RESUMEN

A simple and automated system based on combustion followed by a pyrohydrolysis reaction was proposed for further halogens determination. This system was applied for digestion of soils containing high (90%) and also low (10%) organic matter content for further halogens determination. The following parameters were evaluated: sample mass, use of microcrystalline cellulose and heating time. For analytes absorption, a diluted alkaline solution (6 mL of 25 mmol L-1 NH4OH) was used in all experiments. Up to 400 mg of soil with high organic matter content and 100 mg of soil with low organic matter content (mixed with 400 mg of cellulose) could be completely digested using the proposed system. Quantitative results for all halogens were obtained using less than 12 min of sample preparation step (about 1.8 min for sample combustion and 10 min for pyrohydrolysis). The accuracy was evaluated using a certified reference material of coal and spiked samples. No statistical difference was observed between the certified values and results obtained by the proposed method. Additionally, the recoveries obtained using spiked samples were in the range of 98-103% with relative standard deviation values lower than 5%. The limits of quantification obtained for F, Cl, Br and I for soil with high (400 mg of soil) and low (100 mg of soil) organic matter were in the range of 0.01-2 µg g-1 and 0.07-59 µg g-1, respectively. The proposed system was considered as a simple and suitable alternative for soils digestion for further halogens determination by ion chromatography and inductively coupled plasma mass spectrometry techniques.

RESUMEN

A method for digestion of soils with high inorganic matter content (ranging from 50 to 92%) by microwave-induced combustion (MIC) is proposed for the first time for further halogens (F, Cl, Br, and I) determination by ion chromatography (IC) and also by inductively coupled plasma mass spectrometry (ICP-MS). Microcrystalline cellulose (100-500 mg), used as a combustion aid, was mixed with sample and water or NH4OH solutions (10-100 mmol L-1) were investigated for analytes absorption. The use of cellulose (400 mg) was mandatory to volatilize the halogens from soils with high inorganic matter. It was possible to use diluted absorbing solutions (up to 100 mmol L-1 NH4OH) for halogens retention, providing limits of quantification in the range of 0.06 (I) to 60 (Cl) µg g-1. Accuracy was evaluated using certified reference materials (CRMs), spiked samples, and pyrohydrolysis method. Recoveries for halogens after spiked samples were in the range of 94 to 103% and the results after digestion of CRMs by MIC were in agreement better than 95% to certified values. Blanks were low, relative standard deviation was below 8% for all soils and no statistical difference was observed for results by pyrohydrolysis and MIC methods showing the feasibility of the proposed method for further halogens determination in soil samples.

RESUMEN

Epidemiological research points to the high prevalence of psychiatric disorders among insomniacs. We carried out a cross-sectional study with medical students with the aim of evaluating the association between insomnia and suspicion of psychiatric disorder; 302 medical students were included (184 males and 118 females; mean age = 20.47+/-1.89 years). The main association was tested by logistic regression analysis. The overall prevalence of positivity in a screening test for psychiatric disorder was 22.19%; and of insomnia, 28.15%. Difficulty initiating sleep (OR=3.45), difficulty maintaining sleep (OR=7.61), falling asleep later (OR=1.99) and waking up earlier (OR=1.91) were associated with suspicion of psychiatric disorder. As a group, the variables difficulty initiating sleep, difficulty maintaining sleep, falling asleep after 11 pm, and waking up before 6 am presented an odds ratio of 5.96 for positivity in the screening for psychiatric disorder. Furthermore, difficulty maintaining sleep (OR=2.24) was associated with "being female," and falling asleep later (OR=0.43) was associated with "being male". These results underscore the importance of determining in what cases difficulty sleeping may have severe clinical repercussions or affect performance.

Asunto(s)