Sample Preparation and Measurements

Handbook of Spectroscopy, Volume 1. Edited by Gunter Gauglitz and Tuan Vo-Dinh Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-29782-0 

A sketch of a gas cell with multipass optics in the so-called White arrangement is given in Fig. 6.2. It comprises three spherical mirrors, which can be adjusted for the desired number of passes. Four passes (as shown in Fig. 6.2(a)) is the minimum number of passes in such an arrangement. The achievable maximum number of passes depends on the reflectivity of the mirrors and on the quality of the incoming beam. The latter is partly defined by the size of the IR source. Commer- 

Spectra of compounds with vapor pressure down to 0.001 Torr can be obtained using multipass gas cells. This technique has proved very useful for the detection of atmospheric impurities or trace components in waste and combustion gases. 

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Very fast sample preparation and measurement (20 samples on a sample slide in 1 h)... 

The use of external chemical standards is suitable for many applications. Ideally, chemical standards should be matrix-matched with samples to ensure that they respond to the measurement process in the same way as the samples. In some cases, a sample preparation and measurement process has inherent faults... 

Fig. 1.4.5 Effects of blood storage temperature and delay between sample preparation and measurement on the lactate pyruvate ratio...

Sample preparation and measuring apparatus has been discussed and hence this section will deal with the principal item, the tensile machine, together with grips and extensometer. The tensile machine is in fact very often a universal machine in that, apart from tensile tests, it can also be used for flexural, compression, tear and adhesion tests. The basic elements of a tensile machine are shown diagrammatically in Figure 8.10. 

Electronics for controlling instrument-operating parameters, such as temperature and pressure, have contributed to more stable operation. This produces better repeatability of the system for multiple cycles leading to higher precision of component isolation. Advantage of improved measurement devices can be realized once the sample preparation function is resolved. Computer hardware and software provide expanded capability for signal processing and data manipulation. Stable and precise sample preparation and measurement systems allow accurate analytical information provided that adequate maintenance and calibration practices are applied,... 

Day 3,9 a.m. Set up temperature control on the measurement tempering blocks. At 9 a.m. the samples will have completed their 40-hr cycle and can be transferred to 0°C until 10 30 a.m. They are then held at the measurement temperature and can be measured starting at 11 30 a.m. It should be possible to complete the measurements and make the calculations by noon and then prepare an additional batch in the afternoon. It is also possible to have another set of samples prepared and measured on even-numbered days. 

Because consistency is strongly affected by temperature and concentration of soluble solids, both parameters should be carefully controlled during sample preparation and measurement. Filling the Bostwick reservoir, leveling the product, and releasing the gate must be done in a timely manner to prevent separation of serum and changes in temperature. 

The largest time factor in this procedure is associated with adjusting the Brix level of the samples and equilibrating their temperatures. The time required for sample preparation and measurement is estimated to be 15 min per sample. 

Also he speculated that citrus juices contain two cloud-coagulating enzymes of different thermostabilities. One enzyme, most active at low pH and temperature, appeared to be destroyed by heating the juice at 65 to 70°C (149 to 158°F). The second enzyme, most active at pH 3.0 to 3.3 and about 35°C (95°F), appeared to require heating to 888C (191°F) for inactivation (12). Stevens (13) described a rapid test for pectic enzymes in citrus juice. It involved adding pectin under controlled conditions of temperature and sample preparation, and measuring the time required for flocculation. Stevens, and coworkers (14) further elaborated on the patent work (12, 13). They produced a trend curve of the... 

Uncontrolled species transformations during analysis form another source of error. For methylmercury determinations in sediments it was demonstrated that errors of up to 80% resulted from the formation of the compound from inorganic mercury during separation and analysis [28, 29], For the study of possible species transformations during analysis multiple isotope dilution could be used as a diagnostic tool for identifying the error and bias inherent in specific methods of storage, sample preparation and measurement [30, 31]. 

A sample of the water used to pass through the pump should also be collected. These samples should be taken at the beginning and end of each day s sampling. These blanks assess the adequacy of the decontamination process and also assess the total contamination from sampling sample preparation and measurement processes. 

