An accurate and reliable method for authentication and discrimination of Curcuma xanthorrhiza (CX) from Curcuma longa (CL) by determining the curcuminoid's content and analyzing the HPLC fingerprint combined with discriminant analysis (DA) was developed. By using the proposed method, it was found that CL had higher amount of all curcuminoid compounds compared to CX. Therefore, these two closely related species could be authenticated and discriminated by the amount of curcuminoids present in the samples. Authentication and discrimination of the two species were also achieved by comparing their HPLC fingerprint chromatograms using their typical marker peaks. To be more convincing, an aid from DA was also used. Combination of HPLC fingerprint analysis and DA gave excellent result that the two species were separated clearly, including CX samples adulterated with CL. The developed method was successfully used for quality control of the two plants.

The construction and performance of ion selective electrodes (ISEs) for the determination of chromium(VI) based on PVC membranes modified with 1,5-diphenylcarbazide (DPC) and natural zeolite as ionophores are reported in this study. ISE was fabricated in an optimum composition of chromium(VI)-selective membrane consisting of 29 mol% DPC, 43.6 mol% natural zeolite, 25 mol% plasticizer, and 2.2 mol% PVC. The investigation of the performance of the proposed ISE was evaluated in terms of the Nernstian response, range of concentration, limit of detection, response time, and selectivity coefficient. The proposed ISE displayed a linear potential response over a concentration range of 10 −1 -10 −6 M K 2 Cr 2 O 7 with a Nernstian response of −28.8 mV/decade. Adequate sensitivity for chromium(VI) was offered by the proposed ISE with a limit of detection of 2.14×10 −6 M and a response time of ∼250 s. The fabricated ISE has also been investigated in selectivity studies in the presence of Cu 2+ and Fe 3+ and was found to be more selective in the concentration range of 10 −1 -10 −6 M. Therefore, a novel membrane electrode using a composite of DPC and natural zeolite as an ionophore has shown a satisfactory result for the direct potentiometric measurement of chromium(VI) in the presence of Cu 2+ and Fe 3+ , which may have the potential to be used in real sample analysis.