RID serve as a more appropriate measure than phenol sulfuric acid method for natural water-soluble polysaccharides quantification.

With structural diversity of water-soluble polysaccharides, their precise quantitative analysis by phenol‑sulfuric acid method becomes more difficult and challenging. In this study, the quantification analysis of dextran and glucose in phenol sulfuric acid method was compared in this paper. When the concentration is below 90 μg/mL, the quantification of glucose is close to theoretical value, however, glucose derivatives have significantly different absorption. Later, quantitative factors of water-soluble polysaccharide in RID measurement were investigated. The optimum temperature was 40 °C and linear range was 0.3125-10.0 mg/mL in RID for dextrans (1.0-500 kDa) and glucose derivatives. Method validation studies of the RID method were further performed and compared to conventional phenol sulfuric acid method, which demonstrated that RID measurement is more reliable and satisfactory method. The intervention of water-soluble impurity in RID response should be well control below 6% (w/w). By comparison, the RID measurement could well alleviate drawbacks in phenol‑sulfuric acid method.