Determination of 4-Methylimidazole and 2-Acetyl-4(5)- tetrahydroxybutylimidazole in Caramel Color and Processed Foods by LC-MS/MS
In this study, the quick HPLC-MS/MS method for the simultaneous separation of 2-acetyl-4(5)-tetrahydrox-ybuthylimidazole (THI) and 4-(5)-methylimidazole (4-MI) in alkaline medium was used for caramel color and processed foods in Korea. After a simple sample pretreatment, 51 4-MI-labeled samples were positive for 4-MI and 2 also contained THI. The concentration of 4-MI was 260.5 ~ 24,499.3 μg/kg in caramel color, less than LOD ~ 1,712.5 μg/kg in sauce, 1,242.3, 5,972.2 μg/kg in balsamic vinegar, 2,118.3 ~ 5,802.4 μg/kg in complex seasoning, 82.7 ~ 5,110.6 μg/kg in curry, and 29.9 ~ 464.4 μg/kg in soft drinks. The recovery rate of 4-MI was 97.1 ~ 111.0% in sauce and 81.9 ~ 110.0% in powder and that of THI was 83.6 ~ 106.4% in sauce and 61.2 ~ 99.4% in powder. Our results concluded a safe amount of 4-MI and THI compared to the limit of Korea additive code but the processed foods do not have a limit of caramel color and 4-MI in Korea. Therefore, research and monitoring of 4-MI and THI is needed for processed foods in Korea.
Quantification of 4-methylimidazole in carbonated beverages by ultra-performance liquid chromatography-tandem mass spectrometry
Abstract2- and 4-methylimidazoles (2-MI and 4-MI) are undesired byproducts produced during the manufacture of caramel color used to darken food products such as carbonated beverages. The Office of Environmental Health Hazard Assessment in California listed 4-MI as carcinogen in January 2011 with a proposed no significant risk level at 29 μg per person per day. Thus, a quantitative analytical measurement for 2-MI and 4-MI is desired for reliable risk assessments for exposure. An ultra-performance liquid chromatography (UPLC) coupled tandem mass spectrometric (MS/MS) method was developed for the quantification of 4-MI in beverage samples. Chromatographic separation of 2-MI and 4-MI were achieved by using a PFP reversed-phase column and a stepwise gradient of methanol and distilled water containing 0.1 % formic acid. Identification and quantification of 2-MI and 4-MI were performed using electrospray ionization-tandem mass monitoring the precursor to product ion transitions for 2-MI at m/z 83.1 → 42.2 and 4-MI at m/z 83.1 → 56.1 with melamine at m/z 127.1 → 85.1 as the internal standard. The performance of the method was evaluated against validation parameters such as specificity, carryover, linearity and calibration, correlation of determination (r2), detection limit, precision, accuracy, and recovery. Calibration curves at 10–400 ng/mL were constructed by plotting concentration versus peak-area ratio (analyte/internal standard) and fitting the data with a weighted 1/x. The accuracy of the assay ranged from 93.58 to 110.53 % for all analytes. Intra-assay precision for 2-MI and 4-MI were below 7.28 (relative standard deviation/RSD %) at QC samples. Here we present a new and improved method using UPLC-MS/MS to significantly simplify sample preparation and decrease chromatographic run time. This method allows accurate and reproducible quantification of 4-MI in carbonated beverages as low as sub ng/mL (ppb) levels.
Instrumentation and Automated Photometric Titration Procedure for Total Acidity Determination in Red Wine Employing a Multicommuted Flow System
An automated procedure for photometric titration of red wine and associated instrumentation is described. The procedure was based on the flow-batch approach implemented employing multicommutation. The photometric detection was carried out using a homemade LED-based photometer. The mixing device, LED, and photodetector were attached to the titration chamber in order to form a compact and small-sized unit. The flow system comprised an automatic injector and three-way solenoid valves, which were controlled by a microcomputer through an electronic interface card. The software, written in Quick BASIC 4.5, was designed with abilities to accomplish all steps of the titration procedure including data acquisition and real-time processing to decide about the course of titration in the following step and so forth, until the titration endpoint was reached. The usefulness of the proposed titration system was demonstrated by analyzing red wine samples. When results were compared with those obtained using the AOAC reference method, no significant difference was observed at the 95% confidence level. A relative standard deviation of ca  2% (n=9 ) was obtained when processing a typical red wine sample containing 7.3 gl -1 total acidity expressed as tartaric acid.