Quantification of the diagenesis-designating metals in sediments by ICP-MS: Comparison of different sample preparation methods.

Concentrations of specific metals in sediments are of immense importance in geochemical studies related to diagenetic processes, and quantification can be most reliably performed by ICP-MS after bringing the sample into solution. It is the latter analytical operation that generates a discord as no common sample preparation approach has been yet accepted. To resolve this challenge, we compared different modes of acidic sample digestion (in open and closed systems, applying in the latter case conventional or microwave heating) using a lake sediment reference sample. It was shown that the sample treatment in an autoclave with resistance heating provides the best fit (relative deviation < 7%) to certified values for metals generally used as diagenetic proxies (U, Sm, Nd, Th, La, Sc, Sr, etc.). Furthermore, the thermally convective pressure digestion appears to be more cost-efficient than microwave-assisted digestion (because of lower reagent consumption and cheaper removable PFE liners), an important asset for systematic geochemical mapping. In order to prove the applicability of the developed digestion procedure for different sediments, a marine sample from the East Siberian Sea was analyzed independently in two laboratories and across all representative metals the results acquired were found in good agreement.

Recent developments of capillary electrophoresis in seawater analysis.

Recent applications of capillary electrophoresis (CE) to the determination of various seawater analytes are critically examined, with the aim to reveal method's state-of-the-art and possible future research trends in the area. Given highly developed separation and detection methodology, emphasis is given to the most advantageous sample preconcentration strategies used to evolve the method's practical utility, particularly to low-level analytes. Analytical performance of CE applied to seawater analysis is illustrated with a selection of real-world applications published from 2006, from which it appears that the primary developmental tendency is presently confined to a transit from inorganic to organic seawater analytes.

What are the current analytical approaches for sediment analysis related to the study of diagenesis? Highlights from 2010 to 2018.

This review is aimed at critical analysis of current and emerging capabilities of analytical methods as employed for sediment analysis. An emphasis is given to the most reliable experimental strategies used to acquiring analytical information that is relevant to study the diagenetic processes affecting the composition of sediments. Advanced analytical methodology in use basically rely on the application of mass spectrometry (or a few alternative techniques) to determine various inorganic elements, to measure their isotopic composition, to characterize organic matter, or to identify and quantify its principle components (biomarkers). Also brought into focus are sample preparation techniques which - given the complexity of sediment matrices and the diverse and multiple nature of analytes under scrutiny - are often a key for successful analysis.

Speciation studies by capillary electrophoresis--distribution of rhodium(III) complexed forms in acidic media.

The feasibility of capillary electrophoresis for distinguishing between the rhodium(III) species occurring in different acidic environments has been demonstrated. The separation was optimum under acidic electrolyte conditions in which the complexed Rh species were at their most stable and the electroosmotic flow approached zero, thereby aiding resolution. Identification of the forms of Rh and estimation of their relative equilibrium content were accomplished by use of a diode-array detector. The distribution of the metal complexes was highly dependent on the nature and concentration of the acid and the age of the rhodium stock solutions. On dilution Rh(III) tends to be readily hydrolyzed, giving rise to a wider variety (and a varied distribution) of complexed forms. In 0.1 mol L(-1) HCl, four differently charged chloro complexes--RhCl4(H2O)2-, RhCl3(OH)(H2O)2-, RhCl3(H2O)3, and RhCl2(H2O)4+--were separated and identified. When a stock solution in 11 mol L(-1) HCl was run, Rh produced a major peak ascribed to RhCl6(3-) and two slowly migrating peaks from ions in which one or two of the chloride ligands were probably replaced by water and hydroxyl ion, as a result of hydrolysis. The aquatic cationic species were found to be predominant in HClO4 and HNO3 solutions, whereas only negatively charged forms of Rh(III) occurred in sulfuric acid. This speciation information opens also new possibilities of assessing the catalytic activity of Rh in kinetic reactions.

Analysis of highly saline samples by capillary zone electrophoresis: enhanced direct UV detection of inorganic anions using on-capillary preconcentration and clean-up techniques.

