Determine the molar concentration of thiols based on the molar extinction of reduced Ellman's reagent (13,600).  In other words, divide the absorbance at 412 nm by 13,600.  This is the molar thiol concentration.  Then divide by the molar concentration of the chitosan.  This will give number of thiols per chitosan molecule.  Or you could use cysteine standards treated the same way as your samples and read the thiol concentration off the standard curve.  If the thiols contribute significantly to the molecular weight of the conjugate, you will have to compare the weight of the conjugate to an appropriate control.

I am not familiar with the test you describe, but silver ion is very reactive towards thiols, particularly thiols that will ionize in water. My suggestion is to do a simple titration of your aqueous chitosan solution by using a standard silver nitrate solution [calibrated against KI]. Ue an Orion Ag2S or similar Ag+ specific electrode and any convenient reference electrode, and your basic pH meter in mV mode will do nicely. The inflection point in the resulting mV vs mL titrant curve will give the meq per weight chitosan in your test solution. Do a control titration of a blank solution so you know when you are looking simply at Ag+ in solvent, and so you know when to stop your sample titration [i.e., when the potential begins approaching what you measured for our blank control.

Avoid contacting the aqueous silver nitrate with your fingers (skin), as it will turn your skin black/brown due to forming Ag2S by reacting with protein sulfurs in your skin.

Very simple 

Use DTNB

Refer attached article

Good luck to you

Determine the molar concentration of thiols based on the molar extinction of reduced Ellman's reagent (13,600).  In other words, divide the absorbance at 412 nm by 13,600.  This is the molar thiol concentration.  Then divide by the molar concentration of the chitosan.  This will give number of thiols per chitosan molecule.  Or you could use cysteine standards treated the same way as your samples and read the thiol concentration off the standard curve.  If the thiols contribute significantly to the molecular weight of the conjugate, you will have to compare the weight of the conjugate to an appropriate control.

You can calculate the thiol group concentration in a polymer by using the Ellman reaction (DTNB reagent) and photometry at 412 nm from a calibration curve. For the establishment of the calibration curve you can use e.g. glutathione reduced (GSH), which is commercially available (e.g. from Sigma Aldrich).

However, we have better experience in calculating the thiol group content in thiolated polymers by using Raman spectroscopy. Thiol groups occur at 2572 cm-1 and disulfide groups at 510-512 cm-1 in the Raman spectrum. By integration of the area under the Raman signals the thiol group concentration can be obtained with the help of a calibration.

Can we use Thioglycolic acid as a standard for plotting standard curve. 

Ya you can use thioglycolic acid as a standard or u can use cysteine hydrochloride.  Since thioglycolic acid will be in liquid form, you need to know the exact concentration of it.

I fear that thioglycolic acid is not perfect as a standard in Ellman' reaction. I agree with Thirupathi's answer.

Often cysteine is used for plotting the standard curve in Ellman's reaction, cf.

Marta Roldo, Margit Hornof, Paolo Caliceti, Andreas Bernkop-Schnuerch, Mucoadhesive thiolated chitosans as platforms for oral controlled drug delivery: synthesis and in vitro evaluation

European Journal of Pharmaceutics and Biopharmaceutics 57 (1), (2004), 115-121