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This study investigated sediments quality in coastal-urban rivers of Dar es Salaam, Tanzania along the Indian Ocean coast, that are strongly influenced by human activities. Sediment samples were seasonally collected from fifteen sites and one control location, treated as appropriate, and analyzed by high-resolution inductively coupled plasma mass spectrometer for Cd, Sn, Pb, Cr, Co, Ni, Cu, Al, Mn, Fe, and Zn. Concentrations ranged from 0.06 (Cd) to 92,479 (Al) mg/kg dry weight. Levels were higher during dry season than wet season. Cd, Sn, Pb, Co, Cr, and Zn were enriched in > 50% of the sites. Comparison with risk-based regulatory sediment quality thresholds depicted considerable ecological risk in > 70% of the sites. Evaluation by sediment quality indices identified two hotspots that require intervention. The highest contributors to the Risk Index were Pb and Cd (> 60%). These findings indicate risks to human health and river ecology that call for measures to protect the rivers from further contamination.

The aim of this study was to propose a Process Analytical Technology (PAT) strategy for the quantitative in-line monitoring of an aqueous pharmaceutical suspension using Raman spectroscopy. A screening design was used to study the significance of process variables (mixing speed and height of the stirrer in the reactor) and of formulation variables (concentration of the active pharmaceutical ingredient (API) ibuprofen and the viscosity enhancer (xanthan gum)) on the time required to homogenize an aqueous pharmaceutical model suspension as response variable. Ibuprofen concentration (10% and 15% (w/v)) and the height of stirrer (position 1 and 2) were discrete variables, whereas the viscosity enhancer (concentration range: 1–2 g L−1) and the mixing speed (700–1000 rpm) were continuous variables. Next, a multilevel full factorial design was applied to study the effect of the remaining significant variables upon the homogenization process and to establish the optimum conditions for the process. Interactions between these variables were investigated as well. During each design experiment, the conformity index (CI) method was used to monitor homogeneity of the suspension mixing system in real-time using Raman spectroscopy in combination with a fibre optical immersion probe. Finally, a principal component regression (PCR) model was developed and evaluated to perform quantitative real-time and in-line measurements of the API during the mixing process. The experimental design results showed that the suspension homogenization process is an irregular process, for which it is impossible to model the studied variables upon the measured response variable. However, applying the PCR model it is possible to predict in-line and real-time the concentration of the API in a suspension during a mixing process. In this study, it is shown that Raman spectroscopy is a suitable PAT tool for the control of the homogenization process of an aqueous suspension. Raman spectroscopy not only allowed real-time monitoring of the homogeneity of the suspension, but also helped (in combination with experimental design) to understand the process. Further, the technique allowed real-time and in-line quantification of the API during the mixing process.

The obvious toxicity of cadmium and lead is at the basis of compulsory concentration determinations for lixiviation solutions of ceramic and earthenware household receptacles such as cups, plates, bowls and others. Concentrations in the food simulant which exceed 0.100 ± 0.005mg Cd dm-2 and 1.00 ± 0.05 mg Pb dm-2 for flat receptacles, 0.500± 0.025 mg Cd l-1 and 5.00± 0.25 mg Pb l-1 for low volume (< 5 l) receptacles and 0.250 ± 0.025 mg Cd l-1 and 2.50 ± 0.25 mg Pb l-1 for high volume (> 5 l) receptacles are not acceptable and measures were taken by the EU member state authorities to enforce these norm concentrations. Generally, the uncertainty on the results forwarded by the legislation amounts to 5%. This value does not at all match the pronounced variability observed for several 'identical' trade samples, but rather represents the inherent variability of spectrometric analyses alone. Considering that the coefficients of variation can be as high as ~30%, either the ranges of acceptable concentrations or the maximal allowable concentrations should be corrected. Aware of the negative health e? ects of heavy metal contamination and of the risk increase due to dietary intake, a downward adjustment of the acceptable concentration ranges to 0.07mg Cd dm-2 ± 12%, 0.30mg Cd l-1 ± 12% and 0.10 mg Cd l-1 ± 12% and to 0.8mg Pb.