To obtain the RMSEP, the validation samples prepared and measured independently from the calibration samples are used. The number of validation samples, p, should be large, so that the estimated prediction error accurately reflects all sources of variability in the calibration method. The RMSEP is computed by... 

Obtain chromatograms of duplicate 5-p.L portions of the Hexane Standard Solution, and measure the areas under the hexane and n-nonane peaks. In a similar manner, obtain chromatograms of duplicate 5-p.L portions of the Sample Preparation, and measure the areas under the hexane and w-nonanc peaks. The peak area ratio of hexane to w-nonanc (i.e., sum of hexane areas divided by sum of w-nonanc areas) produced by the Sample Preparation does not exceed that produced by the Hexane Standard Solution. 

Generally, twice a year, they get aerosol samples from filters flown by the Swiss Army at altitudes between 5000 and 12,000 m above sea level. Sample preparation and measurement conditions are the same as described above for the high-volume-sampler filters. Figure 9.16 shows that not only the Be activity increases sharply across the tropopause (around 11,000 m) but also the Cs activities. The Cs/ Cs ratio clearly shows that the Cs in the stratosphere now mainly consists of Cs from the Chernobyl accident. 

In-line In-line implements sampling, sample preparation, and measurement directly in the process, keeping the sample inside the production line. This is the preferred domain of laser diffraction... 

Table 6.10 Results of measured versus added concentration of listed metal in aerosol solvents. The values are the average of three sample preparations and measurements. [Note Correction for density/weight of solvent used in calculation of true concentration averaged between p = 0.77 to 0.82 depending on solvent(s) used]...

Table 7.14 Brief list of common metals and metals in foods, method of sample preparation and measurement method used. The list and sources of effects are by no means exhaustive...

From previous statistical studies on similar systems which Include the combination of errors Involved in sample preparation and measurement of static compressive stress-strain characteristics, the following reproducibility results were obtained (4,5, ) ... 

Unlimited travel, allowing easier sample preparation and measurements after failure. 

The authors thank Andrea Kress and Liz Ramos for diligent sample preparation and measurement support. The art work of Ralph Alvarado is also much appreciated. 

The UPS spectra of lying pentacene (PEN) on Au(lll) [9] and standing PEN on a conducting polymer substrate [10] [poly(3,4-ethylenedioxythiophene)/poly (styrenesulfonate) - PEDT PSS] have been reported before details on sample preparation and measurements can be found in these earlier reports. 

An important precondition for the successful determination of carbon isotope ratios is the prevention of isotopic shifts as a result of the analytical procedures applied. Therefore, five recovery experiments were performed in order to detect changes of the carbon isotope ratios during sample preparation and measurement. The compounds selected for these experiments are known riverine contaminants and comprise hexachlorobutadiene, several musk fragrances, phthalates and other plasticizers, a flame retardant and a pesticide. All recovery samples were spiked with concentrations between approx. 800 ng/L and 1500 ng/L for each compound representing a common abundance level in river systems. 

A breakdown into finer classification is more useful and such a summary listing of techniques for the quantitative determination of elements is given in Table 2.4 (Ihnat 1994, 2000d, Ihnat et al. 2001, Dybc-zynski et al. 1997, Mavrodineanu 1977, Pszonicki and Hanna 1985, Quevauviller etal. 1993). The compilation is by several of the common, major determinative methodologies with further subdivisions into more specific techniques and includes abbreviations. It is by no means a comprehensive documentation (left for a future classification activity) which would include additional major and subtle variants as well as the latest and automated sample preparation and measurement techniques. 

For measuring the resistivity of the films as a function of temperature, a continuous flow cryostat (Oxford Inst. Model CF-1204) with a temperature controller was used. The details of the sample preparation and measurement have been described previously (3). A temperature controlled silicon diode ( 0.1 K) was mounted next to the sample for accurate temperature measurement. X-ray powder diffraction patterns were obtained using a computerized Phillips powder diffractometer (Type AFD 3520) with Ni-filtered CuKa radiaticm. 

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