Heavy metals from environmental matrices

There are many review articles concerning application of USE in food technology [57] and for isolation of bioactive substances from herbs and other plant materials [58], as well as leaching of heavy metals from environmental and industrial samples [59]. Application of ultrasound during sequential extraction of trace elements significantly shortens the whole procedure however, for satisfactory efficiency it is necessary to increase the temperature and modify the matrix. 

Ultrasonic extraction is an effective method for extracting a number of heavy metals from environmental and industrial hygiene samples.In many cases, it provides quantitative recovery of metals and replaces drastic preparation procedures which would otherwise require the use of concentrated acids and the application of high temperatures and pressures (i.e., hot plate and/or microwave extraction). Quantitative extraction can be achieved for some analytes such as As, Cu, Pb, Cd, etc. from plant and animal tissues. Nevertheless, incomplete extraction has been observed from samples containing a typical inorganic matrix (e.g., sediment). A comparison of conventional... 

Finally, Heithmar et al. [110] combined this concentration procedure with a coupled ICP/MS-technique to overcome matrix-caused interferences in the ICP/MS when environmental samples are investigated. These could be both of spectral nature [111] and of a physical-chemical nature [112]. While the former may be mathematically eliminated by introducing respective correction terms in the calibration function, physical-chemical interferences are best be removed by the above-described separation of the heavy metals to be analyzed from interfering alkali and alkaline-earth metal salts. 

The second-order calibration example shown next is from the field of environmental analytical chemistry. A sensor was constructed to measure heavy metal ions in tap and lake water [Lin et al. 1994], The two heavy metal ions Pb2+ and Cd2+ are of special interest (the analytes) and there may be interferents from other metals, such as Co2+, Mn2+, Ni2+ and Zn2+. The principle of the sensor is described in detail in the original publication but repeated here briefly for illustration. The metal ions diffuse through a membrane and enter the sensor chamber upon which they form a colored complex with the metal indicator (4-(2-pyridylazo) resorcinol PAR) present in that chamber. Hence, the two modes (instrumental directions) of the sensor are the temporal mode related to the diffusion through the membrane, and the spectroscopic mode (visible spectroscopy from 380 to 700 nm). Selectivity in the temporal mode is obtained by differences in diffusion behavior of the metal ions (see Figure 10.22) and in the spectroscopic mode by spectral differences of the complexes formed. In the spectroscopic mode, second-derivative spectra are taken to enhance the selectivity (see Figure 10.23). The spectra were measured every 30 s with a resolution of 1 nm from 420 to 630 nm for a period of 37 min. This results in a data matrix of size 74 (times) x 210 (wavelengths) for each sample. 

Experimental results, with both actinides and heavy metals, have demonstrated that the presence of water aids the above reaction scheme 15), It is believed that the water is required to hydrate the metal ion prior to complexation and also aids in deprotonation of the acidic ligand. In SFE from environmental matrices, the presence of water may also aid the breaking of bonds to the binding sites on matrices such as soil, clay and other minerals present in the matrix. This overall reaction scheme is illustrated conceptually in Figure 1. 

Bees and beehive products have been compared with other environmental markers [91]. The authors compared the percentages of lead and cadmium detected in bees, fresh honey, pollen, propolis, and royal jelly with the results derived from the analysis of clover Trifolium pratense L.) and rain. Their findings showed no correlation between the heavy metals found on bees bodies and in beehive matrixes and those detected with other environmental markers. ... 

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