Several chemiluminescence‐based reactions are applicable to the determination of various bio‐pharmaceutically important analytes, and they can be applied for monitoring chemiluminescence emission using flow injection, liquid chromatographic and capillary electrophoretic analysis, as well as for the development of chemiluminescence‐based sensors or in immunoassays. As in general the emission intensity is linearly proportional to the concentration of any of the reagents, the technique allows the analysis of different species involved in the light‐producing reaction, amongst which are the chemiluminescent reagent, oxidants, inhibitors, cofactors, catalysts, some fluorophore, etc. The present overview illustrates some important applications of the last decade on this rather unfamiliar luminescence technique to detectional challenges in the liquid phase. The required instrumentation is limited as no external light source is needed. Also, the technique opens perspectives for increasing detection sensitivity in miniaturized flowing streams. On the other hand, several drawbacks still limit full application, eg dependence of the emission signal upon a number of environmental factors forcing the analyst to make a compromise between separating and measuring conditions, a lack of selectivity in specific cases, the critical detection of the signal at strictly defined periods, especially in the case of sharp emission vs time profiles, and the development of detection devices in capillary electrophoresis. Copyright © 2000 John Wiley & Sons, Ltd.

Several chemiluminescence-based reactions are applicable to the determination of various bio-pharmaceutically important analytes, and they can be applied for monitoring chemiluminescence emission using flow injection, liquid chromatographic and capillary electrophoretic analysis, as well as for the development of chemiluminescence-based sensors or in immunoassays. As in general the emission intensity is linearly proportional to the concentration of any of the reagents, the technique allows the analysis of different species involved in the light-producing reaction, amongst which are the chemiluminescent reagent, oxidants, inhibitors, cofactors, catalysts, some fluorophore, etc. The present overview illustrates some important applications of the last decade on this rather unfamiliar luminescence technique to detectional challenges in the liquid phase. The required instrumentation is limited as no external light source is needed. Also, the technique opens perspectives for increasing detection sensitivity in miniaturized flowing streams. On the other hand, several drawbacks still limit full application, eg dependence of the emission signal upon a number of environmental factors forcing the analyst to make a compromise between separating and measuring conditions, a lack of selectivity in specific cases, the critical detection of the signal at strictly defined periods, especially in the case of sharp emission vs time profiles, and the development of detection devices in capillary electrophoresis. Copyright © 2000 John Wiley & Sons, Ltd.

Making up part of the unique family of restricted access materials (RAM) the Lichrospher ADS (alkyl-diol silica) sorbents have been developed as special packing materials for precolumns used for LC-integrated sample processing of biofluids. The advantage of such phases consists of direct injection of untreated biological fluids without sample clean-up and elimination of the protein matrix together with an on-column enrichment. The plasma samples, with internal standard phenacetin added (not essential), were brought onto the precolumn (C-18 ADS, 25 µm, 25 × 4 mm i.d.) using a phosphate buffer, 0.1 M, pH 7.0. After washing with the buffer, the ADS column was backflushed with the mobile phase phosphate buffer 0.05 M pH 7.0: acetonitrile (80:20), thus transporting the analytes onto a reversed-phase column Ecocart 125-3 HPLC cartridge with a LiChrocart 4–4 guard column, both packed with LiChrospher 5 µm 100 RP-18; after separation detection was performed in UV at 260 nm. Essential features of the method include the novel precolumn packing, the absence of sample pretreatment, a quantitave recovery, good precision and accuracy, as well as a considerable reduction of analysis time compared to conventional manual methods applied in bioavailability studies. Copyright © 1999 John Wiley & Sons, Ltd.

Making up part of the unique family of restricted access materials (RAM) the Lichrospher ADS (alkyl‐diol silica) sorbents have been developed as special packing materials for precolumns used for LC‐integrated sample processing of biofluids. The advantage of such phases consists of direct injection of untreated biological fluids without sample clean‐up and elimination of the protein matrix together with an on‐column enrichment. The plasma samples, with internal standard phenacetin added (not essential), were brought onto the precolumn (C‐18 ADS, 25 µm, 25 × 4 mm i.d.) using a phosphate buffer, 0.1 M, pH 7.0. After washing with the buffer, the ADS column was backflushed with the mobile phase phosphate buffer 0.05 MpH 7.0: acetonitrile (80:20), thus transporting the analytes onto a reversed‐phase column Ecocart 125‐3 HPLC cartridge with a LiChrocart 4–4 guard column, both packed with LiChrospher 5 µm 100 RP‐18; after separation detection was performed in UV at 260 nm. Essential features of the method include the novel precolumn packing, the absence of sample pretreatment, a quantitave recovery, good precision and accuracy, as well as a considerable reduction of analysis time compared to conventional manual methods applied in bioavailability studies. Copyright © 1999 John Wiley & Sons, Ltd.

