' C.: vaporizer temperature. 145' C.; detector temoerature, 114' C . ; helium flon- rate, 110 ml. per minute; hydrogen floii rate, 63 ml. per minute: air flow rate. 1 cubic foot per hour: detector voltage. 130 volts. Procedure for the 1)etermination of Ethyl Acrylate Monomer in Latexes. The column and condition. employed for our general stud:. of t h e silicone greaqe column-flamr ionization system were also uqed for thi- method. The method na$ calibrated using four standards containing 5, 10, 20, and 40 mg. of e t h r l acrylate. Each standard also contained a suitable amount of methyl ethyl ketone as internal standard and ,\as diluted to a total volume of 35 ml. with water. X sample of 2.5 01. for eich standard was injected into the elironlatograph and the areas of the pead- were meawred. =Ireas mere determined h v miiltiplving the peak height bv its nidth a t one-half the peak height. -A inear calibration curve pasqing through the origin was obtained bv plotting he area ratios of ethyl acrylate t o methyl ethyl ketone us. the rernective wei'rht ratios. T o obtain the ethrl acrylate content of a latex, 4 grams of sample were weighed into a bottle. The latex was then mixed n i t h 1 ml of Triton X 305 emulsifier (Rohm & 3aaq Co.) and 2 ml. of a witable aqueous solution of methyl ethrl ketone and diluted to a total volume of 35 ml. n i t h water. I t was thus posiihle earilv and accurately to inject 2.5 b l . of the sample mixture into the chr imatograph with a Hamilton 10 pl. hypodermic syringe. The weight per cent of ethyl acrylate
-RETENTION TIME, MINUTES
Figure 1 . Chromatogram of an aqueous solution of methyl ketones Column: high vacuum silicone grease Concentration range: 0.01 2 to 0.034 wt. each ketone Sample size: 2.0 pl,
% for
monomer present in a given latex was calculated by first determining the weight ratio of monomer to methyl ethyl ketone that corresponded to the respective area ratio experimentally obtained. This weight ratio was then multiplied by 100 times the weight ratio of methyl ethyl ketone to sample to give weight per cent. To maintain good precision and accuracy, the vaporizer of our instrument was cleaned periodically (after 25-50 sample injections) with solvent to remove accumulated polymer. RESULTS A N D DISCUSSION
Silicon Grease Column-Flame Ionization System. K e first determined whether the injection of u p to 6 p l . of water containing very small quantities of organic compounds, into the flame ionization detector would lead to substantial quenching of the flame and subsequent marked reduction in response for the organic components. We prepared a concentrated water-free mixture of four ketones all of which eluted on the tail of the water peak. The mixture consisted of acetone which eluted near the crest of the water peak and methyl ethyl ketone (MEK), methyl isopropyl ketone (NIPK), and methyl isobutyl ketone (MIBK), which eluted a t successively lower portions of the water peak. Portions of this mixture were diluted 100-fold and 1000fold by volume with water. The concentration ranges in the diluted solutions were 0.12 to 0.34 and 0.012 to 0.034 weight per cent for each ketone. The chromatographic peak areas obtained relative to MIBK when 2 to 6 p l . of each of the dilute solutions were injected, were compared with those obtained with the concentrated mixture. The deviations obtained are shown in Table I. S,-A,
Deviation is defined as __ A" where A, is the peak area relative to RIIBK of the component when injected in nonaqueous form and A , is the peak
area relative to MIBK for the same component when injected in dilute aqueous form. TTater gave a very small peak relative to its concentration but was easily detectable. The contour of the water peak was not exactly reproducible but i t usually had a shape similar to that shown in Figure 1. All areas were determined using a compensating polar planimeter in a n attempt to compensate for varying degrees of tailing. Minimum detectabilities for acetone, RIEK, MIPK, and LIIBK, respectively, estimated from the chromatograms obtained with the 1000-fold dilute aqueous solution were 2, 3, 4, and 7 p.p.m. using a 6-pl. sample. The results obtained indicate that organic compounds in dilute aqueous solution that elute immediately after water can be determined using a silicone grease column-flame ionization system with reasonable accuracy and with high sensitivity. Water