The ability to analyze samples with disparate levels of analyte and matrix ions is among the important benefits defining the practical utility of modern capillary electrophoresis. To compensate for the sensitivity limitations regarding trace-level inorganic anions, a number of on-line approaches that should offer an improved S/N ratio in direct UV detection were examined. The novel use of reversed pre-electrophoresis (at the applied voltage opposite to the separation voltage) made it possible to efficiently remove the most part of high chloride levels from the sample and hence to lower the background signal and to inject increased quantities of fast analyte anions. Specifically, by taking these advantages the sensitivity response of iodide was improved by a factor of 5 over normal CE mode. Using isotachophoretic sample stacking, a two-fold increase in detectability was obtained for moderately mobile anions, nitrate and nitrite, that corresponds to the minimum detectable concentrations close to their natural occurrences in seawater. Furthermore, field-amplified sample injection at increased electrolyte-to-sample matrix concentration ratios enabled the maximum S/N enhancement, with detection limits at the level of 10(-6) M and lower in the presence of > or = 5 x 10(4)-fold molar excess of chloride.

Recent progress in capillary electrophoresis of metal ions.

Advances in the fundamental studies and methodology of capillary electrophoresis (CE) as applied to metal ion analysis over the last two years are reviewed, with the objective of providing the interested reader with a state-of-the-art picture of technique's potentialities in the area. In particular, novel strategies for separation selectivity control and CE system innovations designed to enhance the detection sensitivity are described. In addition, a brief overview of the primary metal analytes and samples for which the technique appears to be best suited is given. The current limitations of the technique regarding most of all the implementation for routine use are considered along with the approaches on how they could be addressed. Finally, some pointers as to the likely trends in the future research are discussed.

Element speciation analysis by capillary electrophoresis.

An overview of recent developments in the application of capillary electrophoresis to simultaneous separation and determination of different chemical forms of an inorganic element is presented, with particular emphasis placed on metal speciation analysis. Examples of species analysis are addressed, covering metal ions in different oxidation states, metal complexes with inorganic and organic ligands, metalloid oxoanions, organometallic compounds, ionic non-metal species, etc. The speciation performance of capillary electrophoresis is illustrated by a number of practically relevant applications. The method's strengths and current limitations with regard to chemical speciation studies are critically discussed.

Advances in detection of inorganic ions in capillary electrophoresis.

Recent advances in capillary electrophoresis methodology to improve the detection sensitivity for inorganic ions are briefly reviewed. Specifically discussed are current developments of nonabsorbance-based CE detectors and on-capillary enrichment techniques as well as some possible future perspectives.

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI).

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.

Stability study of novel zinc complexes of pharmaceutical relevance by CE.

CE was used as a stability-indicating assay for zinc mixed-ligand complexes with promised biological activity. CE measurements indicated that Zn(RCOO)2Ln compounds (where R = H, CH3, C2H5, or C3H7; L = caffeine, nicotinic acid, thiourea, or phenazone; and n = 1 or 2) in water tend to decompose at room temperature. For thiourea and phenazone compounds, the degradation products (free zinc ion, carboxylate anion, and the corresponding neutral ligand) were found to increase within a few hours of storage in water. More stable complexes of caffeine and nicotinic acid showed no appreciable changes in CE behavior during the same period of time and only decomposed notably after 10 hr. The stability differences of zinc complexes were characterized in terms of apparent half-life values and rate constants of decomposition reaction. Relationships between the stability and structure of the complexes are discussed, and theoretical interpretation is presented.

Separation of metal ions by capillary electrophoresis: an understanding of the basic principles.

CE has received considerable attention as a highly promising technique for metal ion analysis. Significant advances in resolution have occurred when metal-complex formation is introduced into the separation system. A better understanding of the migration mechanism and the ionic or molecular properties that control the separation of free or complexed metal ions requires a universal approach to be developed for analyzing relationships between migration parameters and charge-to-size characteristics of metal species, whatever their chemical form, as well as electrophoretic system variables. To meet this demand, a number of migration models, which are based on a generally valid equation for electrophoretic mobility as a function of charge density, were derived and evaluated using numerous sets of experimental migration data taken from the literature or obtained in the author's laboratory. Consistent approximation results confirm the validity of generally observed mechanisms of CE in the case of partially complexed metal ions and precapillary-formed metal complexes. The modeling approach proposed also appears to provide reliable and convincing proof for the input of distinctive complexing interactions to separation selectivity in different CE systems.

High-performance liquid chromatography of metal chelates: Environmental and industrial trace metal control.

The methodological aspects of the use of HPLC in determination of metals in the form of their chelates are discussed. Rational schemes for the analysis of complex environmental and industrial samples are presented, including choice of chelating reagent, chelate preparation, metal concentration, separation method and detection method. Examples of the application of HPLC of metal chelates to environmental, production and quality control are presented.