Using rapid centrifugal filtration (<or= 30 min) of diluted samples, the filter membrane prevented compounds with molecular weight higher than the nominal molecular weight limit (NMWL) from transporting through the membrane, thus separating them from compounds with molecular weight smaller than NMWL, which would pass through the membrane. The purpose of this study aims to remove high molecular weight matrix (such as xanthan gum) interferences while achieving a quantitative analysis of the active pharmaceutical ingradients of interest. Two model active pharmaceutical ingredients, L-arginine and amphotericin B, were quantitatively recovered from the diluted syrup vehicle after centrifugation with the filter devices. The reproducibility [% relative standard deviation (RSD), peak area] of the filtered samples was less than 0.5%. For amphotericin B samples. The linear range was 0.28 microg/mL to 28.2 microg/mL. The limit of detection was 0.06 microg/mL. The limit of quantification was 0.28 microg/mL. The viscosity of a syrup vehicle changed linearly with the concentration of xanthan gum. A method was thus developed to determine xanthan gum in the syrup vehicle. The accuracy was within 95.0% to 105.0% at different concentration levels.