Heavy metals, determination

Ottaway, J. M. Heavy metals determinations by atomic absorption and emission spectrometry in Analytical Techniques for Heavy Metals in Biological Fluids, (ed.) Facchetti, S., Amsterdam—Oxford—New York Elsevier 1983... 

J. G. Vlachogiannis, G. V. Vlachonis. Taguchi s method in a marine sediments heavy metal determinations, J. Environ. Anal. Chem., 85(8), 2005, 553-565. 

The speciation of heavy metals determines the treatability of heavy metals. Furthermore, the size of heavy metals plays a critical role in terms of effectiveness of a physicochemical treatment technology. The following list summarizes the general treatability information provided in Table 3.2 ... 

Bismuth-film electrodes (BiFEs), consisting of a thin bismuth-film deposited on a suitable substrate, have been shown to offer comparable performance to MFEs in ASY heavy metals determination [17]. The remarkable stripping performance of BiFE can be due to the binary and multi-component fusing alloys formation of bismuth with metals like lead and cadmium [18]. Besides the attractive characteristics of BiFE, the low toxicity of bismuth makes it an alternative material to mercury in terms of trace-metal determination. Various substrates for bismuth-film formation are reported. Bismuth film was prepared by electrodeposition onto the micro disc by applying an in situ electroplating procedure [19]. Bismuth deposition onto gold [20], carbon paste [21], or glassy carbon [22-24] electrodes have been reported to display an... 

An overview concerning the enzyme-based electrochemical biosensors published during the last 5 years for heavy-metal determinations is reported. Their sensitivity and selectivity toward inhibitors and the factors (pH, buffer, enzyme, and inhibitor concentrations) affecting the analytical characteristics of these biosensors are also discussed. 

It is seen that the amperometric technique is more used for heavy-metal determination in comparison to potentiometric techniques. The research published during the last 5 years concerning heavy-metal determination has shown the applications especially for water samples (Table 14.1). 

C. Malitesta and M.R. Guascito, Heavy metal determination by biosensors based on enzyme immobilised by electropolymerisation, Biosens. Bioelectron., 20 (2005) 1643-1647. 

A water sample requiring heavy metal determination may be evaporated to a smaller volume prior to using atomic absorption spectrometry. 

Khalid, F., M.Z. Iqbal, and M.S. Qureshi. 1996. Concentration of heavy metals determined in leaves and soil from various areas of Karachi City. Environ. Sci. 4 213-219. 

The method closely related to voltammetry is voltohmmetry, which is based on the fact that the lateral resistance of a thin metal film depends on the presence or absence of interacting species at its surface. Resistance measurements show a specific selectivity in the electrode potentials, and magnitude of resistance change depends linearly on analyte concentrations in solution from p.p.b. to p.p.m. range.58 This method is alternative for voltammetry, not only for heavy metals determinations, but also for nonelectroactive species that can be deposited or dissolved under defined potential of resistance. 

Schoning, M. J. Hiillenkremer, B. Gluck, O. Liith, H. Emons, E., Voltohmmetry - a novel sensing principle for heavy metal determination in aqueous solutions, Sens. Actuators B 2001, 76,275-280... 

For chemical monitoring, a list of priority substances has been established that includes metals such as cadmium, lead, and nickel. As far as metals are concerned, voltammetric techniques and more precisely electrochemical stripping analysis has long been recognized as a powerful technique in environmental samples. In particular, anodic stripping voltammetry (ASV) coupled with screen-printed electrodes (SPEs) is a great simplification in the design and operation of on site heavy metal determination in water, for reasons of cost, simplicity, speed, sensitivity, portability and simultaneous multi-analyte capabilities. The wide applications in the field for heavy metal detection were extensively reviewed (Honeychurch and Hart, 2003 Palchetti et al., 2005). 

An atomic absorption spectrophotometer has been applied for heavy metal determination in soils. Concentrations of potassium and sodium were determined with a flame photometer. For the determination of soil fluorides, an ion-selective electrode was used. Statistical methods were applied to describe quantitatively the relationships between industrial emissions and other components of the ecosystems. 

Locatelli C and Torsi G (2001) Heavy metal determination in aquatic species for food purposes. Ann Chim (Rome, Italy) 91 65-72. 

Highlighted spectroscopic methods for heavy metals determination 4.1 Lead... 

Figure 6 (A) PCA score matrix of heavy metal determinations from various coastal waterway locations. (B) PCA loadings and how much the original variables contribute to the principle component.

Other analytical techniques have less frequently been used nuclear magnetic resonance spectroscopy (NMR) (e.g., tocopherols in toothpaste by hyphenated LC-NMR), energy dispersive X-ray fluorescence (ED-XRF) (e.g., heavy metals determination), surface enhanced Raman scattering (e.g., determination of 4-aminobenzoic acid or PABA, in sunscreens), neutron activation analysis (e.g., determination of iron and zinc), and thermometric analysis (e.g., fluoride in toothpaste). 

Urea Another common metabolite that has attracted a great deal of interest is biosensor analysis of urea. Urease, which gives a linear range of at least 0.01-200 mmol 1 offers a clinically useful assay that is independent of the ammonium concentration in the sample, the same as with creatinine. Urease is very sensitive to inhibition by heavy metals. This fact has even been exploited in the design of a reversible procedure for heavy metal determination. Addition of 1 mmol 1 EDTA and 1 mmol 1 reduced glutathione to the buffer protects the urease leading to a very stable enzyme column. 

Besides heavy metal determination, many different organic and inorganic ionic species, such as organic acids and catecholamines, have been quantified by taking advantage of the ability to pre-adsorb them at the electrode surface [8-10]. 

In a first approach, samples directed to heavy metals determination should be immediately analyzed after collection, considering that low concentrations of this elements decrease with time. When a quick analysis is not possible, samples should be stored away from any potentially contaminating source (i.e., contaminated atmosphere, concentrated solutions). In this sense special care must be taken with metal contamination due to distilled water, filters, and containers (i.e., contamination from previous samples, chemical reaction between the sample and the container) [35,36]. 

Historically, electrochemical stripping analysis, commonly using anodic stripping voltammetry (ASV), has been widely recognized as a powerful technique for heavy-metal detection because of the simplicity of the instrument as well as its moderate cost and portability. Moreover, the ASV technique combined with SPEs can handle all scenarios that require rapid, inexpensive, sensitive, and accurate determination in the field of environmental monitoring. Most studies of heavy-metal determination using SPEs show that mercury, gold, silver, bismuth, or other materials that modify the surface of SPEs can improve selectivity or sensitivity. ... 

Conductive electrodes based on metal oxide, e.g., indium-tin oxide (TTO), are widely used in electrochemistry as a support for surface modification with the goal to develop sensors with electrochemical transduction or combined spectroscopic and electrochemical responses or electrochemiluminescence. Inorganic thin films can also be prepared from the assembly of two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs, also defined as anionic clays). These materials can be used to preconcentrate species on the basis of ion-exchange reactions and applied to heavy metal determination or for the detection of organic pollutants. 

Roa Morales G, Ramirez Silva MT, Romero Romo MM, Galicia L (2005) Heavy metal determination by anodic stripping voltammetry with a carhon paste electrode modified with alpha -cyclodextrin. In Palomar M (ed) Applications of Analytical Chemistry in Environmental Research, Research Signpost, Trivandrum, India... 

---