High speed autosamplers

Solid-phase microextraction (SPME). used as a sample introduction technique for high speed gc, utilizes small-diameter fused-silica fibers coated with polymeric stationary phase for sample extraction and concentration. SPME lias been utilized for determination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fuscd-silica fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph. Full automation can be achieved using an autosampler. 

Syringe handling Slow movement of the plunger can almost eliminate the pressure wave but results in enhanced discrimination of sample components. Rapid injection using the hot needle or solvent flush method is preferred. Autosamplers capable of high speed and reproducible injection times provide improved performance. 

FMOC) reagent, which also ensures derivatization of the secondary AAs. A high-speed elution of OPA/ MPA/FMOC derivatives has been observed recently (Table 2, Figure 3B 19 compounds/8 min). In the new improved methods, shorter, thermostated columns of smaller particle size with autosamplers are used, which provide greater sensitivity and reproducibility. 

There are several other factors that are important when it comes to the selection of equipment in a measurement process. These parameters are items 7 to 13 in Table 1.2. They may be more relevant in sample preparation than in analysis. As mentioned before, very often the bottleneck is the sample preparation rather than the analysis. The former tends to be slower consequently, both measurement speed and sample throughput are determined by the discrete steps within the sample preparation. Modern analytical instruments tend to have a high degree of automation in terms of autoinjectors, autosamplers, and automated control/data acquisition. On the other hand, many sample preparation methods continue to be labor-intensive, requiring manual intervention. This prolongs analysis time and introduces random/systematic errors. 

Proteomics research is currently driving HPLC technologies towards high sensitivity, speed, and peak capacities.8 Capillary LC (sometime termed micro LC or nano LC)18,19 is used to enhance mass sensitivity needed to analyze minute sample amounts. System requirements for handling extremely low flow rates and small peak volumes mandate the use of specialized HPLC system such as the one shown in Figure 4.14a, which has a micro-pump, a micro x-y-z autosampler, and a PDA detector with a low-volume flow cell. Figure 4.14b illustrates the performance at 12pL/min of this system. 

Major manufacturers of HPLC instruments include Waters, Agilent (formerly Hewlett Packard), and Shimadzu, PerkinElmer, Thermo, Beckman, Varian, Hitachi, Jasco, Dionex, Gilson, Scientific Systems (SSI), and Isco. The Internet addresses of these companies can be found in the reference section. HPLC is a mature technology and most manufacturers have highly reliable products with sufficient performance and feature sets to be competitive in the market place. However, there can still be significant differences between the vendors on these performance characteristics on systems (dwell volume, dispersion), pumps (low flow, seal life), autosamplers (carryover, speed, sample capacity, minimum sample volume), and detectors (sensitivity, gradient baseline shift). 

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