Samples handling

Two types of samples are usually examined by emission spectroscopy, namely  

Note (1) Both types are found to be suitable for either aqueous or non-aqueous solvents, and 

Monochromators help to isolate and separate the various lines of the sample s emission spectrum. 

Secondly, the dispersion of a prism is never constant over a wide range of wavelength, whereby the identification of either the emission lines or the unknown wavelengths is rather difficult on the basis of simply measuring their dispersions. 

The sample handling unit includes tubes, injection devices, reactors, mixing chambers and connectors, all of which are designed to permit efficient sample manipulation for accomplishing the different analytical steps involved. There are instruments where the entire unit is replaced in order to implement a different analytical procedure. The unit is then called a manifold. In this monograph, the manifold is defined as the portion of the flow system comprising the components related to stream manipulation as well as sample introduction and processing. 

Normally, the tubes used in flow analysis have internal diameters between 0.3 and 2.0 mm. Most analytical applications implemented in unsegmented flow systems are carried out inside 0.5 or 0.8 mm i.d. tubes. 

Some types of PTFE are not suitable for specific analytical applications involving gas generation, because the produced gaseous species may permeate through the tube wall. Moreover, materials melting at relatively low temperatures, such as polyethylene and polypropylene, should be avoided if the related physico-chemical processes are carried out at temperatures above 50°C. For these applications, PTFE should be used. 

Precise introduction of a well-defined portion of the aqueous sample into the carrier stream is fundamental to flow analysis. This is generally accomplished by continuously pumping the sample into the manifold for a fixed period of time (time-based introduction) or by inserting the sample aliquot via a fixed-volume loop attached to a rotary or sliding bar valve (loop-based introduction). Hydrodynamic [48] and nested [49] sample introduction have also been used. 

FIGURE 6.7 Schematic representation of manual sample introduction using syringes with (left) or without (right) a needle. 1 — syringe piston 2 = sample inserted volume 3 = needle 4 = flexible plastic septum 5 = main analytical channel (top view) 6 — Perspex support. 

Obtaining a representative sample and properly dispersing particles in the sample so that they can be measured are the two most important steps before any particle characterization technology can be applied to a particulate material. Without a well-prepared representative sample, the result, no matter how good it is, will be meaningless and irrelevant, and may be often misleading, no matter how good the instmment is. 

Concomitant to UHV compatibility is the requirement for sample cleanliness. This is realized as any undesired high vapor pressure contaminant introduced onto the area to be analyzed will cause vacuum deterioration and will introduce additional signals into the resulting mass spectra. Furthermore, some fraction of the desorbed species will adsorb on to the analysis chamber walls. This will then affect subsequent analysis because, as the vacuum improves, any species adsorbed on the chamber walls will desorb and re-adsorb onto the fresh samples being analyzed. 

In specific cases, prior removal of additional surface layers may be required. This can be carried out through  

Rinsing the sample in specific solvents/reagents before placement of the sample in the introduction chamber 

Heating thermally stable samples while in the introduction chamber. 

Once mounted (samples are usually held down by clips or inserted into spring loaded sample holders), the samples can be introduced into an introduction chamber. These tend to be of a minimal size to allow for quick pump down, with pump-down times typically in the 10-15 min range for clean samples of low porosity. In the case of highly porous samples, it is advisable to pump these down in the introduction chamber for extended periods of time (overnight before analysis may be required). 

Crucial to carrying out an INS experiment successfully is how the sample is mounted in the spectrometer. Different spectrometers require the sample to be cylindrical, annular or flat. In addition, there is the aim of the experiment is the sample to be modified in situ or will any treatments be carried out away from the spectrometer A useful review of sample environment equipment for neutron scattering has been published [42]. There is also the critical question of how much sample should be used. In the following sections these questions will be considered and also, the effect of multiple scattering. 

There are a number of advantages to FT IR methods. Since a monochromator is not used, the entire radiation range is passed through the sample simultaneously and much time is saved (Felgett s advantage)  

FT IR instruments can have very high resolution ( 0.001 cm 1). Moreover since the data undergo ana-log-to-digital conversion, IR results are easily manipulated Results of several scans are combined to average out random absorption artifacts, and excellent spectra from very small samples can be obtained. An FT IR unit can therefore be used in conjunction with HPLC or GC. As with any computer-aided spectrometer, spectra of pure samples or solvents (stored in the computer) can be subtracted from mixtures. Flexibility in spectral printout is also available for example, spectra linear in either wavenumber or wavelength can be obtained from the same data set. 

Several manufacturers offer GC-FT IR instruments with which a vapor-phase spectrum can be obtained on nanogram amounts of a compound eluting from a capillary GC column. Vapor-phase spectra resemble those obtained at high dilution in a nonpolar solvent Concentration-dependent peaks are shifted to higher frequency compared with those obtained from concentrated solutions, thin films, or the solid state (see Aldrich, 1985). 

