Quantitative Analysis of Carbohydrates in Food Samples Using APCI-LC/MS with Post-column Reagent Addition and Ligand Exchange Chromatography

Significance of the Topic

The accurate and sensitive quantification of carbohydrates in food and biological matrices is essential for nutritional analysis, quality control, and biochemical research. Conventional techniques such as GC/MS or HPLC with ELSD, UV or fluorescence detection typically require derivatization steps and are limited to a small number of sugars. A direct LC/MS approach without derivatization offers faster sample preparation, broader analyte coverage and improved workflow efficiency.

Study Objectives and Overview

The primary goal of this study was to establish a derivatization-free LC/MS method capable of quantifying twelve common carbohydrates in food samples. The method combines ligand exchange chromatography with post-column addition of a low percentage of chloroform reagent to enhance ionization under APCI negative mode. Performance parameters including linearity, detection limits, repeatability and real-sample applicability were evaluated.

Methodology and Instrumentation

A single quadrupole LCMS system equipped with an APCI interface was used. Key parameters included

• Column: Shim-pack SCR-101P ligand exchange column (7.9 mm ID x 300 mm L)
• Mobile phase: water, isocratic at 0.60 mL/min
• Post-column reagent: 5% chloroform in methanol at 0.10 mL/min
• Interface temperature: 450 °C; block 200 °C; DL 250 °C
• MS mode: negative ion SIM monitoring [M+Cl]− ions
• Analytes: twelve carbohydrates including mono- and disaccharides and sugar alcohols
• Calibration range: 0.1 or 0.5 to 400 mg/L

Main Results and Discussion

Chromatographic separation by ligand exchange produced baseline resolution for most analytes, with co-eluting isomers distinguished by unique m/z values. All calibration curves exhibited excellent linearity (r2>0.999). Limits of detection ranged from 0.05 to 1 mg/L. Repeatability at 10 mg/L showed RSD values below 5% for ten compounds; ribose was 6.9%. Application to diluted food and beverage samples (sake, soya sauce, soft drink) confirmed the presence and concentration of sugars in agreement with product labels.

Benefits and Practical Applications

This APCI-ligand exchange LC/MS method offers

• Derivatization-free quantification of a broad panel of carbohydrates
• Low detection limits suitable for trace analysis
• High repeatability and linear dynamic range up to 400 mg/L
• Efficient separation of isomeric sugars without additional sample pretreatment

Future Trends and Potential Applications

Advances may include further reduction of organic reagent use, coupling with high-resolution MS for enhanced selectivity, and extension to complex matrices such as plant extracts or clinical samples. Automation of sample preparation and on-line post-column reagent control could improve throughput and reproducibility.

Conclusion

A new APCI-ligand exchange LC/MS method was successfully developed for direct, derivatization-free quantification of twelve carbohydrates in food matrices. Low levels of chloroform reagent enabled effective ionization while maintaining instrument cleanliness. The approach provides high sensitivity, linearity and repeatability, and is directly applicable to real food and beverage samples.

References

1. Application News No. C74, Shimadzu
2. Kato Y Numajiri Y Journal of Chromatography 562 81–97 1991