Salt Matrix Research Articles

Spectral interpretation and interference correction in inductively coupled plasma mass spectrometry

To tackle the several problematic polyatomic interferences in inductively coupled plasma mass spectrometry (ICP-MS), we have developed a software approach based on data reduction of the measured total mass spectrum through multicomponent analysis (MCA). The approach leans on a working knowledge of interferents that are likely to be encountered in a sample matrix, which composition is known by virtue of the total mass spectrum and knowledge of applied solvents. The full isotopic patterns for all elements and expected interferents are used in the modelling MCA matrix of 250 masses × 105 species at maximum. Polyatomic abundances are calculated by the software. Since all species are modelled fundamentally through their known natural abundances, the MCA matrix can be manipulated and reprocessed until interpretation of the mass spectrum and, hence, interference correction are optimal. The optimum is attained by use of the bar graph and calculation modes of the PC software and criteria for properly found isotopic patterns. With optimized models stored in the data base, the user may routinely process samples in one go, and operate the ICP-MS system in a true all-element mode. Use of elemental equations or measurement of large multivariate calibration sets and pure component solutions are superfluous. Data reduction is solely based on the information about the isotopic patterns, present in the measured mass spectrum itself. As a result, in the case of interferences, detection limits may be lowered by one to two orders of magnitude. The approach is illustrated with an industrial example of Hf determined in NdFeB, and with an environmental example. Here, a suite of elements over the 50–82 amu mass range has been determined in different salt matrices in ground water.

Selective flow injection sorbent extraction for determination of cadmium, copper and lead in biological and environmental samples by graphite furnace atomic absorption spectrometry

A flow injection sorbent extraction system was developed for determination of trace and ultratrace cadmium, copper and lead in biological and environmental standard reference materials by graphite furnace atomic absorption spectrometry (GFAAS). Using ammonium diethyldithiophosphate (DDPA) as complexing agent with citrate as masking agent at pH 2, the analytes were selectively preconcentrated with effective removal of the matrixes including the salt matrix in saline water and the other high-content heavy metals in digested biological and geological samples. The two-second eluate containing most of the analyte complexes was collected for the GFAAS measurement. All analytical results obtained were in good agreement with the certified values. Enrichment factors of 12, 13 and 13 compared with 20 μl direct injection of aqueous solution and detection limits (3σ) of 0.003, 0.05 and 0.04 μg l −1 for cadmium, copper and lead respectively, could be obtained with 20-s sample loading at 8.7 ml min −1 for sorbent extraction and 20 μl eluate injection for peak area measurement. The relative standard deviation at 0.1 μg l −1 cadmium, 1 μg l −1 copper or 3 μg l −1 lead was around 2%.

Reference materials for quality assurance in sea-water analysis: performance of total-reflection X-ray fluorescence in the intercomparison and certification stages

The certification of a sea-water reference material (CRM 403) was completed by the Community Bureau of Reference (BCR) of the Commission of the European Communities during an intercomparison exercise in which we were participants along with other highly experienced laboratories, who, beforehand, had given evidence of outstanding performance. Further, we participated in a feasibility study on estuarine water. In both studies we used total-reflection X-ray fluorescence analysis (TXRF) for the determination of V, Mn, Fe, Co, Ni, Cu, Zn, Pb and U on the nmol kg level. The enrichment of the trace metals and the separation from the salt matrix were performed by complexation with sodium dibenzyldithiocarbamate and reverse-phase chromatography. In this paper, the high performance of our TXRF results is compared to other analytical techniques like voltammetric and atomic absorption methods.

Trace metal determinations by total-reflection X-ray fluorescence analysis in the open Atlantic Ocean

The Intergovernmental Oceanographic Commission (IOC), as a major component of its programme “Global Investigation of Pollution in the Marine Environment” (GIPME), maintains a long-standing project on “Open Ocean Baseline Studies of Trace Contaminants”. Initially, the Atlantic Ocean and trace metals were selected. A first cruise with the RV Meteor to the eastern parts of the south and north Atlantic Ocean was successfully organized, in March and April 1990, from Cape Town (South Africa) to Funchal (Madeira, Portugal). Thirteen scientists from laboratories in Europe and North America participated with the first author as coordinator. Four deep-water stations in the Cape Basin, Angola Basin, Cape Verde Abyssal Plain and Seine Abyssal Plain were regularly sampled for at least 36 depths. Additional samples were taken between stations. Samples were distributed to participants and a similar number of additional laboratories. As a central part of our own contribution to the project, we determined the trace heavy metals manganese, nickel, copper, zinc and lead and the lighter selenium by total-reflection X-ray fluorescence analysis. Additional methods applied, inter alia, were anodic stripping voltammetry for lead and cadmium and graphite furnace atomic absorption spectrometry (GFAAS) for cadmium, using two different extraction procedures. For the TXRF, the pre-enrichment of the trace metals and the separation from the salt matrix were performed by complexation with sodium dibenzyldithiocarbamate and reverse-phase chromatography. Generally, very low levels of trace elements were found in filtered and unaltered water samples from these remote areas of the open Atlantic Ocean. Typical examples of the distributions of trace metal concentrations on depth profiles from the four deep-water stations as well as intercomparisons between the stations are presented.

