Solid sampling analysis

Coronel Laboratory for Occupational and Environmental Health Medical Faculty University of Amsterdam Meibergdreef 15 NL-1105 AZ Amsterdam The Netherlands 

SOLID SAMPLING ATOMIC ABSORPTION SPECTROMETRY BASIC PRINCIPLES 

Determination of trace elements in solids is conventionally performed by destruction or digestion of the test substance by acids and subsequential measurement of the elements of interest by an adequate spectrometric, polarographic, or neutron activation method. 

Direct determination of solids may be performed by, e.g.. X-ray fluorescence spectrometry, or by arc or spailr emission spectrometry in case of powders. For special applications many surface techniques are available such as proton-induced X-ray emission (PIXE) and laser microprobe emission spectrometry (LMA). In the case of determination of trace elements on clinical material, however, most of these direct methods have detection limits that are too high to be useful. Moreover, as some of these methods are cormected to an accelerator or electron microscope, usage is somewhat limited for routine determination. 

Other direct methods used more routinely for solid sampling analysis make use of an atomization cell, usually a graphite furnace, and optical spectrometry. Optical spectrometry techniques used are inductively coupled plasma (ICP) and atomic absorption spectrometry (AAS). This last technique, solid sampling atomic absorption spectrometry (SS-AAS), is used by far the most and thus will be dealt with more comprehensively. 

---

The sensitivity, accuracy, and precision of solid-sample analysis have been greatly improved by coupling LA with ICP-OES-MS. The ablated species are transported by means of a carrier gas (usually argon) into the plasma torch. Further atomization, excitation, and ionization of the ablated species in the stationary hot plasma result in a dramatic increase in the sensitivity of the detection of radiation (LA-ICP-OES) or of the detection of ions (LA-ICP-MS). 

Kurfurst U (1998) Solid Sample Analysis - Direct and Slurry Sampling using GF-AAS and ETV-ICP. Springer, Berlin, Heidelberg, New York. 

A suitable method to determine the degree of homogeneity of an element in a material is by repetitive analysis of a large number of small soUd ahquots by direct solid sample analysis. As shown in Figure 4.3, there is a functional relationship between the sample mass used for analysis and the standard deviation of repetitive analysis. 

ScHRON W, Liebmann A, Nimmereall G 2000) Direct solid sample analysis of sediment, soils, rocks and advanced ceramics by ETV-ICP-AES and GF-AAS. Fresenius J Anal Chem 366 79-88. 

Herber RFM (1994a) Solid sampling analysis. In Seiler HG, Sigel A, Sigel H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York. 

Direct solid sample analysis is still mostly a subsidiary method, confined to specific analytical tasks, rather than truly complementary to traditional analysis via solutions. Solid sampling is not standard in routine... 

Solid and slurry sampling using the graphite furnace have been reviewed [220,221]. A monograph dealing with solid sample analysis is available [222]. 

U. KurfUrst, in Solid Sample Analysis (U. KurfUrst, ed.), Springer-Verlag, Berlin (1998), pp. 129-90. 

Nimmerfall G, Schron W (2001) Direct solid sample analysis of geological samples with SS-GF-AAS and use of 3D calibration. Fresenius J Anal Chem 370 760... 

Species distribution studies have shown that trace element (e.g. metals) concentrations in soils and sediments vary with physical location (e.g. depth below bed surface) and with particle size. In these speciation studies the total element content of each fraction was determined using a suitable trace element procedure, for example, solid sample analysis by X-ray emission spectroscopy or neutron activation analysis, or alternatively by dissolution of sample and analysis by ICPOES, AAS or ASV. The type of sample fraction analysed can vary, and a few... 

Figure 4.8 shows an example for this mode of correction applied for the determination of Pb in pig kidney reference material, using direct solid sample analysis. The three-dimensional plot in Figure 4.8a shows that a strong molecular absorption with pronounced fine structure appears short after the atomic absorption signal. Figure 4.8b shows the time-integrated absorbance spectrum of PO,... 

