Mlthyl Ethyl Ketone
i
significant change was observed in any of the retention times it 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 up 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 the 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
491
the two approaches is given in a recent book by Truter (17). By and large, the described procedures were designed for specific problems rather than for general application on a routine, analytical basis. The purpose of this paper is to describe a reliable sequence of techniques, which has shown promise for the rapid quantitative analysis of multicomponent systems whose constituents can be separated by thin layer chromatography. It is based on an extraction procedure and is designed for the routine handling of multiple samples. I n general plan, it follows the operational sequence developed a t the Forest Products Laboratory for the paper chromatographic analysis of purified pulps (13). Accuracy and precision of the techniques as applied to the determination of furoic acid alone and in furoic-hydrosymethylfuroic acid mixtures are demonstrated over a plate loading range of 1 to 100 pg.
98
Q?
_L
-I
f.5 MM. BORE CUT 4 5 'ANGLE
TO
POL YE TH YL ENE T/P
7-
tI
ASBESTOS MAT ZOO MESH S.S. SCREEN
Figure 1. Collector tube for quantitative removal of sample zone from thin layer plate
EXPERIMENTAL
Chromatography. Glass plates (8 by 8 inches) were coated with a 250micron layer of silica gel containing an inorganic fluorescent indicator (silica gel HF264,Brinkman Instruments, Inc., E. Y.) in the conventional manner, using a commercial spreader (Research Specialties Co., Calif.). ilfter air-drying, the plates are heated for 1 hour a t 105' C. just prior to use. Because of the high adsorptive eapacity of silica gel, considerable care must be exercised in the handling and storage of prepared plates to prevent adsorption of the vapors of interfering substances. Serious difficulties were experienced during the earlier stages of this work by the inadvertent exposure of plates to very low pyridine vapor concentrations. Contaminating vapors must ako be avoided during the subsequent aspiration of the separated spots into the collector tubes. The problem of such interference increases with decreasing sample size. Application to the plates of aqueous solutions containing the furoic acidhydroxymethylfuroic acid mixtures to be analyzed was performed either by spotting with a microburet or by means of a precision streaking device. The microburet used was of the mercury displacement type, having an auxiliary tip drawn down from 1/4-inch polyethylene tubing. It was found that the bore of the polyethylene tip must be extremely fine (