Hydrothermally synthesized aluminium phosphate cements

The phase compOSitIOn, exothermal reaction energy, hydrothermal-induced phase transition and development of microstructure in aluminium phosphate cements (APCs), formed by the hydrothermal-catalyzed acid-base reaction between alumina as the base reactant and NH2H2PO4-based fertilizer (Poly-N) as the acid reactant, were investigated. Although the phase compositions of APC depended mainly on the species of alumina and the hydrothermal temperature, the acid-base reaction at 100°C led to the formation of amorphous ammonium aluminium orthophosphate (AmAOP) salt complexes as the major reaction product. The phase transition of AmAOP → crystalline (NH4) 3Al2(PO4)3 and NH4Al(PO4) 2 · OH · 2 · 5H2O occurred at 200°C. Increasing the temperature to 300°C promoted the phase transformations (NH4) 3Al2(PO4)3 → Al2PO4 (OH)3, and NH4Al(PO4)2 · OH · 2 · 5H2O → AlPO4: conversion of non-reactive alumina reactant into γ-AlOOH also occurred. A moderate combination of amorphous and crystalline phases in the cement bodies was responsible for the development of strength. An excessive amorphous → crystal phase transition resulted in a loss in strength, because of the in situ growth of crystalline compounds formed in the amorphous salt matrices, which bind the non-reactive alumina particles into a coherent mass.

Chemical methylation of germanium(II) in model aqueous solutions

AbstractInorganic germanium(II) in micromolar concentrations was reacted with methyl iodide (CH3I) and methylcobalamin (CH3‐CoB12) at various pH values and with different salt matrices. In all experiments monomethylgermanium was the only product. The reaction with CH3‐CoB12 at pH 1 yielded approximately 1.3% of the added germanium, whereas no methylation occurred at pH 7. Reaction yields with CH3I were lowest at pH 1 in 0.1 mol dm−3 KCl (1.6%) and highest at pH 7.6 in artificial seawater (6%). For the reaction of CH3−CoB12 with germanium(II) a free‐radical mechanism is assumed, whereas methylation by CH3I is most likely an oxidative addition mechanism.

On-line preconcentration system for inductively coupled plasma atomic emission spectrometry with quinolin-8-ol and Amberlite XAD-2 resin

An on-line preconcentration system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) was studied. For the retention of metal ions 8-hydroxyquinoline and Amberlite XAD-2 resin were used. This system improved the detection limits of Cd, Cu, Fe, Mn, Ni and Zn by a factor of 100 compared with ICP-AES alone. Owing to this sensitivity and the excellent selectivity towards the transition metal ions with respect to salt matrices, the method was successfully applied to the determination of the above metals in Antarctic sea water. The concentration found ranged between 16 ng l −1 (Mn) and 0.4 μg l −1 (Ni) with a precision of 10%.

Effect of Pellet Pressing on the Infrared Spectrum of Kaolinite

AbstractDiffuse reflectance infrared (IR) spectra show that pressing kaolinite into pellets for transmission IR studies changes relative intensities of hydroxyl peaks between 3700–3600 cm-1. The magnitude of change depends on the absolute pressure, the pressing time and whether a salt matrix is used. Pressing with KBr causes larger differences than pressing neat. Diffuse reflectance IR does not require sample pressing, eliminating this variable in kaolinite studies. This improves IR's ability to distinguish kaolinites according to their hydroxyl group differences and may lead to a better understanding of kaolinite hydroxyl structures.

Analysis of glass ionomer cement with use of scanning electron microscopy

In this study, scanning electron microscopy and x-ray microanalysis techniques were used to examine a silver-reinforced glass ionomer cement. Scanning electron microscopy was used to evaluate surface topography and microstructure. Microcracking and a bimodal pore distribution were observed. The cement consisted of unreacted glass particles surrounded by a silica gel “halo” and embedded in an organic salt matrix. Back-scattered electron microscopy and energy-dispersive spectroscopy detected discrete clusters of silver atoms within the material. Other elements, such as calcium and aluminum, were dispersed homogeneously. Wavelength dispersive spectroscopy was used to detect fluoride, which also appeared to be homogeneously distributed. Electron microscopy and x-ray microanalysis techniques could prove valuable in clarifying the microstructure and fluoride release mechanism of glass ionomer cements. Refinement of some aspects, including sample preparation, will be necessary to obtain consistently reliable results.