Abstract: Striking differences were observed in the use of the electron acceptors involved in the degradation of organic matter by heterotrophic bacterial activity between a muddy and a sandy sediment on the same tidal flat of the Scheldt estuary. These bio-reduction reactions could have a quite different effect on the cycling of trace metals in the sediment as suggested by the results of the mobilization experiments. Trace metal speciation can be described as a function of the redox potential, in view of the fact that the latter is related to the heterotrophic bacterial activity.

Abstract: Different approaches, such as element analyses of the bulk sediment and of the fine sediment fraction (<63 μm), sequential extraction techniques, correlation coefficient, and enrichment factor calculations, clearly demonstrate the differences in geochemical behavior of a muddy and a sandy sediment on the same tidal flat in the Scheldt estuary (Belgium). The geochemical processes in combination with the relatively large transport mobility of dissolved compounds due to the tidal action in the sediment, created compound specific vertical distribution profiles.

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The storage behaviour of mercurychloride and methylmercury chloride solutions in deionized water and in seawater stored in polyethylene (PE), pyrex glass and teflon (PTFE) containers at various concentration levels (4 ppb, 50 ppt, natural seawater concentrations) was studied using various preservatives and container pretreament procedures. For PE bottles, the best results are obtained, after pretreatment of the bottles with an acidified KMnO4 solution, with a 0.05% (v/v) H2SO4+0.02% (w/v) KMnO4 preservative. However, the solution becomes heterogeneous rather fast, due to the formation of a MnO2 precipitate. Acidified (pH 1 with HNO3) deionized or seawater samples stored in pyrex glass BOD-bottles (analyses are carried out in these bottles too) or teflon containers are stable with respect to inorganic mercury for at least 1 month. Instead of acidification an oxidant such as BrCl can also be used to stabilize the solution. Methylmercury solutions (80 ppt) in deionized water (pH 6) and stored in teflon containers are stable for at least 1 month. In glass bottles, the solution should be acidified to pH 1. Methylmercury seems to be unstable in acidified seawater samples (pH 1 with HNO3); after 2 weeks about 60% of the methylmercury is converted into inorganic mercury.

Abstract: A sampling and measuring device which enables the assessment of atmospheric particulate and gaseous mercury concentrations has been tested on Mount Etna Volcano. Particulate matter is collected on a Whatman GF/C of 1.0 m pore-size, gaseous mercury species on a Au-column. The analysis is carried out in two steps: (1) the mercury species collected on the filter or the Au-column are transferred to a fixed analytical Au-column; (2) mercury liberated from this column during the second step is detected with a Mercury Vapour Monitor. Average concentrations of gaseous and particulate mercury in ambient sampling sites on Mount Etna are 3.8 ng m−3 and 0.49 ng m−3 respectively. Average concentrations of gaseous and particulate mercury in the plume of Bocca Nuova on Mount Etna are 15 ng m−3 and 24 ng m−3 respectively. An estimation of the total mercury discharge from Mount Etna amounts to 2.5 10−2 tons day−1.

Summary: A newly developed reversed-phase chiral stationary phase, cellulose tris(4-methylbenzoate), known as Chiralcel OJ-R, has been successfully applied to the direct resolution of the enantiomers of several nonsteroidal anti-inflammatory drugs belonging to the profen group. Among the five barbituric acids tested, the chiral resolution of mephobarbital is especially high. The Chiralcel OJ-R column also proved quite efficient for the enantiomeric resolution of a few representatives of the benzodiazepine group.Variations of mobile phase conditions based on acetonitrile and/or methanol were tested. The results obtained are briefly compared with separations performed using a Chiralcel OJ column under normalphase conditions.

Summary: α-, β- and γ-cyclodextrins, Triton X-100 and n-alkanes (octadecane, paraffin, dodecane, and related compounds) used as dipping enhancers for the HPTLC densitometry of SBD-glutathione may lower the detection limits by a factor of about 2.

