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  • Title: Coupling of ion pair ultrasound assisted-cloud point extraction to microvolume UV-Vis spectrophotometry for speciation analysis of ionic NO2-,NO3- and total NO2-/NO3- without and with reduction in the selected beverage and food matrices.
    Author: Olgaç E, Gürkan R.
    Journal: Food Addit Contam Part A Chem Anal Control Expo Risk Assess; 2020 Nov; 37(11):1811-1830. PubMed ID: 32897814.
    Abstract:
    This study proposes a simple, low-cost, easy to use, fast, accurate and reliable ultrasound assisted-cloud point extraction (UA-CPE) method for the enrichment and speciation analysis of low levels of ionic NO2 -, NO3 - and total NO2 -/NO3 - without and with reduction by micro-volume UV-vis spectrophotometry. The method relies on the reaction of NO2 - with excess iodide at pH 5.5 to form triiodide, and then the extraction of the oxidation product formed by charge transfer into micellar phase of Triton X-114 using cationic redox-sensitive phenazine dye, neutral red (NRH+) as ion-pairing in absence and presence of 1.5 mL of 1.0 × 10-3 mol L-1 Br- ions. The main variables affecting extraction efficiency were studied and optimised in detail. Under the optimal conditions, the calibration curves in solvent were linear over the ranges of 5-100 and 100-1280 µg L-1 with a detection limit of 1.32 µg L-1 while the matrix-matched calibration curves prepared from sample extracts were linear over the ranges of 5-125 and 125-1350 µg L-1 with a detection limit ranging from 1.15 to 1.50 µg L-1 for sample matrices. From pre-concentration of 25-mL sample, pre-concentration and sensitivity enhancement folds of 62.5 and 76.5 were obtained. The accuracy/precision studies after spiking were performed, and observed to be in range of 96.5-99.6% and 1.9-5.7% (15, 75 and 250 µg L-1, n: 5). The speciation analysis of ionic NO2 -, NO3 - and total NO2 -/NO3 - was performed from artificially prepared binary mixtures after reduction with a mixture of Zn and NaCl in acidic media. The free NO3 - contents of samples were calculated from difference between free NO2 - and total NO2 -/NO3 - contents. After validation by analysis of a certified sample, the method was successfully applied to the speciation analysis of the beverage, cured meat, vegetable and milk samples. After pre-treatment with two sample preparation steps, it was observed that the results obtained were also compatible with each other, statistically validating the method.
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