does not extinguish or quench the flame substantially when sample sizes up to 6 pl. are injected. Although some appreciable deviations were observed they can probably be attributed to slight errors in determining peak areas and to nonlinearity of detector response for the concentration ranges covered. Experiments were also made in which a concentrated ketone mixture was diluted 100-fold by volume with carbon disulfide and similarly with xylene (0,m, and p ) . The gas chromatographic peak areas observed with these solutions were compared with those of the concentrated mixture and the two dilute aqueous mixtures described previously. The flame ionization detector is relatively insensitive to carbon disulfide and it elutes well ahead of all the components except acetone in the ketone mixture. The detector is sensitive to xylene but it elutes after the last component in the ketone mixture. Tailing of the ketones was so extensive when both the carbon disulfide and the xylene solutions were injected that
Table I. Comparison of Peak Areas" of Aqueous Ketone Mixtures with Similar Nonaqueous Mixture Sample _ Per cent _ deviation* ~ size, Dilution pl. Acetone hIEK--sIIPx 100foldc 2 - 1.6 -5.6 - 3 . 7
+
4 4 . 2 -1.8 - 1 . 4 6 +13.8 - 2 . 1 - 1 . 4 1OOOfoldd 2 2.1 -7.4 -7.1 4 4.8 -3.1 -1.5 6 +10.0 $ 0 . 8 + 3 . 8 a Relative to methyl isobutyl ketone. Average of duplicates. Concentration range: 0.12 to 0.34 wt. % for each ketone. Concentration range: 0.012 t o 0.034 for each ketone. wt. 70
+ +
VOL. 36, NO. 3, MARCH 1964
489
iI
I
Figure 3. Chromatograms of an alcohol mixture before and after dilution with water using a thermal conductivity detector; polyethylene glycol column Figure 2. Chromatogram of a concentrated ketone mixture Column: high vacuum silicone grease Concentration range: 12 to 34 wt. % for each ketone Sample size 0.8 PI.
reliable measurements of peak areas were impossible. These results were in marked contrast to those obtained with the dilute aqueous solutions. As shown in Figures 1 and 2 the ketones exhibited less tailing when injected in dilute aqueous solution than in concentrated form. It was concluded that the elution of organic compounds leads to substantial reduction in the tailing of these compounds. This can probably be attributed to temporary deactivation of the absorption sites of the solid support by the water. This effect was also observed by Emery and Koerner (2). All work reported on the silicone grease column-flame ionization system was done using one column. To date this column is still usable and it appears that the passage of hundreds of aqueous samples through it has not caused any deterioriation. Polyglycol 400 Column-Flame Ionization System. This system was studied using the same general procedure as employed for the silicone system. Comparable results were obtained. Being a more polar substrate, however, water elutes more slowly
Table II.
from a polyethylene glycol column than from a silicone grease column of equal length and loading. An alcohol mixture was prepared to determine whether the elution of water from a polyethylene glycol column into a flame ionization detector would decrease appreciably its sensitivity to organic compounds. As shown in Figure 3 the mixture contained two alcohols that eluted before water (ethanol and 1-propanol), one high on the tail of the water peak (1-butanol) and two lower on the tail of the water peak (1-pentanol and 1-hexanol). Portions of the concentrated alcohol mixture mere diluted 100-fold and 1000-fold by volume with water. An ether solution was also prepared by diluting the concentrated alcohol mixture 10-fold by volume with diethyl ether. The concentration ranges in the diluted aqueous solutions were 0.06 to 0.40 and 0.006 to 0.040 weight per cent for each alcohol. Sample sizes from 1 to 4 111. of the dilute solutions were chromatographed and the peak areas relative to 1-propanol measured. Area measurements were made by multiplying peak heights by the width a t one half the peak height for all peaks except 1butanol. The butanol peak areas were measured using a planimeter because they were superimposed on the water peak. Figure 4 is a typical chromato gram obtained with the 1000-fold dilut e
Comparison of Peak Areas’ of Aqueous Alcohol Mixtures with Similar Nonaqueous Mixture
Dilution 100 foldc 1000 foldd
Sample size,
Per cent deviationb 1-Butanol 1-Pentanol ~
PI.
