Sample Substrates

Except for some of the fixation studies (for which Raman data were also acquired) and for studies in aqueous media (see later), all sample preparations used reflection-coated glass slides as sample substrates. Raman data are prone to show some glass signatures when these slides are used consequently, some studies that relied on a combination of Raman and IR data were carried out on CaF2 disks. Similarly, CaFj was used as a substrate for IR studies of live cells, as prolonged exposure to water damaged the reflective slides. 

Recently, a potential source of artifacts was pointed out [19] due to a standing electromagnetic wave that forms on all reflective surfaces. The amplitude of this wave depends strongly on the wavelength of the incident radiation and confounds the observed intensities. However, we have shown [16] that the errors for thin flat cells are relatively small, and can be further reduced by data preprocessing methods. 

---

Classical approaches to plant DNA isolation aim to produce large quantities of highly purified DNA. However, smaller quantities of crudely extracted plant DNA are often acceptable for PCR analysis. Another efficient method for preparation of plant DNA for PCR is a single-step protocol that involves heating a small amount of plant tissue in a simple solution. Several factors influence nucleic acid release from tissue salt, EDTA, pH, incubation time and temperature. These factors must be optimized for different sample substrates. EDTA in the sample solution binds the Mg + cofactor required by the Taq polymerase in the PCR, so the EDTA concentration in the solution, or the Mg + concentration in the PCR, must be carefully optimized. 

Average recoveries for fenoxycarb, Ro-16-8797, and Ro-17-3192 for all animal sample substrates ranged from 80% (beef kidney) to 111% (goat kidney), 76% (goat milk) to 93% (beef omental fat), and 56% (dairy milk) to 76% (beef perirenal fat), respectively. The LOQ and LOD were 0.01 ig g and 2.5 ng injected, respectively. 

Labelling the 3-APTHS molecule with "OH groups provides an isotopic tag at the site on the molecule where cross-linking should take place. 3-APTHS hydrolyzed in 97.8 at %, 80 labelled water was spun onto sample substrates in the manner described above and SSIMS spectra were acquired both at room temperature and after heating of the sample to 100°C in vacuum for 1 h. The relative intensity of the oxygen containing ions produced by these samples can be... 

Sample Substrate(s) added ju,L 02 absorbed Excess ju,L 02 consumed... 

Apiezon Wax Sample base plate Silver paste Sample substrate... 

Homogeneous assays, which are not submitted to separation steps, pose different requirements for optimal results, such as the absence of endogeneous enzyme or inhibitors in the sample, substrate depletion, and cross-reactivity. 

For single point measurements, individual cells were selected from the visually acquired sample image, as seen on the screen. For each cell position on the sample substrate, the aperture was selected to straddle the cell, and typically was 30 gm x 30 gm. The cell position and apertures were stored for each cell, and the data acquisition of aU stored positions proceeded automatically. The microscope and optical bench were continuously purged with purified, dry air. In addihon, the sample area in the focal plane of the microscope was enclosed in a purged sample chamber. 

In order to ensure the source of oxygen atom incorporated in the products formed, 0 labelling experiments were carried out for the oxidation of two sample substrates [4] cyclohexane (saturated) and cyclohexene (unsaturated) by using a 50 50 isotopic mixture of... 

Table 6.36 Fields of application of solid sampling substrates.

Only recently has the problem of the loss of pesticide from patches used In the field been addressed ( ). Many studies do not report laboratory or field recovery data for sampling substrates or comment on correction for recovery of the data (,9). Serat ( ) found that cotton gauze retained only 30% of extractable parathlon and 70% of extractable dlcofol under field conditions. He concluded that In the absence of adequate controls to determine the quantity of chemical lost from the fabric collectors there Is no assurance that the extracted depositions represent anywhere near the actual values. This factor seriously limits the usefulness of many older exposure studies. New techniques using fluorescent markers (10) are promising and will undoubtedly lead to more quantitative estimates of contact exposure. 

Matrix assisted laser desorption/ionisation (MALDI) For laser desorption methods a pulsed laser is used to desorb species from a target surface. Therefore, a mass analyser compatible with pulsed ionisation methods has to be used. Typically, time-offlight (TOF) analysers are employed, but several hybrid systems (Q-TOF) and, recently, high resolution Fourier transform ion cyclotron resonance (FT-ICR) analysers have been successfully adapted (see Section 10.2.4). Direct laser desorption rehes on the very rapid heating of the sample or sample substrate to vapourise molecules without decomposition. The more recent development of MALDI relies on the absorption of laser energy by a solid, microcrystalline matrix compound such as a-cyano-4-hydroxy ciimamic acid or sinapinic acid [8, 34]. MALDI has become an extremely popular method for the rapid and sensitive analysis of high-molecular-weight compounds [4]. 

---