Single-gas chromatographic system

FIGURE 10.23 Ideal configurations for a single-gas chromatographic system gas dehv-CTed from cylindo-s [reprinted with permission of Supelco, Bellefonte, PA 16823 (USA)]. 

TWO INDEPENDENT COLUMN/DETECTOR SYSTEMS. This mode of operation actually provides two independent gas chromatographic systems operating simultaneously. Each detector has its own amplifier-electrometer and recorder. The recorders may consist of a dual pen recorder or two single pen recorders. Since the two chromatograms are normally not related to each other and the starts of the analyses do not necessarily have to be simultaneous, the use of two single pen recorders is usually preferred. 

It is prudent to use a well maintained gas chromatograph system as a single source for these values since the total energy measured is multipled by some monetary value per GJ (MMBTU). (See Appendix A). 

A logical development of the carrier gas technique has been the introduction of a gas chromatographic column between the transmission cell and the detector [37 39], This permits gas mixtures to be used for the permeant and their individual transmission rates to be measured. It should be noted that no single gas chromatographic column and detector combination is suitable for all gases. The system must be chosen to suit the permeant and the carrier gases being used. In addition, a pulsed input to the column is required if separation of components is achieved by elution development. This is the most common and versatile method of separation. 

The price of a column ( 200- 800) may be viewed as relatively small compared to the initial, the routine, and preventive-maintenance costs of the instrument. In fact, a laboratory may find that the cost of a set of air and hydrogen gas cylinders of research grade purity for FID operation is far greater than the price of a single conventional capillary column Consequently, the column should be carefully selected for an application, handled with care following the suggestions of its manufacturer, and installed as recommended in the user s instrument manual to derive maximum performance from a gas chromatographic system. 

In reality it is neither practical nor desirable to step the column oven temperature in 10° increments every minute, nor does the stepwise model predict elution times with sufficient accuracy for our purposes. If we now imagine instead that the oven temperature increases in 1° steps every 6 s or even better in 0.1° increments every 600 ms, we can approach a true linear temperature program rate of 10°C/minute as is encountered in modem gas chromatographic systems. Our isothermal retention data at 50 and 60°C are still valid, and we could calculate the peak positions for each 0.1°C step in a tabular format. The problem is that even this small a step is still too large for accurate prediction of programmed-temperature retention times. Instead, we must to turn to calculus and consider an arbitrarily small step size (dt). A simplified relationship of a single-step linear temperature program to elution time can be expressed as follows [13] ... 

In the chemical data systems - filament coil type pyrolyser, Pyro-probe 122.the polymer samples are held in a quartz tube that is inserted into the platinum coil. If pyrolyses are to be conducted at slow rates the pyrolyser is interfaced to a sample concentration (Model 320, Chemical Data Systems) which collected the pyrolysates on a Tenax filled trap. In this way polymer samples can be processed for minutes or hours at slow heating rates and the pyrolysates collected for a single gas chromatographic analysis. When the pyrolysis is complete, the trap is pulse heated and backflushed with the carrier gas. The desorbed pyrolysates are transferred to a gas chromatograph (Model 3700 Varian or equivalent) equipped with a 50 m x 0.25 mm i.d. SE-54 capillary column (Quadrex). 

Kremer L, Spicer LD. 1973. Gas chromatographic separation of hydrogen sulfide, carbonyl sulfide, and higher sulfur compounds with a single pass system. Anal Chem 45 1963-1964. 

Chromatographic fixed-bed reactors consists of a single chromatographic column containing a solid phase on which adsorption and reaction take place. Normally a pulse of reactant is injected into the reactor and, while traveling through the reactor, simultaneous conversion and separation take place (Fig. 3). Since an extensive overview of the models and applications of this type of reactor was presented by Sardin et al. [ 132], only a few recent results will be discussed here. Most of the practical applications have been based on gas-liquid systems, which are not applicable for the enzyme reactions, but a few reactions were also reported in the liquid phase. One of these studies, performed by Mazzotti and co-workers [ 141 ], analyzed the esterification of acetic acid into ethyl acetate according to the reaction ... 

Tor reference. Positive identification can be made only by collecting the compound or transierring it as it elutes directly into another apparatus for analysis by other means, such as infrared or ultraviolet spectroscopy, mass spectrometry, or nuclear magnetic resonance. Commercially available apparatus is available which combines in a single unit both a gas chromatograph and an infrared, ultraviolet, or mass spectrometer for routine separation and identilicalion. The ancillary system may also be microprocessor-based, with an extensive memory for storing libraries of known infrared spectra or fragmentation patterns (in the case of mass spectrometers). Such systems allow microprocessor-controlled comparison and identilicalion of detected compounds. 

---