Measurements of photolysis quantum yields are challenging because of the difficulties in measuring the first-generation photodissociation products, interference from other products or contaminants, sufficient photon fluxes and/or low absorption cross sections of the photolyte to make detectable amounts of products, and quantification of the photon flux. In the case of acetone (and other atmospherically relevant ketones) the uncertainty in the photolysis quantum yield creates uncertainty in the calculated OH radical and acyl peroxy nitrate production in the atmosphere. We present a new method for determining photodissociation product quantum yields by measuring acyl peroxy radicals (RC(O)O 2 ) produced in the photolysis of ketones in air using chemical ionization mass spectrometry (CIMS). We show good agreement of our CIMS method with previously published quantum yields of the acyl radical from photolysis of biacetyl and methyl ethyl ketone (MEK) at 254 nm. Additionally, we highlight the capabilities of this CIMS method through the measurement of photolysis branching ratios for MEK. We suggest future applications of CIMS (in the laboratory and field) to measure RC(O)O 2 and associated photolysis processes.

Electrometric and spectrophotometric titration curves of glycinin were obtained at 0.4 ionic strength and in the presence of 6M guanidine hydrochloride and 6M urea. The electrometric hydrogen ion titration curves were irreversible in the pH range 6.5 to 12.0 in 0.4M KCl, but exhibited reversibility in the pH 2.0 to pH 6.5 range. The forward and backward electrometric titration curves were entirely reversible in 6M guanidine hydrochloride. The spectrophotometric titration curves of tyrosine groups were also irreversible in 0.4M KCl, but reversible in 6M urea. Alkali‐induced denaturation produced a different spectrophotometric titration curve than the curves obtained with glycinin in 0.4M KCl and 6M urea. The electrostatic factor w was lower in the pH 2.50 to 3.75 range than in the pH 3.75 to 6.50 range. This was interpreted to be due to swelling and dissociation into subunits of the glycinin molecule subjected to acid denaturation. The empirical value of w=0.045 derived from the titration of the carboxyl groups in the pH 3.75 to 6.50 range coincided with the theoretically calculated value of 0.040 for a swollen sphere. Group counting and pK values of carboxyl, imidazole, e‐amino, and phenoxy groups under normal and denaturing conditions are also reported.

Optical rotatory dispersion (ORD) studies and infrared spectra in deuterium oxide indicate that native glycinin exhibits mainly a β‐conformation structure. Ultraviolet difference spectra showed that urea ami guanidine hydrochloride at increasing concentrations cause progressive exposure of tyrosine and tryptophan residues. Ultraviolet difference spectroscopy was also used in following the course of acid‐induced denaturation of glycinin. It was observed that acid denaturation starts approximately at pH 3.50 reaching a maximum at pH 2.0. Data obtained by solvent perturbation of native glycinin using perturbants exhibiting mean diameters of 2.0, 4.4, and 7.2 A indicate that approximately 34 to 37 residues (45%of the total) are accessible to these perturbants whereas the accessibility of tryptophan residues is decreased with increasing mean diameters of the perturbant.