Development Of Preconcentration Techniques For Highly Sensitive Metal Analysis Of Water By Molecular Spectroscopy

This thesis is focused on the development of preconcentration techniques for highly sensitive metal analysis of water by molecular spectroscopy. The developed fluidized bed enrichment and colorimetric-solid phase extraction, preconcentration techniques were successfully coupled with near-infrared spectroscopy and spectrophotometry.A fluidized bed enrichment and on-line determination of trace copper in water with near infrared spectroscopy (NIRS) method was developed. The method uses large volume solutions of the analyte for enrichment on the chelating resin D401in a home-made device called fluidized bed enrichment device and then measures spectra of the preconcentrated analyte with diffuse reflectance near infrared spectroscopy (DR-NIRS). The device is able to enrich enough amount of analyte within a short time.40copper aqueous solutions in the concentration range of0.5-4.4μg mL-1were treated with the enrichment device to measure NIR spectra in the spectral region of900-1700nm. The spectra were pretreated with multiplicative scatter correction (MSC) and then were used to build partial least squares (PLS) model with leave-one-out cross validation. Root mean square error of cross validation (RMSECV) was0.2381μg mL-1at PLS factor of5. An independent test set containing five samples was used to assess the model. The relative errors of the five samples were from0.62%to6.06%and the mean relative error (MRE) was2.51%.With a developed on-line fluidized bed enrichment technique, trace Cu2+, Co2+and Ni2+in water was concentrated and determined simultaneously by NIRS directly without any procedure of elution for enriched metal ions. The quantitative analysis is achieved by using multivariate calibration, such as PLS. Sensitivity and accuracy have been improved significantly because large volume mixture solutions were used in the enrichment and on-line measurement of NIR spectra was utilized. The MRE for the Cu2+, Co2+and Ni2+being6.56%,8.70%and10.27%, respectively. RMSECV for the Cu2+,Co2+and Ni2+were0.2924,0.4136and0.3569μg mL-1, respectively. This technique offered a considerable saving of time and money in comparison to the standard techniques of analysis. From the results shown in this work, it can be concluded that NIRS coupled with fluidized bed enrichment has a potential application in the simultaneous determination of trace inorganic elements with comparatively low errors.A simple, sensitive and selective method for the spectrophotometric determination of Ni2+in water samples was developed. The analyte ions were collected on a membrane filter in the form of its red complex with1-(2-pyridylazo)-2-naphthol (PAN), and the absorption spectra of the colored membrane filters were acquired. This preconcentration technique is called colorimetric-solid phase extraction (C-SPE). Effects of pH value, sample volume, and amount of PAN were examined in order to optimize sensitivity. The interference by common other ions was eliminated using appropriate masking agents. The absorbance is linearly related to the concentration of Ni2+in the ranges from0.3-1.5μg L-1, and from2-10μg L-1, respectively, the correlation coefficients (R2) being0.9871and0.9954. Under the optimal conditions, the detection limit is0.1μg L-1. The recoveries in case of spiked samples are between95.0and101.5%, and the relative standard deviations (RSD) range from2.8%to4.1%.As a next step, the developed C-SPE method was applied for the simultaneous determination of trace amounts of Ni, Co and Zn using partial least squares regression (PLS). Nickel, cobalt and zinc are metals that appear together in many samples so their simultaneous determination is very important. In this work, we tried to use the colorimetric-solid-phase extraction (C-SPE) coupled with partial least squares regression for the simultaneous determination of Ni2+, Co2+and Zn2+in water samples after complexation of these metal ions with1-(2-pyridylazo)-2-naphthol (PAN) and then membrane filtration. Under the optimized conditions, the results of individual calibration of every metal ion were very good with high coefficient correlations. But results of the simultaneous determinations showed that there are some serious problems in the experiment as its giving very large errors (above20%) for the analyte metal ions. It is clear that additional insight into the complicated processes associated with reaction of metals with PAN, is needed to resolve the issues of very large errors.