Automatic implementation of the method of standard additions in unsegmented flow systems

An open/closed flow system allowing variable volumes of both sample and standard calibration solution to be introduced was employed to perform automatic calibration in unsegmented flow systems by using the method of standard additions. The dilution loop thus established was used to homogenize the sample and standard mixture in a constant final volume that was subsequently introduced into the main flow system. The procedure allows direct analysis of liquid samples with no pretreatment and avoids matrix effects. Glucose and fructose were enzymatically determined over the ranges of 0.01–0.1 g l−1 and 0.02–0.1 g l−1 with relative standard deviation of ±0.8% and ± 1.0% for the determination of 0.05 g l−1 (glucose) and 0.07 g l−1 (fructose), respectively. Both analytes were determined in various types of drinks with average errors of 3.8% (glucose) and 4.6% (fructose).