Direct sample analysis

C.E.C. Magalhaes, M.A.Z. Arruda, Slurry sampling the technique employment in the direct sample analysis, Quim. Nova 21 (1998) 459. 

Chromatography is often employed in food analysis because separation of analytes is required from interfering matrix components prior to quantification. However, most of the biological molecules present in food matrices (proteins, for instance) are not compatible with organic solvents present in chromatographic mobile phases, which hinders direct sample analysis. Prior sample treatment is needed, with purification and preconcentration of analytes. 

Atomic absorption spectroscopy is an alternative to the colorimetric method. Arsine is stiU generated but is purged into a heated open-end tube furnace or an argon—hydrogen flame for atomi2ation of the arsenic and measurement. Arsenic can also be measured by direct sample injection into the graphite furnace. The detection limit with the air—acetylene flame is too high to be useful for most water analysis. 

Even within a single sample analysis, it is hkely that some of the reported concentrations are known with greater accuracy than others. L oratory personnel will know which concentrations can be rehed upon and which should be questioned. The plant-performance analyst should know at this stage which of the concentrations are of greatest importance and direct the discussion to those components. 

The chemical composition of particulate pollutants is determined in two forms specific elements, or specific compounds or ions. Knowledge of their chemical composition is useful in determining the sources of airborne particles and in understanding the fate of particles in the atmosphere. Elemental analysis yields results in terms of the individual elements present in a sample such as a given quantity of sulfur, S. From elemental analysis techniques we do not obtain direct information about the chemical form of S in a sample such as sulfate (SO/ ) or sulfide. Two nondestructive techniques used for direct elemental analysis of particulate samples are X-ray fluorescence spectroscopy (XRF) and neutron activation analysis (NAA). 

As already remarked in Sect. 4.5.1 (Introduction), LA was primarily designed as a technique for direct sampling in the bulk analysis of solid samples. The main advantages of LA are the possibility of ablating all types of solid material (metals, isolators, glasses, crystals, minerals ceramics, etc.), no special requirements on the... 

Electropherograms of a urine sample (8 ml) spiked with non-steroidal anti-inflammatory drugs (10 p-g/ml each) after direct CE analysis (b) and at-line SPE-CE (c). Peak identification is as follows I, ibuprofen N, naproxen K, ketoprofen P, flurbiprofen. Reprinted from Journal of Chromatography, 6 719, J. R. Veraait et al., At-line solid-phase exti action for capillary electrophoresis application to negatively charged solutes, pp. 199-208, copyright 1998, with permission from Elsevier Science. 

Figure 13.6 Direct RPLC analysis of a blank ground water sample spiked with 4.5 (p-g 1 ETU, (a) with and (b) without column-switching. A 60 X 4.6 mm i.d. column and a 150 X 4.6 mm i.d. column were used for C-1 and C-2, respectively, with pure water as M-1 and methanol-0.025 M ammonium acetate (pH, 7.5) (5 95, v/v) as M-2 S-1 and S-2 aie the interfering peaks. Reprinted from Chromatographia, 31, E. A. Hogendoom et at., Columnswitching RPLC for the trace-level determination of ethylenetlaiourea in aqueous samples , pp. 285-292, 1991, with permission from Vieweg Publishing.

Figure 13.7 Selectivity effected by employing different step gradients in the coupled-column RPLC analysis of a surface water containing 0.40 p-g 1 bentazone, by using direct sample injection (2.00 ml). Clean-up volumes, (a), (c) and (d) 4.65 ml of M-1, and (b) 3.75 ml of M-1 transfer volumes, (a), (c) and (d), 0.50 ml of M-1, and (b), 0.40 ml of M-1. The displayed cliromatograms start after clean-up on the first column. Reprinted from Journal of Chromatography, A 644, E. A. Hogendoom et al, Coupled-column reversed-phase liquid chromatography-UV analyser for the determination of polar pesticides in water , pp. 307-314, copyright 1993, with permission from Elsevier Science.

The second technique involves direct sampling of the reactor effluent (Figure 5-2). In this technique, a sample of reactor effluent is collected in an aluminized polyester bag for separation and analysis. 

This feasibility study shows that determination of pellet wt by fast neutron oxygen activation analysis can be used for quality assurance inspection of M34 primers. Either direct oxygen analysis, where a comparison standard (such as lucite) is used, or a ratio method, utilizing the Cu in the cup-anvil combination as an internal standard, can be applied. In general, the uniformity of production primers is quite satisfactory, as is usually the case where production procedures are standardized. It seems likely that the light pellet is one which has been improperly manufd and will probably be well below specifications in pellet wt. Production experience with such primers indicates that only one in 3x10s primers is expected to show low pellet wt therefore, one would not expect to find a reject in a small sampling. Nevertheless, detection and rejection of this one bad unit is critical for the prevention of weapon malfunctions and possible injuries to personnel... 

Direct instrument control (or the lack of it) was an important issue for the earlier version of CDS. The scheme of connecting the detector channels through A/Ds to CDS worked well in analytical laboratories across the pharmaceutical industry. The scheme provided enough flexibility so that the CDS could collect data from a variety of instruments, including GC, HPLC, IC, SFC, and CE. It was equally important that the CDS could be connected to instruments that were manufactured by different vendors. It was not uncommon to find a variety of instruments from different vendors in a global pharmaceutical research company. The disadvantage of this scheme was that the instrument metadata could not be linked to the result file of each sample analyzed. It could not be guaranteed that the proper instrument parameters were used in sample analysis. Another need came from the increased use of... 

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. 

Direct calibration of methods and instrumentation i.e. ensuring that an analytical device is giving a correct reading. For some types of direct soUd sample analysis, sample results can be calibrated using several CRMs with suitable matrices (Kur-furst 1998) see also Section 4.4. 

Yields a sample ready for direct further analysis (no concentration or clean-up steps)... 

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