Sample injection systems

The sample injection system is very important and critical because GC makes use of very small amounts of the samples. A good and ideal sample injection system should be the one where the sample must not— 

There are different modes of handling liquid, solid and gaseous samples in a GC which will be discussed briefly here  

The sample is vapourized as a plug and carried right into the column by the respective carrier gas. Sample size ranges between 1-10 pi. 

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A flow scheme for the basic form of ion chromatography is shown in Fig. 7.3, which illustrates the requirements for simple anion analysis. The instrumentation used in IC does not differ significantly from that used in HPLC and the reader is referred to Chapter 8 for details of the types of pump and sample injection system employed. A brief account is given here, however, of the nature of the separator and suppressor columns and of the detectors used in ion chromatography. 

Sample injection system. Introduction of the sample is generally achieved in one of two ways, either by using syringe injection or through a sampling valve. 

Sample Injection System There are in all three different modes of sample injection system that are used in HPLC, namely ... 

High Performance Liquid Chromatography (HPLC) (Chapter 30) gives an elaborate discussion of theoretical aspects. Instrumentation encompasses the various important components e.g., solvent reservoir and degassing system pressure, flow and temperature pumps and sample injection system ... 

Harrison, D. J., Manz, A., Pan, Z., Liidi, H., and Widmer, H. M. (1992). Capillary electrophoresis and sample injection systems integrated on a planar glass chip. Anal. Chem. 64, 1926-1932. 

Many manufacturers now offer other sample injection systems compatible with the vacuum lock used for the solids probe. These include small (e.g., 75-ml) heatable batch inlet systems, usually accessible via syringe (gas syringe or GC microliter syringe for liquids), which can be particularly useful as inlets for mass reference compounds. Other probes are designed as flexible, easily removed connections to a gas chromatograph via some form of interface. 

The essential components of the instrumentation are a solvent reservoir, a solvent delivery system (pump), sample injection system, packed columns, a detector(s), and a data processing system. 

A. Manz, D.J. Harrison, E.M.J. Verpoorte, J.C. Fettinger, A. Paulus, H. Ludi and H.M. Widmer, Planar chips technology for miniaturization and integration of separation techniques into monitoring systems Capillary electrophoresis on a chip, J. Chromatogr. A, 593 (1992) 253-258. D.J. Harrison, A. Manz, Z.H. Gan, H. Ludi and H.M. Widmer, Capillary electrophoresis and sample injection systems integrated on a planar glass chip, Anal. Chem., 64 (1992) 1926-1932. 

The sample injection system allows the injection of sample volumes from 1 to 500 pL. To prevent depressurization of the system, samples are injected through special six-way valves to which a sample loop has been attached. The sample is injected directly into the loop by means of a microliter syringe (filling position) while the eluent flows to the column. The eluent flow is then directed via the sample loop to the column when the valve is switched to the injection position. 

Procedure Use a gas chromatograph equipped with a hotwire detector and a suitable sample-injection system or on-column injection. Under typical conditions, the instrument contains a 1/4-in. (od) x 6- to 8-ft column, or equivalent, maintained isothermally at 70° to 80°. The flow rate of dry carrier gas is 50 to 80 mL/min, and the sample size is 15 to 20 pL (for the hot-wire detector). The column selected for use in the chromatograph depends on the components to be analyzed and, to a certain extent, on the preference of the analyst. The columns 1, 2, 3, and 4, as described under Toluene, may be used as follows (1) This column separates acetone and methanol from their aqueous solution. It may be used for... 

Figure 4.20. Headspace sample injection system (positioned in a heated oven)...

HPLC apparatus consists of a mobile-phase reservoir, a sample injection system, a column, a detector, and a recorder. The operation of most of these components is self-evident, and a schematic diagram of an HPLC apparatus is shown in Fig. 3. 

There are many sample preparation techniques listed in texts, from a simple filtration or centrifugation to many other kinds of extraction procedures, including both liquid-liquid and solid-phase extraction. When any type of sample preparation is used, it often is done manually if only a few samples are involved. If a large number of samples are to be analyzed, the entire procedure should lend itself to automation. Regardless of the number of samples, most sample preparation is done off-line that is, the samples are prepared first with one of the methods listed, then placed into an automated sample injection system for sequential analysis of all samples. 

Harrison DJ, Manz A, Fan ZH, Ludi H, Widdmer HM. Capniary Electrophoresis and Sample Injection Systems Integrated on a Planar Glass Chip. Anal Chem 1992 64 1926-32. 

GBC Scientific Equipment offers a Micro Fourier Rheometer, MFR 2100. The rheometer applies a squeezing motion to the sample, performing analyses on sample volumes less than 100 p.1. An automated sample injection system is included in the instrument design. The rheometer is capable of handling low-viscosity fluids, 1 mPas, with storage modulus measurement down to 10-4 Pa. Using a different measurement technique, both benchtop and in-line, the real-time ultrasonic rheometer and fluid characterization device uses spatially resolved ultrasonic... 

Figure 4.12 Schematic of the PDMS multichannel device interfaced to ESI-TOF-MS with sample injection system and ESI voltage connection. (Reprinted with permission from ref. 21).

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