Determination of nitrate and nitrite in human saliva with a specially designed microfluidic paper-based analytical device (μPAD)

For many years, the concentration of nitrite and nitrate anions in human saliva was believed to be correlated with disfunctions and infections in the mouth. However, recent studies have reported some benefits to the presence of these ions in the oral cavity. In any case, there is a connection between the NOX salivary concentration and the human health and therefore it has become more and more relevant to understand this connection. Nowadays, there are several methods that allow this determination for a number of concentration ranges and types of samples, but these methods have limitations like requiring high volume of reagents and sample, the time of analysis, the use of complex lab equipment, the need of constant power, specialized technicians, the production of toxic waste, among others.info:eu-repo/semantics/publishedVersio

Microfluidic paper-based analytical devices for the determination of salivary NOx

info:eu-repo/semantics/publishedVersio

Determination of nitrate and nitrite in human saliva with a specially designed microfluidic paper-based analytical device (μPAD)

info:eu-repo/semantics/publishedVersio

On-hand tool for ammonium and urea determination in saliva to monitor chronic kidney disease – design of a couple of microfluidic paper-based devices

In this work, two microfluidic paper-based analytical devices (μPADs) were developed for the quantification of urea and NHx in human saliva to aid in the diagnosis/monitoring of chronic kidney disease (CKD). The NHx determination was based on the conversion of ammonium to ammonia, followed by its diffusion through a hydrophobic membrane and then the color change of bromothymol blue (BTB) indicator. In the urea determination, prior to the ammonium conversion and BTB color change, the enzymatic conversion of urea into ammonium was produced, using urease. Several optimization studies were carried out to attain a quantification range of 0.10–5.0 mM with 0.032 mM limit of detection for the NHx μPAD, and a determination range of 0.16–5.0 mM with 0.049 mM limit of detection for the urea μPAD. The method accuracy was assessed, and the measurements obtained with NHx μPAD were compared with the ones obtained from an ammonia ion selective electrode; while the measurements of the urea μPAD were compared with the ones obtained from a commercially available kit. There were no statistically significant differences between methods, proving that both NHx and urea μPAD were effective on-hand tools for CKD monitoring in saliva. To evaluate their functionality as point-of-care devices, stability studies were also performed and revealed that both NHx and urea μPAD were stable when stored in a vacuum for 2 and 1 month, respectively. After the sample introduction, the NHx μPAD could be scanned within the first 2 h and the urea μPAD within 1 h.info:eu-repo/semantics/publishedVersio

Design and assembly of microfluidic paper-based analytical devices (µPAD) for the quantification of nitrite and nitrate in saliva

info:eu-repo/semantics/publishedVersio

Exploiting solid phase extraction in a sequential injection system for phosphate determination in fertilized soil leachates

info:eu-repo/semantics/publishedVersio

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%. Graphical abstract: [Figure not available: see fulltext.]info:eu-repo/semantics/acceptedVersio

Development of a flow method for the determination of phosphate in estuarine and freshwaters - Comparison of flow cells in spectrophotometric sequential injection analysis

A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 mu M PO43-) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 mu M) was achieved using both detection systems.info:eu-repo/semantics/submittedVersioninfo:eu-repo/semantics/acceptedVersio

Liquefaction optimization of Crataegus monogyna Jacq

The objective of this work was to evaluate the potentiality of Crataegus monogyna Jacq. residues to be liquefied by polyhydric alcohols and the chemical transformations observed in this process with subsequent use to produce polyurethane foams. The variations on liquefaction yield were determined at different temperature, time, material/solvent ratio and granulometry. Results show that liquefaction performed at 180 °C with a 1:10 material/solvent ratio increases along time, reaching a maximum at 60 min. Similarly, liquefactions made during 60 min with a 1:10 material/solvent ratio show that there is an increase in liquefaction yield with the increase in temperature until 180 °C. A higher temperature could increase the liquefaction yield but would lead to a higher energy consumption in the process. There seems to be no significative advantage in increasing material/solvent ratio above 1:7, although the liquefaction yield increases for higher ratios. Granulometry testing shows that the smaller the particle the best is the liquefaction percentage. It was concluded that the best liquefaction yield, of approximately 81%, was obtained with a temperature of 180 °C, for 60 min and particle size <80 mesh for Crataegus monogyna Jacq. This material has good properties to be converted in a liquid mixture that can be used later, on the production of polyurethane foams.info:eu-repo/semantics/publishedVersio