Modified Graphites for Chelation and Ion Exchange James L. Hern' and John H. Strohl" Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506
Several compounds that have ion-exchange or chelation properties have been adsorbed on granular graphite and coke. The resulting materials have been found to exhibit ion-exchange and chelation properties similar to typical commercial exchange resins. However, the exchange capacities are lower (approximately 1000 times) than commercial materials. Particular attention has been devoted to the chelation of several metals on Eriochrome Black T (EBT) modified graphite columns. Separations of Fe3+ from multicomponent solutions of Fe3+, NiZ+,Co2+, MgZ+, and Ca2+ are possible by adjusting the pH of these solutions. Application of an electrical potential enables removal of metal ions from the modified graphite columns. The mechanism of this removal is thought to be the electrochemical generation of H+ ion.
Removal of metal ions from aqueous solutions by means of ion-exchange and chelating resins has, for many years, been a n important technique in analytical and water purification methods. Numerous synthetic resin based ion exchangers and a few chelating materials (also resin based) are available with varying chemical exchange properties. T h e industrial value of these exchangers is very great and although the existing commercial products are very effective as exchangers, there are major reasons for further development in this area. First, there are very few chelation exchangers available. With the exception of Chelex 100, exchangers with chelation properties are not commercially available. Materials of this type are very valuable because of their specificity toward the transition metals. Secondly, the price of resins is too high for large scale operations. Until now, t h e majority of chelation and ion-exchange materials have been produced as an insoluble synthetic resin with numerous active exchange groups attached to the large cross-linked polymer lattice or as inorganic zeolites. These active groups interact with ions in solution either by ion exchange or formation of a complex to effectively remove them from the solution. This removal mechanism in conjunction with a large effective capacity (due largely to the porosity of the resin beads) makes these materials very attractive for industrial and analytical needs. There are many other organic compounds, however, which exhibit unique chelating and ion-exchange capabilities. The method described in this paper shows that when many of these organic compounds are irreversibly adsorbed on granular graphite or coke, exchange and chelating materials result which can be used for removing certain metal ions from aqueous solutions. T h e irreversible adsorption of organic compounds on graphite materials has been substantiated in several previous reports ( 2 - 4 ) . However, until recently ( 4 , s )there has been little mention of utilizing complexing or ion-exchange properties of adsorbed organics for purposes of removing or separating certain metal ions. In this paper, the exchange 'Present address, United States Department of Agriculture, Agricultural Research Senice, Division of Plant Sciences, West Virginia University, Morgantown, W.Va. 26506 0003-2700/78/0350-1954$01 00/0
properties and possible uses of some modified graphites are reported. Graphite with adsorbed organic compounds containing sulfonic acid groups almost always exhibits marked ion-exchange characteristics. Though having lower capacities than conventional resins. the graphite columns are very effective at exchanging low concentrations of cations. Granular graphite and coke with adsorbed complexing agents, such as Eriochrome Black T (EBT) or dibenzo-18-crown-6. give rise to materials with definite chelating properties. Several metals are shown to be held on these columns at different p H values. Thus, separations of multicomponent solutions are possible by proper control of solution pH. T h e electrochemical properties of graphite are such that H+ ion can be efficiently produced by anodic current. In this way metals which are chelated to organics adsorbed on the graphite surface can be released by electrochemically changing the p H of the solution. Using this concept, iron has been effectively removed from EBT-graphite columns by applying anodic currents large enough to produce substantial amounts of H' ion. This characteristic makes t h e regeneration procedure of these materials particularly attractive.
