Instruments gas chromatographic

Instrumentation Gas-chromatographic determination for rice grain, water and soil... 

Instrumentation Gas-chromatographic determination, high-performance liquid chromatographic determination... 

The analysis of polynuclear aromatic hydrocarbons pollutants was performed on a Fisons Instrument Gas Chromatograph GC-800 series, connected to a Fisons Instrument Mass Selective Detector (MS) MD-800. 

Precision The precision of a gas chromatographic analysis includes contributions from sampling, sample preparation, and the instrument. The relative standard deviation due to the gas chromatographic portion of the analysis is typically 1-5%, although it can be significantly higher. The principal limitations to precision are detector noise and the reproducibility of injection volumes. In quantitative work, the use of an internal standard compensates for any variability in injection volumes. 

Instrumental Interfaces. The basic objective for any coupling between a gas chromatograph (gc) and a mass spectrometer (ms) is to reduce the atmospheric operating pressure of the gc effluent to the operating pressure in the ms which is about 10 kPa (10 torr). Essential interface features include the capability to transmit the maximum amount of sample from the gc without losses from condensation or active sites promoting decomposition no restrictions or compromises placed on either the ms or the gc with regard to resolution of the components and reliability. The interface should also be mechanically simple and as low in cost as possible. 

The first (direct reading) method is fairly simple and results are available immediately. However, the instruments have limited sensitivity and must be recalibrated periodically. The second (absorption in a liquid or adsorption on a medium) and third (gas container) methods are generally considered more sensitive and more accurate method for trace analysis by gas chromatographs, infrared... 

Gas chromatograph (GC) An analytical instrument with an internal tube or column that contains a solid sorbent, which allows some components of an injected sample to pass more quickly than others, separating the substances in the sample. 

Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatograph separates the components of a mixture in time, and the mass spectrometer provides information that aids in the structural identification of each component. The gas chromatograph, the mass spectrometer, and the interface linking these two instruments are described in this chapter. 

Flammable atmospheres can be assessed using portable gas chromatographs or, for selected compounds, by colour indicator tubes. More commonly, use is made of explos-imeters fitted with Pellistors (e.g. platinum wire encased in beads of refractory material). The beads are arranged in a Wheatstone bridge circuit. The flammable gas is oxidized on the heated catalytic element, causing the electrical resistance to alter relative to the reference. Instruments are calibrated for specific compounds in terms of 0—100% of their lower flammable limit. Recalibration or application of correction factors is required for different gases. Points to consider are listed in Table 9.10. 

The most common types of preparative-scale gas chromatographic instruments are based on pacXed column technology [489-491]. The primary objective in preparative-scale gas chromatography is to obtain a high sample throughput. An inevitable result of this goal is that either resolution or separation time, or both, must be compromised. The primary method... 

High speed separations, particularly with narrow-bore HCOT columns of 100 aicroneters or less, places special demands upon the instrument design [131,134,148-150]. The gas chromatograph... 

GC-IMS-MS instruments are ideally suited for laboratory studies, as a complex mixture can be separated ionisation in relatively clean systems can take place and the identity of the ions can be studied and verified by mass spectrometry [315]. However, the cost of such systems is quite prohibitive, and their complexity confines their utilisation to the laboratory. In GC-IMS-MS, the gas chromatograph is used to preseparate the components of the sample, with the IMS used as its detector. The ions that constitute the mobility spectrum are then further characterised by MS. 

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