Ethanol
1
+3.8
2 4
1
+5.3 +5.4 +1.0
2 4
$3.9
f1.8
++ 21.1 .2 - 3.6 -
3.2 -20.7 -17.5
+1.8 +3.7 f3.0 +5.3 +1.7 +4.4
Relative to 1-propanol. Average of duplicates. e Concentration range: 0.06 to 0.40 wt. yo for each alcohol. Concentration range: 0.006 to 0.040 wt,. Yofor each alcohol. ~~~~~
490
~~
ANALYTICAL CHEMISTRY
1-Hexanol +5.8 +7.3 +3.2 +8.1 f3.6 $4.6
Figure 4. Chromatogram of an aqueous solution of alcohols Column: polyethylene glycol Concentration range: 0.006 to 0.040 wt. each alcohol Sample size 4.0 pl.
% for
aqueous solution. Comparing these relative peak areas with those obtained with the ethereal alcohol solution the deviations (same definition as above) given in Table I1 were calculated. An ether solution of the alcohols rather than the concentrated alcohol mixture was used as the basis for comparison in order to reduce the alcohol concentration differences between aqueous and nonaqueous solutions. From Table I1 it can be seen that most of the deviations obtained for alcohols that elute on the tail of the water peak are not significantly different from those obtained for ethanol which elutes ahead of water. The largest deviations occurred when 1-butanol was injected in very dilute aqueous solution (0.016 wt. %). These deviations, while appreciable, indicate that even when organic peaks elute very near the crest of the water peak, semiquantitative results can be obtained using this system. The minimum detectabilities for ethanol, 1-propanol, 1-butanol, 1pentanol, and 1-hexanol, respectively, estimated from the chromatograms obtained with the 1000-fold dilute aqueous solution were 0.1, 0.1, 0.3, 0.5, and 0.6 pap.m.using a 4-pl. sample. ils concluded for the silicone grease column, it appears that the sensitivity of the flame ionization detector is not markedly decreased and the hydrogen
Mlthyl Ethyl Ketone
i
significant change was observed in a n y of the retention times i t appears likely that repeated injection of water will not reduce the life of the column appreciably using the stated conditions.
Table 111.
Wt. yo Added Found
Determination of Ethyl Acrylate Monomer in Latexes. T h e gas chro-
RETENTION TIME, MINUTES
I
Figure 5. Chromatogram of ethy acrylate and methyl methacrylate when present in an aqueous polymeric emulsion; high vacuum silicone grease column
flame is not extinguished by the presence of u p to 4 pl. of wvttter eluting from polyethylene glycol 40Ci column. I t also appears probable that alcohols that elute with water when present in aqueous solution can b ? determined if a polyethylene glycol-f ame ionization system is employed. d simple test was performed to determine if the life of the polyethylene glycol column would be considerably shortened by repeated injections of water. A sample of a concentrated alcohol mixture mas in ected before and after 10 successiye iniections of water (10 pl. each a t 2 minute intervals). We measured the retmtion times for each of the alcohols both before and after the water treatmsnt to determine whether any stripping of the polyethylene glycol had ocourred. Since no
matographic method for ethyl acrylate monomer in dilute latexes provides further evidence of the capability of t h e flame ionization detector t o respond t o organic compounds in dilute aqueous solution. Sufficiently high sensitivity, precision, and accuracy can be easily obtained in this manner. As shown in Figure 5 both ethyl acrylate and methyl ethyl ketone, used as a n internal standard in the method, elute on the tail of the water peak. Figure 5 also indicates where methyl methacrylate would elute using the conditions of the ethyl acrylate method. We have found that both acrylates can be quantitatively determined simultaneously when present together