Welchrom® SAX/PSA is composed of an equal amount of SAX in the upper layer and an equal amount of PSA in the lower layer. The SAX packing materials in the upper layer can absorb the acidic substances in the sample matrix, while the PSA in the lower layer can absorb the organic acids, fatty acids, pigments and other interferents in the sample, which are widely used in the analysis of multi-pesticide residues in food.