Preparation of sample

Often it is necessary to use some chemical procedures to prepare a sample for spectroscopic analysis. This section will not detail such methods, since they are available in standard texts and references. Some of the more common techniques will be given to indicate some of the possibilities. 

A most common procedure with plant and animal tissue is to destroy and remove organic matter by ashing. Either a wet or dry ashing technique can be used. In addition to removing organic matter, this process also concentrates the metal ions and atoms into a more usable sample. The ashing procedure can be modified to produce either a solid or liquid sample. 

Frequently a concentration step is desirable in the pretreatment of a sample. If the sample can be placed in solution, several concentration techniques are available, including precipitation, ion exchange, solvent extraction, and electrolysis. Concentration steps are more difficult if the sample must remain a solid some possibilities for solid powder samples include high-temperature distillation, flotation, and magnetic separation. 

If it is desired to remove considerable matrix material, it may be that quantitative removal is unnecessary. For example, if the matrix substances make up 95 % of the sample and 90 % of the matrix can be removed, a tenfold concentration of the desired constituents results. 

Each sample concentration problem should be approached on the basis of type of sample and of the analytical data desired. A suitable separation method can then usually be devised. 

Preparation of grapes can be performed by adding an adequate aliquot of 10% HC104 to the destemmed sample, homogenizing using Ultra-turrax 

For HTCO analysis, manufacturers offer various combinations of instruments. Since it is difficult if not impossible to draw up an exhaustive list of all commercially available and laboratory-made apparatus, we only mention, with one example each, a few of the most frequently used configurations. Some instruments (e.g.. Ionics) use a combination of high temperature (900 °C) and pure platinum as catalyst. Others (e.g., Shimadzu), use platinised alumina catalysts at lower temperature (680 C). Analytik Jena sells an instrument working with a CuO catalyst at 950 °C. Antek produces a total nitrogen analyser based on the same principle (900 °C, on silica beads). The combination used by Sugimura and Suzuki (1988) which triggered the controversy on DOC concentrations was close to the Shimadzu design. The sample was injected vertically into a furnace filled with 3 % Pt on aluminium oxide, at 680 °C. 

The following data and information mostly derive from personal experience (field and laboratory) with a Shimadzu TOC5000 apparatus for carbon and a Sievers NOA270B for total nitrogen. 

Polyphenolic compounds can interfere in the analysis of red wines, and amino acids in the analysis of grape juices. Consequently several methods for isolating biogenic amines from wines and juices have been proposed liquid-liquid extraction with butanol of the sample preliminarily concentrated and adjusted to pH 1.5 (Almy et al, 1983) in general, for SPE is preferred strong cation exchange (SCX) under 

Most of the analytical techniques applied in art conservation research require the preparation of the sample prior to the analysis step. Although the sample preparation procedures vary in a wide range, five basic types of procedures can be established grinding, dissolving, derivatizing, melting and embedding. 

Powdering, or grinding, of samples is a simple preparation method required in a number of spectrometric and spectroscopic techniques, such as x-ray diffraction (XRD), nuclear magnetic resonance (NMR), differential thermal analysis (DTA), thermogravimetric analysis (TG), or ATR-FTIR spectroscopy. Control of the particle size during grinding must be taken into account in attempting to obtain reliable results. 

Dissolution of the sample is the method required in a number of spectroscopic and chromatographic techniques (e.g., UV-Vis spectrophotometry, atomic absorption spectroscopy (AAS), high performance liquid chromatography (HPLC), and thin-layer chromatography (TLC)). Selection of the suitable solvent is essential 

Application of gas chromatographic techniques is restricted by the necessary volatility that the analyzed compounds should exhibit. A derivatization reagent is added, in a prior step, to render volatile the components of the analyzed organic materials. In some cases, a prior step consisting of an acid or alkaline hydrolysis of the organic material is necessary for releasing the molecular constituents of the polymeric structure. Inclusion of a prior step in the preparation procedure devoted to the suppression of interfering species is sometimes included. 

Melting of samples is necessary for performing the analysis of ceramics and glass materials by means of x-ray fluorescence (XRF). Lithium tetraborate is added as flux for lowering the melting temperature. The homogeneous disks that form can be considered a solid solution of the sample compounds in the binder. 