EXPERIMENTAL Chemicals and Materials. AU compounds were of the highest available commercial purity and no further purification was attempted. All other reagents were analytical reagent grade. Asbury Artificial No. 1 graphite was extracted with dilute hydrochloric acid several times and rinsed twice with dilute ammonium hydroxide. This procedure removed iron sulfide and other impurities associated with the graphite. The graphite particles were separated into respective sizes by sieving, and 100/150 mesh graphite was used in all experiments. Coke was obtained from a local coke industry and purified in the same manner as the graphite. Granular active carbon (Nuchar WV-G, 12-40 mesh) was obtained from West Virginia Pulp and Paper, Chemical Division. Alumina F-20 was purchased from Alcoa Chemicals. Instrumentation. A Varian Model 1000 atomic absorption spectrophotometer was used for all atomic absorption analysis. The electrochemical experiments were all carried out with a Princeton Applied Research Model 170 Electrochemistry System. For the experiments using a hanging mercury drop electrode, a Princeton Applied Research Model 9323 hanging mercury drop electrode was used. In all flow systems except those used in conjunction with high performance liquid chromatography (HPLC), anFMI Model RRP pump was used. A Waters Model 6000A HPLC pump was employed in all HPLC related work. A Sargent SRL recorder was used for recording absorption changes from the atomic absorption spectrophotometer and a Beckman Model 76 pH meter monitored pH changes in the potential controlled experiments. The construction of the graphite flow cells and chromatography columns was as follows. Simple Flow Systems. These systems were 5 m m i.d. chromatography columns obtained from the Fischer and Porter Co. (catalogue no. 174-257). Slight modifications were made at the top so as to encompass an injection septum and a hose fitting. Atomic adsorption spectrophotometry ( U S )or a hanging mercury drop electrode (HMDE) was used for analysis of the effluents flowing from the column. Figure 1 shows the flow system. Potentiornetricaliy Controlled Graphite Flou Coiurnns. Figure 2 shows in detail the flow cell used. A 5 cm x 20 cm length of C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978 r -
1955
Table I. Capacities of Ion-Exchange Modifed Graphites
I
-
'-a .
compound adsorbed 2,7-naphthalenedisulfonic acid
Figure 1. Chromatography column and HMDE detector. (a) Solvent entrance from pump, (b) septum (sample entrance), (c) fritted glass disk, (d) modified graphite, (e) reference electrode, (f) large septum, (9) HMDE, (h) counter electrode, and (i) solvent exit
Figure 2. Potential controlled graphite column. (a) Reference electrode, (b) large septum, (c) injection septum, (d) electrolyte exit, (e) rubber
stopper, (f) Pyrex outer tube, (9) fritted glass disk, (h) small bore tubing, (i)Teflon tubing to detector, (j)contact electrode (Pt), (k) solvent entrance, (I) counter electrode contact, (m) electrolyte entrance, (n) counter electrode, (0)porous Vycor with modified graphite, and (p) glass beads 100/150 mesh Pyrex tubing was fitted with rubber stoppers and holes were cut in the stoppers so as to tightly encompass an 18-cm length of 1-cm Vycor (:7930) glass tubing obtained from Corning Glass Works. This glass is porous so as to provide the necessary electrical bridge between the working and counter electrodes. Holes were also cut to allow for electrolyte entrance and exit a t the top of the cell. A piece of small bore Pyrex tubing with a small diameter Tygon hose was fitted into the bottom of the stopper. A medium coarse fritted disk was also positioned between the small bore Pyrex and the Vycor to keep the column material from passing through the cell. Between the modified graphite material and the fritted disk, 2 cm of 100/150 mesh glass beads were positioned. At the top of the cell a solvent entrance, reference and working electrode, and sample injection port were constructed as shown in Figure 2. The counter electrode was coiled around the Vycor column. With this cell, samples could be injected at the injection port (c), pass through the modified graphite column (k) and the effluent could be analyzed as it exited through tube (i). Potential control of the graphite bed was accomplished with the three-electrode configuration shown in the diagram in connection with a PAR model 170 potentiostat. The operating characteristics of this type cell have been described earlier (6).
