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Anal. Chem. 1981, 53, 731-732
concentration of 1% (v/v) in the sample solution was adequate to reduce the pII to less than 2. For more highly buffered samples, such as seawater and certain types of waste waters, it may be necessary to add more acid.
ACKNOWLEDGMENT The authors wish to thank C. Khoo for carrying out the statistical analysis.
LITERATURE CITED (1) “A Guide to the Sampllng and Analysis of Water and Wastewater”; Report No. 95/79; Victorian Environment Protection Authorlty: East Melbourne, Australia, Oct 1979; p 13. (2) “Notes on Water Sampling”; Vlctorlan Environment Protection Authority: East Melbourne, Australia, May 1976; p 134.
RECEIVED for review March 6,1980. Accepted November 10, 1980.
Gas Chromatographic Determination of Polyacrylamide after Hydrolysis to Ammonia Gary G. Hawn” Alcolac Inc., 3440 Fairfield Road, Baltimore, Maryland 2 1226
Charles P. Talky GAF Corporation, 1361 Alps Road, Wayne, New Jersey 07470
Polyacrylamide is frequently used in such diverse fields as water treatment, paper making, petroleum recovery, and mineral processing. Application dosages of polyacrylamide and various cationic or anionic copolymers of polyacrylamide are usually a t the parts-per-million level. lJnfortunately, very few analytical techniques are available for measuring polyacrylamide at these low levels. Crummett and Hummel (I) have outlined two procedures, a distillation-nesslerization method and a turbidimetric method using “Hyamine 1622” (dimethyl [2- [2- [4-(1,1,3,3-tetramethylbuty1)phenoxyl ethoxyjethyl]benzenemethanaminium chloride). The polyacrylamide must be partially hydrolyzed for it to produce turbidity with “Hyamine 1622”. Attia and Rubio (2) developed a turbidimetric procedure which eliminated the need for hydrolysis, whereby polyacrylamide was precipitated directly with tannic acid and quantified by nephelometry. While the techniques described above are accurate and sensitive, colorimetric and turbidimetric procedures are subject to various matrix interferences. We have developed a procedure which has the potential to quantify low levels of polyacrylamide and to eliminate many interferences from matrix effects. The most serious limitation to this method is that other chemical compounds which can liberate ammonia will interfere with the m a y . However, this assa.y has proven useful and accurate in various applications, including the analysis for trace levels of polyacrylamides, leached from food grade paper, as required by the Food and Drug Administration. The derivatization procedure with l-fluor0-2,4-dinitrobenzene has been documented and has been shown to be simple, rapid, and quantitative with various amines (3).
EXPERIMENTAL SECTION Reagents. l-Fluoro-2,4-dinitrobenzene.Purchased from Eastman Organic Chemicals and used without further purification. (Caution: This material is reported to be an experimental carcinogen and mutagen, according to ref 4.) Borate Buffer. Prepared by dissolving 2.5 g of powdered sodium borate decahydrate (Na&3407.10H20)in 100 mL of distilled water. Polyacrylamide Stock Solutions. Prepared by dissolving 1.00 g of polyacrylamide in 1 L of distilled water followed by diluting 1,2,5, and 10 mL of this solution to 1L of distilled water. This gives final stock solutions of 1,2,5,and 10 ppm of polyacrylamide. 2,4-Dinitroaniline. Purchased from Aldrich and used without further purification. Procedure. By use of a volumetric pipet, 100 mL of the polyacrylamide stock solutions was concentrated to 1-2 mL under
