Solid Sample Preparation

There is greater similarity in the behavior of stretched melts and solid samples prepared by, e.g. pressure molding, probably, for the reason of parallelism in structure formation and destruction caused by deformation in melts and the amorphous regions of solid matrices. It is also possible to use identical equations for longitudinal viscosity and strength which present them as functions of the filler concentration [34]. 

Destructive solid sample preparation methods, such as digestion and mineralisation, are well known as they have been around for some time they are relatively cheap and well documented [13-15]. Decomposition of a substance or a mixture of substances does not refer so much to the dissolution, but rather to the conversion of slightly soluble substances into acid- or water-soluble (ionogenic) compounds (chemical dissolution). 

Figure 8.2 Modem solid sample preparation flow-chart...

Solid samples preparation procedures vary with their specific form of presentation, namely ... 

R. D. McDowall, J. C. Pearce, and G. S. Murkitt, Liquid-solid sample preparation in drug analysis, J. Pharm. Biomed. Anal., 4 3 (1986). 

Harbour JR, Hopper MA, Marchessault RH, Dobbin CJ, Anczurowski E (1985) Photoacoustic spectroscopy of cellulose, paper and wood J Pulp Pap Sci 11 J42-J47 Hauser M, Oelichmann J (1988) A critical comparison of solid sample preparation techniques in infrared spectroscopy Microchim Acta (Wien), Spec Issue, I 39-43 Hergert HL (1971) Infared spectra In Sarkanen KV, Ludwig CH (eds) Lignins Occurrence, formation, structure and reactions Wiley-Interscience, New York, 267-293 Hirschfeld T (1987) In McClure GL (ed) Computerized quantitative infrared analysis ASTM, Philadelphia, 169-179... 

As noted earlier, some of the steps that precede the insertion of the treated sample into the instrument for measurement (e.g. dissolution, clean-up, preconcentration, individual separation, derivatization) can have a critical influence on accuracy and precision depending on the particular step. All analytical processes include a sample preparation step which is a function of a number of factors such as the physical state of the sample, the nature of the sample matrix and analytes or the type of detector, for example. The first distinction therefore refers to the nature of the sample solid, liquid or gas. Solid samples are the most difficult to process as most analytical instruments cannot handle them. Therefore, the first operation in solid sample preparation involves transferring the target analytes to a liquid phase. This can be carried out in various ways including total dissolution of the test sample or partial dissolution or separation of a portion thereof. The different choices, which can be assisted by ultrasound, are depicted in Fig. 2.2, and discussed in the following sections. 

Wang, M.Z. and Fitzgerald, M.C. (2001) A solid sample preparation method that reduces signal suppression effects in the MALDI analysis of peptides. Anal. Chem. 73, 625—631. 

The total elapsed time is substantially less with SFE extraction than with conventional liquid-solid extractions. Moreover, the hands-on time required of the operator for the pre-extraction steps prior to SFE (5-10 minutes) would be only a fraction of the total hands-on sample preparation time required by employing tradition preparation processes (30 minutes) - an advantage over traditional methods. In the case of the vitamin-A active compounds, the extraction and analysis for four samples with two replicates each (a total of 8 extractions and 8 analyses) using the conventional manual method requires 4 hours. For the combined SFE and analyses for the 8 extractions and 8 analyses, the total elapsed time is 3 hours. However, until an operator has worked with both SFE and traditional liquid-solid sample preparation, it is not obvious that the operator intervention (or hands-on) time is much different. It is estimated that this may be as much as 70 % of the 4 hours in the traditional method and as little as 10 % in the 3 hours of the SFE method. 

A solid sample prepared by either crushing a mixture of crystals in a mortar or by resolidification of a molten mixture afforded a similar result. 

Figure 3.6 TEM image for shell-cross-linked PI320-6-PFS53 cylindrical micelle solid samples prepared by drying a drop of THF solution on a carbon-coated copper grid. THF is a common solvent for both blocks. Scale bar = 250 nm. (From Wang et al.49 Reproduced with permission.)...

