Determination of Nitrite in Milk- and Soy-Based Nutritional Ingredients by Derivatization with 2,3-Diaminonaphthalene and Fluorescence Spectrometry

J AOAC Int. 2017 Nov 1;100(6):1831-1835. doi: 10.5740/jaoacint.17-0118. Epub 2017 Jun 30.

Abstract

Nitrite (NO2-) is an inorganic anion that can be found in various powdered milk- and soy-based nutritional ingredients as an incidental contaminant. Reliable determination of NO2- in nutritional ingredients is of paramount importance to ensure the safety of finished products. The derivatization reaction of NO2- with 2,3-diaminonaphthalene with the formation of fluorescent 2,3-naphtotriazole has been adapted to milk- and soy-based nutritional ingredients. The sample preparation consisted of protein precipitation with Carrez solution, simple pass-through cleanup of extracts utilizing a carbon black-based cartridge and derivatization, followed by batch fluorometry. The method was validated in six representative ingredient matrixes-i.e., whole-milk powder, nonfat dry milk, milk protein concentrate, whey protein concentrate, sodium caseinate, and soy protein isolate. Recovery values were 82-109%, whereas within-day and intermediate precision were 0.6-5.2 and 3.6-11% (RSDs), respectively. The method LOQ was 0.1 or 0.2 µg/g sodium nitrite (NaNO2), depending on the ingredient matrix. Surveyed NO2- concentration levels in 25 lots of 10 types of nutritional ingredients ranged from between less than 0.1 to 29 µg/g NaNO2. This method is proposed as a more sensitive and rugged alternative to the widely used ion chromatographic and colorimetric approaches.

Publication types

  • Video-Audio Media

MeSH terms

  • 2-Naphthylamine / analogs & derivatives*
  • 2-Naphthylamine / chemistry
  • Animals
  • Food Analysis / methods*
  • Food Contamination / analysis
  • Limit of Detection
  • Milk / chemistry*
  • Nitrites / analysis*
  • Reproducibility of Results
  • Soybean Proteins / analysis
  • Spectrometry, Fluorescence / methods*

Substances

  • Nitrites
  • Soybean Proteins
  • 2,3-diaminonaphthalene
  • 2-Naphthylamine