ANALYTICAL CHEMISTRY, VOL. 50, NO. 14. DECEMBER 1978
are destroyed and the metal cations released. This represents an innovation in regenerating spent chelation columns. The economic justification for this procedure is evident: electricity is cheaper than reagents. Coke, which is readily available a t relatively less expense than graphite, has also been shown to be useful as a support material. Though coke appears to he more porous than the graphite surveyed, it shows little increased capacity over these graphite materials.
LITERATURE CITED (1) K . Dunlap and J. Strohl, Anal. Chem., 44, 2166 (1972). (2) R. L.Bamberger, Ph.D. Dissertation, West Virginia University, Morgantown, W.Va., 1969. (3) C. Giles, A. D'Silva, and I. Easton, J . CoibidInferface Sci., 47, 766 (1974).
1959
(4) J. H. Strohl and K . S. Sexton, Sep. Sci., 9, 557-561 (1974). (5) K. Dunhp, Ph.D. Dissertation, West Virginia University, Morgantown, W.Va., 1972. (6) J. H. Strohl and J. L. Hern, Anal. Chem., 46, 1941 (1974). (7) A. I. M. Keulemans, "Gas Chromatography", 2nd ed.,Reinhold, New Yo&, 1959. (8) R. F. Lane and A. T. Hubbard, J . Phys. Chern., 77, 1401 (1973).
RECEIVED for review May 30, 1978. Accepted September 11, 1978. This study was partly supported by the Water Research Institute, West Virginia University, with funds allotted under the Water Resources Act of 1964 (PI, 88-379) administered by the Office of Water Research and Technology, U S . Department of the Interior. The work was done as part of Project A-030-U7VA,John H. Strohl, Principal Investigator.
Determination of Acrylamide Monomer in Polyacrylamide and in Environmental Samples by High Performance Liquid Chromatography Norman E. Skelly" Analytical Laboratories, The Dow Chemical Company, Midland, Michigan 48640
Edward
R. Husser
Designed Latexes and Resins Research, The Do w Chemical Company, Midland, Michigan 48640
Water soluble compounds such as acrylamide and methacrylamide have sufficient lipophilic character such that they can be retained and separated on HPLC reverse-phase columns using water as the eluent. By employing a lowwavelength ultraviolet detector, these compounds can be measured with high sensitivity. This technology has been applied to the measurement of trace acrylamide monomer in wipe and aqueous impinger samples, and acrylamide in polyacrylamide. The chromatographic method is identical for both analyses. The relative precision at the 9 5 % confidence level for acrylamide in wipe samples and in polyacrylamide was k5.8% and f7.4 %, respectively.
Polyacrylamides produced from acrylamide monomer find extensive use as flocculants and in secondary oil recovery. In order to ensure safety of these products, sensitive and specific analytical methods are required to measure residual acrylamide monomer ( I ) . -4crylamide in water solution has been measured by various gas Chromatographic methods including bromination and extraction ( 2 - 4 ) . More recently, differential pulse polarography (5)was employed for trace levels of acrylamide. These methods generally require derivatization, extraction, or some sample cleanup prior to measurement. T h e measurement of acrylamide monomer in polyacrylamide has been studied by gas chromatography (161, ultraviolet spectrophotometry ( 7 , 8 ) , polarography (8-11 ), and liquid chromatography (12, 13). These methods generally require some manipulation of the extract following extraction before the final analysis can he made. 0003-2700/78/0350-1959501.00/0
A high performance liquid chromatographic (HPLC) method using the reverse-phase mode was investigated for these two problems: acrylamide monomer in polymer, and acrylamide in wipe and impinger samples. The final quantitative methodology is the same for both analyses. No sample preparation is required following extraction of the sample prior to injection. EXPERIMENTAL Liquid Chromatograph. A modular liquid chromatograph was used. It consisted of a Perkin-Elmer LC-55 variable wavelength detector, a model 396-31 Milton Roy instrument minipump, a Rheodyne model 70-10 injection valve with PO-pL loop, a Sargent-Welch model SRG recorder having 1-100 mV output. and a Whatman Inc. Partisil-10 ODs-2, 4.6 