Suitable solvents are those which dissolve lignin to the maximum extent possible without interfering significantly with the lignin NMR signals. Usually the solvent is deuteriated. The solvent deuterium NMR resonance is usually used for the field-frequency lock signal. The most common lignin solvents and their relevant 

Deuterium oxide (DzO) alone or mixed with DMSO-d6 is suitable for dissolving lignosulfonates (Hassi 1984) that are not completely soluble m any other solvents 

For highest signal/noise ratio, the concentration (C) has to be as high as possible (S/N a C) as long as the solutions are not too viscous A suitable concentration is between 20 and 30% (w/w) (400 to 600 mg m 1 8 ml DMSO-dA m a 10-mm tube) Nevertheless, all concentration ranges down to 100 mg in 1 8ml solvent may be used provided the number of acquisitions, NA, is increased since S/N improves proportionately with VNA 

A 10-mm OD tube is filled to a depth of at least 4 cm to provide adequate sample height, to minimize any vortex formation, a Teflon vortex plug is used 

NMR tubes are thoroughly cleaned by successive washing with acetone and distilled water and subsequently dried in an oven All metal ion-containing cleaning solutions should be avoided 

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For small-scale preparation of samples for scientific studies, the precursor polymer may be dissolved in xylene at 80°C, followed by addition of the cation source. A gelled fluid is normally obtained immediately, and the ionomer is recovered as a powder by chopping the gel in a large excess of acetone using a laboratory blender. 

As a method of research, has been used high-performance liquid chromatography in reversed - phase regime (RP HPLC). The advantage of the present method is the following the additional information about AIST and FAS composition (homologous distribution) simple preparation of samples (dilution of a CS sample of in a mobile phase). 

Determination of Na " and Na" ions in raw cosmetic materials was conducted with the developed method of flame photometry. A necessity of development of method of samples preparation arose up in the work process, as this spicily-aromatic raw material contained pectin in amount 0.1-0.5% and that prevented preparation of samples by standard method of extracts dilution and required incineration of analyzed sample, time of analysis was increased in 60 times. It was established that CaCl, solution with the concentration 0,4 % caused destmctions of the carbopol gel. It was established that the addition of 0,1% CaCl, and 0,1% NaCl salts solutions into the system intensified the effect of negative action of these salts onto the gel stmcture and the gel destmcted completely. 

Environmental analytical association Ecoanalytica produce standai d samples during last 12 years. Two topics will be discussed. The first is the principles of development of staictures and maintenance of quality of standai d samples. The organization of manufacture and maintenance of their stability ai e considered too in the report. Besides them authors consider scientifically-methodical aspects of preparation of samples for experimental check of technical competence of analytical laboratories and also samples for interlaboratory tests. 

For the preparation of samples for X-ray fluorescence spectroscopy, lithium metaborate is the preferred flux because lithium does not give rise to interfering X-ray emissions. The fusion may be carried out in platinum crucibles or in crucibles made from specially prepared graphite these graphite crucibles can also be used for the vacuum fusion of metal samples for the analysis of occluded gases. 

E. Rapkin, Guide to Preparation of Samples for Liquid Scintillation Counting , New England Nuclear Corp, Boston, Mass (1975)... 

Solid samples are generally treated in one of two ways. If completely soluble, they can be dissolved directly and completely in a suitable solvent. Alternatively, if the samples contain insoluble materials that are of no interest, then they can be extracted with a selected solvent to obtain the relevant compounds in solution. The extract can be subsequently filtered or centrifuged to remove any unwanted substances that make up the sample matrix. The procedure will differ, depending on the amount of the substances present that are germane to the analysis. The preparation of samples for LC analysis from solid... 

N, /V-dimethylformamide.60 The sugars were isolated on a column of Dowex-50 X8 in the calcium form.6 Both d-(1-i3C)- and D-(2-l3C)-ribose are now commercially available. These sugars allowed the preparation of samples of AIRs labeled with 13C either on C-T or on C-2 In conclusion, four ribonucleosides are now available practically fully labeled at a single position.58... 