The solid-sample preparation is usually achieved by the deposition on a metallic surface of the solution of matrix and analyte with a concentration suitable to obtain the desired analyte/matrix ratio. The solution is left to dry under different conditions (simply at atmospheric pressure, reduced pressure, or under a nitrogen stream). This method is usually called the Dried Droplet Method. In all cases, what is observed is the formation of an inhomogeneous solid sample, due to the different crystallization rate of the matrix and analyte. Consequently, the 10 molar ratio is only a theoretical datum In the solid sample, different ratios will be found in different positions and the only way to overcome this is to average a high number of spectra corresponding to laser irradiation of different points. 

A classical liquid-solid sample preparation technique is Soxhlet extraction. The apparatus consists of a pot of extracting solvent which is refluxed to provide fresh hot solvent to drip through the solid sample. Solubility is maximized by using the clean hot solvent for dissolution. The sample is contained in a porous thimble held between the solvent flask and the reflux condenser. The Soxhlet technique is not often used in routine pharmaceutical sample preparations for two reasons the high temperature can cause degradation which is unacceptable for stability-indicating assays, and the technique is difficult to perform on multiple samples because of time and space requirements. 

Another technique used for ionization of elements for MS determination is the spark-source technique (SS-MS), which presupposes solid sample preparations. A recent application of this technique on biological samples was described by Moody and Paulsen (1988). To avoid spectral interferences from organic ions, the samples were burnt in an oxygen stream. Mercury was collected in a liquid nitrogen trap, dissolved and coprecipitated with Ag as sulfide. The detection limit was probably in the range 10-100 g/kg dry matter. 

A solid/solid sample preparation method, consisting of mixing analyte and matrix without any solubilization procedure, was reported for the MALDI analysis of some polyamides (e.g., poly(examethylene terephthalamide) and Ny )... 

In eqn [10], Cf is the concentration of analyte in the prepared standard, Aa is the analytical response to the analyte in the sample, and Astd is the analytical response to the analyte in the prepared standard. For solid samples, preparation of valid calibration standards is more difficult because the analyte in the real sample may be bound in a different form from that in the standard. These so-called matrix effects are difficult to overcome however, the method described next provides a viable approach. 

For many years, the traditional sample preparation methods, such as the Soxhlet extraction, were applied. Most of these methods have been used for more than 100 years, and they mostly require large amounts of organic solvents. These methods were tested during those times, and the analysts were familiar with the processes and protocols required. However, the trends in recent years are automation, short extraction times, and reduced organic solvent consumption. Modern approaches in solid sample preparation include microwave-assisted solvent extraction (MASE), pressurized liquid extraction, accelerated solvent extraction (ASE), matrix solid-phase dispersion (MSPD), automated Soxhlet extraction, supercritical fluid extraction (SEE), gas-phase extraction, etc. 

Smear films best suited for viscous and grease-like materials (including solid samples prepared as a mull)... 

A schematic block diagram of the newly designed chirped-pulse Fourier transform microwave spectrometer CP-FTMW, combined with a ps-pulsed laser ablation system, is given in Fig. 3. The spectrometer, which uses the basic operation of the CP-FTMW instrument [18], is described elsewhere [63], with only the relevant details to this experiment being described here. It operates in the 6.0-18 GHz region. The solid sample, prepared as usual as a rod shape, was placed in a laser ablation nozzle, similar to that previously described [61] (1 in Fig. 3) and vaporized using the second (532 nm) or third (355 nm) harmonics of a ps Nd Y AG laser (i.e. Ekspla, 20 ps, 15 mJ/pulse) (2 in Fig. 3). A motor controller (3 in Fig. 3) allows a DC motor (Oriel Motor Mike 18074) (4 in Fig. 3) to rotate and translate the rod up and down along the injection system to achieve the maximum exploitation of the... 

Heat extraction techniques for solid sample preparation in GC are static and dynamic headspace analysis (SHS, DHS, HS-SPME and HSSE), thermal desorption (TD-GC, TD-GC-MS), pyrolysis and thermochromatography. Nomenclature is not unambiguous as to DHS, TD and PT. The terminology purge-and-trap is usually preferred for the simplest dynamic technique in which it is not necessary to subject the sample to either solvents or elevated temperatures. Scheme 2.7 shows the family of headspace sampling techniques. Headspace sorptive extraction (HSSE) and HS-SPME represent high capacity static headspace. 

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