Development of Extraction and Analytical Methods of Nitrite Ion from Food Samples: Microchip Electrophoresis with a Modified Electrode MUHAMMAD J. A. SHIDDIKY, † KYUNG-SUN LEE,JUNGIK SON,DEOG-SU PARK, AND YOON-BO SHIM* Department of Chemistry and Center for Innovative Biophysio Sensor Technology, Pusan National University, Busan 609-735, South Korea. † Present address: School of Chemistry, Monash University, Clayton, Victoria 3800, Australia Two simple and fast methods for the extraction of the nitrite ion (NO 2 - ) from food samples have been developed. The methods were characterized by UV-visible spectroscopic and electrochemical measurements, and their performance for NO 2 - extraction was compared with a standard method. The extraction methods yielded relative recoveries between 100 and 120% with good reproducibility of 3.9% (RSD, n = 4) in UV-visible experiments. Microchip electrophoresis with electrochemical detection (MCE-ED) coupled with a copper (3-mercaptopropyl)trimethoxysilane [Cu(II)-MPS] com- plex-modified carbon paste electrode (CPE) has been employed to detect NO 2 - in extracted samples. The Cu(II)-MPS complex was synthesized and characterized by voltammetry, XPS, and FT-IR analyses. Experimental parameters affecting the separation and detection performances of the MCE-ED method were assessed and optimized. The potential for the electrocatalytic reduction of NO 2 - for MCE-ED was found to be -190 mV (vs Ag/AgCl). When extracted food samples were analyzed by the MCE-ED method, a reproducible response for the NO 2 - reduction (RSD of 4.3%) at the modified-CPE reflected the negligible electrode fouling. A wide dynamic range of 1.0-160 ppm was observed for analyzing standard NO 2 - with a sensitivity of 0.05106 ( 0.00141, and the detection limit, based on S/N = 3, was found to be 0.35 ( 0.05 ppm. No apparent interference from NO 3 - , other inorganic ions, and biological compounds was observed under the optimal experimental conditions. A standard addition method for real samples showed wide concentration ranges of 1.10-155 and 1.2-150 ppm for analyzing NO 2 - in ham and sausage samples, respectively. KEYWORDS: Nitrite extraction; microchip electrophoresis; electrochemical detection; Cu complex- modified electrode; food analysis INTRODUCTION The nitrite ion (NO 2 - ) is one of the major pollutants in food- product, medicinal, agricultural, and biological samples (1 ). NO 2 - and nitrate ions are widely used as fertilizers in agriculture. NO 2 - exists in beverage and food products as a preservative because it provides highly effective protection against food- poisoning microorganisms. However, high concentrations of NO 2 - in the human body cause diabetes and nervous system disorders (2 ). The health problems associated with NO 2 - are related to the formation of endogenously carcinogenic N-nitrous compounds (nitrosamines and nitrosamides) within the acidic conditions of the stomach and their subsequent implication in the pathology of gastric cancer (3 ). Upon reaching the stomach, NO 2 - is converted into nitrous acid, which can act as a powerful nitrosating agent (3 ). Additionally, microorganisms could take part in the formation of N-nitrous compounds by nitrate reduc- tion to NO 2 - and degradation of proteins to amines and amino acids (4 ). On the other hand, the half-life of the nitric oxide (NO) in biological samples is short as it is rapidly oxidized to stable metabolites NO 2 - and nitrate (5 ). Therefore, monitoring of NO 2 - and nitrate has been employed as they are indicators of in vivo NO production in biological samples. Due to all of these concerns, the demand for the extraction and accurate measure- ment of NO 2 - in food samples and other products that have a high consumption by humans has recently arisen. Thus, it is important to analyze the NO 2 - ion in food samples. However, direct analysis of NO 2 - in real food samples is not suitable for a number of reasons. Often, real samples contain a large amount of organic and inorganic particles, which must be removed to prevent disruption of fluid handling by fouling or blockage of the analytical systems used to analyze them. Prior to the analysis of NO 2 - in food samples with conventional analytical methods, it is necessary to separate the complex background matrix in initial *Corresponding author (e-mail ybshim@pusan.ac.kr; telephone +81-51-510-2244). J. Agric. Food Chem. 2009, 57, 4051–4057 4051 DOI:10.1021/jf900230x © 2009 American Chemical Society Published on Web 4/17/2009 pubs.acs.org/JAFC