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The rapid growth of biotechnological research in the last years has emphasized the demand for simple and robust analytical techniques applicable to bioprocess monitoring.On-line determination of certain chemical species in bioprocesses is of significance with regard to controlling a process more efficiently, for reasons of economy, environmental quality and product quality. 1Automatic systems for on-line process control based on flow analyses were developed and used in the monitorization of chemical species in natural waters and industrial effluents. More robust systems with simple operation and a minimum of maintenance are therefore needed in order to advance the routine application to the industrial processes. The sequential injection analysis (SIA) comprising only a single propulsor system, single valve and a single channel, has been conceived and found to overcome the difficulties related to the conventional flow systems, such as, manual reconfiguration of the flow channel, high reagent consumption due to the continuous flow operation and frequent recalibration of the system. Routine application of the conventional flow systems for bioprocess monitoring is largely restricted to research laboratories, as the robustness and ease of operation are not sufficiently good for process control. 2-7Nitrite and nitrate are chemical species in waters that need monitoring, due to their known toxicity to animal and human metabolism, especially when children are concerned. Nitrate is related with methaemoglobinaemia (Blue Baby Syndrome) and there is a possible relation with stomach cancer and hypertension. [8][9][10][11][12] The nitrogen content, as nitrite and nitrate, of lakes, rivers and streams usually arises from the groundwater, sewerage effluent or drainage and leaching from agricultural land. 13 The last is the most significant input and nitrate levels have increased substantially because of the increased use of nitrogen-based fertilisers. [13][14][15] Several methods are available for the nitrite and nitrate determination in waters, [15][16][17] including direct ultraviolet spectrophotometry, derivatization with sulfosalicylic acid, use of a nitrate-selective electrode and reduction to nitrite followed by derivatization, e.g., with N-(1-naphtyl)ethylenediamine dihydrochloride (N1NED) and sulfanilamide.In this paper, the design of a fully automated and robust system based on SIA, allowing the simultaneous monitoring of nitrite and nitrate in wastewaters, is described. The nitrite determination is based on the Griess-Llosvay reaction: nitrite in the presence of sulfanilamide and N1NED produces, by diazotization and coupling reaction, a colored compound that can be spectrophotometrically detected at 543 nm. Nitrate is determined after reduction to nitrite in a copperized cadmium column. 18 The parameters that affect this determination were evaluated. The working characteristics of this system are rapid, sensitive and accurate, and applicable to the monitorization of nitrite and nitrate levels in wastewaters. Experime...

There is an increasing need of process analysers to monitor water chemical parameters such as nitrite, nitrate, phenolic compounds and sulphate in natural water streams and industrial effluents due to the widespread industrial use of sulphuric acid [1], the increased use of nitrogen-based fertilizers over the last years [2][3][4] and the extensively phenolic compounds use as pesticides, herbicides and fungicides [5].The limits of emission values in the discharge of wastewaters, presented in the Portuguese Legislation [6] are 50 mg.dm -3 for nitrate, 2000 mg.dm -3 for sulphate and 0.5 mg.dm -3 for phenolic compounds.Automatic systems for on-line process control based on flow analyses were, already, developed and used in the monitorization of chemical species in wastewaters and industrial effluents. Flow injection analysis (FIA) has often been used as a technique to solve environmental analytical problems since its introduction by Ruzicka and Hansen in 1975 [7].The demand for mechanically simple and robust flow injection methodology, as advanced by the needs of process analytical chemistry, associated to reliability, long-term stability and low frequency of maintenance required for process analysers, have been the driving force behind developing a sequential injection technique. While manual reconfiguration of the flow channel, high reagent consumption due to continuous flow operation, frequent assistance of peristaltic pumps and frequent recalibration of the system is acceptable in laboratory applications, these are obstructive in terms of cost and manpower in a process environment. The sequential injection analysis (SIA) conceived comprising only a single propeller system, single valve and a single channel allows to overcoming the difficulties related to the conventional flow systems. Minimising the number of mechanical components is beneficial for a process control environment as it increases the reliability of the apparatus [8][9][10][11]. This paper describes a SIA system for the simultaneous determination of nitrite, nitrate, sulphate and phenolic compounds in wastewaters. The nitrite determination is based on the Griess-Llosvay reaction: nitrite ion is diazotized with sulphanilamide [12] and the product of diazotization is coupled with N-(1-naphthyl)-ethylenediamine (N1NED) to form a coloured azo dye which is measured spectrophotometrically at 540 nm. Nitrate is reduced on-line to nitrite in a copperized cadmium column and analysed as nitrite. The sulphate determination is based on the turbidimetric determination using barium chloride as reagent and the phenolic compounds determination (determination of the sum of compounds possessing a phenolic moiety) is based on the oxidative coupling with 4-AAP in alkaline solution, measuring the absorbances of the formed suspension and coloured compound, respectively, spectrophometrically at 540 nm. Abstract. A sequential injection analysis (SIA) system for the simultaneous determination of nitrite, nitrate, sulphate and phenolic compounds, in wastewaters has been deve...

Foi desenvolvido um sistema de análise por injeção sequencial, baseado na formação do cátion FeSO 4 + e detecção espectrofotométrica a 355 nm, para a determinação de sulfato em águas residuais. Os principais interferentes foram avaliados. O sistema proposto é totalmente automático e permite o monitoramento de sulfato em amostras. O desvio padrão relativo (RSD) obtido foi inferior a 2,4%. O sistema apresentou uma resposta linear entre 10 e 1000 mg L -1 . A velocidade de amostragem obtida foi de 72 amostras por h.A sequential injection analysis system based on the formation of the cation FeSO 4 + and the spectrophotometric measuring of the absorbance at 355 nm has been developed for the determination of sulphate in wastewaters. The main interferents were also evaluated. The proposed system is fully automatized and is able to monitor sulphate in samples. The relative standard deviation (RSD) obtained was smaller than 2.4%. The linearity of response was obtained between 10 and 1000 mg L -1 . The sampling rate was 72 samples per hour.

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