X 250 mm reverse-phase column. The analytical column was protected with a guard column 2.1 X 60 mm in size containing pellicular reverse-phase packing. A 3000 psig pressure gage was located between the pump and the injection valve. Reagents. W a t e r Eluent. Laboratory deionized water was circulated through a Millipore Corp. Milli-Q Water System. It was then degassed by laboratory vacuum. Acrylamide, Eastman Kodak, electrophoresis grade; methanol, Hurdick and Jackson, distilled in glass grade were used for standards and solvent, respectively. Liquid Chrornatogrnphic Conditions. The water eluent was pumped at 2 mL/min which gave a pressure of about 1600 psig. The variable wavelength ultraviolet detector was set at 208 nm. Recorder response was at 0.02 aufs for the analysis of environmental samples and generally 0.04 aufs for acrylamide monomer in polymer. Chart speed was 0.2 in/min and injection volume 20 /lL. Acrylamide in Aqueous Impinger and Wipe Samples. Calibration. A 1 and 10 ppm solution of acrylamide in water were 3: 1978 American Chemical Society
1960
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table I. Acrylamide Retention Time as a Function of Octadecyl Loading on HPLC Column acrylC,, amide loading, retention column % time, min manufacturer
H ? CH2=C-C-NH2 Acrvlamide 10 ppm I " water "I water
1 00 cm Cell
Whatman Inc. Waters Assoc. Whatman Inc. Merck Inc. DuPont
T 0 1 AU 1_
Partisil 1 0 ODS p-Bondapak
5
2.6
10
5.8
Partisil 10 ODS-2
15
5.2
RP-18
22
2.7
Zorbax ODS
25
3.6
C18
Table 11. Recovery of Acrylamide Added t o Filter Paper
\
acrylamide, p g added found L
I
I
1 E3
200
220
I 240 i!9"?le"g:1
I
I
1
260
280
300
rm
Figure 1. Ultraviolet spectrum of 10 ppm acrylamide solution prepared. Twenty pL of each was injected and the peak height recorded. Procedure. Twenty pL of aqueous impinger samples taken as described ( 5 ) was injected. Whatman KO.2,4.5-cm filter paper moistened with water was used to wipe surface areas. The paper was then placed in bottles. Fifteen mL of water was added and they were allowed to stand for 30 min with intermittent shaking. Twenty FL of extract was injected and the peak height compared to the standard for concentration measurement. Acrylamide Monomer in Polyacrylamide. Calibration. A 10 ppm acrylamide standard was prepared in 80120 v / v methanol-water. Twenty pL was injected and the peak height recorded. Procedure. Five g of polyacrylamide was placed into a 4-02 bottle. Fifty mL of 80-20 methanol-water was added and the mixture placed on a mechanical shaker for 3-4 h. Twenty pL of the clear phase was injected and the peak height recorded. The above extracts were also examined by ion exclusion liquid chromatography by the method of Husser et al. (12).
5.0
5.3
5.0 10.0
4.8 10.7 10.4
10.0 20.0 20.0
50.0 100.
200.
19.3 19.2 48.8 99. 204.
recovery, % 106 96 107 104
97 96 98 99 102 av 101%
DISCUSSION From the ultraviolet spectrum given in Figure I,it can be seen that the lower the wavelength, the more intense the absorbance for acrylamide. Analogously, the lower the wavelength chosen for monitoring the acrylamide separation, the more sensitive the measurement will be. Water, being the eluent, gives excellent ultraviolet transparency. The acrylamide response was found to be linear from 1-500 ppm in solution using a 20-pL injection. This equates to 0.02-10 pg acrylamide injected. Area response obtained from a computing integrator was also found to be linear. Sensitivity of acrylamide detection is about 0.1 ppm in solution based on a 20-pL injection. By monitoring the separation a t a wavelength lower than 208 nm, increasing injection volume, and decreasing attenuation, sensitivity can be increased an order of magnitude. T h e maximum absorbance for acrylamide occurs a t 198 nm. Retention of the acrylamide on reverse-phase columns was the strongest for those having intermediate loadings of octadecyl silane, while those having very high and very low loadings gave short retention times. Table I gives the octadecyl loadings and acrylamide retention times from five commercially available HPLC columns. The percent loadings were obtained from the respective companies' promotional literature.
