Antiserum (100 μl) was transferred to a microanalysis tube of 500 μl volume and 4 M ammonium sulphate was added 10 times with each volume of 20 μl and mixed thoroughly after the addition of each 20 μl. pH was adjusted to 7.8 by addition of 0.5 μl of 1 N sodium hydroxide. The solution was left for 1 h at room temperature with occasional mixing and then centrifuged (4000-6000 rpm) for 5 min. The supernatant was carefully removed and discarded while the pellet was re-suspended in 100 μl of sterilized distilled water. Following this, it was dialyzed overnight with 400 ml of 0.02 M PBS (pH 7.8) after transferring to small dialysis chamber.