Stock solutions of PTSO were prepared by weighting 25 mg of
PTSO (95% purity) and dissolving it in 25 mL of methanol. Calibration
solutions in the concentration range from 20 to 100 mg L1
were obtained from the stock solutions by the adequate dilution
with methanol. Calibration curves showed adequate linearity (coefficient
of determination, R2 > 0.995).