Indirect extraction-spectrophotometric determination of 2-(thiocyanomethylthiol)benzothiazole in chrome tanning liquors after its breakdown to 2-mercaptobenzothiazole

The simple extraction-spectrophotometric procedure is proposed in this work for the determination of 2-(thiocyanomethylthiol)benzothiazole (TCMTB) in chrome tanning liquors after its breakdown to 2-mercaptobenzothiazole (MBT). The sample (50 μl) was 4-fold diluted with deionized water and the conversion of TCMTB to MBT was obtained with cysteine (400 μl, 0.1 mol l−1) in alkaline conditions (pH 10). After acidification to pH 2.5 (100 μl phosphoric acid, 2 mol l−1), the extraction was carried out with 800 μl of ethyl acetate, containing 0.2% of β-mercaptoethanol and absorbance was measured at 324 nm with the cut-off filter 295 nm. To avoid possible errors due to MBT presence in the sample, this same sample was taken for blank, but the reagents were added in form of one acid solution (omitting the conversion step). The calibration range was 10–120 μg ml−1 of TCMTB with the regression coefficient 0.9999, the quantitation limit was 2.80 μg ml−1 and the within day precision was 3.34 and 0.20%, respectively, for 10 and for 100 μg ml−1 of TCMTB. The results obtained in the analysis of the three industrial liquor samples by the proposed procedure were in a good agreement with the results obtained using liquid chromatography method.