Determination of carbohydrates in soluble coffee by anion-exchange chromatography with pulsed amperometric detection: interlaboratory study.

A collaborative study was conducted to validate a liquid chromatographic (LC) method to determine the free and total (after acid hydrolysis) carbohydrate profile of soluble coffee. Carbohydrates were separated on a pellicular anion-exchange column using pure water as mobile phase, and were detected by pulsed amperometry. Eleven collaborators were sent 6 test samples of commercial soluble coffee for duplicate analysis. They were also sent a practice sample with known levels of free and total carbohydrates and material for preparation of all standard solutions. The reproducibility relative standard deviations (RSD R ) were 9.9-59.5% for mannitol, 35.6-72.6% for fucose, 4.9-21.1% for arabinose, 4.1-13.0% for galactose, 6.1-24.3% for glucose, 10.0-41.6% for sucrose, 20.2-37.7% for xylose, 10.6-40.0% for mannose, 15.5-71.7% for fructose, and 17.8-97.9% for ribose. Precision in the determination of free and total carbohydrates was very similar. The average repeatability RSD r and RSD R values were 4.5 and 14.3%, respectively, for carbohydrate levels above 0.3%. The precision of the technique was considered good, regardless of the usual peak integration problems always encountered in LC, the low levels of free carbohydrates, the hydrolysis step, and the relative lack of experience of most participating laboratories. The method allows good and reproducible separation of all major carbohydrates found in soluble coffee and is, therefore, suitable for routine analysis.