Infrared spectra may be obtained for gases, liquids, or solids. The spectra of gases or low-boiling liquids may be obtained by expansion of the sample into an evacuated cell. Gas cells are available in lengths of a few centimeters to 40 m. The sampling area of a standard IR spectrophotometer will not accommodate cells much longer than 10 cm long paths are achieved by multiple reflection optics. 

Liquids may be examined neat or in solution. Neat liquids are examined between salt plates, usually without a spacer. Pressing a liquid sample between flat plates produces a film 0.01 mm or less in thickness, the plates being held together by capillary action. Samples of 1-10 mg are required. Thick samples of neat liquids 

For assays of stable materials with wide ranges of tolerable error, sample handling is of little concern. For assays of labile materials, especially assays for purity or for minor components, controlled sample handling procedures need to be established. There are three potential ways in which a sample may become contaminated, namely by the sampling tools, sample containers, and degradation on storage. 

Once a sample has been drawn, it should be provided with a unique label, noting the date at which it was separated from the bulk. Since samples 

Several authors have used the calorimeter for measurements of metabolic activity in soil [80, 87-99]. One of the difficulties with measurements of natural samples are of course the complexity of the system, in which many physico-chemical reactions may contribute substantially to the measured heat output. By using sterilised soil samples, a contribution of 10% of the total heat output was shown to originate from non-biological reactions [95]. The 

Quadrupole or radio-frequency mass analyzers have only recently become available with the mass range and resolution 42) to be of general use in inorganic and organometallie mass spectrometry, although they have been popular as small mass spectrometers built into specific systems as reaction monitors. They do have the advantage of essentially linear 

The details of ion sources, recently reviewed by Chait (45), and adequately covered in the major mass spectrometry texts will just be mentioned briefly, and the potential mass spectrometer user is advised to investigate the facilities in his laboratories. 

Most common ion sources are categorized as closed or tight, the inside of the cage typically being on the order of a 5-mm cube, the only passages to its interior being the electron entrance and exit slits, the positive ion exit slit, and one or more small holes for the sample inlet 

Chemical ionization (Cl) sources (48, 49) use electron bombardment of a reagent gas at higher pressures than normally found in a mass spectrometer ion source, i.e., torr. Sample ionization follows via an ion-molecule reaction, often accompanied by a proton transfer to yield a quasi-molecular ion  

This method of ionization usually causes minimum fragmentation of the molecule under investigation, and thus can be useful in establishing molecular weights, but as little fragmentation occurs it may be of less use as an aid in structure elucidation. 

FIGURE 3.4. Optical system of double-beam IR spectrophotometer. 

Solutions are handled in cells of 0.1-1 mm thickness. Volumes of 0.1-1 ml of 0.05-10% solutions are required for readily available cells. A compensating cell, containing pure solvent, is placed in the reference beam. The spectrum thus obtained is that of the solute except in those regions in which the solvent absorbs strongly. For example, thick samples of carbon tetrachloride absorb strongly near 800 cm1 compensation 

The solvent selected must be dry and transparent in the region of interest. When the entire spectrum is of interest, several solvents must be used. A common pair of solvents is carbon tetrachloride (CC14) and carbon disulfide (CS2). Carbon tetrachloride is relatively free of absorption at frequencies above 1333 cm-1, whereas CS2 shows little absorption below 1333 cm-1. Solvent and solute combinations that react must be avoided. For example, CS2 cannot be used as a solvent for primary or secondary amines. Amino alcohols react slowly with CS2 and CC14. The absorption patterns of selected solvents and mulling oils are presented in Appendix A. 

Another source that contributes to frequent differences in results during technical transfers is inefficient extraction. This is often attributed to the 

One of the challenges faced during the transfer of HPLC methods is to ensure that samples used in the transfer are from identical batches of materials. Associated with this challenge is the determination of the appropriate number of 

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Porro, T. J. Pattacini, S. C. Sample Handling for Mid-Infrared Spectroscopy, Part 1 Solid and Liquid Sampling, Spectroscopy 1993, 8(7), 40-47. 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

Fig. 1. LIMS procedure flow chart (sample handling and reporting) (4).

Owing to the light and air sensitivity of the carotenoids and retinoids, sample handling is a critical issue. It is recommended to conduct extraction of these materials with peroxide-free solvents, to store biological samples at —70° C under argon and in the dark, to perform the analysis under yellow light, and to use reference compounds of high purity (57). 

Although simple analytical tests often provide the needed information regarding a water sample, such as the formation and presence of chloroform and other organohaUdes in drinking water, require some very speciali2ed methods of analysis. The separation of trace metals into total and uncomplexed species also requires special sample handling and analysis (12). 

