Selective Retention by Porous Polymer Adsorbents Application to Formaldehyde Determination Lawrence S. Frankel, Paul R. Madsen, Richard R. Siebert, and Karl L. Wallisch Rohm and Haas Company, 5000 Richmond Street, Philadelphia, Pa. 19137
ACCURATE DETERMINATION of low levels of formaldehyde in Table I. Summary of the Interference Results at a Constant industrial chemical plant atmospheres has become increasFormaldehyde Level of 1.2 ppm ingly important since the establishment of a 3-ppm threshold Concenlimiting value (TLV) by the Occupational Safety & Health tration, AbAct ( I ) . The colorimetric determination of formaldehyde ppmQ sorbance Sample with chromotropic acid (1 ,8-dihydroxynaphthalene-3,6-disul0.41 Formaldehyde fonic acid) offers adequate sensitivity (2, 3). The selectivity Formaldehyde and 1,2-dichloroethane 100 0.41 of colorimetric methods is typically evaluated with regard t o Formaldehyde and 2-propanol 5 0.39 ambient air standards. A selectivity study geared t o the Formaldehyde and toluene 2 0.41 Formaldehyde and methylal 50 0.61b determination of formaldehyde via the chromotropic acid method in car exhaust and related ambient air samples has Concentration of other pollutants in a 5.0-liter air sample. been reported (3). Significant interference from alcohols b Measured at twentyfold dilution with excess scrubber solution. larger than ethanol, olefins, and some aromatic hydrocarbons was reported. Many industrial plant environments typically bility of this approach has been previously reported (5-8). contain high levels of organic pollutants. This type of enThe major organic components present were 2-propano1, divironment would be expected t o require more stringent selecmethoxymethane (methylal), 1,2-dichloroethane, and toluene. tivity criteria. The results of the enrichment study provide the starting We wish t o report a method for selectively removing most point for the determination of formaldehyde in the same organic compounds when it is desired t o determine formaldeindustrial environment by the chromotropic acid method. hyde and other small polar molecules. The method is based The selectivity of the chromotropic acid method was first on selective adsorption on a high surface area styrene-divinylconsidered with regard t o the organic components present in benzene adsorbent, Porapak Q (Waters Associates). the environment in question. Five separate portions of EXPERIMENTAL scrubber solution were aliquoted and spiked with a n equivalent of 1.2 ppm formaldehyde in a 5.0-liter air sample. Each The reagents used for the determination of formaldehyde of the previously discussed pollutants was then spiked into one were prepared and standardized as previously described (2). of the aliquots retaining the fifth aliquot as a control. The A 0.1 aqueous solution of formaldehyde was prepared by refluxing paraformaldehyde in water until it dissolved. This level of the spike of the other pollutants is from five t o ten solution was used for calibration. The color development of times greater than the average level actually found t o be the sulfuric chromotropic acid scrubber solution was achieved present. The results are summarized in Table I. Toluene, by heating at 100 “C for 15 minutes (3). The absorbance was 2-propanol, and 1,2-dichloroethane do not show significant measured at 580 nm in a 1-cm cell on a Perkin-Elmer Model 202 interference. Methylal shows a very large interference. This Spectrophotometer. A calibration curve showed only slight is not unexpected since methylal hydrolyzes to formaldehyde negative deviation from Beer’s law a t the equivalent of 3 ppm in an acidic medium (9). The extent of this interference can formaldehyde in a 5-liter air sample. The scrubber is availbe appreciated by comparing the observed molar absorpable from Arthur H. Thomas Co. (No. 8254-R25). A total tivities. The molar absorptivity of methylal measured at a volume of 5.0 liters was collected at a flow rate of 1.0 liter! minute. The above sampling conditions conveniently cover concentration equivalent to 50 ppm in a 5.0-liter air sample the 0.2-3.0 ppm range. Previous studies indicate that the was 10,700. The molar absorptivity of formaldehyde meascrubber efficiency is greater than 95 a t the above flow rate sured a t a concentration equivalent t o 0.3 ppm in a 5.0-liter (192). air sample was 17,800. A molar absorptivity of 16,300 for Porapak Q, SOilOO mesh, was purchased from Applied formaldehyde was calculated from data available in the literaScience Laboratories. The properties of this adsorbent have ture (3). Since the TLV of methylal is 1000 ppm compared been previously described ( 4 ) . The adsorber used to selecto 3 ppm for formaldehyde ( I ) , it is imperative that methylal tively remove interfering species contained 500 mg of Porapak not be reported as formaldehyde. Q in a 5-mm glass tube. This adsorber is to be attached The previous adsorption technique used for the enrichment to the chromotropic acid scrubber train. and determination of methylal immediately suggests a method RESULTS AND DISCUSSION for the removal of the methylal interference in the determinaThe environment in question was first studied by enriching the organic pollutants on Porapak Q. The general feasi( 5 ) F. W. Williams and M. E. Umstead, ANAL.CHEM., 40, 2232 (1968). (1) Fed. Regist., 36, 10503 (1971). (6) A. Dravnieks, B. K. Krotoszynski, J. Whitfield, A. O’Donnell, (2) U.S. Dept. of Health, Education, and Welfare, Public Health and T. Burgwald, Emiron. Sci. Tecliml., 5, 1220 (1971). Service, Division of Air Pollution, Robert A. Taft Sanitary (7) J. Gelbicova-Ruzickova, J. Novak, and J. Janak,J. Chromatogr., Engineering Center, Cincinnati, Ohio 45226, P.H.S. Publication 64, 15 (1972). NO. 999-AP-11. (8) F. E. Saalfeld, F. W. Williams, and R. A. Saunders, Amer. (3) A. P. Altshuller, D. L. Miller, and S. F. Sleva, ANAL.CHEM., 33, Lab., 3, 8 (1971). 621 (1961). (9) L. F. Fieser and M. Fieser, “Organic Chemistry,” 2nd ed., (4) S. B. Dave, J . Chromatogr. Sci., 7, 389 (1969). Reinhold, New York, N.Y., 1950, j i 216. ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
