4 rapid and accurate method for the determination of oxygen in inert cover gases was required for experiments involving oxygen-sensitive materials. The method developed is spectrophotometric, utilizing the oxygen-pyrogallol complex. The apparatus is constructed in a manner which allows for direct calibration. Blank, or reference solution, values are determined for each analysis. Equilibrium conditions are established with the aid of a 70" C. controlled temperature bath. Beer's law is obeyed for a range of 0 to 800 micrograms of oxygen. The method has been applied to the determination of traces of oxygen in nitrogen, argon, helium, and hydrogen.ECENT projects at this laboratory involving high purity R inert gas "blankets" necessitated analysis of samples for trace oxygen on a routine basis. Various difficulties were encountered in applying the methods proposed in the literature. A variety of colorimetric methods based on oxidation of ferrous iron and subsequent determination of ferric iron color complexes is reported by Mellan (4). Most of these complexes were found t o be somewhat unstable and nonreproducible. The method of Shaw ( 5 ) showed promise, but vas rather involved for routine application, as was that of Hand ( 3 ) . The latter was, however, the most sensitive and consistent of all methods tried. One 10 ASPIRATOR TO SAMPLE SOURCE LJ Figure 1. Apparatus significant lack of all methods was a means of determining a reliable reagent and procedural blank. Blanks could be determined on separate samples, but the variance between blanks was greater than the per cent of oxygen in the sample in question. Most of the methods investigated involved complicated apparatus and subsequent difficulty in applying the method routinely. I O C 8C W 0 z a E 6C z v) 2 0: a t-4 c 8 2c C 0 -ixio-2gms O X Y G E N o-ix 1 0 -3 g m s O X Y G E N -3 X ~o -~g m s OXY GEN --CORNING FILTER #50 5 0 4 5 0 550 6 5 0 75c Figure 2. Transmittancy Curves W A V E L E N G T H ( M k )The method here described was devised with an eye to accurate routine determination of traces of oxygen in gas samples. "Blanks" are determined for each run and represent true reagent and operational values. The method is colorimetric and is based on the oxidation of an alkaline solution of pyrogallic mid.The pyrogallol-oxygen complex undergoes a rearrangement before a ronstant optical density is reached. Willstatter and Heiss ( 7 ) have postulated that the oxidation of pyrogallol progresses through several intermediates. The authors have found
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