Speciation studies

Many different methods are being used for speciation studies. Some of them are already 

Some years ago, a microprocessor-controlled flow-stream system was introduced for the determination of ultratrace levels of easily reducible mercury in water samples (Stockwell et. al., 1989). The system is based on an autosampler, reduction unit, gas-liquid separator, gold trap and APS monitor and allows processing of 8 samples per hour. For sample volumes of 4S mL, a detection limit (3 s of the blank values) of 0.1 ng/L was found with an analytical precision of 5 % (Cossa et al., 1995). 

More recently, a system has been proposed for the computer-controlled processing of discrete seawater samples involving photo-oxidation and dual amalgamation (Gerwinski et aL, 1996). Rather than by a peristaltic pump, the volume flow is exclusively driven by carrier 

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The technique can be used to measure concentrations in the range 10 6-10 9M and as such is eminently suitable for the determination of trace metal impurities of recent years it has found application in the analysis of semiconductor materials, in the investigation of pollution problems, and in speciation studies. 

The most widely studied interactions between biologically active ligands and organotin(lV) cations relate to the amino acids and their derivatives (N- or S-protected amino acids and peptides), though new data on several of the most commonly occurring amino acids are still being published. This is specially true for aqueous speciation studies. Nice and very detailed reviews were published in this area by Molloy and Nath. ... 

Okamoto K and Yoshinaga J (1999) Proper use of reference materials for elemental speciation studies. In Fajgelt A and Parkany M, eds. The use of matrix reference materials in environmental analytical processes, pp 46-56. Royal Sodety of Chemistry, Cambridge. 

The artificial separation between organic and inorganic mass-spectrometric methods is now narrowing, as shown by speciation studies (Section 8.8). Plasma-source MS (PS-MS), mainly as ICP-MS and MIP-MS, has been particularly effective when applied to speciation analysis. Direct speciation is also possible with electrospray MS (ESI-MS). 

Koch, K. R. Miller, J. Westra, A. N. On the liquid-liquid extraction of Pt(IV/II) from hydrochloric acid by N-Acyl(aroyl)-N, N -dialkylthioureas a multinuclear (1H, 13C and 195Pt) NMR speciation study of the extracted complexes. International Solvent Extraction Conference, Cape Town, South Africa, Mar. 17—21, 2002, 327-334. 

Ultraviolet spectroscopy has been applied to the determination of lead and lead speciation studies [407]. Scaule and Patterson [408] used isotope dilution-mass spectrometry to determine the lead profile in the open North Pacific Ocean. 

Bloxam et al. [482] used liquid chromatography with an inductively coupled plasma mass spectrometric detector in speciation studies on ppt levels of mercury in seawater. 

Advantages High analysis rate 3-4 elements per hour Applicable to many more metals than voltammetric methods Superior to voltammetry for mercury and arsenic particularly in ultratrace range Disadvantages Nonspecific absorption Spectral interferences Element losses by molecular distillation before atomisation Limited dynamic range Contamination sensitivity Element specific (or one element per run) Not suitable for speciation studies in seawater Prior separation of sea salts from metals required Suspended particulates need prior digestion About three times as expensive as voltammetric equipment Inferior to voltammetry for cobalt and nickel... 

Batley [28] examined the techniques available for the in situ electrodeposition of lead and cadmium in estuary water. These included anodic stripping voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen and in situ electrodeposition on mercury coated graphite tubes. Batley [28] found that in situ deposition of lead and cadmium on a mercury coated tube was the more versatile technique. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals were then determined by electrothermal atomic absorption spectrometry, Hasle and Abdullah [29] used differential pulse anodic stripping voltammetry in speciation studies on dissolved copper, lead, and cadmium in coastal sea water. 

Pinheiro, J. P., Mota, A. M., Simoes Gonsalves, M. L. S. and van Leeuwen, H. P. (1998). The pH effect in the diffusion coefficient of humic matter influence in speciation studies using voltammetric techniques, Coll. Surf. A, 137, 165-170. 

Donard OFX, Martin FM. Hyphenated techniques applied to environmental speciation studies. TRAC Trends Analyt. Chem. 1992 11 17-26. 

In mercury speciation studies, pressurized liquid extraction (PLE), microwave-assisted extraction (MAE), and supercritical fluid extraction (SEE) are employed [33]. In particular, methyl-mercury is extracted by the Westoo method [33,34], which consists in a leaching process with hydrochloric acid, the extraction of the metal chloride into benzene or toluene, the addition of ammonium hydroxide that converts the metal species to hydroxide and the saturation with sodium sulfate. Most of the HPLC methods reported in literature for the determination of organomercury compounds (mainly monomethyhnercury, monoethyhnercury, and monophenylmercury) are based on reversed... 

For the determination of organotin compounds (tributyltin, triphenyltin, triethyltin, and tetra-ethyltin) a MAE is proposed before the normal phase (NP) HPLC/UV analysis [35], In organotin and arsenic speciation studies, hydride generation is the most popular derivatization method, combined with atomic absorption and fluorescence spectroscopy or ICP techniques [25,36], Both atmospheric pressure chemical ionization (APCI)-MS and electrospray ionization ESI-MS are employed in the determination of butyltin, phenyltin, triphenyltin, and tributyltin in waters and sediments [37], A micro LC/ESI-ion trap MS method has been recently chosen as the official EPA (Environmental Protection Agency) method (8323) [38] it permits the determination of mono-, di-, and tri- butyltin, and mono-, di-, and tri-phenyltin at concentration levels of a subnanogram per liter and has been successfully applied in the analysis of freshwaters and fish [39], Tributyltin in waters has been also quantified through an automated sensitive SPME LC/ESI-MS method [40],... 