Minimization of interferences in inductively coupled plasma mass spectrometry using on-line preconcentration

A semiautomated system is used to preconcentrate Ti, V, Mn, Fe, Co, Ni, Cu, Cd, and Pb, in order to remove high salt matrices. The preconcentration system accepts digests with acid concentrations equivalent to 0.8-1.4% HNO{sub 3}, neutralizes them, and loads them onto a macroporous iminodiacetate resin. The alkali and alkaline-earth metals, along with deleterious anions such as chloride, are washed off the resin before and analyte metals are eluted with nitric acid. A total of 13 isotopes of the analytes are measured. An examination of the apparent concentration efficiencies, as well as the behavior of two internal standard elements added to the eluate stream, indicates that the elution front matrix enhances the inductively coupled plasma mass spectrometry response of the analytes. Investigation of the nature of the blank signal suggests that the detection limits of several of the isotopes could benefit by much larger preconcentration factors, while those of vanadium, copper, cadmium, and lead are currently limited by reagent purity and laboratory contamination. The preconcentration system is evaluated on several simple synthetic matrices, as well as on synthetic seawater and three wastewaters. Digestion of samples containing natural organic chelators is required.

Studies on antimony trifluoride in thiocyanate salt matrices. Evidence for the formation of fluoro-thiocyanato anti-mony(III) species

Abstract Antimony trifluoride can be dissolved in fused KNCS or NH4NCS giving yellow-orange solutions which are stable only for a short time just above their melting point. Infrared an Mossbauer results on solidified samples reveal the formation of mixed fluoro-thiocyanato antimony(III) species and indicate a different behaviour in the two matrices.

Effect of Salt Matrices on the Atomization of Cadmium and Manganese in Graphite Furnace Atomic Absorption Spectrometry

The effects of NaCI, CaCl2 and MgCl2 salts on the atomization process of Cd and Mn elements in a graphite furnace were investigated. The absorbance signals as a function of pre-atomization temperatures were obtained for the analyte, matrix and the analyte in the matrix. In addition, the matrix and the analyte were injected separately on the graphite surface. The comparison of the obtained data with the thermochemical and physical properties of the matrix and the analyte led to conclusions about the interference mechanisms. The type of interference that affects the sensitivity of the analyte depends on the thermal behavior of the matrix before and during the atomization of the element in the graphite furnace. If chlorine atoms are formed by the decomposition of the matrix at temperatures close to the atomization temperature of the element, formation of a metal chloride in the gas phase is responsible from the decrease in the sensitivity. On the other hand, when the matrix is present as a solid or liquid in the graphite furnace while the element atomizes, the occlusion of the element in the matrix occurs. The change of the sensitivity depends on the physical and chemical nature of the analyte and the matrix.

Pre-concentration efficiency of chelex-100 resin for heavy metals in seawater : Part 1. Effects of pH and Salts on the Distribution Ratios of Heavy Metals

The chelating characteristics of Chelex-100 resin were studied for selected heavy metals in seawater medium. The results of batch equilibrium and breakthrough experiments show that the metal-chelating efficiency of the resin is lower in seawater than in freshwater. These differences are caused by the complicated speciation of heavy metals in seawater medium and by the high concentrations of magnesium and calcium present which act as competitors to heavy metal ions. The optimal pH values for column operation are strongly affected by the salt matrix. Careful choice of experimental conditions is necessary to avoid losses of cadmium and manganese from seawater. For better performance, seawater samples should be adjusted to pH 6–7 before loading onto a Chelex-100 column.

Determination of copper in concentrated matrices by flow injection with inductively coupled plasma atomic emission spectrometry

Determination of copper in solutions containing various sulphate compounds, such as H2SO4, Na2SO4, K2SO4, MgSO4 and ZnSO4 at concentrations up to 200 g l–1 are reported. The chosen technique was flow injection inductively coupled plasma atomic emission spectrometry. Of the materials mentioned above, ZnSO4 has a particularly strong influence on the copper emission. At slow carrier flow-rates, increased solution viscosity leads to peak broadening and reduced peak height. As carrier flow is increased, peaks sharpen and these viscosity effects are overcome. Thus, at a flow-rate of 13.2 ml min–1, copper peaks in either aqueous or high salt matrices are not significantly different in height.The method developed has been applied to the determination of copper in a Burt filtrate taken from a zinc plant, a solution high in sulphate salts. Flow injection using both a standard calibration plot and the standard additions method has been applied to the filtrate. The procedure has been shown to offer advantages in speed over an existing xanthate technique, which relies on copper precipitation to separate it from interferences, with re-dissolution prior to analysis. The precision of the method is generally better than 8% RSD, with copper recoveries of 90–115%.

