3-Meth y l-2- Benzothiazo lone Hyd razone Method for Aldehydes in Air: Collection Efficiencies and Molar Absorptivities SIR: A number of publications have discussed the 3-methyl-Zbenzothiazolone method for aliphatic aldehydes and its applications to analyses of atmospheric and emission samples (1-5,6-8). A m o d i e d method has been reported that significantly increases the sensitivity and also eliminates the turbidity that occurs in the original procedure (6). No measurements of the collection efficiencies of aldehydes other than formaldehyde have been reported. In the modified method, only the molar absorptivity for formaldehyde has been measured (6). In the present work, the collection e5ciencies for propionaldehyde in nitrogen were determined with the original and the modified reagents. The collection efficiencies for both acetaldehyde and propionaldehyde in air were determined for the modified procedure. In addition, the molar absorptivities were obtained for the products formed by acetaldehyde and propionaldehyde in the modified procedure. EXPERIMENTAL
Collection efficiencies were measured by passing volumes of 1.5 to 10 liters of nitrogen or air containing 1 to 2
p.p.m. aldehyde from a plastic film container at 0.5 liter/minute through three bubblers in series, each containing 10 ml. of either 0.2% or, as in the modified procedure, o.05y0 of the aqueous 3-methyl-Zbenzothiazolone hydrazone collection solution. The concentrations in the containers were determined from the volumes injected from microsyringes into a known volume of gas and from gas chromatographic determinations of concentrations on replicate samples. To minimize errors in injection from the microsyringes, the aldehydes were pre-diluted in ethanol, so that the amounts of liquid used were in a volume range allowing reproducible injections into the containers. Molar absorptivities were obtained both from samples of aldehyde in air and directly from appropriately diluted ethanolic solutions of acetaldehyde and propionaldehyde. The values were obtained for the maxima near 660 mp. DISCUSSION
The collection efficiency for formaldehyde originally reported as 95 to 99% is based on an incorrect theoretical absorbance value (8). After correction, the collection e5ciency is reduced to about 88%. The collection e5ciency for formaldehyde in the modified procedure is reported to be 84% (6). Values for 1418
ANALYTICAL CHEMISTRY
collection efficiencies obtained in this work for acetaldehyde or propionaldehyde in air were about 75% in the first bubbler and 22% in the second of the three bubblers. The collection efficiencies for propionaldehyde in nitrogen were the same in both the original and the modied procedures; however, the collection efficiency for propionaldehyde in nitrogen in the first bubbler was only 65%. The 75% efficiencies obtained for acetaldehyde and for propionaldehyde and the 84% efficiency previously reported for formaldehyde (6) suggest that the reagent is not contributing appreciably to the solution of the aldehydes. The collection efficiencies are simiiar to those expected for physical solution in water. For example, an average collection efficiency of 84% has been measured for formaldehyde in water at room temperature ( 4 ) . The increase in efficiency noted for propionaldehyde when collected from air rather than nitrogen indicated some possible oxygen effect on the solution of aldehyde. The results indicate the need for at !east two bubblers in series particularly when the sampling mixtures consist wholly or largely of acetaldehyde and higher-molecular-weight aliphatic aldehydes. Higher collection efficiencies,90 to 950/0, have been reported for collection of lower concentrations of aldehydes (about half of which was formaldehyde) from atmospheric mixtures using larger volumes of air (2,3). The molar absorptivity at 628 mp for the product of the reagents with formaldehyde has been reported as 50,OOO (4). In the present work the peak at 660 mp was used. This peak appeared to yield more consistent shape and more reproducible wavelength than the lowerwavelength maxima for acetaldehyde and propionaldehyde products. For acetaldehyde, the W m p peak averaged 5 to 10% lower intensity than the lowerwavelength peak. For propionaldehyde, the two peaks were of almost equal intensity, with the 66O-mp peak showing perhaps 2 to 3% more intensity than the lower-wavelength peak. Although these differences in intensity were shown in the spectra of the solutions from the first bubbler, the spectral curves obtained from the solutions in the second or third bubblers showed little difference in intensity at the two wavelengths. In fact, at the lower absorbancies obtained for these solutions, the curve9 were almost flat from 660 m p down to almost 660 q. The molar absorptivity at 660 m p obtained from vapor mixtures of
*
acetaldehyde in air was 58,OOO 2500; the corresponding molar absorptivity from mixtures of propionaldehyde in air was 50,OOO f 2500. In a limited number of experiments, the molar absorp tivity was obtained directly from ethanolic solutions of the aldehydes diluted to the pg./ml. range. For acetaldehyde the molar absorptivity obtained in this way was the same, within the uncertainties in the measurements, as that obtained from the vapor mixtures. For propionaldehyde, the molar absorptivity from the solutions appeared to be 5 to 10% lower. This result is unexpected, since any losses of aldehyde in preparing or storing the vapor mixtures should result in lower absorbance and hence in computation of a lower molar absorptivity for any given initial concentration. Comparisons of the relative intensities obtained in the original and modified procedures show that the modified procedure on the average was six times more sensitive than the original procedure for propionaldehyde. Similarly, computation from the ratios in molar absorp tivities and dilution factors for the two procedures indicates that the modified procedure is about seven times more sensitive than the original procedure for acetaldehyde. These sensitivity factors compare well with a sensitivity factor of somewhat over six reported for formaldehyde in the modified os. the original procedure (6). UTERATURE CITED
(1) Altshuller, A. P., Klostennan, D. L., Leach, P. W., Hindawi, I. J., Sigsby, J. E.. Intern. J . Air Water PoUufia 10,si (1966): (2) . , Altshuller. A. P..Lene. L. J., AN L. CEXEM.35, isl (19~).-’ (3) Altshuller, A. P., McPherson, S. P., J . Air PoUution Control dssoe. 13, 109 (1963). (4) Altshuller, A. P., Miller, D. L., Sleva, S. F., ANAL.CEXEM. 33, 621 (1961). (5) Hauser, T. R., CllmminR, R. L., ANAL.CEXEY. 36, 679 (1964). (6)Leach, P. W., Leng, L. J., Bellar, T. A., Sigsby, J. E., Altshuller, A. P., J . Air PoUutia Control Assoe. 14, 176 (1964). (7)Reckner, L. R., Scott, W. E., Biller, W. F. 30th Midyear Meeting American Petroleum Institute, Div. of Refining, IMontreal, Canada, May 10, 1965. (8) Sawicki, E., Hauser, T. R., Stanley, T. W., Elbert, W., ANAL. CFIEM.33, 93 (1961).
I. R. COHEN
A.
P. AL~HULLEE
Division of Ah Pollution Robert A. Taft Sanitary Engineering Center Cincinnati, Ohio 45226
