Lead ETAAS

Work Item B determination of mercury by CVAAS after pressure digestion. Work Item C determination of lead and cadmium by ETAAS after dry ashing. Work Item D performance criteria and general considerations. 

Work Item F determination of lead, cadmium, chromium and molybdenum by ETAAS after pressure digestion. 

Work Item H determination of lead and cadmium by ETAAS after microwave digestion. 

Human activities often mobilize and redistribute natural compounds in the environment to an extent that they can cause adverse effects. Much attention has been paid to the determination of trace of pollutant elements on account of their significant effect on the environment. The potential of USAL has been put into use in environmental element analysis. Thus, the US leaching of cadmium from coals and pyrolysed oil shale prior to ETAAS [56] resulted in a twofold increase in precision, better detection limits and decreased background absorbance in relation to total digestion. Cadmium has also been successfully leached with US assistance from ash samples with subsequent flow-injection coid-vapour atomic absorption spectrometry [57]. Additional examples include the leaching of germanium from soiis with an uitrasonic probe in 10 min [58] or that of lead from coal in 60 s [59]. 

Trimethyl- (TriML) and triethyllead (TriEL) compounds were obtained from Alfa products (Johnson Matthey) and their purity was verified as follows carbon, hydrogen and chloride relative masses in the TriML and TriEL calibrants were determined by elemental microanalysis the chloride concentration was determined by ion chromatography. Total lead was determined in the calibrants by electrothermal atomic absorption (ETAAS) using two different acid digestion procedures (concentrated nitric... 

The second interlaboratory study generated detailed discussions one ETAAS technique employed did not include a separation step but the participant stated that EDTA extraction would only extract organic lead compounds this technique was considered to be suitable for the analysis of a simple solution containing only one lead compound but would not be suitable for mixtures of lead species, e.g. the technique would not allow the separation of TriML and TriEL in a natural rainwater sample. In cases where different organolead compounds are to be determined in natural samples or solutions containing different lead compounds, ETAAS should be coupled to a separation technique, e.g. GC or HPLC. 

In the case of lead, it was recommended that calibration be performed by standard additions to take matrix effects into account. Similar problems of precipitation in CRM 610 were experienced by one laboratory, which withdrew its results obtained by HR-ICPMS, DPASV and ETAAS. 

Some instrumental methods (INAA, XRFA) analyse directly the aerosol filter or portions of filters. Recently such approach is intensively tested for other methods especially ETAAS. For the majority of instrumental methods however treatment of the filter is required leading to a liquid extract. Wet ashing with different acidic mixtures is very popular though dry ashing in a furnace, followed by acid dissolution is also used. The choice of the method depends not only on the measurement technique and the range of substances to be analyzed but also on the chemical form of the element (Kneip and Kleinman, 1982). For example high temperature secondary aerosols may contain refractory oxides or silicates and the treatment requires fusion or hydrofluoric acid dissolution. 

ETAAS. In ETAAS atomization takes place in an electrothermal atomizer which is heated to the appropriate temperature programme. The detection limits of the method are about two or three orders of magnitude better than FAAS. It is applicable to about 40 elements but generally for about 20 elements detection limits at the ng and pg level can be reached. Commensurable or better sensitivities have only INAA, ICP-MS and stripping voltammetry. Therefore ETAAS is widely used for environmental analysis. However the method suffers from serious interferences leading to systematic errors due to thermochemical processes in the atomizer. Background absorption is also a potential source for systematic errors. Spectral interferences are additive and cannot be corrected by the popular standard addition method. ETAAS is also not free of memory effects for refractory elements. 

According to present possibilities in respect to number of determined elements, accuracy, precision and detection limits INAA is still the leading method, followed by ETAAS and ICP-AES. According to potential and perspectives ICP-MS is undoubtedly the most promising technique. However it must be clearly stated that there is not a... 

