New microfluidic paper-based analytical device for iron determination in urine samples.

Iron is an important micronutrient involved in several mechanisms in the human body and can be an important biomarker. In this work, a simple and disposable microfluidic paper-based analytical device (µPAD) was developed for the quantification of iron in urine samples. The detection was based on the colorimetric reaction between iron(II) and bathophenanthroline and the reduction of iron(III) to iron(II) with hydroxylamine. The developed µPAD enabled iron determination in the range 0.07-1.2 mg/L, with a limit of detection of 20 µg/L and a limit of quantification of 65 µg/L, thus suitable for the expected values in human urine. Additionally, targeting urine samples, the potential interference of the samples color was overcome by incorporating a sample blank assessment for absorbance subtraction. Stability studies revealed that the device was stable for 15 days prior to usage and that the formed colored product was stable for scanning up to 3 h. The accuracy of the developed device was established by analyzing urine samples (#26) with the developed µPAD and with the atomic absorption spectrometry method; the relative deviation between the two sets of results was below 9.5%.

Design and Functionalization of a µPAD for the Enzymatic Determination of Nitrate in Urine.

In this work, the design of a microfluidic paper-based analytical device (µPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination µPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed µPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14-1.0 mM. The designed µPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at -20 °C. The accuracy of the nitrate µPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples.

Sequential injection spectrophotometric method for screening bromate produced as an ozonation water disinfection by-product.

The aim of this work was the development of an automatic sequential injection analysis method to monitor the ozonation process for water disinfection. The determination was based on the reaction between bromate and o-dianisidine in the presence of bromide in acidic medium. The determination parameters were studied and adjusted to enable bromate quantification in the range 0.35-4.0 mg BrO3-/L with a limit of detection of 20 µg BrO3-/L. The choice of a sequential injection procedure enabled a minimal consumption of reagents and no need for sample pre-treatment. The developed sequential injection proved to be accurate with < 5% relative deviation when compared to ICP-MS and an average of 101% in recovery percentages studies. It was effectively applied to monitor an ozonation process enabling the follow-up of the process with real-time quantification of the bromate content.

Novel microfluidic paper-based analytical devices (µPADs) for the determination of nitrate and nitrite in human saliva.

In this work, two different microfluidic paper-based analytical devices (µPADs) were developed for the quantification of nitrite and nitrate in human saliva samples, in order to aid in the diagnosis of some diseases and health conditions associated with these ions. The development of these nitrite and nitrate µPADs involved several studies to optimize their design and construction, including an interference assessment and stability studies. These µPADs allowed a nitrite determination in a range of 5-250 µM with limits of detection and quantification of 0.05 µM and 0.17 µM, respectively, and a nitrate determination in the range 0.2-1.2 mM with limits of detection and quantification of 0.08 mM and 0.27 mM, respectively. As for the stability, both of the µPADs were stable when stored in vacuum at 4 °C (the nitrite µPAD for at least 60 days and the nitrate µPAD for at least of 14 days) and, after the sample placement, the nitrite and nitrate µPADs could be scanned within the first 4 and 2 h, respectively. The nitrite µPAD measurements were compared with the ones obtained from the standard colorimetric method and there were no statistically significant differences between these two methods. To evaluate the accuracy of nitrate µPAD measurements, 4 certified water samples were used and recovery studies using saliva samples were performed.