Afterwards, 6 g of anhydrous magnesium sulfate and 1.5 g of sodium chloride were added, then
extracted by shaking vigorously on vortex for 5 m and centrifuged for 10 m at 4,000 rpm. An aliquot of 4 ml was transferred from the supernatant to a new clean 15 ml centrifuge tube containing 100 mg PSA and 600 mg anhydrous magnesium sulfate