2401
tion of formaldehyde. Porapak Q can be used to adsorb methylal. Previous work indicates that small polar gases elute very quickly on Porapak Q (IO). We find that formaldehyde and watt:r co-elute on a 6-ft Porapak Q chromatographic column. The dynamic capacity of a 500-mg Porapak Q adsorber was evaluated for possible breakthrough of methylal. The sampling conditions were those described earlier for the determination of formaldehyde: 5-liter sample collected at a flow rate of 1.0 liter/minute. A standard gas mixture of 50 ppm methylal was prepared in a Saran (Dow Chemical Co.) bag. The standard gas mixture was pulled through a sampling train into a chromotropic acid scrubber. The first sample did not have an adsorber in the sampling train. The second sample was identical to the first except a 500-mg adsorber was placed in front of the chromotropic acid scrubber. The absorbance of the second scrubber solution showed no increase over a blank indicating quantitative retention of methylal on the adsorber. The next major question is how quantitatively does formaldehyde break through the adsorber under our sampling conditions. The first experiment was designed to determine the residence time of formaldehyde on the 500-mg adsorber. The Porapak Q adsorber was placed in a gas chromatograph equipped with a thermal conductivity detector. A 37% aqueous solution of formaldehyde was injected into the adsorber gas chromatograph column. The elution time of formaldehyde was determined as a function of carrier gas flow rate at ambient room temperature. At carrier gas flow rates of 30, 400, and 480 ml/minute, elution times of 300, 30, and 17 seconds were obtained. This result implies that for our sampling rate of 1.O liter/minute, formaldehyde is retained for a few seconds. This is a very small fraction of the total collection time of 5.0 minutes. A second more direct quantitative experiment was performed to definitively establish this crucial point. A standard formaldehyde gas mixture was prepared in a large polyethylene bag (approximately 200 liters) by passing an air sample over solid paraformaldehyde. Gaseous formalde-
hyde tends to deposit on the walls of the sampling bag and in the pump and sampling train (11). Several runs of the sampling train were required to obtain a constant absorbance in the scrubber solution. Immediately after this was accomplished, adsorption tubes containing either 300 or 500 mg of Porapak Q were in turn installed just before the chromotropic acid scrubber. This was followed by a final run of the system with no adsorption tube present. The recovery of formaldehyde with the adsorption tubes in the sampling train was quantitative and independent of the amount of Porapak Q utilized. Formaldehyde is a commonly used industrial chemical and would be classified as potentially more hazardous to health that most other pollutants. For this reason, it would probably be one of the first pollutants studied to determine cgmpliance with the Occupational Safety and Health Act. In utilizing the chromotropic acid method for the determination of formaldehyde, it is recommended that one sample be taken with and one sample without an adsorber as a check for possible interferences. Previous work indicates that the chromotropic acid method for the determination of formaldehyde is affected by alcohols larger than ethanol, olefins, and aromatic hydrocarbons ( 2 ) . Most of these interfering species were evaluated at a five- to ten-fold excess over formaldehyde. In some plant environments, the relative values could often be considerably larger. Selective adsorption on Porapak Q could be utilized to remove virtually all of the interfering species with the possible exception of some of the volatile olefins. The approach developed here could be applied to selectively remove some interfering species when attempting to analyze other light polar gases. As a starting point, our results suggest that if the component of interest elutes before water on a Porapak Q gas chromatograph column, the approach is feasible. Clearly, the flow rate and sample time must be considered,
(10) H. M. McNair and E. J. Bonelli, “Basic Gas Chromatography,” Varian Aerograph, Walnut Creek, Calif., 1969.
(11) J. F. Walker, “Formaldehyde,” 3rd ed., Reinhold, New York, N.Y., 1964, p 37.
RECEIVED for review April 19,1972. Accepted July 27,1972.
Rapid Spectrophotometric Determination of Arsenic in Iron and Steel 0. P. Bhargava, J . F. Donovan, and W. G. Hines Chemical & Metallurgical Laboratories, The Steel Company of Canada, Limited, Wilcox Street, Hamilton, Ontario, Canada
INTHE PAST, reagents such as quercetin, morin, and rutin have been employed for the absorptiometric determination of arsenic. However, most recent methods employ either arsenomolybdenum blue ( I , 2 ) or the absorption of evolved arsine in a pyridine solution of silver diethyldithiocarbamate (3). A polarographic method ( 4 ) has been described for the ( I ) P. Paklans, A m l . Cliim. Acta, 47,225 (1969). (2) W. R. Nall, Aiialyst (Loridon),96, 398 (1971). (3) T. Kaneshige, M. Takizawa, and H. Nagai, Jap. Aual., 13, 780 ( I 964). (4) M. V. Susic and M. G. Pjescic, Analyst (Londo/i),91,258 (1966). 2402
determination of arsenic in steel but the lower limit is 0.01 arsenic. To our knowledge, arsine evolution and its consequent absorption in silver diethyldithiocarbamate to determine arsenic in steel has not been reported. While some methods note that the conditions must be followed exactly, none describe the precise conditions required for steel. The steel was dissolved under oxidizing conditions, the arsenic(V) was reduced to the trivalent state in the presence of potassium iodide and stannous chloride. Finally, the evolved arsine was absorbed in a pyridine solution of silver diethyldithiocarbamate.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
