J.M. Estela

Flow techniques in water analysis

In the present work the main flow techniques for the analysis and monitoring of several parameters of interest in the quality control of different types of waters are reviewed. Firstly, a review involving the advantages and disadvantages of flow techniques, from those currently out-dated, such as segmented flow analysis (SFA), to the most modern techniques, such as flow injection analysis (FIA), sequential injection analysis (SIA) and multi-commutation techniques (MCFA), is carried out. On the other hand, a new technique, the multi-syringe flow analysis (MSFA) is hereby described for the first time as both a fast and robust alternative. Its possibilities, limitations and potential advantages when using this technique either on its own or coupled to SIA, which carries out a previous sample handling, are outlined.

Potentiometric Stripping Analysis: A Review

Abstract A bibliographic review (150 references) on potentiometric stripping analysis (PSA) is performed. Theoretical, instrumental, analytical applications and advantages, and inferences of other modern PSA techniques are considered, like derivative PSA, constant-current PSA, multichannel potentiometric monitoring stripping analysis, differential PSA, constant-current enhanced PSA, derivative adsorptive PSA, kinetic PSA and reductive PSA. Implementation of PSA in flow systems is also considered, namely continuous-flow and flow-injection systems.

Evaluation of spectrophotometric methods for determination of orthophosphates by sequential injection analysis

Abstract Three methods for the determination of orthophosphate have been studied by using the same sequential injection analysis manifold, namely the vanadomolybdate, the Malachite Green and the molybdenum blue methods. The calibration graphs were linear up to 18.0, 0.4 and 4.0 mg P l −1 , respectively. Relative standard deviations and detection limits for vanadomolybdate, Malachite Green and molybdenum blue were 2.1%, 18% and 1.7% and 0.15, 0.01 and 0.01 mg P l −1 , respectively. The three methods were applied to the determination of phosphate in several water samples, both from natural and waste origin at a frequency of about 30 determinations per hour.

Monitoring of environmental parameters by sequential injection analysis

The use of sequential injection analysis (SIA), as applied to the control of environmental parameters, is reviewed. Its advantages and drawbacks are compared with those of flow injection analysis (FIA). FIA is simpler and easier to handle, has a higher sample throughput, and may be controlled manually, but SIA is more robust and versatile and better adapted for multiparametric and stopped flow techniques.

A new instrumental implementation of sequential injection analysis

The performance of a new system for sequential injection analysis equipped with a liquid driver constituted by an ordinary burette for conventional automatic titrations actuated by a stepper motor was assessed. The proposed system circumvents the high cost of conventional liquid drivers and the problems typically posed by highly absorbing chromogenic reagents, which provide a varying background in this technique.

Simultaneous spectrophotometric determination of calcium and magnesium in water

Abstract A method for the simultaneous spectrophotometric determination of calcium and magnesium based on the formation of their complexes with 4-(2-pyridylazo)resorcinol is proposed. The absorbance band yielded by the mixture was resolved by applying a computer multilinear regression program to the corrected, standardized spectrum of each metal ion as standard. The proposed method is straightforward and rapid and provides a linear determination range of 0.10–4.0 μg ml −1 for calcium and 0.15–2.5 μg ml −1 for magnesium. It was satisfactorily applied to the analysis of various types of water.

Solid phase extraction – Multisyringe flow injection system for the spectrophotometric determination of selenium with 2,3-diaminonaphthalene

In the present work, a solid phase extraction (SPE) is hyphenated with an automatic MSFIA system to improve the selenite determination based on the reaction of selenite with aromatic o-diamines (such as 2,3-diaminonaphthalene (DAN)) to form the piazselenol complex. This reaction is greatly influenced by acid concentration, temperature, the time needed for colour development, and presence of foreign ions. For these reasons a thermostatic bath, glycine, and Na(2)-EDTA are used as heater, buffer, and masking agent, respectively. The principle of the determination is based on the sorption of the piazselenol onto a C(18) membrane disk, followed by its elution by acetonitrile. The piazselenol can then be detected by absorptiometry or fluorometry, both detection techniques being tested in our system. The best detection limit (1.7 microg L(-1)) and RSD (3.04%) are obtained by absorptiometry at 380 nm. Environmental samples were spiked and analyzed, with recoveries close to 100%.

Simultaneous spectrophotometric determination of metal ions with 4-(pyridyl-2-azo)resorcinol (PAR)

SummaryA new method for the simultaneous determination of the divalent ions of cadmium, cobalt, copper, lead, manganese, nickel and zinc in binary, ternary and quaternary mixtures based on the application of a multiple linear regression programme to the spectra of the complexes of these ions with 4-(pyridyl-2-azo)resorcinol (PAR) was developed. The detection limits afforded by the proposed method range from 0.02 μg/ml for Co(II), Mn(II), Ni(II) and Zn(II) to 0.10 μg/ml for Pb(II). The method is rapid and quite simple as it entails no prior separation, and was successfully applied to the analysis for the above-mentioned ions in synthetic samples and real alloys.

Resolution of a multicomponent polycyclic aromatic hydrocarbon system in micellar media by linear variable angle fluorescence applying distinct chemometric techniques

The simultaneous spectrofluorimetric determination of aromatic polycyclic hydrocarbons of environmental interest, namely benzo[a]pyrene, benzo[e]pyrene, benzo[ghi]perylene, coronene, dibenzo[a,h]anthracene and indeno[1,2,3-cd]pyrene, in micellar media by using the non-ionic surfactant polyoxyethylene 10 lauryl ether (POLE) was investigated. In order to employ the highest sensitivity signals for the determination of each of the compounds in the mixture, the corresponding linear variable angle fluorescence spectra were recorded. Owing to the high spectral overlap observed, resolution of the multicomponent system was carried out by applying known algorithms such as multiple linear regression, partial least squares regression type 1 and artificial neural networks. The results obtained for both synthetic mixtures and water samples of two different origins spiked with known amounts of hydrocarbons of interest were satisfactory.

Multicomponent techniques in sequential injection

The application of multicomponent techniques in sequential injection analysis is considered. Such a scarcely selective chromogenic reagent as 4-(2-pyridylazo)resorcinol allowed the simultaneous spectrophotometric determination of Ca and Mg in environmental samples. The process was carried out in a fully automated fashion by using a personal microcomputer running software for instrumental control and data acquisition and processing. The ensuing method features a linear determination range of 1–20 and 2–40 mg l–1 for magnesium and calcium, respectively, and a sample throughput of 60 h–1. The results are compared with those provided by batch and flow injection methodology.