SAMPLE PREPARATION PROCEDURES FOR DETERMINATION OF Cr_2O_3 IN LEATHER SAMPLES USING ICP-AES AND AAS

摘要

Three different sample preparation procedures were applied to leather samples, representing four different steps of the tanning process namely, after the tanning step (wet blue), after the retanning step (crust), after normal finishing and after a silicon finishing process. The sample preparation procedures are the conventional procedure in which the samples are fused at 800℃ with a mixture of Na_2CO_3, K_2CO_3 and borax followed by dissolving in boiling water and filtering. The other two suggested procedures are an ashing/fusion procedure in which the leather sample is ashed at 1000℃ followed by an alkali fusion step with NaOH, Na_2O_2 and Na_2CO_3 while in the second procedure the leather sample is refluxed with concentrated HNO_3. Both procedures lead to complete dissolution of the leather sample. Chromium and consequently Cr_2O_3 was determined in the prepared sample solutions by using inductively coupled plasma atomic emission spectrometry (ICP-AES) and flame atomic absorption spectrometry (AAS). The obtained results revealed that the direct acid digestion procedure by requiring minimum additive chemicals and no fusion step without leaving any residue represents a convenient procedure for the complete dissolution of leather samples that can be analyzed for Cr using an appropriate analytical technique such as AAS or ICP-AES. The accuracy of the conventional method could be increased by increasing the Na_2CO_3/ K_2CO_3/ borax mixture from 4-fold that of the leather sample to 5-fold and, in addition, by raising the ashing temperature from 800℃ to 900℃ in order to ensure the complete dissolution of the sample.