Fast Interpretation Of 3D Liquid Chromatography Signals: Application To The Study Of Organic Matter In Wastewaters

Abstract

The aim of this work is to propose a very simple method for the selection and interpretation of the relevant individual spectra of a set of absorbance spectra, as for example in a 3D chromatogram. The method is based on the rank computation of the matrix of experimental values, after or during a chromatographic run. From a classical chromatographic system with a rapid scanning spectrophotometer (diode array detector for example), a computer is used for data acquisition of absorbances of the whole UV spectrum, and later computation. Firstly, acquisition is performed until the end of the elution and then the program gives the number and the corresponding spectra of relevant fractions. If another run is needed, for a different sample for example, the procedure makes it possible to check whether the detection signal is independent of the previous spectra. Different applications are presented for the study of organic matter in wastewaters by low pressure liquid chromatography.     

The Chemical Dehydrochlorination of Polyvinyl Chloride. A New Method for Polyenic Sequences Evaluation

Abstract

The chemical dehydrochlorination of polyvinyl chloride was studied in solution in tetrahydrofuran. The dehydrochlorinated products were characterized by their chlorine contents and by UV/visible spectroscopy. The absorption spectra of dehydrochlorinated PVC consist of a series of absorption maxima between 200 and 600 nm due to the formation of conjugated polyenic sequences. In this article we describe a new method for polyenic sequences evaluation based on deconvolution of the experimental spectrum. A comparison with the former technique usually employed is presented.     

A Study of Two Atomic Absorption Methods for the Determination of Sub-Microgram Amounts of Arsenic and Selenium

Abstract

Two atomic absorption accessory units were studied for the determination of arsenic and selenium in waters. One involves a flame mode while the other a flameless mode. Each was analyzed for requirements in speed per analyses, sample sizes required, potential interferences, coefficients of variation, and in overall ease in use.

Although the flameless mode could determine lower levels of arsenic and selenium than the flame mode, it was hampered by some severe interferences. Advantages of these accessories in their use over conventional wet chemical methods included: speed per analysis, elimination of time-consuming concentration steps, and elimination of using fragile equipment and noxious solvents.     

PE AND UV SPECTRA OF LINEAR AND CYCLIC POLYSILANES AND ASSIGNMENT BY AB INITIO CALCULATIONS

Abstract

Ab initio calculations have been performed on linear and cyclic polysilanes including permethylsubstituted compounds. Koopmans' approximation was used for assigning experimentally obtained PE and UV spectra. The PE spectrum of octamethylcyclotetrasilane and the UV spectra of cyclopenta and cyclohexasilane are presented for the first time.     

The Photo-Fenton Oxidation — A cheap and efficient wastewater treatment method

Advanced Oxidation Processes (AOPs) for wastewater treatment are gaining more importance since biological treatment plants are often not sufficient for highly contaminated or toxic wastewaters. In order to find out the most efficient and cheap AOP, investigations were concentrated on methods that can use sunlight. The systems TiO₂/UV, Fe²⁺/H₂O₂/UV (Photo-Fenton reaction), Fe²⁺/O₂/UV and Fe²⁺/O₃/UV were compared. Since the Photo-Fenton system was the most effective, pilot plant experiments with industrial wastewaters and sunlight experiments were carried out. Finally a rough cost estimate shows that Photo-Fenton treatment with sunlight is far cheaper than other available AOPs, namely ozonization.     

Multi-Residue Analysis by Liquid Chromatography-Mass Spectrometry Coupling. Application to Drinking and River Waters

Abstract

The coupling between liquid chromatography and mass spectrometry with an APCI or ESI interface (in positive or negative mode) is used here for multi-residue analyses in natural waters, covering basic and neutral pesticides as well as acid pesticides. The methods developed are applied to drinking and, river waters after the samples are concentrated by liquid-liquid extraction or solid phase extraction on C18 cartridges. Comparisons are made between UV detection and mass spectrometry and between two chromatographic methods for acid substances. The quantitation limits range from 0.01 to 0.1 μg/l according to the substance.     

Broad Spectrum Analysis of Ionic and Non-Ionic Organic Contaminants in Urban Wastewaters and Coastal Receiving Aquatic Systems

Abstract

A comprehensive analytical protocol for the qualitative and quantitative assessment of ionic and non-ionic organic contaminants in urban wastewaters, coastal seawater, and sediments is outlined. Liquid-liquid extraction (LLE) and adsorption onto polymers (polyurethane foam) or macroreticular resins (Amberlite, XAD-2) for the extraction of a wide variety of dissolved contaminants are evaluated. Organic extracts are resolved into fractions of increasing polarity by a combination of silica-alumina adsorption and gel permeation chromatography. HRGC-MS analysis of these fractions, using different ionization techniques, namely electron impact (EI), positive (PICI) and negative ion chemical (NICI) ionization, and the direct use of FAB-MS on the original extracts enabled the identification of a broad spectrum of anthropogenic compounds (290) in the different aquatic compartments. The decoupling of these contaminants between the water-dissolved and particulate phases is discussed.     

