Direct injection of sample

Conditions columns, Asahipak GS320 (vinyl alcohol copolymer gel), 50 cm x 7.6 mm i.d. eluent, 0.1 M sodium phosphate containing 0.3 M sodium chloride pH 7.0 flow rate, 1 ml min-1 detection, UV 250 nm direct injection of sample. Peaks l, protein, 2, orotidine 3, creatinine, and 4, uric acid. 

Despite their distinct advantages, on-line SPE and column-switching proce-dures do not always represent ideal separation techniques. In many cases, only a small number of samples can be analyzed before contamination of the precolumn by proteins occurs. Alternative techniques that prevent the adsorption of macromolecules onto column packings and allow direct injection of sample extracts are those based on use of specific LC columns. Shielded hydrophobic phase (27), small pore reversed-phase (28), and internal surface reversed-phase (29, 30) columns can be used to elute proteins in the excluded volumes, allowing small... 

For direct injections of sample extracts Equation 6 or 10, Appendix 22... 

A 96-well SPE system for the simultaneous extraction of drugs and metabolites in biological matrices developed by Wu and coworkers (Simpson et al, 1998) is shown in Figure 6.39. In this approach, smaller elution volumes (75-200 FL) are used to improve SPE performance. This volume reduction allowed for the direct injection of samples without any evaporation and reconstitution. The collection plate that contains the elution fraction is loaded to an autosampler that is compatible with 96-well plates, thereby, eliminating the transfer to injection vials. This quantitative process improvement led to an improved analytical performance, considerable savings in time, and reduced cost. 

Capillary electrophoresis can be a powerful tool for separation and quantification of ionic substances found in soil samples. Separation speed and direct injection of samples to the capillary without labor-intensive sample preparation are the major advantages of the method for a range of samples (Cengiz and Sakul 2001). 

Determination of trace elements or anions. (i) Direct injection of sample into carrier stream of... 

Breath Collection in sampling tube direct injection of sample GC/FID 100 ppb 100 Sherwood and Carter 1970... 

Figure 4.3 Arrangement of HPLC equipment for termination of reaction by direct injection of sample. A sample is removed from the reaction mixture and transferred directly to the injection port for introduction onto the column. The HPLC column is protected by a guard column, which removes debris. The eluent flows through the detector, from which a signal is displayed on a recorder. The area of each peak is electronically integrated.

Unlike RP chromatography, NP chromatography enables the direct injection of samples extracted into a nonpolar solvent. 

LC/MS analysis of anthocyanins and their derivatives in wine can be performed by direct injection of sample without a prior sample preparation. Several methods using different chromatographic conditions have been proposed, four of which are reported in Table 3.12. 

When direct injection of samples is used, the water content of the samples may interfere with flame ionization detectors unless precautions are taken. This interference can be prevented by saturating the carrier gas with water, using a short section of column containing water (38, 39, 64, 76). Alternatively, a section of drying column may be used to remove water vaporized from the sample (38, 75, 77). 

I. Ethanol. Numerous GLC methods have been devised for the analysis of ethanol in biological fluids. Four main types of procedure may be distinguished, namely, those preceded by distillation (F2, M7), those employing extraction (Cl, L14), those using direct injection of sample or diluted sample (B17, C16, D6, Ml, M6, P4, S14), and those... 

Optimizing the resolution enhances the accuracy and precision of quantitative analysis and can also improve method robustness. It can even reduce the amount of sample preparation provided that the optimized method can handle a direct injection of samples with more complex matrices. Improved separation efficiency also translates into a higher number of components that the method is able to separate, the so-called theoretical peak capacity. Economical benefit may result from simphfied workflows with less sample preparation and improved data quality to account for more accurate analyses. 

