Oxygen, determination reagent blank

Procedure Pipet 0.5 mL each of the Standard Solution, the Test Preparation, and water (the reagent blank) into separate 1-cm cells. Using water as the reference, determine the absorbance of the solutions at a wavelength of 340 nm. Add 2.5 mL of Phosphate Buffer and 0.2 mL of NAD Solution to each cell. Cover the cells to exclude oxygen. Mix by inversion, and allow them to stand for 2 to 3 min at 22° 2°. Determine the absorbances of the solutions as before. Calculate the percentage of aldehydes, expressed as acetaldehyde, in the sample taken by the formula... 

Limit the volume of "standard addition solution to less than 0.05 cm in order to avoid dilution errors. Lower the electrode into the sample cell and again pass oxygen free nitrogen for 2 min. Immediately read the new peek height at - 0.9 V. Similarly, determine the peak height at - 0.9 V on the degassed polystyrene-free reagent blank solution. 

Since ET-AAS is a trace element technique, special equipment is required to minimize the risks for contamination or analyte loss at the critical sample preparation stage of the analytical procedure. To minimize blank levels, additions of reagents to the sample should be limited, and for this reason dissolution techniques such as oxygen combustion and microwave-assisted wet digestion in closed cells are to be recommended. Sulfur- and halide-containing reagents may cause interferences in the determination of certain elements by ET-AAS and should thus be avoided. 

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