Sample preparation on-line

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

FIGURE 9.5 2D-LC system set-up with integrated on-line sample preparation. 

Before compounds in biological matrices can be analyzed by LC/MS/MS, the samples must undergo a preparation procedure. There are a variety of techniques available for sample preparation including offline sample preparation techniques (liquid-liquid extraction, protein precipitation, and solid phase extraction) and on-line sample preparation... 

Kaiser [3U used on-line sample preparation to determine trace anions in solvents, including isopropanol, acetone and Af-methylpyrrolidone. A large solvent injection can interfere with both the ion exchange separation and the conductivity detection by causing large disturbances in the baseline. In this application the anions were concentrated on a AG9-HC guard column and then the solvent was sent to waste before it could enter the analytical column. After the solvent was cleared from the AG9-HC concentrator column, the AG9-HC concentrator was switched in line with the AS9-HC analytical column for the separation. The method detection limits for chloride, sulfate, phosphate and nitrate are reported in the sub pg/1 range. 

The processes of sample preparation should not be too onerous or slow otherwise there is little incentive to use sensors. Faced with an awkward or slow sample preparation phase for sensor use, the analyst might as well as consider whether instrumental analyses with their often higher sensitivity and specificity (and which, in any case, are regarded as the gold standard for industrial measurements), coupled with on-line sample preparation procedures, might be a more efficient and effective route to chemical information. 

Li, M., Alnouti, Y., Leverence, R., Bi, H., and Gusev, A. I. (2005a). Increase of the LC-MS/ MS sensitivity and detection limits using on-line sample preparation with large volume plasma injection. J. Chromatogr. B Anal. Technol. Biomed. Life Set 825 152-160. 

Souverain, S., Rudaz, S., and Veuthey, J. L. (2004b). Restricted access materials and large particle supports for on-line sample preparation An attractive approach for biological fluids analysis. J. Chromatogr. B Anal. Technol. Biomed. Life Sci. 801 141-156. 

A list of the 64 analytes and their method performance is shown in Table 6.6. The increased number of analytes is possible because of improvements to the collision region of the MS/MS system that provide increased sensitivity and reduced memory effects. In addition, robotic systems for sample handling and on-line solid-phase extraction (SPE) of plasma samples were integrated with the LC/MS/MS system (Figure 6.22). An isocratic reversed-phase HPLC method provided a cycle time of 4.5 min per sample. The on-line sample preparation and short analysis resulted in an increased sample throughput that required less time from the scientist. The... 

Sample preparation in CE is similar to sample preparation in HPLC (Section 3.8). It is usually performed off-line in CE, because commercial instrumentation does not allow for on-line sample preparation. The exception is sample preconcentration, which is readily performed on-line. Sample preparation includes any manipulation of the sample, such as weighing, filtration, dilution, or derivatization, prior to introduction into the CE system. 

MICROSCALE ON-LINE SAMPLE PREPARATION 3.1. Capillary Electrophoresis... 

On-Line Sample Preparation for Biological Fluids. There is a continuing demand for high-throughput bioanalytical method based on... 

D. R. Doerge, M.I. Churchwell, K.B. Delclos, On-line sample preparation using RAM in the analysis of the soy isoflavones, genistein and daidzein, in rat serum using LC-ESI-MS, Rapid Commun. Mass Spectrom., 14 (2000) 673. 

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