In contrast to a direct injection of dc or ac currents in the sample to be tested, the induction of eddy currents by an external excitation coil generates a locally limited current distribution. Since no electrical connection to the sample is required, eddy current NDE is easier to use from a practical point of view, however, the choice of the optimum measurement parameters, like e.g. the excitation frequency, is more critical. Furthermore, the calculation of the current flow in the sample from the measured field distribution tends to be more difficult than in case of a direct current injection. A homogenous field distribution produced by e.g. direct current injection or a sheet inducer [1] allows one to estimate more easily the defect geometry. However, for the detection of technically relevant cracks, these methods do not seem to be easily applicable and sensitive enough, especially in the case of deep lying and small cracks. 

The direct injection of thermally unstable samples onto a capillary column. 

Ohm s law the statement that the current moving through a circuit is proportional to the applied potential and inversely proportional to the circuit s resistance (E = iR). (p. 463) on-column injection the direct injection of thermally unstable samples onto a capillary column, (p. 568) one-taUed significance test significance test in which the null hypothesis is rejected for values at only one end of the normal distribution, (p. 84)... 

Z. Yu and D. Westerlund, Char-acterization of the precolumn biortap 500 C g for direct injection of plasma samples in a column-switching system , Chromatographia, 47 299-304(1998). 

Even if the components of the sample are at concentrations where direct injection of a suitable volume is possible, all samples should be filtered before placing on the column for the reasons discussed... 

Headspace analysis has also been used to determine trichloroethylene in water samples. High accuracy and excellent precision were reported when GC/ECD was used to analyze headspace gases over water (Dietz and Singley 1979). Direct injection of water into a portable GC suitable for field use employed an ultraviolet detector (Motwani et al. 1986). While detection was comparable to the more common methods (low ppb), recovery was very low. Solid waste leachates from sanitary landfills have been analyzed for trichloroethylene and other volatile organic compounds (Schultz and Kjeldsen 1986). Detection limits for the procedure, which involves extraction with pentane followed by GC/MS analysis, are in the low-ppb and low-ppm ranges for concentrated and unconcentrated samples, respectively. Accuracy and precision data were not reported. 

Direct Injection of Amines. In the course of developing methods for investigation of in vivo formation of NMOR and NPYR in rats treated with precursor amines and nitrite, it was necessary to determine the contamination levels of the amines by the nitrosamines. Spiegelhalder et al (32) reported the presence of nitrosamines in all secondary and tertiary amine samples which they examined, using vacuum steam distillation followed by extraction and GC-TEA determination. 

Environmental monitoring of chloroacetanilides requires methods that have the capability to distinguish between complex arrays of related residues. The two example methods detailed here for water monitoring meet this requirement, but the method for metabolites requires sophisticated mass spectral equipment for the detection of directly injected water samples. In the near term, some laboratories may need to modify this method by incorporation of an extraction/concentration step, such as SPE, that would allow for concentration of the sample, so that a less sensitive and, correspondingly, less expensive, mass spectral detector can be used. However, laboratories may want to consider purchasing a sensitive instrument rather than spending time on additional wet chemistry procedures. In the future, sensitive instrumentation may be less expensive and available to all laboratories. Work is under way to expand the existing multi-residue methods to include determination of additional chloroacetanilides and their metabolites in both water and soil samples. 

Future efforts in the field of environmental analysis will be focused on several fronts, including analyte enrichment and measurement, on-line and on-site techniques, multi-residue methodology, direct injection of aqueous samples into LC/MS/MS... 

Principles and Characteristics Extraction or dissolution methods are usually followed by a separation technique prior to subsequent analysis or detection. While coupling of a sample preparation and a chromatographic separation technique is well established (Section 7.1), hyphenation to spectroscopic analysis is more novel and limited. By elimination of the chromatographic column from the sequence precol-umn-column-postcolumn, essentially a chemical sensor remains which ensures short total analysis times (1-2 min). Examples are headspace analysis via a sampling valve or direct injection of vapours into a mass spectrometer (TD-MS see also Section 6.4). In... 

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