in the same latex. The precision of the ethvl acrvlate method was measured by determining the area ratio of ethyl acrrlate to MEK in nine aqueous standards, five of which contained a latex. The concentration range covered was 0 009 to 0.131 mt. % ethyl acrylate in water. The mean relative standard deviation was &1.3%. The accuracy of the procedure was determined by analvzing a latex sample (containing no detectable quantity of ethvl acrylate monomer) both before and after several known additions of ethvl acrylate. The data shown in Table I11 indicate that the method gives acceptable ac-
Accuracy of Method for Ethyl Acrylate
0,060 0.128 0.220 0.450
0.058 0.126 0,213 0.457
Relative
error, yo -3.3 -1.6 -3.2 +1.6
curacy. The minimum detectability for ethyl acrylate was estimated to be 0.25 mg. using a 5-gram sample. ACKNOWLEDGMENT
The authors acknowledge the assistance of Bernard s. -ironson who performed some of the experimental work described in this paper. LITERATURE CITED f 1) Bodner. S.J.. Mavneux.' S.J.. .&NAL. ' CHEW30, 1384'( 1958). (2) Emery, E. RI., Koerner, IT. E., Ibid., 33, 146 (1961). (3) Hunter, I. R., Ortegren, V. H., Pence, J. W., Zbid., 32,682 (1960). (4) Kunp, J. T., Rhitnev, J. E., Cavagnol, J. E., Ibid., 33, 1505 (1961).
(6) Selsen, F. M., Epgertsen, F. T., Holst, J. J., Zbid., 33, 1150 (1961). (6) Shamas, P.. Claver. G. C., Zbid., 34. ' 433 (1962'). ' (7) Smith, B., Acta Chem. Scand. 13, 480 (1959). (8) Swoboda, P. A. T., Chem. & Ind. (London) 1960, 1262. (9) Tweet. 0.. Miller. IT. K.. ASAL. ' CHEM. 35, 852 (1963): (10'1 Zaremho, J. E., Lysyj, I., Ibid., 31, 1833 (1959).
RECEIVEDfor review October 1, 1963. Accepted November 15, 1963. Pittsburg Conference on Analytical Chemistry and Applied Spectroscopy, March 1963.
Techniques for Quantitative Thin Layer Chromatography M. A. MILLETT, W. E. MOORE, and J. F. SAEMAN Forest Products tabora tory, U . S. Department of Agriculture, Madison, Wis.
b A reliable sequence of techniques i s described
for h tem rapid routine quantitative analysis clf materials separated b y thin layer chromatography. Application of unknown i s made either by spotting or by the use of a precision streaking device-the latter also serving to apply indicator reagents. Following irrigation, the substrate and separated component:; are picked up in vacuum collector tubes fashioned from sections of 5-rnm. borosilicate tubing. By varying lube length and diameter, sample sizes ranging from micro to preparative can be handled, Chromatographic elution of sample
from the resulting powder columns i s accomplished through transfer of solvent from a reservoir by means of a thread wick. Elution volumes are minimal, 100 pl. providing quantitative recovery of a separated component, thus favoring subsequent examination by micro ultraviolet, infrared, and gas chromatographic techniques. Using furoic and hydroxymethylfuroic acids as model compounds, the techniques have been applied over a plate loading range of 1 to 100 pg. Data are given to illustrate the precision and accuracy of each step in the overall procedure.
HILE THIK LAYER CHROM4TOG RAPHY has found wide a p
plication as a qualitative tool in the characterization of the components of chemical mixtures, its quantitative aspects have been less widely recognized. As with paper chromatographv, the quantitative techniques thu. far described are based either on the direct determination of a component through measurement of spot size or color intensity, or upon an extraction of the ceparated component from the substrate followed by chemical, optical, or weight determination. of its quantity. X discusion of the relative merits of VOL. 36, NO. 3, MARCH 1964
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