Abstract: The behaviour of copper and zinc in the Scheldt estuary, both in the particulate and the dissolved phase, is discussed for the period 1982–1983. The longitudinal particulate copper and zinc profiles fall below the dilution line, which is attributed to mixing and mobilization processes. In the dissolved phase both metals show a production region in the end member of the estuary, for copper a pronounced mid estuarine maximum is observed. Study of the metal speciation suggested that organic ligands might keep heavy metals in solution, especially in area of intensive production, and promote the subsequent export of these metals downstream the estuary.

Abstract: Sediments were sampled on the ‘Groot Buitenschoor’, an intertidal flat located at about 60 km from the Scheldt's river mouth. Hg concentrations ranged from 30 to 1756 ng g−1. The concentrations were strongly correlated with fine grain fraction, organic matter content and sulphide concentrations. Incubation experiments were performed in order to determine the potential methylation rate of Hg as well as biotic and abiotic factors influencing this transformation. About 1 to 2% of the added inorganic Hg is converted into methylmercury. This conversion rate points to the same equilibrium ratio as was observed in natural sediments, indicating an equilibrium between methylation and demethylation reactions in the sediments. Incubation of a sterilised sediment sample significantly decreased the methylation rate, but the methylmercury concentrations observed are still ten times higher than the natural (unspiked) sediment. This result could be due to a chemical (non-enzymatic) methylation of mercury. Sulphate reducing bacteria are the main species responsible for the methylation of Hg at this site. Addition of Na2MoO4, a specific inhibitor of sulphate reducing bacteria, decreased the methylation rate to the abiotic level (sterilised sediment). High sulphate reduction rates, however, lead to lower methylation rates. Increased formation of sulphides due to microbial sulphate reduction leads to enhanced HgS formation and this reaction competes with the methylation process. HgS is in fact the major product formed by the reaction of sulphate reducing bacteria with Hg species. About 50% of the Hg spiked to the sediments is transformed into HgS during the incubation experiments, and that compound is practically unavailable for methylation in contrast to other bound forms of Hg.

From the three commercially available bimanes, monobromobimane (Thiolyte MB) can be easily used as a fluorescence label for various biomedically important thiols such as acetylcysteine. The optimum reaction conditions for the chemical derivatization reaction applied to acetylcysteine, the reversed-phase chromatographic system and the precautions to be taken for obtaining reproducible analytical data are outlined. RP-18 HPLC occurs using aqueous acetic acid-acetone mixtures with a fluorescence detector installed at 380 nm and 470 nm as excitation and emission wavelengths, respectively. Penicillamine is used as an internal standard, and cysteine and homocysteine can be determined with the same system. Picogram sensitivities can be reached and the influence of potent reducing agents such as sodium borohydride, tributylphosphine and dithioerythritol is discussed. The suggested method allows a specific and sensitive estimation of the mucolytic acetylcysteine in the presence of its disulfide oxidation products in various pharmaceutical formulations.

In the chemical reaction of phenylglycidyl ether with glutathione, NMR analysis showed that the major product of nucleophilic attack of the thiol group of glutathione was at the least substituted carbon of the epoxide yielding the normal product. An analytical reversed phase HPLC system indicated that this reaction was regioselective with a ratio of 92-8 for the normal vs the abnormal product (attack at the more substituted epoxide carbon). This HPLC method shows promise for following the glutathione transferase and hydratase detoxification of the phenylglycidyl ethers. The S-9 rat liver homogenate detoxification of the phenylglycidyl ether per se was regiospecific yielding only the normal main reaction product of the chemical reaction and a minor amount of phenoxy-propanediol.

The determination of total Hg in various environmental matrices was investigated using energy-dispersive x-ray fluorescence (EDXRF) spectrometry on both powdered and digested samples and cold vapor atomic absorption spectrometry (CV-AAS) on digested samples. Several microwave decomposition procedures were evaluated. The use of different acid mixtures, microwave power settings and decomposition times were compared, in addition to the analysis of wet and freeze dried samples. A set of standard reference samples were used to evaluate the procedures. An H2SO4–HNO3–H2O2 mixture was found to be optimal for the complete mineralization and digestion of biological samples for Hg by CV-AAS, whereas for EDXRF both HNO3–H2O2 and H2SO4–HNO3–H2O2 mixtures gave good results. The detection limit of EDXRF could be significantly decreased (from 0.2 μg g^-1 to 0.058 μg g^-1) by performing the analysis on digested samples. Good agreement was obtained between the EDXRF and CV-AAS analysis. The results were also in good agreement with certified values. The methods were applied to environmental samples (coal, vegetation, fish and sediment) and human hair in a coal mining area and in locations where coal is used for cooking in Vietnam. © 1998 John Wiley & Sons, Ltd.

