Simultaneous determination of nitrite, nitrate, sulphate and phenolic compounds, by sequential injection analysis, in wastewaters

Abstract

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...

A review on sequential injection methods for water analysis

“…This means that by using the same manifold but placing different reagents on the selection valve ports, and changing the operational parameters, more than one analyte can be determined. From the listed papers, over 40% involved the determination of more than one analyte [34-36,39,40,45,49-53,55,59-61,72,74,78,83-85, 94,96,101-104,106,107,114,116,117,119,120,132,135,138,140,141,145, 148,149,153,155], with close to 18% describing the determination of more than two analytes [34][35][36]40,45,[49][50][51]53,74,83,78,102,101,116,140]. Some more detailed examples of bi-parametric determinations will be detailed in Section 3.4.2, as they usually involve quantifying two oxidation states.…”

“…Oxidation and reduction treatments were not limited to the determination of metals as the determination of nitrite and nitrate is also very common [96,107,108,116,117,132,155]. In all these works, nitrate is reduced to nitrite, most of them involving a cadmium column [96,107,108,116,117,132] once again emphasising the easy assembly of a device (column) to a SI system. Fig.…”

“…There was one exception to the use of the cadmium column as Oms et al [155] described the reduction with hydrazine. In the end, most of these works represent a bi-parametric determination of both anions [96,116,117,132,155] but a couple present the results as total nitrogen [107,108]. The work by Thomas et al [140] described the determination of nitrite and total nitrogen (obtained from sample digestion) but made no reference to the value of nitrate.…”

“…Spectrophotometry was the most widely used method of detection, although there were also quite a few methods that involved electrochemical detection. Almost 20% each of the listed references, described the determination of nitrite [67,96,107,118,116,117,132,131,140,155] and phosphate [52,77,107,120,119,135,134,[140][141][142]. For monitoring aquatic media, it is important not only the determination of these anions individually, but also the ratio…”

A Low-Cost Light-Scattering Detector for the Flow-Injection Nephelometric Determination of Sulfate

“…6 FI systems based on precipitation reactions have also been widely applied for the determination of drugs, such as thiamine, 7 promethazine, 8 amitriptyline, 9 and chlorhexidine. 10 The determination of sulfate using barium chloride as a precipitating agent has previously been applied in both FI [11][12][13][14] and SI 15,16 systems. A liquid-drop windowless optical cell has been developed for FI turbidimetric or nephelometric determination of sulfate by precipitation with barium ion.…”