disodium salt anthraquinone-1-sulfonic acid sodium salt Congo red p-biphenylsulfonic acid anthraquinone-1,8-disulfonicacid disodium salt 1,2-naphthaquinone-4-sulfonic acid sodium salt benzenesulfonic acid sodium salt 2,4,6-trinitrobenzenesulfonicacid anthraquinone-l,5-disulfonic acid disodium salt untreated graphite untreated coke
capacity for sodium ion pmol/g of modified graphite 25%) 1.1 1.9
3.9 1.2 1.0 1.0
1.0 1.2 1.5 0.0 0.0
Adsorption of Organic Materials. The adsorption procedures for different compounds depended on the solubility properties of the organic materials. Water solutions of all but M) were prepared and passed through the two adsorbates (graphite beds followed by thorough rinsing with distilled water. The final rinse was to ensure that all excess of material was removed before samples were introduced into the columns. EBT (-W3 M) was dissolved in a 50% (by volume) ethanol-water solution which was then allowed to flow through the bed. The graphite was then rinsed with an ethanol-water solution followed by a distilled water rinse. Dibenzo-18-crown-6 M) was passed through the graphite in an acetone solution. The column was rinsed then with pure acetone. This rinse was then followed by an acetone-water solution and finally by a distilled water rinse. The adsorption of these materials was observed to be irreversible in the solutions used for this study, with the exception of a few instances when very positive electrical potentials were applied. These instances will be explained elsewhere in this paper. The amount of organic material adsorbed was determined for the EBT-graphite material and found to be approximately 1 @mol per gram of graphite. A simple spectrophotometric method was used for this determination. A known amount of EBT was dissolved in a measured volume of ethanol-water solution. The total amount of EBT was in excess of the amount which would be adsorbed by the graphite. This was then passed through a known weight of graphite and the absorbance of the effluent was compared to that of the initial solution at a wavelength of 535 nm. The amount of surface adsorption was not determined for the other organic materials; however, the graphite was always saturated with the organic material being used. Capacity Determinations. Zon-Exchange Columns. These studies were to determine ion-exchange capacities of the modified graphites having adsorbed organic compounds with available ion-exchange groups. The columns were first rinsed with 1.0 M HC1 followed by distilled water until no detectable (by titration) H+ was present in the effluent. Fifty mL of 1 M NaCl was then passed through the column and the effluent titrated with 0.017 M NaOH. The exchange capacity per gram of graphite was then calculated from the amount of expelled H+. Table I shows the capacity of nine modified graphites. Chelating Columns. The purpose of these studies was to determine the number of moles of metal ions which would be removed from solution per gram of modified graphite. The column capacity vs. pH could easily be determined by adjusting the acidity of the initial solution. The following procedure was used to determine the capacity. The modified graphite (10 g) was packed as a slurry in a 5-mm i.d. liquid chromatography column. One hundred mL of a solution of the proper pH containing no metal ion was first passed through the column. After the pH of the column had been established, 50 mL of 1.0 X lo-' M metal ion
1956
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
Table 11. Capacities of Chelating Modified Graphite capacity for metal ions (pmol/g of modified graphite 110%) Ion Fe3+
Mg2+
compound adsorbed
pH 3.0
4.0
8.0
EBT dibenzo-18-crown-6 PAN xylenol orange EDTA murexide EBT modifed coke untreated graphite untreated coke
0.75 0.70
-
-
0.55
-
0.0 0.0 0.0 0.0
-
1.20 -
-
0.0 0.0
_ j
0.0 -
-
0.0 0.0
-
-
-
-
0.0 0.0
-
-
,
8.5 0.80
.
-
-
-
, !
.~
J r
-
._.
L 1
Flgure 3. Detector response, hanging mercury drop electrode. Injection;
0.20rnLof0.01 MFe(NO,),,O.l M K C I . €=-0.15Vvs.Ag,AgCi. pH = 2.5. Flow rate = 1.5 mL/min buffered at the same pH was passed through the column. This was followed by buffered rinse until no metal ion could be detected in the effluent. The final solution was 50 mL of 0.1 M HC1 which removed the chelated metal ions. This solution was collected and analyzed by atomic absorption spectrophotometry. The capacities are recorded in Table 11. EBT modified coke was treated in the same manner and its capacity for Fe3+is also given in Table 11. In the course of these chelation and ion-exchange studies, the capacities of untreated graphite and coke were determined. There was no evidence that coke or graphite alone exhibited any chelation or ion-exchange properties at these concentrations or capacity levels. Chelation Chromatography. These experiments were performed to determine the feasibility of separating certain metal ions utilizing differences in their retention times in similar solutions. At the pH values used for these experiments, the metal ions are not held totally on the column, but their flow through the column is retarded by the reversible chelation-solution solvation equilibrium. Metals with different retention times would emerge from the column in different portions of the effluent. In this manner, separations could be achieved without changing solvent pH or other variables. The chromatography system used is shown in Figure 1. The metal ions in the effluent stream were detected amperometrically with a hanging mercury drop electrode at constant potential. Metal ion samples were injected into the column which had a solution of the proper pH flowing at a carefully controlled rate. A PAR 170 Electroanalytical System was used to control the mercury electrode at -1.0 V vs. a Ag-AgC1 reference electrode. The current was proportional to the metal ion concentration in the effluent. Typical detector response is shown in Figure 3. The sensitivity of the detection can be noted in this figure by observing the current increase after injection of 0.05 mL of 0.01 M Fe(NO& directly into the effluent stream. Potential Controlled Columns. A schematic representation of this system is given in Figure 4. The objective of this series of experiments was to determine if chelated metal ions could be expelled from the columns when positive electrical potentials were applied from an external source. Metal ion in the effluent was detected by an atomic absorption spectrophotometer. The AAS
Figure 4. System for studying the effect of applied potential to modified graphite columns
nebulizer was fitted with a syringe needle and inserted into the effluent stream. The AAS response was recorded on a strip chart recorder. Potential control of the graphite bed was accomplished with the PAR Model 170. The standard three-electrode configuration was used with an SCE reference electrode and a P t wire counter electrode. The cell is represented in Figure 2. A Beckman 40297 flow through pH electrode was also incorporated in the effluent stream to determine if the production of H+ ion at the graphite electrode was significant. These results are discussed elsewhere in this paper.
