The Kjeldahl Method as a Primary Reference Procedure for Total Protein in Certified Reference Materials Used in Clinical Chemistry. II. Selection of Direct Kjeldahl Analysis and Its Preliminary Performance Parameters

Abstract

To select a Kjeldahl procedure suitable for the determination of total protein in reference materials used in laboratory medicine, we reviewed in our previous article Kjeldahl methods adopted by clinical chemistry and found an indirect two-step analysis by total Kjeldahl nitrogen corrected for its nonprotein nitrogen and a direct analysis made on isolated protein precipitates. In this article, we compare both procedures on various reference materials. An indirect Kjeldahl method gave falsely lower results than a direct analysis. Preliminary performance parameters qualify the direct Kjeldahl analysis as a suitable primary reference procedure for the certification of total protein in reference laboratories.

Fu Brick Tea Alleviates Chronic Kidney Disease of Rats with High Fat Diet Consumption through Attenuating Insulin Resistance in Skeletal Muscle

“…4,18 Total protein contents were determined by a method with the Kjeldahl method. 19 The polyphenolic compositions of FTE were analyzed by UPLC instrumentation (Thermo Fisher Scientific, Waltham, MA, USA). A gradient mobile phase consisting of phase A (100% acetonitrile), phase B (100% methanol), and phase C (0.1% formic acid water) was used for chromatographic separation.…”

“…The contents of total polyphenols and flavonoids were determined by colorimetry as described previously. , Total protein contents were determined by a method with the Kjeldahl method . The polyphenolic compositions of FTE were analyzed by UPLC instrumentation (Thermo Fisher Scientific, Waltham, MA, USA).…”

Comparative study on the effect of Plantago psyllium and Ocimum basilicum seeds on anthropometric measures in nonalcoholic fatty liver patients

“…We measured macronutrients and fiber components of PP and OB. Crude fiber by assessment tool (PP: 33 and OB: 31%) and dietary fiber by Association of Official Analytical Chemists (AOAC) 199/43 method (PP: 80 and OB: 59%),[ 13 ] carbohydrate by Fehling method (PP: 0.5 and OB: 1%),[ 14 ] protein by Kjeldahl method (PP: 18 and OB: 25%),[ 15 ] and fat by Soksele method[ 16 ] (PP: 1.5 and OB: 20%) were measured at the beginning of study.…”

Citizens protein project: A self-funded, transparent, and concerning report on analysis of popular protein supplements sold in the Indian market

“…All products were subjected to the analysis of total protein content (Kjeldahl method), [ 6 ] detection and quantification of fungal aflatoxin (high-pressure liquid chromatography and fluorescence detection), [ 7 ] pesticide residue detection and estimation (gas and liquid chromatography and tandem mass spectrometry), [ 8 ] detection and quantification of heavy metals (arsenic, cadmium, lead, mercury, thalium, and copper by inductively coupled plasma mass spectrometry), [ 9 ] steroid detection (gas chromatography-mass spectrometry using HP-5ms column), [ 10 ] and complete profiling of organic and inorganic contents (gas chromatography coupled to mass spectrometry). The quality control measures implemented during the analyses, including internal standards, calibration checks, and validation protocols were as per rules and guidelines laid by industry standards and approved by government regulations.…”