Development and Validation of Chromatographic Methods for the Analysis of 4-Methylimidazole and Taurine in Carbonated Beverages

Abstract

This study described the optimization, validation, and application of anlaytical methods for determination of two hazardous compounds, namely: 4(5)- methylimidazole (4-MEI) and taurine that are usually found in carbonated drinks. 4-MEI was derivatized with 4-chloro-7 nitrobenzo-2-oxa-1,3- diazole (NBD-Cl) reagent and then determined using UV-Vis spectrophotometry and high performance liquid chromatography with photodiode array detecor (HPLC-PDA). The main parameters affecting the derivatization reaction between 4-MEI and NBD-Cl were optimized and gave excellent linearity with correlation coefficient (r2 = 0.9998 and 0.9999) in the range of (1.0-50)mgL-1 and (0.5-50) mg L-1 for UV-Vis spectrophotometry and HPLC-PDA, respectively. The limit of detection (LOD) was found to be 0.183 mg L-1 and 0.152 mg L-1, and limit of quantification (LOQ), 0.550 mg L-1 and 0.457 mg L-1 for UV-Vis spectrophotometer and HPLC-PDA analysis respectively. The precision or relative standard deviation (RSD%) of the absorbance for intra-day and inter-day were 2.598 and 3.987 %, respectively. Good percent recoveries in range (91.8–106)% and (94.3-108)% were obtained for UV-Vis spectrophotometry and HPLC-PDA analysis, respectively. The developed methods were successfully applied for determination of 4-MEI in some soft drinks available in local markets i.e. Coca cola, Pepsi, Cola light, Pepsi diet, Veno and Vimto. Two derivatzation methods using NBD-Cl and o-phthalaldehyde-sodium sulfite (OPA-Na2SO3) reagents were optimized and used for determination of taurine in energy drinks. The taurine-NBD derivative was determined using HPLC-PDA and HPLC coupled fluorescence detection (HPLC-FLD). In both validated methods, the derivatization product was separated on Inertsil ODS-3 analytical column with acetonitrile and 0.1% trichloroacetic acid (30:70, v:v) as mobile phase. The eluted derivative was detected at 472 nm by HPLC-PDA for absorption and at 472 nm for excitation and at 530 nm for emission by HPLC-FLD. Good linearity was achieved for taurine (r2 = 0.9998 and 0.9993) in the range of 5.0-50 mg L-1 and 5.0-50 µg L-1, the LOD was 0.296 and 0.616 ×10-3 mg L-1, the precision for peak area was 0.78% and 0.61% for HPLC-PDA and HPLC-FLD, respectively. Recovery of taurine, however, ranged from 92% to 103.3% for both. The methods of determination of taurine after derivatization with OPA-Na2SO3 was optimized and validated. The taurine- OPA-Na2SO3 was measured using HPLC-PDA and UV-Vis spectrophotometry. The method was linear in the range of 0.5-20 mg L-1 and 0.5-15 mg L-1 , with correlation coefficient (r2) of 0.9998 and 0.9996, LOD of 0.109 mg L-1 and 0.141 mg L-1 , intarday precision of 1.816% and 1.278%, interday precision of 2.858% and 2.236% , for HPLC-PDA and spectrophotometry, respectively. Recovery of taurine, however, ranged from 90% to 105% for both. These validated derivatization methods were successfully applied for determination of taurine in energy drink samples namely: Red bull, Tornado, Kratingdeang, Bison and Tiger.