RESULTS AND DISCUSSION The adsorption of several organics on graphite materials is known to proceed irreversibly in aqueous solutions under normal conditions ( I ) . Although the exact mechanism of the adsorption on the surface is not totally understood, the important fact shown by these studies is that many of the functional groups available for chelation or ion exchange are unaffected by the adsorption process. T h e availability of ion-exchange groups has been demonstrated with several organics which have sulfonic acid groups. T h e capacities of the modified graphite ion-exchange columns for Na+ ion are reported in Table I. T h e stability of the exchange material was determined by storage of several grams of modified graphite in water and in 0.1 M HCl solutions. In each case after several weeks the exchange capacities showed no detectable variations in either solution. Chelating Compounds. Several organic chelating compounds have been adsorbed on granular graphite material and shown to exhibit chelation exchange properties. Table I1 shows the results of chelation capacity studies of modified graphite columns for Ni”,CoZt, Fe3+,CaZt, and MgZt. For those materials which did not exhibit chelation properties when adsorbed, the maximum pH at which no chelation was detected is reported. The only compounds adsorbed on the graphite and coke which showed significant chelating capacity were EBT and dibenzo-18-crown-6. Also related in this table is the p H above which the particular cation is immobilized to a maximum extent on the chelation column. Removal of
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
capacity vs, p~ for 5 metal ions, ~ ~ ~EBT-~ raphite ~ i 100/150 mesh. 0 , Fe3+;x , Ni2+; @ CoZt; 0, Mgz+; C$'
~i~~~~ 5,
+,
Table 111. Removal of F e 3 +from Multicomponent System Using EBT-Modified Graphite at a pH of 3.0 ions of multicomponent solution
1957
~ Figure i : 6. Elution curves for Fe3+ on an EBT--graphitecolumn at various pH values. Column, 18 g EBT-graphite. Detector, HMDE. E = -0.15 V vs. Ag. ASCI. Injections, 0.10 mL of 0.01 M Fe(NO&, 0.1 M KCI. Curve 1, pH = 1 .OO. Curve 2, pH = 1.50. Curve 3, pH = 2.00. Curve 4, pH = 3.00. Flow rate, 1.5 mL/min
Fe3+ Ni2+ Coz+ Mg2+ Ca2+ %removal by EBT column hl of of 5 mL of all five ions % removal by EBT column hl of of 5 mL of all five ions
98
0.0
94 ^
J
- "'
-
\
Figure 8. HPLC ioi? chromatography of Ni2+ and Fe3+. Column, 1 m X 2 mm of EBT-graphite 100/150 mesh. Detector, HMDE. E = -0.70 V vs. Ag, ASCI. Sample injection: 0.02 mL of 0.01 M Fe3t, 0.01 M Ni2+, and 0.1 M KCI. Flow rate, 0.2 mL/min Figure 10. pH vs. time curve of 0.1 M KCI solution (adjusted to initial pH of 3.5 with HCI) flowing through a granular graphite electrode column (Figure 2). (a) Application of 4-1.2 V vs. SCE. Flow rate, 1 mL/min
I ,- ,
4
. . . - -
, L:.rL.
-_,.... __.. -4
>~4-.
