IC–MS Analysis of Low Molecular Mass Organic Acids in Beverages

Leo (Jinyuan) Wang and Bill Schnute, Dionex Corporation

Organic acids are present in many matrices and play crucial roles. Extensive research involving low molecular mass organic acids (LMMOA) has been performed in food chemistry since these acids contribute to the organoleptic properties of food and beverages, including flavor, color, aroma, taste, shelf-life, and health effects. Developing a profiling method to monitor LMMOA levels in raw materials and final products is very desirable. Many reported methods focus on limited numbers of LMMOAs and are incapable of providing a complete LMMOA profile.

This application note describes a profiling method using ion chromatography (IC) on a hydroxide selective anion exchange column to separate 32 LMMOAs including the resolution of critical pairs (such as isomeric LMMOAs), and mass spectrometry (MS) for selective and sensitive detection.

Experimental

IC–MS analysis was performed on an ICS-2000 Reagent-Free™ IC (RFIC™ ) system coupled to an MSQ Plus™ mass spectrometer by an electrospray ionization interface.

Chromeleon® chromatography management software was used for instrument control, data acquisition and processing, and report generation.

MSQ Plus Conditions

Desolvation Solvent: Acetonitrile at 0.2 mL/min

Ionization Interface: Electrospray Ionization (ESI) source

Nebulizer Gas: Nitrogen gas at 80 psi

Probe Temperature: 550°C

Needle Voltage: 3000 V

Scan Mode: Negative Selected Ion Monitoring (SIM)

See the table in Figure 1 for SIM scan parameters for each analyte.

Results

The standard chromatogram (Figure 1) shows 32 LMMOAs successfully analyzed by this IC–MS method. Detection limits ranged from 34 pg to 135 pg. With the enhanced low mass detection from MSQ Plus, formic and acetic acid can be detected at 0.5 and 12.5 ng respectively. Linearities with correlation coefficients (R²) > 0.99 were achieved for each analyte in concentrations over three orders of magnitude except for lactate, acetate, and formate due to the lower detection sensitivity for those specific compounds.

Figure 1

This method for LMMOA analysis has been successfully applied to beverages, including green tea, grape juice, and wine. More than 20 LMMOAs were detected in two brands of green teas, and more than 25 LMMOAs were detected in two brands of grape juices and wines (white and red). Figure 2 shows the conductivity and MS SIM chromatograms of LMMOAs detected in a red wine sample.

Figure 2

Conclusion

Determination of LMMOAs is optimized using IC–MS with RFIC, providing a selective and sensitive detection technique for beverage analysis.

MSQ Plus is a trademark of Thermo Fisher Scientific Inc. Reagent-Free and RFIC are trademarks and Chromeleon and IonPac are registered trademarks of Dionex Corporation.

Dionex Corporation

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