Autosamplers

Not far behind computerized data acquisition and analysis, autosamplers are one of the biggest factors in automation, allowing long unattended series of analyses, therefore releasing the operator for other tasks. Autosamplers also give considerable improvement in reproducibility. Autoinjectors for HPLC, GC

and SFC are generally of Cartesian displacement or of carousel types.

High Performance Liquid Chromatography

HPLC is considered to be the major chromatographic technique available today for involatile or heat-sensitive substances. Sample injection is commonly performed using a switching valve via an external or internal sampling loop. Sample containers range from simple vials with a wide range of volumes to different types of microtitre plates (96 and 384 wells), with the option of temperature control. Using 384-well microtitre plates, some modern instruments can store and handle over 4600 samples unattended. Many autosamplers have three injection modes, total, partial and centred loop filling, depending on the sample volume limitations. In recent years the need for faster analysis has been a major consideration; therefore, the shortest time required between two injections (injector cycle time) appears to be an important criterion for autoinjectors, and may be less than 20 s in the fastest. Other important criteria are injection precision and the level of carryover, with typical values below 0.3% (relative standard deviation) and 0.02% respectively for the best instruments.

Gas Chromatography

Because of its extremely high separation efficiency, speed of analysis and wide range of sensitive detectors, GC and particularly capillary GC is an appropriate procedure for analysing many compounds in a great variety of applications, provided these compounds are volatile, thermally stable and with reasonable polarities to avoid problems encountered with derivatization procedures. However, until recently its major critical point was the injection of large volumes, especially when traces of organic compounds have to be analysed, and the suitability of the sample solvent. The injector influences accuracy, precision, resolution and analyte recovery. The use of new automatic injection devices has provided the means to enhance the limit of detection significantly. Five modes of operation (split, split-less, direct, cold on-column injection, and programmed temperature vaporizer) allow maximum injector flexibility. Among these, the programmed temperature vaporizer (PTV) is of major utility for the automated injection of large sample volumes (Figure 2). This technique is based on the selective elimination of the solvent, while simultaneously trapping the components with a much lower volatility. Liquid samples are introduced into a large capacity, sorbent-packed liner inserted in the injector head. By temperature-programming the liner, the solvent is vented through the split exit while analytes are retained. The split valve is then closed and the injector is rapidly heated to transfer the analytes to the GC column. With such a technique, injection volumes in split-less capillary GC can be increased up to 1 mL and this procedure therefore brings enormous improvements in limits of detection.

Static or dynamic headspace sampling, is another interesting way of injecting volatile compounds from complex matrices into a GC. In this process, the vapour in equilibrium above a sample held at constant temperature in a sealed vial is drawn and analysed. Headspace GC is used to analyse a wide range of compounds in solid and liquid complex matrices, and fully automated devices are available today with computer-activated heating and pneumatic systems.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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