An alternative method for the measurement of mineral sulphide in wastewater

A simple and rapid procedure for sulphide measurement in crude oil refinery wastewater has been developed. This method is based on the knowledge of the UV response of sulphur compounds and the mathematical deconvolution of the sample spectrum using reference spectra (specific compounds or aggregate spectra). The detection limit of the method is 0.5 mg l(-1) for a quartz cell pathlength of 10 mm. The range is up to 15 mg l(-1). The method has been validated for crude oil refinery wastewater. Compared to conventional methods, the UV determination is quicker and easier to run.     

Determination of Creatinine in Plasma by the Apparent Content Curves Method

Summary

A mathematical method that avoids spectral interferences in creatinine determination in plasma by the Jaffé reaction is proposed. The experimental conditions are studied and the accuracy and precision of the method are tested against two reference methods. The proposed method provides good results and it is suitable for creatinine determination in plasma.     

Rapid Synergistic Extraction And Atomic Absorption Spectrometric Determination Of Iron In Environmental Samples Using Tributyl Phosphate And N-Phenyl-2-Furylacrylohydoroxamic Acid

Abstract

Iron (III) was rapidly extracted as its ternary complex with tributyl phosphate and N-phenly1-2-furylacrylohydroxamic acid (PFHA) from weakly acidic (pH 1.0-1.5) solutions into isobutyl methyl ketone and was determined atomic absorption spectrometrically. The method tolerated the presences of a large number of anions and cations commonly associated with iron, and was successfully tested with certified samples of coal fly ash, alloys, and plant tissues. It was also applied to the analysis of animal tissues, natural waters, and wastewaters; validating it by standard addition technique. PFHA was selected from nine new hydroxamic acids.     

Off-Line and On-Line Preconcentration Techniques for the Determination of Phenylureas in Freshwaters

Abstract

Phenylurea herbicides are analysed by reversed-phase liquid chromatography using UV detection at 244 nm after a concentration step in order to determine ppb or sub-ppb levels in drinking and river waters. With an average UV detection limit of 5 ng, a 500 ml sample volume is necessary to reach the 10 ppt level for spiked LC grade water samples and enables easy determination of concentrations below the ppb level for river water samples. Off-line and on-line methods are compared for the concentration step. Off-line concentration consists in a liquid sorption on n-octadecyl silica (C18) and elution by a suitable organic solvent. Polar phenylureas have low retention volumes on C18 silica and consequently the length of the concentration column has to be 10 cm to concentrate them at the ppb level from 100 ml of water and longer for lower levels of detection. Nevertheless, we show that increasing the size of the concentration column does not improve the limits of detection because of the numerous interferences also concentrated when percolating high volumes of water. On-line technology can be used only with short precolumns and requires a sorbent with a great retention for phenylureas. The copolymer-based PRP-1 is found to be an excellent sorbent and it is then possible to apply on-line precolumn technology with preconcentration through two precolumns (10 × 21 mm ID) in series, the first one being packed with C18 silica and the other with the PRP-1 polymer. Interfering compounds are then trapped onto the first precolumn acting as a filter and common phenylurea-breakthrough volumes on the PRP-1 precolumn are higher than 500 ml. Knowing the amounts preconcentrated on both precolumns and using UV and electrochemical detection help the identification of phenylureas in river water.     

Comparative Spectrophotometric,Spectrofluorometric, and High‐performance Liquid Chromatographic Study for the Quantitative Determination of the Binary Mixture Felodipine and Ramipril in Pharmaceutical Formulations

Abstract

Two‐component mixtures of felodipine (FLD) and ramipril (RMP) were assayed by derivative UV spectrophotometry, spectrofluorometry, and high performance liquid chromatography (HPLC). The spectrophotometric methods included a zero‐crossing first‐ and second‐order derivative procedure and a derivative compensation technique for the determination of binary mixtures with overlapping spectra. The spectrofluorometric method was based on first‐ and second‐order derivatives of the emission spectra (zero‐crossing point). Results from these methods were compared with those obtained by an exclusively developed isocratic reversed phase HPLC method. A reversed‐phase Adsorbosil DS analytical column, with methanol‐acetonitrile‐water (50∶30∶20, v/v) mobile phase at a flow rate of 1.5 ml/min, was used with a UV detector. The temperature was set at 25±0.2°C. Results obtained by the spectrophotometric and spectrofluorometric methods were comparable to those obtained by the HPLC method, as far as analysis of variance (ANOVA) test results were concerned. It is concluded that the developed methods are equally accurate, sensitive, and precise; with direct and simple application to pharmaceutical formulations of felodipine and ramipril combination, without interference from common pharmaceutical adjuvants.     