For quantitative work, it is necessary to estimate the concentration of 5-amino-l-(P-D-ribofuranosyl)imidazole in aqueous solution. It seems that the only available method is the Bratton-Marshall assay, which was originally developed for the estimation of arylamines in biological fluids. The principle of the method is the spectrometric estimation of a salmon-pink colored dyestuff obtained by diazotation in situ, followed by coupling with /V-( 1 -naphthyl)ethyl-enediamine.65 The only remaining problem then is to know the molar extinction of this dye because pure samples of AIRs are not available. A value of 16800 at 520 nM was obtained for the dyes prepared from a model compound, 5-amino-l-cyclohexylimidazole-4-carboxylic acid (54), which is crystalline. A comparable molar extinction can be expected for the dye prepared from imidazole 55, if the carboxyl group does not exert too much influence on the chromophore. Actually, its influence is perceptible even with the naked eye, the dyestuff prepared from 53 having a somewhat different, wine-red color, with max>520 nM. The molar extinction for 55 is 17400 at 500 nM. When the decarboxylation of 54 was conducted under mild acidic conditions (pH 4.8, 50°C, 1 hour), estimation of 5-aminoimidazole 55 by the Bratton-Marshall method led to the conclusion that the reaction was almost quantitative.66 Similar conditions for the final decarboxylation were adopted in the preparation of samples of AIRs labeled with stable isotopes.58... 

The basic technology for the preparation of sample material is similar in all TLC preparations, irrespective of the origin of the hpid and specific preparation method for a variety of biological samples [43]. The most important factor is the solubihty of the sample. The lipid sample must be completely soluble in the dissolving solvent prior to the application and must be free from water. Either toluene or chloroform is commonly used as the solvent to dissolve hpid materials. The dissolving solvent should be nonpolar in namre and volatile at such a concentration that the hpid components in the sample are completely adsorbed throughout the entire thickness of the layer as quickly as possible. Although sample sizes as small as 1 to 10 pi can... 

E. Procedure. The procedure section should unambiguously describe the stepwise preparation of samples, standards, and blanks. Instrumental variables should be described. Weight and volume measurements should include the acceptable range. The procedure should also include methods for any calculations. Procedures should include, but are not limited to, the following recommended elements ... 

Many of the classical techniques used in the preparation of samples for chromatography are labour-intensive, cumbersome, and prone to sample loss caused by multistep manual manipulations. During the past few years, miniaturisation has become a dominant trend in analytical chemistry. At the same time, work in GC and UPLC has focused on improved injection techniques and on increasing speed, sensitivity and efficiency. Separation times for both techniques are now measured in minutes. Miniaturised sample preparation techniques in combination with state-of-the-art analytical instrumentation result in faster analysis, higher sample throughput, lower solvent consumption, less manpower in sample preparation, while maintaining or even improving limits. 

Like tetrasulfur tetranitride, salts of trisulfur trinitride and of pentasulfur tetran-itride (particularly alkali-metal salts) are heat- and friction-sensitive explosives. Preparation on a scale limited to 1 g, and care in use of spatulae or in preparation of samples for IR examination is recommended. 

N. Menguy and E. Larquet of IMPMC (UPMC) are sincerely thanked for their support in TEM Tomography studies. K. Gaid and C. Louis are acknowledged for their contribution to the preparation of samples. The authors are grateful to C nano-IdF for financial support (CCD acquisition, Camel project). 

Finally, in order to make a comparison of the amount of polymer that could be physisorbed, as distinct from terminally-grafted, one sample (S12/PS19, Table III) was prepared in which "dead" PS19 was added to a dispersion of silica S12 in DMF, using essentially similar conditions and quantities as in the preparation of sample S12/PS13a by the grafting route. 

For those who are concerned with the preparation of samples for the direct 14C counting systems, this summary vividly illustrates the effects on the final age value as a result of the addition of ppm levels of modern carbon for samples in different age ranges. For a sample with an actual age of 75,000 years, for example, a 100 ppm addition of modern carbon results in approximately a 5000-year error in the final measured age. Hopefully, contamination of a sample with modern carbon would be a relatively rare occurrence. A more probable situation would involve the addition of carbon differing in age from the original samples from several hundred up to several tens of thousands of years. 

Nuclear magnetic resonance (NMR) can be used like IR to help identify samples. But if you thought the instrumentation for IR was complicated, these NMR instruments are even worse. So I ll only give some generalities and the directions for the preparation of samples. 

The usefulness of the ultracentrifuge in the preparation of samples rather than in the production of analytic data should not be overlooked. Preparative ultracentrifuges have utility in fractionating polymer samples and in freeing them from easily sedimented impurities. 

The Analysis of Agricultural Materials, 2nd edn, R.B. 427. HMSO, London, (1979) Method 2, p. 6. Preparation of Samples of soil Method 8, p. 21. Boron, water soluble in soil Method 57, p. 134. Nitrogen in soil Method 62, p. 148. Organic matter in soil Method 63, p. 151. Particle size distribution in soil... 

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