First: You need to evaporate your sample to dryness, to remove any traces of water or another solvent with labile hydrogens

Second: For 1mg of dry sample add 20uL of pyridine and 80 uL of derivatizing agent. Incubate for 30 minutes at 80 ° C

Third: rectify the final volume to 200uL adding isooctane.

Note: You must be careful with the use of pyridine and the derivatizing agent.

hello juan,thanks for your answer.could you please tell me the reference of this method.....so that i would also connect to that.Please

Water is the main problem. You must dry your sample. Your can use an oprotic solvent as Acetonitrile (0.5-1 mL) and add 50-100 uL 

Ref: Ruiz-Matute. Derivatization of carbohydrates for GC and GC-MS analyses, JCB, 2011.

Get rid of any trace of water. A smart way to do so is to blow down the sample with nitrogen after addition of 0.5-1 mL acetonitrile (dried on molecular sieves) - repeat twice.

Dry and store pyridine on KOH (if you plan to use it-in my experience its use is sometimes questionable).

Consider the possibility of derivatization with hydroxylamine chlorhydrate (or methoxylamine) in pyridine before silanization (great for sugars and keto/aldo compounds)

Hello, evaporate to almost dryness and add BSTFA as solvent. Ultrasound for 5 min then 60°C for 30min. Injection to GCMS