Comparison Of Analytical Techniques For The Determination Of Trace Elements In Rain Water

Abstract

Summary-Two methods for the determination of cadmium, copper and lead in EPA reference precipitation sample, corresponding to 1987, 1988, 1989 and 1990 BAPMoN Intercomparison Program, have been compared: graphite furnace atomic absorption spectroscopy (GFAAS) and anodic stripping voltametry (ASV). A relatively good agreement was found between the two techniques and with the reference values. The results for the analysis of Cl and F by spectrophotometry, Ca, Mg, Na, K and Zn by AAS, and Fe, Mn, Cu, Ni, Pb and Cd by GFAAS in the same sample, corresponding to 1988 and 1989, showed good agreement with the stated values. The results of Easter Island rain waters for the years 1990 and 1991 are presented.     

Spectrophotometric study of complex formation equilibria in the presence of interference using hard-soft net analyte signal method: application to drug-metal complexation

In this article, the ability of a new and efficient hard–soft method, previously proposed by our research group, is reported for modeling of the complex formation equilibria in the presence of interferences. This method is based on the net analyte signal (NAS) concept, which is a part of total signal that is directly related to the concentration of the component of interest. It monitors the concentration changes of any chemical species involved in the evolutionary process without requiring any pure spectra or having previous knowledge about the presence of the interferences. The proposed hard–soft method based on net analyte signal (HS-NAS) only needs a chemical model for one of the species involved in the reaction under study. The reliability of the method was examined by applying it to the measured data and spectrum of the known real systems of Fe²⁺–azithromycin and Ca²⁺–tetracycline.     

A new quantitative and low-cost determination method of nitrate in vegetables, based on deconvolution of UV spectra

A new UV-spectrophotometric method for the determination of nitrate in vegetables is presented. The method is based on the spectral deconvolution: UV spectrum of a sample is considered as a linear combination of absorption spectra, named reference spectra. The combination of a small number of spectra of reference allows to reconstitute the shape of UV spectrum of an unknown sample. There have been several fresh vegetables (lettuce, curly lettuce, oak-leaf lettuce), as well as frozen spinaches that have been tested. The results obtained were comparable to those obtained with the reference HPLC method (official European reference method for the determination of nitrate in foodstuffs). The nitrate content varied from 377 to 3240 mg kg⁻¹ of fresh vegetables, and 545 to 1190 mg kg⁻¹ of frozen spinach. The recovery of added nitrate ranged from 91 to 99%. The results were obtained with a laboratory spectrophotometer and also with a dedicated field-type spectrophotometer. This method does not require almost any consumable, is quantitative and very fast reading with easy and low maintenance.     

Wine Phenolics: Optimization Of HPLC Analysis

Abstract

Without previous extraction wine phenolics could be analysed by RP-HPLC via direct injection of the wine samples into the column. In order to optimize the analytical procedure the results obtained with two different columns of slightly different polarity and three different gradient elution systems have been compared.

The separated phenolics were further tentatively identified by means of their retention times and UV spectra which were recorded with a Photodiode Array detector     

A new phenanthropyran and a new biphenanthrene from the rhizomes of Dioscorea septemloba and their antioxidant activities

Abstract

A new phenanthropyran, dioscorone B (1), and a new phenanthrene (2), together with seven known compounds (3–9), were isolated from the 75% ethanol extract of Dioscorea septemloba rhizomes. The chemical structures of these compounds were elucidated by comprehensive spectroscopic methods including NMR, HRESIMS, IR, and UV spectra. Compounds 1–5 were first isolated from genus Dioscorea. The proton and carbon chemical shifts of compounds 1–9 were unambiguously assigned based on the 1D-NMR and 2D-NMR data. Compounds 1–5 and 8–9 were first tested for their antioxidant activities. Compounds 1 and 2 showed excellent activities with IC₅₀ values of 0.07?±?0.10?μM and 0.13?±?0.09?μM, respectively.     

The Assembling and Application of an Automated Segmented Flow Analyzer for the Determination of Dissolved Organic Carbon Based on UV‐Persulphate Oxidation

Abstract

A simple and reliable methodology developed on an automated segmented flow analyzer has been implemented for the determination of organic forms of carbon in aqueous solutions. Conversion of dissolved organic matter to carbon dioxide is performed by a UV‐persulphate oxidation. After oxidation, the concentration of carbon dioxide in the sample induces a change in pH that will alter the color intensity of a phenolphthalein solution. The color intensity of the solution is measured automatically by colorimetry. Caffeine and acid ascorbic were tested in order to assess the accuracy of the analytical methodology. Reproducibility tests demonstrated a very good precision for natural waters and for organic compounds. Salinity changes showed no interferences, which suggests how appropriate this methodology is for routine analysis and how useful and convenient it is for shipboard work on ocean and estuarine research.     

Preparation and Identification of a New [Cr2(NTA)2(μ-OH2)]·2H2O Complex

[Cr₂(NTA)₂(μ-OH₂)]·2H₂O is prepared by heating nitrilotriacetic acid (H₃NTA) with an aqueous suspension of freshly precipitated Cr₂O₃·nH₂O. Elemental analysis, IR spectra, UV/vis spectra, X-ray diffraction, thermogravimetric analysis, mass spectra and magnetic susceptibility measurements suggest the existence of a Cr-Cr bond. One of the three water molecules acts as a bridging ligand (μ-H₂O) while the other two are waters of crystallization.