Figure 4.8. Least-squares BC for molecular spectra with rotational fine structure determination of Pb in the BCR 186 Pig Kidney CRM at 217.001 nm using HR-CS ET AAS and direct solid sample analysis (a) absorbance over time and wavelength after correction for continuous absorption (b) reference spectrum absorbance over wavelength integrated over time for NH4H2P04 (the dotted line represents the center pixel) (c) absorbance over time and wavelength after subtraction of the reference spectrum using least-squares BC.

Figure 4.17. Three-dimensional graph for Cr in the NIST 8415 Whole Egg Powder SRM in the vicinity of the 357.87 nm line pyrolysis temperature 700°C, atomization temperature 2500°C direct solid sampling analysis.

Figure 4.19. Determination of Pb in biological reference materials in the vicinity of the 217.001 nm line pyrolysis temperature 700°C, atomization temperature 1700°C Ru permanent modifier direct solid sampling analysis (a) wavelength integrated over time for the NIST 8414 Bovine Muscle SRM (b) wavelength integrated over time for NIST 8415 Whole Egg Powder (c) absorbance over time for Whole Egg Powder, recorded at selected pixels in the vicinity of the analytical line.

Figure 4.20. Three-dimensional graphs for Se in the BCR 186 Pig Kidney CRM pyrolysis temperature 800°C, atomization temperature 2000°C Ir permanent modifier direct solid sampling analysis (a) in the vicinity of the 196.026 nm line (b) in the vicinity of the 203.985 nm line.

When the graphite furnace is used for extreme-trace analysis, relative standard deviations are in general above 10 relative percent. The solid sample analysis described in section II.B.l, using a steel chip and the rectangular cuvette, leads to an RSD of 13 relative percent in the determination of a... 

The increased interest in glow-discharge techniques, initially in the academic world and later among instrument manufacturers, can be ascribed largely to their performance in solid sample analysis. 

Veeeept P, Boonen S, Moens L and Dams R (1998) Solid sampling by electrothermal vaporization-inductively coupled plasma-atomic emission and mass-spectrometry (ETV-ICP-AES/-MS). In Kur-fiirst U, ed. Solid Sample Analysis, Direct Slurry Sampling using GF-AAS and ETV-ICP, pp. 191-246. Springer-Verlag, Berlin. 

Herber, R.F.M. (1991). Solid sampling atomic absorption spectrometry and matrix composition of organic reference materials. Pure Appl. Chem. 63,1213-1220 Herber, R.F.M. (1993). Solid sampling analysis in Seiler, H.G., Sigel, A. and Sigel, H. 

This distribution can be expected in case of solid sampling analysis when rare particles of a high analyte content are encountered (Kurfurst, 1991). 

An atomizer based on glow discharge techniques is commercially available for the analysis of solid metal samples by AAS. It will be discussed in the applications sections under solid sample analysis. 

Gunther D, Hattendorf B (2005) Solid sample analysis using laser ablation inductively coupled plasma mass spectrometry. Trends Anal Chem 24 255-265... 

Although most samples are commonly presented as liquids for atomic emission spectroscopy, direct solid sample analysis has the advantage that no major pretreatment or dissolution steps are required [44]. This minimises dilution errors or contamination from reagents and reduces the reagent and manpower cost per sample. In addition, improved detection Hmits may be obtained if microsamples or microanalysis are possible without any further dilution. However, the analyst has to ensure that the solid material sampled is representative of the bulk material. ICP-AES has generally a remarkable tolerance for total dissolved sohds compared to ICP-MS or flame AAS so that, depending on the overall matrix, between 2 and 25 % suspended sohds can be coped with. Therefore, most of the sohd sample introduction devices described below are dedicated for ICP-AES. 

Generally, AES systems are calibrated with multi-element standard samples. In the case of sparks, arcs, glow discharges, and laser ablation, solid samples are required, which are rarely available in large enough numbers to provide a satisfactory calibration. Hence, in solid sample analysis secondary standards are usually prepared. 

---