In the present work, an automated procedure for photometric ammonium determination in rainwater using a multicommuted flow analysis approach is proposed. A homemade LED based photometer was designed to couple a flow cell with a path length of 100 mm in order to improve sensitivity. After establishing the adequate operational conditions, the proposed procedure was applied for the determination of ammonium in rainwater samples. The assessment of accuracy, by applying the paired t-test between these results and the results obtained using a reference method, showed that there is no significant difference at a 95% confidence level. Other useful features such as a linear response ranging from 0.05 to 1.20 mg L À1 NH 4 + ; a detection limit of 19 mg L À1 NH 4 + ; a blank relative standard deviation (n ¼ 15) of 2.9%; a reagent consumption of 1.5 mg sodium salicylate and 0.15 mg sodium nitroprusside; a waste generation of 3.1 mL per determination; and a sampling throughput of 38 determinations per hour were also achieved.

Neste trabalho, é descrito um fotômetro de baixo custo baseado em um par de LEDs idênticos, empregando um, como fonte de luz e o outro como fotodetector. O equipamento, incluindo o fotômetro e o módulo de análises, foi projetado para implementar um procedimento de titulação automático empregando o processo de multicomutação por injeção em fluxo (MCFIA). O sistema proposto dispunha de meios para realizar a titulação fotométrica sem a necessidade de empregar curva analítica. A utilidade foi comprovada analisando amostras de vinagre e sucos de limão, laranja, abacaxi, maracujá e cajú. A exatidão foi verificada comparando os resultados com outros, obtidos empregando procedimento manual, e não foi observada diferença significativa no nível de confiança de 95%. Amostras com diferentes concentrações de ácido, tais como suco de limão (1.084,73 mmol L ) foram tituladas usando a mesma solução titulante, e sem modificação do sistema de titulação.In this work, a reliable and inexpensive photometer based on twin LEDs assembled as a radiation source and as a photodetector is described. The setup including the photometer and flow system module was designed to implement an automated titration procedure employing the multicommuted flow injection analysis (MCFIA) process. The proposed system was able to carry out photometric titration without using analytical curve to achieve the sample concentration. Its usefulness was proven by analyzing vinegar and lemon, orange, pineapple, maracock, and acajou juices. Accuracy was accessed comparing results with those obtained employing a manual procedure and no significant difference was observed at 95% confidence level. Samples presenting different acid concentrations such as lemon juice (1084.73 mmol L -1 ) and pineapple juice (14.42 mmol L -1 ) could be titrated using the same titration solution without any modification of the titrating setup.

The present work proposes an automatic procedure for photometric determination of olive oil acidity, employing a miniaturized multicommuted flow-batch analysis setup without the use of calibration curves. Under microcomputer control, the proposed setup was able to mimic the manual procedure suggested by the European Commission Regulation. A homemade LED-based photometer was designed by coupling a radiation source and a photodetector to the titration chamber, creating a compact and downsized unit. The photometric titration of olive oil was carried out using potassium hydroxide solution in an n-propanol medium, which was done without any previous pretreatment, thereby allowing that a true photometric titration procedure in a non-aqueous medium was carried out for the first time. After establishing better operational conditions, the proposed procedure was applied to determine acidity in olive oil samples. The accuracy was assessed by applying the paired t-test to results obtained using a reference method, and there was no significant difference at a 95% confidence level. Other useful features were achieved, including a relative standard deviation of 1.8% (n ¼ 6), a sample consumption of 125 mL per determination, an effluent generation of 1.4 mL per titration, and a sampling throughput ranging from 40 to 50 determinations per hour, whereby indicating that it could be an effective alternative for routine analysis of olive oil.

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