Direct analysis of solid samples

Nowka R, Muller H (1997) Direct analysis of solid samples by graphite furnace atomic absorption spectrometry with a transversely heated graphite atomizer and D2-background correction system (SS GF-AAS). Fresenius J Anal Chem 359 132-137. 

Noweoy R, Marr IL, Ansari TM, Muller H 1999) Direct analysis of solid samples by GFAAS -determination of trace hea-vy metals in barytes. Fresenius ( Anal Chem 364 533-540. 

Direct analysis of solid samples or analytes present on solid surfaces without any sample preparation has always been a topic of interest. Desorption electrospray ionization (DESI) is an atmospheric pressure desorption ionization method introduced by Cooks et al., producing ions directly from the surface to be analyzed, which are then sampled with the mass spectrometer [22, 37]. DESI is based on charged liquid droplets that are directed by a high velocity gas jet (in the order of 300 m s ) to the surface to be analyzed. Analytes are desorbed from the surface and analyzed by mass spectrometer (Eig. 1.15). 

The introduction of inductively coupled plasma (ICP) in inorganic mass spectrometry means that there is an effective ion source operating at atmospheric pressure. Whereas solid mass spectrometric techniques allow direct analysis of solid samples in ICP-MS, the determination of trace impurities or isotope ratios in solid samples is often carried out after digestion and dissolution of the material. For the determination of trace impurities and isotope ratios in liquids, an additional nebulization... 

To an increasing extent, LA-ICP-MS is the method of choice for the direct analysis of solid samples with respect to the analysis of long-lived radionuclides. Most applications of LA-ICP-MS... 

Advantages brought about by the direct analysis of solid samples as compared with the analysis of dissolved samples include a shorter total analysis time (prior dissolution steps are not required), low cost (chemical reagents are not used), less risk of contamination and less destruction of the sample. In addition, some techniques can extract information about chemical speciation e.g. XPS provides information about oxidation states and chemical bonds) and spatial composition, i.e. information with lateral resolution allowing mapping of the surface and analysis with depth resolution, of particular interest for thin-film analysis. 

H. Muller. Direct Analysis of Solid Samples by Graphite Furnace Atomic Absorption Spectrometry, Fresenius J. Anal. Chem. 1997,359, 132. 

Conventional AA instruments (Figure 1) use a flame atomization system for liquid sample vaporization. An air-acetylene flame (2300°C) is used for most elements. A higher temperature nitrous oxide-acetylene flame (2900°C) is used for more refractory oxide forming elements. Electrothermal atomization techniques such as a graphite furnace can be used for the direct analysis of solid samples. 

Ren and Salin [36] showed that direct analysis of solid samples is possible, by using furnace vaporisation with Freon modification and inductively coupled plasma mass spectrometry. The relative standard deviations obtained for several metals in marine reference sediments varied from 3 to 15%. 

One of the advantages of GFAAS is the direct analysis of solid samples without prior decomposition, this technique has been reviewed by Bendicho and de Loos-Vollebregt (1991). The solid samples can be introduced directly or as a slurry. Calibration can be with aqueous standards, synthetic solids, standard additions or with SRMs. SRMs have been used for calibration for solid sampling of plant material (Schmidt and Falk, 1987). Examples of the use of solid samples with ETAAS are shown in Table 9-4. In many cases a matrix modifier is used with the sample, this allows the matrix to be volatilised at the pyrolysis stage without analyte loss, particularly important with volatile analytes such as Cd and Pb. (Ure, 1990). 

For analysis of solutions, ICP-mass spectrometry (ICP-MS) is very promising (Houk et al., 1980 Houk, 1986 Bacon et al., 1990). Recent advances in separation and preconcentration techniques are discussed by Horvath et al. (1991). Bacon et al. (1990) report that although ICP-MS is a multi-element technique, recent papers tend to concentrate on a small number of target elements. With isotope dilution mass spectrometry (IDMS), detection limits are further reduced (Heumann, 1988) IDMS is also suitable for accurate speciation in very low concentration levels of elements (Heumann, 1990). For the direct analysis of solid samples, glow discharge mass spectrometry (GD-MS) (Harrison etal., 1986) is of interest. Tolg (1988) has suggested that a substantial improvement in the absolute detection power of GD-MS, as applied to micro analysis, can be expected, at least in comparison with the ICP as ion source. 

Slurries An alternative to dry and wet decompositions is the preparation of slurries, which have been shown to provide a convenient way to introduce solid material into the plasma torch. The solid sample is not digested rather, it is finely ground and suspended in a liquid to be then introduced as an aerosol of fine, hydrated, solid particles. Thus, the direct analysis of solid samples as slurries reduces both the risk of sample contamination and the time required for sample preparation. 