Sample Handling System. Venous or capillary blood, urine, and cerebrospinal fluid are specimens routinely used in medical diagnostic testing. Of these biological fluids, the use of venous blood is by far the most prevalent. Collection devices such as syringes and partial vacuum test tubes, eg, Vacutainer, are used to draw ten milliliters or less of venous blood. At collection time, the test tubes are carefully labeled for later identification. 

The tissue to be analyzed is placed directiy onto the gel. Using the tissue itself and not tissue extracts has advanced the study of proteins that are difficult to extract from tissue, or are damaged by the extraction procedure. Dtif is an important advancement in the area of sample handling and appHcation where direct appHcation of a soHd to a gel matrix may actually enhance resolution. 

Use of remote sampling, handling, and container opening techniques. This can be achieved with robots, or, more commonly, by using... 

LC-GC, therefore, shows promise for forensic science applications, reducing sample handling and preparation steps by essentially using an on-line LC column in place of one or more extraction steps. This is followed by a traditional high resolution GC analysis. The methods described here for pesticides and hormones could be readily adapted to a variety of analyses, especially those involving fatty matrices. Such as tissues, food or blood. 

Procedure. To 100 mL of distilled water, add 5mL of concentrated sulphuric acid, cool and then add 5 g of pure boric acid when this has dissolved cool the mixture in ice. Transfer gradually from a weighing bottle about 0.5 g (accurately weighed) of the sodium peroxide sample (handle with care) to the well-stirred, ice-cold solution. When the addition is complete, transfer the solution to a 250 mL graduated flask, make up to the mark, and then titrate 50 mL portions of the solution with standard 0.02 JVf permanganate solution. 

For greater details on the techniques of LS counting in general, including the specialized nuclear instrumentation required and sample handling and preparation, see Refs 5, 6 7... 

The inherent lability of alkene- and hydroxyalkanesulfonates, variations in isomer composition, and the presence of the disulfonates are features which complicate AOS analyses. Improper sample handling, such as exposure to high temperatures, can also alter active matter composition. Consequently, analytical procedures have been developed that minimize potential sources of error. 

Wotschokowsky, M., Witzenbacher, M., Godau, S. 5th. Int. Symp. on Sample Handling of Environmental and Biol. Samples in Chromatography. Poster Na 36/91, Baden-Baden 1991. 

Nitridoborates of lanthanum and the lanthanides were obtained from reactions of lanthanide metal or lanthanide metal nitride with layer-like (a-)BN at elevated temperatures (3>1200°C). These reactions require elaborated techniques in the inert gas sample-handling and the use of efficient heating sources, such as induction heating. Only some compounds remain stable in this high-temperature segment, and the yields of such reactions are often limited due to the competing stability of binary phases, allowing only the most (thermodynamically) stable compounds to exist. 

An interesting development is the combination of HPLC and on-line measurement of reducing capacity or antioxidative activity. This approach allows both direct identification of antioxidative species in complex foods and quantification of the contribution to the overall antioxidative capacity in the absence of synergistic and antagonistic effects. Major advantages are less sample handling and the ability to rim large series of samples in an automated process. 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

Lazar, I. M., Karger, B. M., Multiple open-channel electroosmotic pumping system for microfluidic sample handling. Anal. Chem. 74 (2002) 6259-6268. 

TCDD). The majority of these samples have been collected and analyzed at an average cost of 700 per sample. This includes per diem, labor, equipment, expendable supplies, transportation, and 400 per analysis by contract laboratories. An evaluation of this data has suggested that field sampling and sample handling methods have a significant impact upon the precision and accuracy of the resulting data which, in turn, impact the cost and feasibility of various remedial options. 

Field measurements provide savings in sample handling and analysis time, and they eliminate costly delays when re-sampling is required. In addition, they permit important real-time decisions by the on-scene cleanup coordinator regarding removal of sufficient contaminated soil to effect the desired cleanup while avoiding the removal of low-level contamination beyond that required. 

For a detailed discussion of the art of sample handling and data acquisition for blood gas measurements, see National Committee for Clinical Laboratory Standards. Blood gas pre-analytical considerations specimen collection, calibration, and controls Proposed Guideline. NCCLS publication C27-P, Villanova, Pennsylvania, NCCLS, 1985... 

Similar to most Hg sampling methods, sampling sediments and soils require care in avoiding contamination artifacts due to improper sample handling. However, because Hg concentratiorrs are much higher in soUd matrices than in water, if corrrmonly accepted trace-metal protocols are used, substantial contamination artifacts should be exceedingly rare. Also, because sediment Hg concentration profiles... 

Cali JP, and Reed WP (1976) The role of the National Bureau of Standards standard reference materials in accurate trace analysis. In Lafleur PD, ed. Accuracy in Trace Analysis Sampling, Sample Handling, and Analysis, NBS Special Publication 422, Vol i pp 41-63. National Bureau of Standards, Washington, DC. 

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