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- Seasonal monitoring of inland bathing waters using a sequential injection method as a fast and effective tool for nutrient quantification (N : P)Publication . Mesquita, Raquel B. R.; Machado, Ana; Santos, Inês C.; Bordalo, Adriano A.; Rangel, António O. S. S.In this work, an expedite flow method for the combined determination of major nutrients, nitrogen base ions (nitrate, nitrite and ammonium) and phosphate, is described for seasonal monitoring of inland bathing waters. Individual determinations were adapted and comprised within the same manifold to attain a comprehensive assessment of the environmental status of natural waters. The multiparametric determination was performed to explore the features of a sequential injection analysis technique yielding a real-time assessment of various parameters and effective in-line sample handling. The sequential injection multiparametric method enabled the determination within the ranges: 15.0-150 mu M nitrate; 0.15-5.00 mu M nitrite; 1.00-60 mu M ammonium; and 0.2-30 mu M phosphate. The determination rates provided a full nutrient analysis within 7 minutes, an overwhelming improvement in relation to the individual determination of each parameter. The described method was successfully applied to seasonal monitoring of six inland bathing waters dealing in-line with sample variability.
- A greener alternative for inline nitrate reduction in the sequential injection determination of NOx in natural waters: replacement of cadmium reduction by UV radiationPublication . Machado, Ana; Marshall, Graham; Bordalo, Adriano A.; Mesquita, Raquel B. R.The use of sequential injection analysis (SIA) for key nutrient determination in water has been previously described using a copperised cadmium column to attain nitrate reduction to nitrite prior to determination, yielding hazardous waste. Here, a greener alternative is proposed for nitrate reduction using a UV lamp, aiming to avoid the use of cadmium. This method was based on the colorimetric Griess reaction for nitrite determination, after the UV reduction of nitrate. The reduction was performed inline during the determination of nitrite, minimizing both effluent production and the overall determination rate. Its application to natural waters, namely river water, proved to be effective as the results were comparable to those obtained with the reference procedure. Furthermore, certified reference samples were analysed, and an average of 3% relative deviation was observed. A limit of detection of 5.30 mM was achieved, enabling the nitrate determination in the dynamic range of 25-500 mM with a determination rate of 24 h(-1), and with a recovery percentage rate around 100%.
- Sequential injection methodology for carbon speciation in bathing watersPublication . Santos, Inês C.; Mesquita, Raquel B. R.; Machado, Ana; Bordalo, Adriano A.; Rangel, António O. S. S.A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO2), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO2 and TC was based on colour change of bromothymol blue (660 nm) after CO2 diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO2. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611 nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24-3.5 mg C L-1), CO2 (1.0-10 mg C L-1), TC (0.50-4.0 mg C L-1) and alkalinity (1.2-4.7 mg C L-1 and 4.7-19 mgC L-1) with limits of detection of: 9.5 mu g C L-1, 20 mu g C L-1, 0.21 mg C L-1, 0.32 mg C L-1, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.
- Improvement of the Sandell-Kolthoff reaction method (ammonium persulfate digestion) for the determination of iodine in urine samplesPublication . Machado, Ana; Lima, Lurdes; Mesquita, Raquel B. R.; Bordalo, Adriano A.
- Can non-fortified marine salt cover human needs for iodine?Publication . Lobato, Carolina B.; Machado, Ana; Mesquita, Raquel B. R.; Lima, Lurdes; Bordalo, Adriano A.Iodine deficiency remains a worldwide problem with two billion individuals having insufficient iodine intake. Universal salt iodisation was declared by UNICEF and WHO as a safe, cost-effective, and sustainable way to tackle iodine deficiency. In Portugal, the few studies available unravel an iodine status below the WHO guidelines for pregnant women and school-aged children. In the present study, the iodine levels of household salt consumed in Portugal was assessed, for thefirst time. Non-iodised (median 14ppm) and fortified (median 48 ppm) marine salt samples showed iodine levels lower than the minimum and above the maximum threshold recommended by non-mandatory Portuguese law and WHO recommendations, respectively. This study calls attention to the fact that marine salt per se, in spite of containing a natural high amount of iodine, requires further fortification in order to be used as an effective tool to deal with iodine insufficiency.
- Development of a robust, fast screening method for the potentiometric determination of iodide in urine and salt samplesPublication . Machado, Ana; Mesquita, Raquel B. R.; Oliveira, Sara; Bordalo, Adriano A.In this work, a potentiometric flow injection method is described for the fast bi-parametric determination of iodide and iodate in urine and salt samples. The developed methodology aimed for iodine speciation with a potentially portable system (running on batteries). The iodate reduction to iodide was effectively attained in line within the same manifold. The iodide determination was accomplished in the dynamic range of 2.50×10−6– 1.00×10−3 M and the total iodine dynamic range, resulted from iodide plus iodate, was 3.50×10−6– 2.00×10−3 M. The calculated limits of detection were 1.39×10−6 M and 1.77×10−6 M for iodide and iodate, respectively. A determination rate of 21 h−1 for the bi-parametric iodide and iodate determination was obtained for sample injection. The urine samples (RSD < 5.8% for iodide and RSD < 7.0% for iodate) results were in agreement with those obtained by the classic Sandell-Kolthoff reaction colorimetric reference procedure (RD < 7.0%) and standard samples from Centers for Disease Control and Prevention, Atlanta, USA (CDC) international inter-laboratory EQUIP program. The developed flow method was also successfully applied to the iodide and iodate determination in salt samples (RSD < 3.1% for iodate and iodide), with comparable results to conventional procedures. No significant interferences were observed interference percentage < 9% for both determinations.