The present invention provides systems and methods for attenuating the effect of ambient light on optical sensors and for measuring and compensating quantitatively for the ambient light. A dilution gas inlet receives a dilution gas, and a sample gas inlet receives a sample gas. The detected transition rate is based on the first gain control value. When an application detects such output it notifies the system, which monitors the frequency of the dynamic output. , or to a temperature within the range of from 400 C. The present invention further provides salt of -N-Boc-ritalinic acid with -1-phenylethylamine as new intermediate in the preparation of dexmethylphenidate hydrochloride.