- 1
Figure 9. Effect of applied potential on EBT-graphite column. Column, 35 cm X 1.5 cm. Detector, atomic absorption spectrophotometer. Injection, 1 mL of 0.1 X M Fe(NO,),. Initial pH, 3.5. pH after application of 1.2 V vs. SCE, 2.1. (a) Time of applied potential. Flow
rate, 1 mL/min
M Fe3+ solution. I t is evident from these graphs that the affinity of the modified graphite is different for Ni2+ and Fe3+ at this p H . P a r t d is the response curve for a 0.2-mL sample of 0.005 M Ni2'-0.01 M FeSt solution. Packing of EBT-graphite material in a high performance liquid chromatography column ( 2 mm X 1 m) and subsequent use with a n H P L C system produced the elution curves in Figure 8. T h e o r e t i c a l P l a t e s . An estimate of the number of theoretical plates ( p ) in t h e H P L C and the regular LC modified graphite columns was made using the relationship ( 7 )
p = (4R/W2
(3)
where R is the retention time and W is the base width for the Fe3+ elution curves. Twice the half width of the peaks was used as the base width and R was evaluated as the corrected retention time with respect to a n unretained peak time. Values of p ranging from 8 to 10 for the LC columns were observed. In the HPCL columns, p values as large as 75 were calculated a t p H values of 1.5. E f f e c t of Applied P o t e n t i a l . T h e results of the studies presented show the effect of a n applied voltage on the chelating properties of t h e modified graphite columns. T h e hypothesis to be tested was that upon making the column material more anodic, the complex might be broken up more readily. Hubbard (8)has reported that application of positive potentials could indeed inhibit the Fe3+ complex formation a t electrode surfaces in instances where 3-allylsalicylic acid was adsorbed on Pt electrodes. No noticeable changes occurred on the modified graphite, however, until the potentials applied were anodic enough to produce currents of about 20 mA/g of graphite. This increase in current increased the H t concentration within the electrode bed. T h e production of H + ion in t u r n changed the p H and broke up t h e EBT-Fe complex. T h e effect of electrolytic H t production is shown in Figure 9. This experiment was performed in a manner similar to the other chromatography experiments, but with a n atomic absorption spectrophotometer used as a detector for the
effluent stream (Figure 4). A flow-through p H electrode was also incorporated in the effluent path to record p H changes. With this apparatus, a sample of Fe3+ was injected into the E B T modified column and t h e effluent Fe3+ concentration was monitored. Upon applying a more positive voltage to the graphite material, changes in the Fe3+content of the effluent were followed with AAS. At the same time, any changes in p H were also observed. Figure 9 shows that Fe3+ is removed from t h e modified graphites only when currents become substantially anodic. At potentials where Fe3+ is effectively removed from the column, changes in p H due to electrolytic production of H t ion are substantial. Figure 10 shows the p H change as a function of time after a positive potential of +1.2 V vs. SCE was applied to the column. In these experiments, the p H stabilized at a value of approximately 2. It appears from this observation that the primary reason for cation removal is the lowering of the p H by electrolytic production of Ht ion. Charge repulsion may play a role in the weakening of the metal-EBT complex; however, all of the results could be adequately explained by the p H change induced by current flow. T h e stability of the organic modified graphite was good under all the potentials attempted in this work. Often when freshly prepared E B T columns were used, a small amount of bleeding of violet-blue solution was observed when the first positive potential was applied. This happened only when the columns had Fe3+ complexed on them. On columns of E B T alone, no bleeding was observed upon application of positive potentials. After this initial observation, no colored solution could be observed leaving the column and no property changes were detected. It was felt that this bleeding was due primarily to a loosely adsorbed layer in excess of the expected monolayer. For this reason, when the modified graphite bed was initially polarized, the loosely held EBT-Fe complex was discharged. The primary adsorbed monolayer, however, was bound tightly and could not be removed by the potentials which were applied. Capacity studies, carried out on t h e graphite material after E B T bleeding was observed, showed no effective reduction in column capacity or properties. Many organic materials adsorbed on granular graphite or coke exhibit chelation and ion-exchange properties suitable for removing certain metal ions from aqueous solutions. T h e specificity of the chelation materials can be useful for removing individual components from multicomponent solutions although the capacities are too low for most practical applications. Chelation chromatography using modified graphites has been shown to be effective for separating specific species in solution such as Ni2+and Fe3+. H P L C techniques utilizing modified graphites show definite promise in metal ion analysis. EBT-graphite columns have been shown to be affected by applied electrical voltages. Since complex formation on t h e graphite surfaces is p H dependent, when electrochemical production of H+ ion becomes sufficient, the metal complexes
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14. DECEMBER 1978
are destroyed and the metal cations released. This represents a n 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. T h e 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
