**preparation of cholinesterase reagent**
  -dissolve R1 in 30 ml and R2 in 1 ml of DI water 
  -mix R1 and R2 after 15 min after complete dissolving of R1 and R2
  -aliquot 1 ml of reagent in plain vaccutte after proper washing of vaccutte
  -keep frozen
  -use 1 vaccutte of reagent as and when required
  -preserve the residual reagent after use