Aziz A., Broekaert J. A. C., Laqua K. and Leis F. (1984) A study of direct analysis of solid samples using spark ablation combined with excitation in an inductively coupled plasma, Spectrochim Acta, Part B 39 1091-1103. 

Laqua K. (1985) A contribution to the direct analysis of solid samples by spark erosion combined to ICP-OES, in Sansoni B. (ed) Instrumentelle Multielementanalyse. Verlag Chemie, Weinheim. 

K. Sereenonchai, P. Saetear, N. Amomthammarong, K. Uraisin, P. Wilairat, S. Motomizu, D. Nacapricha, Membraneless vaporization unit for direct analysis of solid sample, Anal. Chim. Acta 597 (2007) 157. 

Analysis of Solids with Electrothermal Atomizers In most methods based on electrothermal atomizers, samples are introduced as solutions. Several reports, however, have described the use of this type of atomizer for the direct analysis of solid samples. One way of performing such measurements is to weigh the finely ground sample into a graphite boat and insert the boat into the furnace manually. A second way is to prepare a slurry of the powdered sample by ultrasonic agitation in an aqueous medium. The slurry is then pipetted into the furnace for atomization. ... 

The glow-discharge source appears to be more stable than the spark source and is less expensive to purchase and operate. It is particularly useful for the direct analysis of solid samples. Commercial quadrupole and double-focusing m.iss spectrometers with glow-discharge sources are now on the market. 

Special cup tubes are designed for the direct analysis of solid samples (Figure 71). With this technique samples can be weighed directly into the cup. The cup acts as the L vov platform and gives rise to the temperature gradient between the tube wall and cup (Figure 72). When cup tubes are used, aqueous standards are usually adequate for calibration since the cup... 

Many samples occur naturally in solid form and a number of advantages can be gained if solid samples are introduced directly into the plasma source. Pretreatment or dissolution steps are not required, and contamination from reagents is minimized. Dilution errors are also eliminated and sample losses are avoided. Sample preparation is the most time-consuming step in conventional plasma spectrometry when samples are introduced in solution form into the plasma. The direct analysis of solid samples reduces reagent and manpower costs. Improved absolute detection limits may be obtained, analysis of microsamples or localized segments of samples are possible, and the sample vaporization, atomization, and excitation steps may be separated and optimized. 

This was also mentioned earlier in context with mass spectrometry and LIBS. The unique system is suitable for direct analysis of solid samples and combines the sensitivity and isotopic measurement capability of the ICPMS with the spatial resolution of a laser system shown in Fignre 1.30 (Gnnther and Hattendorf 2005). The system combines a pulsed laser, preferably with short wavelength photon (like 193 nm from an excimer laser) in order to achieve clean ablation without melting of the sample with an ICPMS instrument (any kind is suitable). The sample is placed in a chamber (ablation cell) and a flow of gas (nsnaUy argon with some helium) carries the particles that are ablated from the sample by the laser into the torch of the ICPMS. 

Most of the mass spectrometry analyses are conducted under vacuum environment. However, ambient mass spectrometry is a rapidly growing field that provides fast and direct analysis of solid sample surfaces or liquid samples introduced on a suitable surface (Alberici et al. 2010 Weston 2010 Huang et al. 2010 Chen et al. 2010). For that, different ambient ionization MS methods, such as atmospheric pressure desorption/ionization on porous silicon (AP-DIOS) (Huikko et al. 2003), desorption electrospray ionization (DESI) (Takats et al. 2004), direct analysis in real time (DART) (Cody et al. 2005), desorption atmospheric pressure chemical ionization (DAPCI) (Takats et al. 2005), and desorption atmospheric pressure photoionization (DAPPI) (Haapala et al. 2007), have been successfully used in the direct analysis of compounds fi"om various samples, such as body fluids (Cody et al. 2005 Chen et al. 2006), finiits, plant leaves (Luosujarvi et al. 2010), milk (Yang et al. 2009), banknotes (Cody et al. 2005), textiles (Cody et al. 2005 Chen et al. 2007), and pharmaceutical formulations (Ifa et al. 2009 Gheen et al. 2010), just to mention a few, without any sample pretreatment. 

J. A. C. Broekaert, F. Leis, K. Laqua A Contribution to the Direct Analysis of Solid Samples by Spark Erosion Combined to ICP-OES," in B. Sansoni (ed.) Instrumentelle Multieleinentanalyse, Verlag Chemie, Weinheim 1985. 

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