Syngas reactions: Part XI. The ruthenium ‘melt’ catalyzed oxonation of internal olefins

The hydroformylation of internal olefin substrates to give predominantly linear ‘oxo’ alcohols is catalyzed by ruthenium carbonyl ‘melt’ catalysts, wherein the ruthenium carbonyls are dispersed in low m.p. quaternary phosphonium salts. The anionic ruthenium cluster, [HRu 3(CO) 11] −, is the predominant metal carbonyl species in the reactant solutions. Improved alcohol linearity can be achieved through addition of certain chelating N- and P-donor ligands, such as 2,2'-bipyridyl, as well as by the choice of quaternary phosphonium salt matrix. Mixed metal catalysis, particularly Ru-Co, allows the corresponding aldehyde to be the predominant product fraction. These reactant solutions show the presence of both ruthenium carbonyl and [Co(CO) 4] − anionic species.

Laser-enhanced ionization detection of trace copper in high salt matrices

Laser-enhanced ionization (LEI) is used to determine trace levels of metals in high salt matrices, an analysis that is difficult by conventional methods. Copper is presented in detail to demonstrate the capability of the method. Three-dimensional spectra of the stepwise excitation of copper are presented which illustrate the one photon, stepwise, and two-photon transitions. Seven copper transitions have been studied for analytical utility, and detection limits have been determined for each. Ionization interferences were accommodated by both matrix matching and separation of the interferences using ion exchange resin. Absolute determinations at the 0.05-ng level are possible with the use of a Teflon microsampling cup for low volume quantitative analysis. In addition to copper, silver, cobalt, iron, and nickel have been detected within the same dye tuning range. Twelve new LEI transitions have been identified for these elements along with detection limits.

Cadmium determination in biological materials using graphite furnace atomic absorption spectrometry with palladium nitrate-ammonium nitrate modifier.

A mixture of palladium nitrate and ammonium nitrate is proposed as the modifier for cadmium determination in biological materials. It allows the use of pyrolysis temperatures of 800-850 /sup 0/C and markedly reduces background absorption due to inorganic salt matrices. This modifier allows direct determination of cadmium in blood, serum, and urine with detection limits (2sigma) of 0.4, 0.14, and 0.10 ..mu..g L/sup -1/, respectively, using calibratio against matrix-free reference solutions.

Development of materials based on acid-base reaction cements

Acid-based reaction cement are composite materials consisting of a metal salt matrix incorporating glass or metal oxide filler particles. The cements are used in dentistry and the construction inductry. In the past 15 years a new water-based cement, the glass-ionomer, has been developed for dentistry. Since it is adhesive to metals and has controlled release characteristics, the cement has been exploited in the development of coatings, surgical splint bandages and controlled release devices for trace elements, pharmaceuticals and pesticides. Both environmental and performance requirements have provided the impetus for the development of these products.

Direct determination of molybdenum in mineral waters by atomic absorption spectrometry with electrothermal atomization

A new method for the direct determination of molybdenum by ETA-AAS in mineral waters without prior separation or concentration is proposed. With careful control of the graphite furnace conditions selective volatilization of the salt matrix is successfully attained. The possible spectroscopic interference due to common metals as well as the reproducibility, precision and repeatability of the method has been studied and the molybdenum content of 21 mineral waters measured.

Determination of zinc and copper in urine using Zeeman effect flame atomic absorption spectroscopy

Zinc and copper were determined in urine using polarized Zeeman effect flame atomic absorption spectrophotometry. For the zinc assay, urine was diluted 1/10 with deionized water. Concentrations could be determined by comparison to standards in a salt matrix or in a commercial urine control. The linearity of the assay was 350 μg/l, the detection limit was 1.2 μg/l and the within-run relative standard deviation (rsd) was 2.08%, 3.06%, 0.71% and 1.29% for specimens with zinc concentrations of 202 μg/l, 206 μg/l, 1003 μg/l and 1032 μg/l, respectively. The between-run rsd was 2.34% for a mean zinc concentration of 461 μg/l. For the copper assay, urine was aspirated directly and concentrations were determined by standard additions. The linearity of the assay was 5000 μg/l, the detection limit was 4.6 μg/l and the within-run rsd was 24.49%, 16.10%, 4.00% and 3.19% for specimens with copper concentrations of 9.8 μg/l, 11.8 μg/l, 50.0 μg/l and 50.2 μg/l, respectively. The between-run rsd was 8.78% and 4.72% for specimens with copper concentrations of 21.1 μg/l and 40.3 μg/l, respectively.