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The candidate reference materials of endosulfan sulfate and bifenthrin in black tea have been developed according to the requirements of ISO Guide 34 and 35. Preparation of candidate material includes grinding and sieving of the black tea leaves, spiking the black tea powder by both analytes, homogenization, and bottling. Homogeneity and short-term stability test were performed using a GC-µECD instrument. Meanwhile, the characterization was carried out by a collaborative study using both of GC-µECD and GC-MS instruments. The uncertainty budget was evaluated from sample inhomogeneity, short-term instability and variability in the characterization procedure. In a dry mass fraction, endosulfan sulfate was assigned to be 491 µg kg-1 with a relative expanded uncertainty of ± 33.2%, and bifenthrin was assigned to be 937 µg kg-1 with a relative expanded uncertainty of ± 18.5%. The candidate reference materials are aimed to support the need of matrix CRM especially for the measurement of pesticide residue for quality assurance work done by laboratories in Indonesia.

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Classified as food additives, the use of benzoic acid and acesulfame K to preserve foods is finite due to health and environmentreason.In this study, anefficient and fast method for simultaneous determination of benzoic acid and acesulfame-K in soft drinks was validated using high performance liquid chromatography with diode array detector (HPLC-DAD) on a C18 column. The method showed results satisfaction as the coefficient determination for benzoic acid and acesulfame-K were 0.9998 and 0.9991 respectively. The LOD for both compounds found at 0.02 mg/kg and the LOQ were found at 0.07 and 0.06 mg/kg for benzoic acid and acesulfame-K respectively. The recovery studies proved that the method has a good recovery ranging from 96103% for both benzoic acid and acesulfame-K with %RSD varies from 1.6 - 4.6% at different concentrations. The validated method then applied to the inter-laboratory comparison sample conducted by the National Quality Control Laboratory for Drug and Food (NQCLDF), Indonesia, using traceable standard reference materials. Uncertainty evaluation using bottom-up approach showed that the method has reasonable uncertainty value with uncertainty budget derived from weighing process, recovery studies, method precision, calibration curve and standard solution. The uncertainty value (k=2, in confidence level 95%) for benzoic acid was found to be 4% at reported concentration of 343 mg/kg and for acesulfame-K was found to be 6.5% at reported concentration of 195 mg/kg. In conclusion, the validated method offered a simple and fast method, as well as economical reagents consumption indicating its possible application as an alternative method for a routine analysis.

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