Steady-state fluorimetric pH titrations of three fluorescent indicators of differing charge-type were carried out in aqueous methanol solutions containing up to 64 mol% methanol. The plot of the ratio of the relative fluorescence efficiency of the indicator acid to that of its conjugate base versus the product of the formal hydrogen ion concentration and the appropriate Bronsted kinetic activity factor gives straight lines for titrations in each mixed solvent, just as it does in water, but only if the constant terms in the Bronsted factor are modified to account for the bulk dielectric constant in each solvent. The product of the formal charges on the proton and the particular conjugate base studied in each titration must also be included in the Bronsted factor. This supports the hypothesis that a valid operational pH can be defined and kinetic parameters related to proton transfer can be extracted from the fluorimetric titrations in mixed solvents.

A microbore LC system applying native fluorescence detection is described for analysis of the nonsteroidal antiinflammatory agents diclofenac and naproxen in pharmaceutical preparations, allowing the visualization of some diclofenac decomposition products. The suggested system is practical and specific and offers detection limits of 0.2 ?g ml-1 for diclofenac and of 1 pg ml-1 for naproxen (solutions to be injected). Moreover, the solvent consumption is reduced by a 10-fold factor compared to the classical HPLC setup.

Two cellulose-based chiral stationary phases were compared on their feasibility to resolve a representative number of 2-arylpropionic acids : a new experimental phase (Tolylcellulose, EXP B101) manufactured by Bio-Rad RSL and the Chiralcel OJ phase by Daicel. Both columns were tested under normal phase conditions, applying a n-hexane:isopropanol mobile phase. The Bio-Rad column was also assayed under reversed phase conditions using a methanol and perchlorate buffer system. Enantiomeric separation without prior derivatization of most 2-arylpropionic acids was far better on the Chiralcel OJ column than on the Bio-Rad column, the latter performing somewhat better under reversed phase conditions. Prior derivatization of the carboxylic acid group with an amine (naphthylmethylamine, (2-methyl)benzylamine) or an alcohol (benzylalcohol) permitted to separate the tested drugs to different extents on both columns.

The influence of reducing agents (sodium borohydride, tributylphosphine, dithioerythritol and dithiothreitol) on the conversion of disulfides into their parent thiols, with specific application to cysteine was investigated. Dithioerythritol and dithiothreitol were found to be most suitable for this reaction. A contact time of one hour at room temperature provided quantitative reduction as tested using cystine as a pure disulfide standard. A modified fluorescence labelling procedure with monobromobimane followed by reversed-phase HPLC allows quantitation of the parent thiol and the disulfide content when completing the labelling reaction with and without preliminary treatment with reducing agent. The effects of various bimane reducing agent ratios on the yield of the reaction are discussed. Precautions should be taken when dealing with complex matrices with respect to reagent concentrations and ratios.

To realize chlorophyll a analysis, a method is proposed that combines the sensitivity of fluorimetric determinations and the inherent selectivity and accuracy of chromatographic separations. A partial application of the overlapping resolution mapping (O.R.M.) method led to the use of a methanol:acetone:water (75:22:3, v/v) mixture for the isocratic separation by high pressure liquid chromatography on a reserved phase C-18 column of at least sixteen chloropigments and degradation products in a natural extract.Ten replicate measurements of a 50μg. 1-1 standard showed a reproducibility of 3%, while a detection limit of 84 pg chlorophyll a was estimated.

A large number of mono-, bi- and tricyclic amines and alcohols were used for the derivatization of six 2-arylpropionic acids. The effect of the bonded aromatic portion on the enantiomeric separation using a tris(4-methylbenzoate)cellulose column was studied. Small modifications of the bonded groups close to the chiral centre pointed out their predominant steric effect to the chiral recognition process rather than electronic influence. Varying ratios of methanol and perchlorate buffer composing the mobile phase were applied to elute the different series within comparable analysis times.

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