The 3-Methyl-2-Benzothiazolone Hydrazone Method for Aldehydes in Air: Collection Efficiencies and Molar Absorptivities.

Abstract

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)(2)(3)(4)(5)(6)(7)(8).A modied 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. EXPERIMENTALCollection 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. DISCUSSIONThe 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 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 ...

Formaldehyde in the Indoor Environment

“…The MBTH method − (3-methyl-2-benzothiazolinonehydrazone) is a nonselective colorimetric method for the determination of aliphatic aldehydes of low molecular weight. MBTH reacts on aldehydes to give an azide.…”