Rapid and sensitive measurement of dissolved gases by permeable membrane mass-spectrometry.

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Flash induced oxygen evolution was measured using a permeable membrane-mass spectrometer. Evolved gases were introduced through a gas-permeable membrane (0.024 mm thick, silicone rubber; General Electric, USA) to a quadrupole mass analyzer (MSQ 15OA; ULVAC, Japan). The paper disk of the lyophillized PS II membranes was gently immersed in 0.3-1.5 ml of 50 mM Hepes/NaOH (pH 6.8) which had been flushed with Ar gas. The reaction chamber (1 cm in diameter) was closed with a gas-tight, acrylic piston lid. After incubation in the dark for 5 to 10 min at 25ﾟC, the oxygen evolution was measured at the ion peak of 32 m/e under a Xe flash (30-50 J, t_<1/2> = 0.03 ms; Sugawara Kenkyusho, Japan) at dark intervals of 20-30 s. The half-decay time of the signal of the flash induced oxygen evolution was about 2 s when the thickness of the sample solution was 0.1 mm. The oxygen-evolving activity of the resuspended lyophillized PS II membranes was 0.27 mmol of oxygen (mg Chl)^<-1>h^<-1> under continuous … More light which was 70% that of the control PS II membranes. We examined the effect of lyophillization on the oscillation pattern of oxygen evolution by flash illuminations. The oxygen evolution of the control PS II membranes was maximal at the third flash and oscillated with a period of 4 flashes. The lyophillized PS II membranes which were immersed in Hepes buffer, however, showed the maximal evolution of oxygen at the sixth flash, indicating the water-oxidizing enzyme was apparently reduced to "S_<-2> state" by lyophillization. After preillumination the oxygen evolution of the lyophillized membranes oscillated as the control membranes did. Moreover, the miss-hit and double-hit probabilities and S_1/(S_0+S_1) for the oxygen evolution pattern of the lyophillized and preilluminated PS II membranes were similar to those of the control membranes. The lyophillization reduces the water-oxidizing enzyme, and the two photons return the enzyme to the S_0 state only in the presence of the water bound the the high-affinity sites in the enzyme. Less