Simple and fast fabrication of microfluidic paper-based analytical device by contact stamping for multiple-point standard addition assay: Application to direct analysis of urinary creatinine.

In this work, a microfluidic paper-based analytical device (µPAD) for simultaneous multiple-point standard addition assay was fabricated by rubber stamping the hydrophobic barrier pattern onto a laboratory filter paper. The µPAD has a central zone from which an applied sample flows into eight surrounding narrow channels to which had been added the standard solutions. Each channel is connected to a circular area loaded with the reagent. The opposite end of this reagent zone is connected by second narrow channel to the final circular detection zone. The µPAD was applied to the measurement of creatinine in human urine. After addition of a urine sample, the orange-colored product arising from the Jaffé reaction is formed at the eight detection zones. A digital image of the µPAD is then recorded and the ratio of the red/green (R/G) intensity obtained using the ImageJ™ program is used in the quantitation of creatinine. The normal standard addition calibration line is constructed using the intensity ratio against the added creatinine concentrations (50-1000 mg L-1). Good linearity was achieved (r2 ˃ 0.99). There were no significant differences between the creatinine content using an HPLC method (paired t-test at 95% confidence, tstat = 1.78, tcritical = 2.26, n = 10). The use of simultaneous multiple-point standard addition calibration allows rapid determination of creatinine in urine with elimination of matrix interference.

Fast and simple method for semiquantitative determination of calcium propionate in bread samples.

Calcium propionate has been widely used as a preservative in bakery and in bread. It is sometimes not carefully used, or a high concentration is added to preserve products. High consumption of calcium propionate can lead to several health problems. This study aims to develop a fast and simple semiquantitative method based on color complex formation for the determination of calcium propionate in a bread sample. A red-brown complex was obtained from the reaction of ferric ammonium sulfate and propionate anion. The product was rapidly formed and easily observed with the concentration of propionate anion >0.4 mg/mL. A high-performance liquid chromatography (HPLC) method was also developed and validated for comparison. Twenty-two bread samples from three markets near Bangkok were randomly selected and assayed for calcium propionate using the above two developed methods. The results showed that 19/22 samples contained calcium propionate >2000 mg/kg. The results of the complex formation method agreed with the HPLC method.

Development and Validation of LC-MS/MS Method for Quantitative Determination of Adenosine, Guanosine, Xanthine and Uric acid in Widely Consumed Vegetables in Thailand.

In this study, a triple quadrupole LC-MS/MS electrospray ionization method was developed and validated for quantitative determination of adenosine, guanosine, xanthine and uric acid in fifteen widely consumed Thai vegetables. The method was successively developed by using caffeine as internal standard. The lower limit of quantitation (LLOQ) was 0.2 µg/g for adenosine and guanosine, and 1.0 µg/g for uric acid and xanthine. The method was fully validated according to USFDA guidelines and all performance characteristics were found acceptable. Subsequently, the developed and validated LC-MS/MS method was applied to determine the four interest substances in fifteen widely consumed vegetables in Thailand. The results showed that all vegetables included in the study could be classified as low adenosine, guanosine, xanthine and uric acid containing foods since the concentrations of these substances were less than 50 mg per 100 g. This finding was enormously valuable information for hyperuricemia and gouty patients.