Lead. Ca interferences were again suspected to affect the signal when ICP-AES was used. This was verified by the addition of Ca to the calibrant solution, which yielded similar interferences. Here again the very low Pb content extracted in steps 1 and 2 in the second intercomparison hampered firm conclusions to be drawn. In the case of step 2, a very high discrepancy was noted between the ETAAS results and the FAAS results (one order of magnitude). However, all the FAAS results were actually recognized to be below the limits of determination and were consequently withdrawn. When ETAAS was used as the technique of final determination, the use of the matrix modifier was highly recommended. As for copper, the small number of accepted sets of data (5 laboratories of which 3 were ETAAS, 1 ICP and 1 ICP-MS) were found to be insufficient to draw any firm conclusions. 

The main difference between gasoline and diesel fuel, as far as ETAAS are concerned, is the sample volatility. Gasoline sample can be injected directly in the electrothermal atomizer and vaporized without formation of any residue, while diesel fuel undergoes partial pyrolysis during the thermal treatment before the atomization occurs. The pyrolysis can lead to the formation of a carbonaceous residue. The carbonaceous buildup affects the atomization of carbide forming elements such as Ni and V [3]. In this work, diesel fuel samples were diluted with a suitable solvent to reduce the formation of carbon residues. 

Fig Recordings of ETAAS atomization signals for lead in water samples using on-line sorbent extraction separation and preconcentration, (a) Blank (b) 0.100 fig P Pb standard (c)... 

One of the first applications of ETAAS to the analysis of clinical samples was the determination of lead in blood. It was also one of the first examples for which the importance of the STPF concept for accurate results was demonstrated [24]. ETAAS is nowadays an established technique for that application which was shown to give reliable and reproducible results on a routine basis [25]. 

AAS is the most widely used analytical technique for the determination of lead in biological materials [57,58], The majority of AAS methods employ the electrothermal atomic absorption spectrometry (ETAAS) technique, using either Zeeman background correction or deuterium background correction for the determination of lead in biological fluids [55,59-65], Urine is less often employed as an indicator of exposure however, similar problems associated with AAS determination of lead exist for blood as well as urine (1) incomplete atomization (2) volatile lead salts (3) spectral interferences (4) buildup of carbonaceous residue reducing sensitivity and precision. These analytical problems are eliminated by optimal sample preparation, e,g., dilution, addition of matrix modifiers, deproteinization, and background correction and calibration by matrix-matched standards [66],... 

In general, the furnace programs used to atomize lead are optimized with regarding to linearity of the method and background absorption. Even though furnace programs and matrix modifiers reduce matrix effects, they do not eliminate interferences. Consequently matrix-matched standards or standard addition are essential for accurate determination of lead [57,62]. Examples of recent ETAAS methodologies for blood lead determination are shown in Table 4. 

TABLE 4. Methodologies and Analytical Characteristics of Some Selected Methods for Determination of Lead in Whole Blood by ETAAS... 

Cadmium, cobalt, copper, iron, lead, nickel and zinc by ETAAS... 

O. Acar. Determination of cadmium, copper and lead in soils, sediments and sea water samples by ETAAS using a Sc + Pd + NH4NO3 chemical modifier. Talanta 65 672-677, 2005. 

N. Carrion, A.M. Itriago, M.A. Alvarez, and E. Eljuri. Simultaneous determination of lead, nickel, tin, and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS. Talanta 61 621-632, 2003. 

Hydride generation is a common method for the detection of metalloids such as As, Bi, Ge, Pb, Sb, Se, Sn and Te, although other vapours, e.g. Hg or alkylated Cd, may also be determined. This technique improves the sensitivity of the analysis substantially. Since the sample is in the gas phase, the sample transport efficiency is close to 100%. The hydrides atomize readily in the flame, although this approach is usually used in conjunction with a quartz T-piece in the atom cell. Methods have been developed that trap the hydrides on the surface of a graphite tube for use with ETAAS. This leads to preconcentration and further improvements in detection limit. 

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