Time M i n u t e s
Figure 2. Standard HPLC chromatogram for the determination of acrylamide in wipe samples The recovery of acrylamide monomer added to filter paper was studied to simulate the condition used for wipe sample analyses. Known amounts of the monomer from an aqueous standard solution were syringed onto filter paper contained in a vial. .4fter allowing sufficient time for the paper to dry, 15 mL of water was added. The solutions were shaken intermittently during the 30-min extraction period. Following this, 20 pL of extract was injected onto the HPLC column and chromatographed as described previously. Chromatograms of standards are given in Figure 2, the recovery data are presented in Table 11, and the precision in Table 111. The latter were determined by measuring one concentration level
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
1961
Table 111. Acrylamide Determination Precision Data acrylamide, p g 18.9 19.5 19.8 19.5 18.6 18.2 19.8 19.1 19.8 18.9 av std dev re1 std dev precision
19.2p g 0.56 p g 2.9% i 5.8% (95% confidence level)
Table IV. HPLC Retention TimesQ for Acrylamide and Related Compounds compound min acrylic acid p-hydroxypropanamide acetamide acrylamide propanamide acrylonitrile methacrylamide butanamide methacry lonitrile a Partisil-10 ODs-2, water, 2.0 mL/min, aufs.
1.4 2.1
3.0 5.4 7.3 11.8
18.0 20.8 46. 208 nm, 0.04
Table V . Precision Data for the Determination of Acrylamide Monomer in Polyacrylamide acrylamide, ppm
Tsm? U nutel
Figure 3. HPLC chromatograms of an acrylamide standard and po-
lyacrylamide extract Table VI. Comparison of Acrylamide Monomer Concentration in Polyacrylamide b y HPLC and Ion Exclusion Chromatography acrylamide monomer, ppm polyacrylamide polymer HPLC IE A B C D E
179 176 166
F
170 169 183 184 176 177 185 av 1 7 7 p p m std dev 6.6 ppm re1 std dev 3.7% re1 prec t 7.4% (95% confidence level) five times on two different days. The recovery of acrylamide monomer from airborne vapors and dust has been studied by McLean et al. ( 5 ) . Their studies were carried out using Mine Safety Appliance No. 42513 all-glass midget impingers containing 15 mL of water. Air containing acrylamide flowing through the impingers in series showed no breakthrough in the second impinger a t concentrations of 0.03 to 3.0 mg/m3 over a 4-h sampling time. This is 16 times longer than the suggested minimum sampling time necessary to detect the current TLV. Therefore only one impinger is necessary for normal sampling. The retention times for acrylamide and related compounds are given in Table IV. No known impurities were observed a t the retention time of acrylamide. Since the HPLC procedure separates acrylic acid and other potential impurities from acrylamide found in polyacrylamide extracts, resin treatment and solvent extraction is not necessary as is the case with the ultraviolet spectrophotometric method (8). The resin treatment has been shown to adsorb some of the acrylamide; therefore the standard must by
G
H I J K L M N 0 P
Q R
s
T a
259 282 74 197 117 181 178 209
237 275 74
191 110
99
184 168 212 113 99
525 539 715 731 644
513 527 707 736 634
116
23 23 KDQ 3
25 19
5
7
2
3
ND = Not detected.
conditioned in an identical manner. Typical chromatograms for an acrylamide standard and polymer extract are given in Figure 3. T h e precision value was determined as described previously and is presented in Table V. A comparison of acrylamide monomer in polymer results obtained by the HPLC method was made with those of the ion exclusion method of Husser et al. (12). The results are given in Table VI. Good agreement between the methods was obtained. The extraction of acrylamide monomer from polyacrylamide has been extensively studied previously (6). Three different polyacrylamides were subjected to an extraction study as a function of time (Figure 4). I t was found that extraction is complete in one hour or less. However, because the mesh size
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
is a stronger eluent than water alone; therefore, the peak obtained will be lower in height but slightly broader in shape. When compared with an equivalent standard injected from a water matrix, the peak height is 10% smaller but the peak area should be identical. No plugging of the HPLC column was observed following injection of the polymer extracts. If particulate matter is present, it is strongly recommended that extracts be filtered. After extended column use, it is recommended that the column be eluted with 50% methanol-water solution to remove trace impurities that may be more strongly retained than the components being separated.
