Speciation Analysis of Environmental Samples

In the past few years, the determination of chemical species of elements (e.g. As, Hg, Sn species) has become of increasing concern due to their high toxic impact (see a review from Craig [16]). Some of these compounds (e.g. methyhnercury, tributyltin) are now included in the black list of compounds to be monitored in the marine environment according to an EEC Directive (amendment of the Directive 76/464/EEC). Consequently, a wide variety of analytical techniques have been developed recently and are described in the literature, e.g. for Sn speciation [17,18], As speciation [19], Hg speciation [20], Pb speciation [21] and Se speciation [22]. 

Analytical techniques used for the determination of chemical species are 

---

Heisterkamp M., De Smaele T., Candelone J. P., Moens L., Dams R. and Adams F. C. (1997) Inductively coupled plasma mass spectrometry hyphenated to capillary gas chromatography as a detection system for the speciation analysis of environmental samples, J Anal At Spectrom 12 1077-1081. 

Morabito, R. (1995) Extraction techniques in speciation analysis of environmental samples. 

Organotin compounds R SnX4 are speciated in the analysis of environmental samples by alkylation to the tetraalkylstannanes such as R SnHt4 , which are then identified by GLC/MS or HPLC/MS, and tetraalkylborates (e.g. NaBEt4), which are stable to water, are often used for this purpose in preference to Grignard reagents (Section 23.3).29 31... 

Due to nanoliter per minute flows of CE the concentration-based detection limits are seriously degraded in comparison with those obtained by LC, limiting the application of CE in Cd speciation analysis of real samples. In any case, there are CE strategies (e.g., large volume sample stacking) that are able to preconcentrate the analytes and have been successfully applied to real samples in order to improve the detectability of Cd species in MTs by CE-ICP-MS. Figure 2 shows typical electrophoretic results by a hybrid technique for speciation of Cd-MTs in fish samples of environmental monitoring interest. 

The discipline of analytical chemistry is wide and catholic. It is often difficult for a food chemist to understand the purist concerns of a process control chemist in a pharmaceutical company. The former deals with a complex and variable matrix with many standard analytical methods prescribed by Codex Alimentarius, for which comparability is achieved by strict adherence to the method, and the concept of a true result is of passing interest. Pharmaceuticals, in contrast, have a well-defined matrix, the excipients, and a well-defined analyte (the active) at a concentration that is, in theory, already known. A 100-mg tablet of aspirin, for example, is likely to contain close to 100 mg aspirin, and the analytical methods can be set up on that premise. Some analytical methods are more stable than others, and thus the need to check calibrations is less pressing. Recovery is an issue for many analyses of environmental samples, as is speciation. Any analysis that must... 

Zhang, N., J.S. Suleiman, M. He, and B. Hu. 2008. Chromium (Ill)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection. Talanta 75 536-543. 

This section is not intended to give a comprehensive account of environmental sampling problems, but rather to emphasize the importance of giving the necessary thought to sampling technique. Because many environmental samples are biologically active even when handed into the analytical laboratory, they must be stored and handled accordingly, especially if speciation studies are to be performed rather than total element analysis. 

J. Leenaers, W. van Mol, H. G. Infante, F. C. Adams, Gas chromatography-inductively coupled plasma-time-of-flight mass spectrometry as a tool for speciation analysis of organomercury compounds in environmental and biological samples, J. Anal. Atom. Spectrom., 17 (2002), 1492-1497. 

