Spiked fibers

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

Plant material. Weigh 25 g of the chopped and frozen sample into a blender jar. To check recoveries, spike the fortification samples with the appropriate volume of metabolite standard at this point. Add 200 mL of acetonitrile-water (4 1, v/v) to the jar, and blend the sample at medium speed for 5 min. Filter the extract through a Buchner funnel fitted with a glass-fiber filter pad into a 500-mL round-bottom flask containing 10 drops of Antifoam B and 3 mL of 10% aqueous Igepal CO-660 (nonionic surfactant). The flask is connected to the Buchner funnel by means of an adapter suitable for applying vacuum to the system. 

Blank and spiked samples were created by pipeting standard amounts of TRIS and Decabrom onto 10 cm2 areas (2x5 cm) of glass fiber filter leaving blank (2x5 cm) blocks between each spiked area. The filter was then used to collect a 2038 m3 air sample in the Research Triangle Park, NC. This filter was shipped to the field and returned for analysis. The results of analysis of areas of the filter are shown in Table IV. These results indicate the overall recoveries for sampling, shipping and storage as well as extraction recovery from this filter. 

Seo et al. (1999) used a planar optic biosensor that measures the phase shift variation in refractive index due to antigen binding to antibody. In this method, they were able to detect S. enterica serovar T) himurium with a detection limit of 1 x 10 cfu/ml. When chicken carcass fluid was inoculated with 20 cfu/ml, the sensor was able to detect this pathogen after 12 h of nonselective enrichment. A compact fiber optic sensor was also used for detection of S. T) himurium at a detection limit of 1 X 10" cfu/ml (Zhou et al., 1997, 1998) however, its efficacy with food samples is unproven. Later, Kramer and Lim (2004) used the fiber optic sensor, RAPTOR , to detect this pathogen from spent irrigation water for alfalfa sprouts. They showed that the system can be used to detect Salmonella spiked at 50 cfu/g seeds. An evanescent wave-based multianalyte array biosensor (MAAB) was also employed for successful testing of chicken excreta and various food samples (sausage, cantaloupe, egg, sprout, and chicken carcass) for S. T) himurium (Taitt et ah, 2004). While some samples exhibited interference with the assay, overall, the detection limit for this system was reported to be 8 x 10 cfu/g. 

An example of a CILA using optical fibers has been described by Wang et al. [114] for the analysis of 6-mercaptopurine (6-MP). The template, 6-MP, was oxidized to a strong fluorescent compound by H202 in alkaline solution. Upon optimization of the H202 and NaOH concentrations and of the assay temperature, the sensor showed a linear response in the 1.0 x 10 s to 6.0 x 10 6 g mL-1 range with a detection limit of 3.0 x 10-9 g mL-1. Cross reactivity to metal ions, amino acids, and carbohydrates was tested and the sensor was applied to the analysis of 6-MP in spiked serum. 

The above conditions were satisfied with a ratchet-buckle and single flexible 1.5 inch strap. The force capable of being applied through the lever-ratchet mechanism provided more than enough force from thumb or fingers to tourniquet any size limb. The strap was stressed so that it formed a bow shape in the center and formed the favorable round shape that is preferable for decreasing strain on tissue and nerves. The ratchet-buckle consisted of spikes to penetrate a fiber-woven belt that was very successful in defeating mud, sand, and blood, example shown in Fig. 1.3. 

Thermal desorption (TD) (see Section 2.6.1) compared with solvent desorption of adsorbent tubes requires less preparation since the samples are transferred on-line from the desorber to the GC. TD of indoor SVOC samples from Tenax TA tubes and quartz fiber filters is possible (Clausen and Wolkoff, 1997b) and air samples of phthalates from chamber studies are easily analyzed using TD (Clausen et al., 2004). TD recovery may be estimated by comparing spiked tubes with direct solvent injection using the same GC (Clausen and Wolkoff, 1997b). 

Air analysis for some of the individual pesticides of this class has been published by NIOSH. These pesticides include mevinphos, TEPP, ronnel, malathion, parathion, EPN, and demeton (NIOSH Methods 2503, 2504, 1450). In general, pesticides in air may be trapped over various filters, such as Chro-mosorb 102, cellulose ester, XAD-2, PTFE membrane (1 pm), or a glass fiber filter. The analyte(s) are extracted from the filter or the sorbent tube with toluene or any other suitable organic solvent. The extract is analyzed by GC (using a NPD or FPD) or by GC/MS. The column conditions and the characteristic ions for compound identifications are presented in the preceding section. Desorption efficiency of the solvent should be determined before the analysis by spiking a known amount of the analyte into the sorbent tube or filter and then measuring the spike recovery. 

The most sensitive method for CVAA has recently been reported by Wooten et al. (39) using solid-phase microextraction to concentrate the derivatized analyte. Urine, with added ammonium acetate buffer and PhAsO as an internal standard, was derivatized directly with 1,3-propanedithiol and the derivative concentrated on a poly(dimethylsiloxane) (PDMS) solid-phase microextraction (SPME) fiber. Analysis was by automated GC/MS using SIM of the isotopic MH+ ions. An impressive detection limit of 7.4pg/ml was reported, using a benchtop GC/MS system. The method was validated using spiked human urine. 

Electrode surface activation can be improved simply by electrochemical pretreatment. Determination of nitroaromatic compounds in water and soil spiked samples have been reported at electrochemically activated carbon-fiber microelectrodes. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The detection limit obtained can be approximately 0.03 iigml-1 for all the nitroaromatic compounds (Agui et al. 2005). Chen and coworkers reported an effective field-deployable tool for detecting nitroaromatic compounds with an electrochemically pre-anodized screen-printed carbon electrode (SPE) (Chen et al. 2006). 

Myoviridae—Isometric or elongated heads and a tail complex consisting of central tube, contractile sheath, collar, base plate, six short spikes, and six long fibers... 

Coke formed on solid surfaces during the pyrolyses of acetylene, ethylene, ethane, propylene, and butadiene were examined by using a scanning electron microscope. Seven types of coke have been identified braided filament, uniform diameter filament, needle or spike, ribbon, fluffy or cottonlike fibers, knobby, and amphorous. The first four types contained metal (especially iron) and were magnetic. Magnetic cokes formed sometimes on Incoloy 800, stainless steel 304, stainless steel 410, and Hastelloy X surfaces, but never on Vycor glass or aluminized Incoloy 800 surfaces. Conditions at which each type of coke was formed are discussed. 

In these conditions the electromyogram shows typical appearances (B21a, R2a). In neuropathy, the individual denervated muscle fibers are free to discharge spontaneously, and thus at rest partially denervated muscle shows repeated single spike (fibrillation) potentials, or some-... 

Fiber type and working conditions for the HS-SPME method are reported in Table 5.13. It is worth mentioning that it is necessary to calibrate the method every time the fiber is changed using a wine pre-treated with charcoal, spiked with different quantities of standard solutions, as established in the calibration method proposed (Fedrizzi et al. 2007a 2007b). 

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