The elimination of the distillation procedure in the Kjeldahl method

Abstract

Several attempts have been made to modify the Kjeldaht method for determination of nitrogen in order to avoid the distillation. For example, Marcali and Rieman 1 use the formaldehyde method, and Harvey ~-determined nitrogen in unicellular algae on the submicro scale (5-30 #g) using a hypobromite titration. He showed that the mercury catalyst did not interfere in the titration. So far little use appears to have been made of Koltho//and Stenger's method a involving titration of ammonium salts with calcium hypoehlorite, hence a study has been made of its application to the Kjeldahl process a.The most likely interference in the titration would be the catalyst used in the digestion. Several were tried but all save mercury interfered, either because of their colour masking the endpoint or because they reacted with the titrant. Mercury did not interfere, and the precipitation of its oxide daring the addition of alkali is a useful indication of the approach of the neutrMisation point. Sodium hypochlorite was preferred as titrant because it is more readily available than the calcium salt. Tartrazine was used as indicator in the final titration with hypochlorite ~.The procedure has been used both on the micro and semimicro scale for a limited number of compounds. All those tried have yielded satisfactory results. When pre-reduction is necessary the direct titration is unapplicable, for all the reducing agents tried interfere with the end-point.It would be of advantage to carry out the digestion and titration in the same vessel, and various modified digestion vessels have been * We have great pleasure in dedicating this paper to our good friend Professor Dr. R. Strebinger on the occasion of his 70th birthday.

Food

“…A modified Kjeldahl method with Nessler reagent used colorimetrically has been found satisfactory for total nitrogen estimation in sugar house waste waters (317), and determination of organic nitrogen by the Kjeldahl method without distillation is possible (1,15).…”

“…A rapid colorimetric method for starch in apples of commercial harvest and storage maturity range has been offered (40). The test takes about 15 minutes to carry out. A method for starch in cereals involves extracting the simple sugars with ethyl alcohol, bringing the residual starch in solution with perchloric acid, and then determining the starch spectrophotometrically with anthrone reagent (48).…”

Kjeldahl Determination of Nitrogen without Distillation.

“…Belcher and Bhatty (3) verified the same method using different catalysts and reported that except for Hg all other catalysts interfere, and this interference is removed by the presence of an excess of potassium bromide which is added to liberate calcium hypobromite. Belcher. West and William (4) further modified the technique on a micro scale by using sodium hy-pochlorite which according to these authors, at controlled pH, is stable for 1 week.…”

Volumetric and Gravimetric Analytical Methods for Organic Compounds

“…The distillation can be omitted in the Kjeldahl procedure if the hypochlorite titration of Kolthoff and Stenger (78) is used. Mercury must be used as the catalyst (10).…”