Valve injectors, liquid chromatography

For liquid chromatography, a sample of the mixture solution is injected through a loop injector which allows a quantity of the solution to be placed in a small tubular loop at atmospheric pressure. By manipulating a valve, the high-pressure flow of solvent to the column is diverted through the loop, carrying the sample with it (Figure 35.5). 

The D4 content of the samples was determined by reverse-phase high-pressure liquid chromatography (HPLC) with a Varian 5500 liquid chromatograph. A DuPont Zorbax ODS (Cis) column was used with a Wilmad infrared detector set at 12.45 xm to monitor the Si-CHa vibration. The mobile phase was an 83 17 mixture of acetonitrile and acetone at a flow rate of 0.8 mL/min. A Rheodyne injector valve operating on compressed air was used with a 10-p,L sample loop for reproducible injection volumes. Ethyl acetate was used to dissolve the samples for analysis. 

High Performance Liquid Chromatography. Tissue extracts were analyzed with a Varian model 5020 liquid chromatograph equipped with a Rheo-dyne model 7120 loop injector valve, a Tracer 970 variable wavelength detector set at 257 nm, an automated Hewlett-Packard 3385A printer-plotter system for determining retention times and peak areas, and a Waters /x Bondapak column (3.9 mm i.d. X 300 mm) for carbohydrate analysis. The buffer was eluted isocratically at 1 mL/min with a 1 4 (v/v) mixture of 0.01 M monobasic sodium phosphate (pH 4.46) and methanol. The minimum amount detectable was 10 ng. 

Liquid Chromatography System. The solvent delivery system was constructed of two lO-mL stainless-steel syringe pumps (MPLC Micropump, Brownlee Labs, Santa Clara, CA). By splitting the pump effluent between the mlcrocolumn and a restricting capillary (1 20-1 2000), Isocratlc separations were achieved reproduclbly at column flowrates as low as 0.005 pL/mln, and gradient separations as low as 0.1 pL/mln. Samples of 0.5 to 50 nL volume were Introduced by the split Injection technique with a 1- L valve Injector (Model ECI4W1., Valeo Instruments Co., Inc., Houston,... 

Figure 4 Apparatus for solvent purification by frontal chromatography 1, glass column with cooling jacket 2, glass sinter 3, silica gel or alumina adsorbent 4, siphon-type injector 5, container for unpurified solvent 6, PTFE tube 7, moisture trap 8, valve 9, container for purified solvent. (Reproduced with permission from Buszewski B, Lodkowski R, and Trocewicz J (1987) Purification of solvents for liquid chromatography. Journal of High Resolution Chromatography and Chromatography Communications 10 527-528.)...

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