A multidisciplinary approach is required in order to achieve total speciation. This approach is not only desirable but essential for the proper design of the experiments and interpretation of the results. Over the next few years, it is to be expected that more information relevant to speciation studies would become available. Thk would lead to a more informed choice of methods and techniques. In addition, on the basis of this knowledge, accurate computer simulation of the distribution of species in a wider variety of biological systems could be accomplished. 

I) Faradaic electrochemical methods. From a general analytical point of view, electrochemical techniques are very sensitive methods for identifying and determining the electroactive species present in the sample and, in addition, they also are able to carry out speciation studies, providing a complete description of the states of oxidation in which the ionic species are present in the object. Other applications and improvements obtained by their hyphenation with other instrumental techniques, such as atomic force microscopy (AFM), will be described in the following chapters. 

Carbonate has proved to be a versatile ligand. Its coordination mode expands from 1 to 6, the last one is visualized when each atom binds two metal ions simultaneously. In recent years, significant progress has been made in the synthesis, structure, and magnetic properties of polynuclear carbonato complexes of transition metal ions. Such studies have also been extended to lanthanides and actinides. The speciation studies of these metal ions in aquatic environments in the presence of carbonate have resulted in significant... 

Recent trends in phosphorus speciation utilizing separation techniques considering HLPC, CE and gel electrophoresis in ICP-MS have been examined by Shah and Caruso.115 For speciation studies, ICP-MS of phosphorus is combined with a biomolecular mass spectrometric technique such as (ESI- or MALDI-MS).116-118... 

Inorganic mass spectrometry requires the development of suitable reference materials, such as matrix matched standard reference materials for trace, surface (including depth profiling and microlocal) analysis and/or the creation of matrix independent calibration procedures. The development of species specific standards will be intensified for speciation studies in the future. 

ESR examination of nonchemically isolated fulvic acids showed that Mn2+ was the primary paramagnetic species observable (60, 61). Most likely, the soluble-colloidal fraction we identified in the speciation studies consisted primarily of such complexes. Because the ESR spectral characteristics of Mn in fulvic acid complexes are quite similar to Mn(H20)62+, Alberts et al. (62) suggested that the metal-fulvate interaction was weak. Stronger interaction would be expected to lead to changes in peak shape. This view leaves unexplained the ability of the complexes to survive the isolation procedure s long ultrafiltration steps, because weak interactions are usually associated with reversible complexation. 

RPLC-ICP-MS has been used for clinical analyses by a number of workers, particularly with regard to speciation studies. 

Potentiometry differs from all other analytical techniques by its ability to detect an ion s activity in a sample. This unique property makes ISEs particularly useful for bioavailability or speciation studies. The response of an ISE is described by Nernst equation ... 

APPROACHES IN CHEMICAL SPECIATION STUDIES IN MARINE WATERS... 

Kramer, C.3.M., 1986. Approaches in chemical speciation studies in marine waters. In P. 

After a brief introduction on terminology, this overview summarizes the experimental and theoretical modelling methods applied in trace metal speciation studies, emphasizing the dissolved fraction as defined by 0.95 pm filtration. The experimental approach comprises interactions with organic - and inorganic ligands, speciation schemes, biological experiments and interactions with particles and colloids. 

Interest in trace element speciation studies in natural waters has increased considerably during the last decade. It has become apparent that data on total concentrations of any element rather than on individual well defined chemical entities, are often inadequate to identify transport mechanisms, ultimate fate and toxicity of particular elements to organisms. A study of the different trace metal species and their relative distribution will assist in understanding the chemical processes that take place in the highly reactive estuarine zone and in the open sea. These processes include the rate at which chemical processes take place, the participation in geochemical processes (precipitation/dissolution, adsorption/desorption). 

Different approaches in trace metal speciation studies (with some examples). 

In the (aquatic) environment elements occur in particulate-, colloidal- and dissolved forms. These forms are usually distinguished by filtration or centrifugation. Traditionally, a 0.45 um (membrane)- filter separates the particulate from the dissolved forms. This may result in the passage of colloidal fractions through the filter, classifying colloidal matter incorrectly within the dissolved fraction. Although the interaction between dissolved and particulate (surface) fractions cannot be neglected, it is common in speciation studies to consider the "dissolved" fraction. The dissolved forms of trace elements are mainly present as ... 

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Other techniques applied to speciation studies are potentiometric stripping analysis (PSA) (Oagner and Aren, 1982), pseudopolarography (Brown and Kowalski, 1979), electrophoresis (Rohl, 1982), several chromatographic techniques, XAD-1 and -2 (Mackey,... 

CCcu and K determination by DPASV analysis. To illustrate the possibilities of speciation studies, an example of the application to natural waters will be presented in this section, with special reference to the determination of the complexation capacity for copper of marine waters. 

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