a stream of nitrogen. Each solution was transferred to a 25-mL vial which has a screw cap with a Teflon rubber laminated disk. After 3 mL of 10 N NaOH was added, the vial was sealed and placed in an oven at 95 OC for 15 h. The flask was allowed to cool to room temperature and then placed in a dry ice/acetone bath for 5 min, allowing the contents to freeze. Five milliliters of 6 N HC1 was added to neutralize the contents, and the solution was quantitatively transferred to a 50-mL glass-stoppered volumetric flask by washing with distilled water. If the pH of the solution is very acidic at this point, several drops of dilute NaOH are added to bring the pH to the range of 5-6. To this flask are added 10 mL of the borate buffer and 2 drops (-0.1 mL) of l-fluoro-2,4-dinitrobenene.The flask is stoppered, shaken until a yellow color begins to form, and placed in an oven at 60 O C for 30 min. After the mixture was cooled, 5 mL of 10 N NaOH is added followed by 1.0 mL of toluene. The flask is shaken vigorously for 1min, and distilled water is added until the toluene layer is well up into the neck of the flask. The ammonia derivative which is formed, 2,4-dinitroaniline, was quantified by injecting a ~ - Maliquot L of the toluene layer on a Hewlett-Packard Model 57204 gas chromatograph equipped with a flame ionization detector. A 2 m X 2 mm glass-coiled column packed with 3% OV-225 Gas Chrom Q was used for the analysis. The column oven was held at 225 O C with the detector and injector kept at 250 OC. The Nz carrier gas flow was maintained at approximately 20 mL/min. An external standard of 2,4-dinitroaniline was used for quantification. The peak areas were determined with a Hewlett-Packard Model 3350 2B laboratory data system.
RESULTS AND DISCUSSION Four standard solutions of polyacrylamide were analyzed
as described in the Experimental Section. The 100-mL sample of the 1.0 ppm polymer standard contains 0.1 mg of polyacrylamide. The amount of 2,4-dinitroaniline which can be formed, based on 100% hydrolysis and liberation of ammonia, can be calculated as follows: w t polymer X (mol wt 2,4-dinitroaniline)/(mol w t monomer unit) = w t 2,cdinitroaniline (1)
0.1 mg X 183/71 = 0.258 mg 2,4-dinitroaniline (2) The amount of 2,4-dinitroaniline formed from the other standards is calculated in a similar manner. Higuchi and Senju (5)have shown that a conversion limit of about 60% exists in the alkaline hydrolysis of polyarcylamide under moderate conditions. However, we feel that the
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Anal. Chem. 1981, 53,732-734
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range of expected levels of 2,4-dinitroaniline produced from the polyacrylamide standards. The polyacrylamide standard solutions of 1,2, 5, and 10 ppm were analyzed according to the outlined procedure. The recovery of ammonia, calculated from the calibration curve and based upon quantitative hydrolysis, derivatization, and extraction, ranged from 92 to 106%. A Hewlett-Packard Model 9820A desk top computer was used to determine that the method was linear over the 1-10 ppm range with a relative standard deviation of 6.25%. A sample chromatogram is shown (Figure 1) which depicts the separation of the ammonia derivative from solvent and other impurities. There are several advantages to this assay. The analytical procedure has proved to be simple, rapid, and reproducible, while eliminating many matrix interferences. The lower detection limit found in this work was 1.0 ppm of polyacrylamide; however, the sensitivity could be enhanced by increasing the sample size and concentrating the extracting solvent. Also, various copolymers of polyacrylamide should be able to be assayed for in a similar manner.
4
0
2
4
6
6
MIN.
Figure 1. Chromatogram of toluene extract of polyacrylamide hydrolysate derivatized with l-fluoro-2,4-dinitrobenzene.
LITERATURE CITED (1) Crummett, W. B.; Hummel, R. A. J.-Am. Wafer Works Assoc. 1963, 55, 209-219. (2) Attia, Y. A.; Rubio, J. Br. Polym. J . 1975, 7, 135-138. (3) Dubin, D.T. J . BIOI. Chem. 1960, 235, 783-786. (4) Sax, N. Irving “Dangerous Properties of Industrial Materials”,5th ad.; Van Nostrand Reinhokl: New York, 1979. (5) Hlguchi, M.; Senju, R. Polym. J . 1972, 3 , 370-377.
huge excess of sodium hydroxide and the prolonged, elevated temperature of our hydrolysis most likely yield nearly quantitative liberation of ammonia. A conventional calibration curve of peak area vs. concentration (milligrams of 2,4-dinitroaniline) was prepared by weighing the appropriate amount of 2,4-dinitroaniline into a volumetric flask, diluting to volume with toluene, and making serial dilutions. The curve was prepared to cover the
RECEIVED for review August 15, 1980. Accepted December 19, 1980.
