Reihenbestimmungen von Stickstoff im Ultramikromaßstab. Kjeldahlveraschung und Phenol-Hypochlorit-Reaktion

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Abstract
Samples containing 0. 5-8 [mu]g N were heated for 1 hr. at 325-345[degree]C in small test tubes with a 50 [mu]l of sulfuric acid combustion mixture (8. 40N H2SO4, 0. 63[image] Na2SO4 and 0. 02[image] HgCl2 in water). 0. 5 ml water, 1 ml potassium phenolate (1. 43[image] phenol, 1. 50[image] potassium hydroxide, 0. 34[image] acetone and 0. 001[image] Na-EDTA in water) and 1 ml hypochlorite solution (0. 4% active chlorine in 0. 1[image] KOH) were then added and mixed. After standing at room temperature for 80-200 min, the resulting blue color was measured photometrically against a blank between 570 and 650 m[mu] and compared with a standard curve. Thus 500 N -determinations can be performed per day with an error of <[plus or minus]3%. The sources of error and control of the methods for biological material (influence of pH, metal ions, method of combustion, catalysts, pipetting, cleaning of apparatus etc.; specificity, stability, reproducibility; comparison with N-determinations according to Dumas and the semi-micro Kjeldahl method) are described and discussed.