Electronic pressure control

Applications On a comparative basis, HTGC is a relatively new tool and extremely valuable for the analyses of extracted polymer additives, as shown by industrial problem solving. For satisfactory analysis of in-polymer additives by HTGC two specific conditions are to be met. The instrument should be equipped with a cool on-column injection port to better preserve some of the additives and/or their by-products that may be thermally labile. The instrument must also have electronic pressure control so that some of the very high-boiling components, such as Irganox 1010, are... 

The reaction was followed continuously by measurement of H2 vented, through an electronic pressure controller (Rosemount Inst, model 5866) set at 9 bar, using a wet gas meter. Liquid samples, of 0.5 mL each, preceded by 0.5 mL to flush the line, were removed for NMR analysis at times corresponding to a spread of conversions from 10 to 90% as estimated from the cumulative hydrogen evolution. Spectra were recorded on 0.1 mL samples accurately diluted with 0.5 mL of D2O containing... 

H. Smith and R. Sacks, Pressure-tunable GC columns with electronic pressure control , Anal. Chem. 69 5159-5164 (1997). 

Gas permeance through the membranes was measured in the pressure-controlled dead-end mode [18], The disc-shaped membranes were placed in the commercially permeance cells, K250 and K500 as mentioned before. Maximum operation temperatures were 300 and 600°C respectively. The membrane was fitted in the cell with the microporous top-layer at the gas feed side. The pressure difference over the membrane was adjusted by an electronic pressure controller. The gas flow through the membrane was measured by electronic mass flow meters. A schematic representation of the permeance set-up is given in Figure 5. 

The pressure at the head of the column (several tens to hundreds of kPa) is stabilized either mechanically or through an electronic pressure control (EPC) in order that the flow rate remains constant at its optimal value. This device is valuable because if the analysis is performed with temperature programming, the viscosity of the stationary phase and by consequence the loss of charge in the column, increase with temperature. Therefore to maintain the carrier gas flow constant, the pressure must be finely tuned to compensate this effect. The result is a faster analysis and a longer life for the column. 

S. S. Stafford (Ed.), Electronic Pressure Control in Gas Chromatography, Hewlett-Packard, Wilmington, DE, 1993. 

The analytical procedure for extraction and class separation was adapted from Venkatesan et al. (1987) and consisted of repeated ultrasonic solvent extractions using hexane/acetone followed by saponification of the free fatty acids in KOH/methanol. The organic extract was then divided into three fractions containing aliphatics (w-alkanes), PAH and n-alcohols, and sterols using open column chromatography on 10% water-deactivated silica. Free fatty acids and n-alcohols were derivatized by BSTFA prior to analysis on GC-MS. All determinations were performed using a Hewlett Packard 5890 series 11 gas chromatograph equipped with a split/splitless injector and an electronic pressure control. The column was a 30 m X 0.25 mm ID coated with a 0.25 /rm, 5% phenyl-methylsilicone phase (J W DB-5MS) at a head pressure... 

A dramatic decrease of the time of analysis can be achieved by using narrower columns combined with an adjusted improved electronic pressure control system. As today in most forensic science laboratories the procedures developed with the normal capillary GC instrumentation are part of a quality management system, a major change using the possibilities of Fast GC requires a new validation. This, together with the high level of performance reached during the last 15 years in capillary GC, may to some extent slow down the process of innovation in this area. 

GC/MS system gas chromatograph Agilent 6890N, equipped with automatic injector, Agilent 7683 with a 100-vial tray, and split/splitless injector with electronic pressure control (EPC) up to 150 psi combined with orthogonal acceleration TOF mass spectrometer, model GCT premier (Waters Corp., Milford, MA). 

Injector Split/splitless inlet with an electronic pressure control, split ratio range 1 20-1 50... 

F. David, L. Vanderroost and P. Sandra, Analysis of Polymer Additives Using the HP5890 Series 11, Cool on Column Inlet with Electronic Pressure Control, Hewlett Packard Application Note No. 228-149,1991. 

Flow programming offers advantages such as reduced separation lime, less column bleed, and lower eluting temperature for labile compounds but has not been widely used in gas chromatography because temperature programming is experimentally easier to perform. In 1990, electronic pressure control (EPC) [30J was developed, which allows operation in the constant-pressure, constant-flow, and pressure-programming modes. Whether temperature programming will be re-... 

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