Preparation of Polar Glass Capillary Columns Cecil E. Higgins Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830
One of the problems the analyst faces is that the glass capillary column might break or deteriorate before completion of a series of analyses. Column deterioration is a problem particularly associated with the use of polar wall coatings such as the UCONs (polypropylene glycols), which, however, give excellent separations of such complex mixtures as the gas phase of tobacco smoke (1-3) and air pollutants sampled near coal gasifiers ( 4 ) . The inconvenience caused by column deterioration or breakage can be minimized if reproducibly behaving columns can be prepared quickly. The static method of Bouche and Verzele (5)is considered the most effective method for column coating (6, 7) but is time consuming. Most of the time required for column preparation is spent on evaporation of the solvent. Grob (8)has described a rapid method for coating capillary columns by the static coating procedure using pentane as solvent for apolar materials. Unfortunately, the polar phases used in the work reported here are insufficiently soluble in pentane. Therefore, this Aid for Analytical Chemists describes a method in which diethyl ether as the stationary phase solvent is evaporated at a rapid but smooth and controlled rate at subambient temperature to produce long (-70 m) columns in approximately 2 days.
EXPERIMENTAL SECTION Column Preparation. Columns approximately 80 m long X 0.25 mm i.d. were drawn at an 80:l ratio by a Shimadzu GDM-1 glass drawing machine (Shimadzu Scientific Instruments, Inc., Columbia, MO) from 7 mm 0.d. soft glass capillaries (2.50 i 0.25 mm i.d. and 2.25 i 0.15 mm wall thickness). Etching was done 0003-2700/81/0353-0732$01.25/0
according to the dynamic method of Schomburg, Dielmann, Husmann, and Weeke (9) by passing dry HC1 gas through the column for 2 h at 450 OC. The column then was flushed with helium for 2 h at 200 O C , and the ends were sealed until just before coating. The column walls were coated by the static method (5) with 0.21% (w/v) UCON 50 HB 660 or UCON 50 HB 2000 in ether. Diethyl ether (Mallinckrodt,Inc., St. Louis, MO) in an Erlenmeyer flask was degassed under house vacuum (100-200 torr) while being stirred by a glass-encased magnetic stirring bar. To 48.5 mL of this cold, degassed ether in a 50-mL volumetric flask was added 100 pL (0.105 g) of the UCON. After UCON dissolution, the solution was warmed to room temperature before making final volume adjustment, if needed. The column was immersed in a water bath maintained at 19 0.1 “C. Cooling the bath below ambient temperature was accomplished by flowing cold tap water through 0.64-cm coiled copper tubing (13 13-cm 0.d. loops). Below 19 O C , a 250-W Vycor heater (Corning Glass Works, Corning, NY) supplied heat upon activation by a mercury-to-wire thermoregulator connected to a The LaPine electronic relay (LaPine Scientific Co., Chicago, L). bath water was gently stirred mechanically by a Variac-controlled metal stirrer (Talboys Instrument Corp., Emerson, NJ). A 5-mL volume of solution, added to a reservoir connected to a three-way stopcock, was pushed through the column by helium at 20 psig. When the solution level was at the inlet end of the column, pressure was reduced with a quick-release valve (type 67R, Fisher Controls Co., McKinney Division, McKinney, TX). With solution protruding from the column’s exit end, the end of the column was submerged 2 or 3 cm in cold Apiezon N grease (IO),previously melted in a 1-dram vial to degas and homogenize before use. Immediately the stopcock was rotated to the vacuum
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0 1981 American Chemical Society