E
-
150
r
d
-100
LITERATURE CITED D. D. McCollister,F. Oyen. and V. K . Rowe, Toxicoi. Appl. Pharmacol., 6 , 172 (1964) B. T. Croll and G. M. Simkims, Analyst(London), 9 7 , 281 (1972). A . Hashimoto. Analyst (London). 101, 932 (1976). H. Arimitsu, Suido Kyokai Zasshi, No. 473, 10, (1974). J. D. McLean, J. R. Mann, and J. A. Jacoby. Am. Ind. Hyg. Assoc J . , 39, 247 (1978). B. T. Croll, Ana/yst(London), 96, 67 (1971). F. Vajda, Acta Chim. Acad. S o . Hung.. 53, 241 (1967). D. C . MacWilliams, D. C. Kaufrnan, and B. F. Waling, Anal. Chem.. 37, 1546 (1965). E. M. Skobets. G. S. Nestyuk, and V . I . Shapoval, Ukr. Khim. Zh., 28. 72 (1962). F. Vajda, Banyasz. Kut. Intez. Kozlem., 10 (1-2), 221 (196546). S. R. Betso and J. D. McLean, Anal. Chem., 48, 766 (1976) E. R. Husser. R. H Stehl, D. R. Price, and R. A . DeLap, Anal. Chem., 49, 154 (1977). F. J. Ludwig and M. F. Risand, Anal. Chem., 50, 185 (1978).
50
0 2
0
6
4
8
T i n e Fio~rs1
Figure 4. Extraction of polyacrylamide with 80-20 methanol-water
as a
function of
time
of polyacrylamides can vary, together with other properties, each product should be extracted as a function of time to ascertain the optimum conditions. T h e standardization for the acrylamide monomer in polymer determinations must be made from a standard prepared in 80-20 methanol-water. This solvent composition
RECEIVED for review July 26, 1978. Accepted September 15, 1978.
Effects of Operating Variables on Peak Shape in Gei Permeation Chromatography Joseph L. Glajch, Doris C. Warren,' Mary A. Kaiser,* and L. B. Rogers" Department of Chemistry, University of Georgia, Athens, Georgia 30602
The effects of flow rate, solute molecular weight, added dead volume, and different detectors on peak shape in a gel permeation chromatographic (GPC) system have been studied. Toluene and three monodispersed polystyrenes, having nominal molecular weights of 37 000, 110 000, and 233 000 were examined using the second moment, the standard deviation of the Guassian component of the peak (u), and the exponential tailing function (7). Detector effects reflected primarily the cell volume and not the additional dead volume that included its connecting tubing. The addition of 25 pL of narrow-bore tubing between the injector and the column slightly decreased the second moment of the peak. The use of u values, in addition to the second moment, also allowed confirmation of previous predictions based on computer simulation studies showing peak spreading as a function of molecular weight.
The analysis of peak shape in chromatograph), using both simulated and real data, continues t o receive a great deal of attention as data acquisition and reduction techniques become more sophisticated. A dramatic increase in the use of laboratory minicomputers and microprocessor systems in conjunction with Chromatographic apparatus allows the analyst to collect easily the digitized chromatograms which can then be used in peak shape studies. Although a Gaussian probability function is the simplest approach (and for a first approximation of system behavior, the most widely used), an exponentially modified Gaussian is now the model preferred by many chemists for describing the actual peak shapes. Sternberg ( 1 ) was one of the first investigators to point out the causes and problems of asymmetric peaks in gas chromatography. Grushka (2) and others (3-7) have extended the characterization of these peaks. The exponentially modified Gaussian can he described by c
'Present address, Department of Chemistry, Houston Baptist University, 7502 Fondren Road, Houston, Tex. 77074. 2Present address, Central Research and Development Department, E. I. DuPont de Nemours & Company, Inc., Wilmington,Del. 19898. 0003-2700/78/0350-1962$01.00/0
C 1978 American Chemical Society