Wang, R.Y., Hsu, Y.L., Chang, L.F., Jiang, S.J. Speciation analysis of arsenic and selenium compounds in environmental and biological samples by ion chromatography -inductively coupled plasma dynamic reaction cell mass spectrometer. Anal. Chim. Acta 590, 239-244 (2007)... 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

Laboratory methods. Huorimetry has been used widely for selenium analysis in environmental samples but is being superseded by more sensitive instrumental methods. Some of the instmmental methods used for arsenic speciation and analysis can also be used for selenium. In particular, HPLC and HG can separate selenium into forms suitable for detection by A AS, AFS (Ipolyi and Fodor, 2000), or ICP-AES (Adkins et al, 1995). Only Se(IV) forms the hydride, and so Se(VI) must be prereduced to Se(IV) if total selenium is to be determined. This is normally achieved using warm HCl/KBr followed by co-precipitation with La(OH)3 if necessary (Adkins et al., 1995). KI is not used, since it tends to produce some Se(0), which is not reduced by HG. La(OH)3 collects only Se(IV), so the prereduction step to include the contribution from Se(VI) is required before co-precipitation. Other methods of preconcentration include co-precipitation of Se(IV) with hydrous iron oxide or adsorption onto Amberlite IRA-743 resin (Bueno and Potin-Gautier, 2002). 

The analysis of environmentally-relevant samples is a major field of application. Based on the work of Garbarino and Taylor [421], a method has been proposed by the US EPA (Environmental Protection Agency) [422] and later by DIN [423] for waste water analysis. The latter, standardized procedure describes the sample decomposition, the analytical range for 22 elements and frequent interferences of ICP-AES in waste water analysis. For the analysis of natural waters, hydride generation [424], preconcentration based on liquid-liquid extraction of the dithiocarbamate complexes [425], adsorption of trace elements onto activated carbon [426] and also co-precipitation [e.g. with In(OH)2] [427], etc. have been reported and special emphasis has been given to speciation (as given in the Refs, in [428]) and on-line preconcentration [134]. 

A variety of methods for the determination of total metals and metal species/fractions have been described. While the most common method of sample decomposition of environmental samples is probably acid digestion, other approaches, most notably the use of fusion, have some specialist application areas, e.g. geological samples. The area of metal speciation is an ever expanding one, with new approaches being developed and evolving on a regular basis. The major limitation to this area of activity is the development of robust and reliable approaches to analysis. Some selected examples have been provided to assist the reader to evaluate some of the procedures that have already been developed. However, after reading this chapter you will have quickly realized that the methods are limited to only a few metal species. 

Although it is beyond the scope of this article to consider detailed collection and sample preparation procedures for environmental samples, here are some general considerations for speciation analysis of air, water, biological material, and soils/sediments. The collection of samples in air has focused upon the determination of hydrides and methylated compounds of elements such as arsenic, lead, mercury, and tin. The sample may be introduced into a preevacuated container, or with a pump. The analytes may be isolated using cryotrapping techniques or adsorbent cartridges. For best results, it is recommended to collect the entire gas sample in a container, coated... 

The concentrations of organolead compounds found in the different environmental compartments are often in the pgm, ngl , and ng per g levels for air, water, and sediment and biological tissues, respectively. However, inorganic lead forms can simultaneously be present in the same samples at a 1000-fold higher level. For this reason, the instrumentation necessary to carry out lead speciation analysis in real samples requires the isolation, separation, and sensitive detection of the individual organolead species in the presence of thousands of... 

Atomic absorption spectrometry (AAS) was established as the most popular gas chromatography (GC) detection technique for lead speciation analysis in the first years of speciation studies. The increase of the residence time of the species in the flame using a ceramic tube inside the flame and, later, the use of electrically heated tubes, made out of graphite or quartz where electrothermal atomization was achieved, provided lower detection limits but still not sufficiently low. Later, the boom of plasma detectors, mainly microwave induced plasma atomic emission (MIP-AES) and, above all, inductively coupled plasma atomic emission and mass spectrometry (ICP-AES and ICP-MS, respectively) allowed the sensitivity requirements for reliable organolead speciation analysis in environmental and biological samples (typically subfemtogram levels) to be achieved. These sensitivity requirements makes speciation analysis of organolead compounds by molecular detection techniques such as electrospray mass spectrometry (ES-MS) a very difficult task and, therefore, the number of applications in the literature is very limited. 

---