Chromatography valves

Columns used for internal chromatography operations are most conveniently dry-packed outside the glovebox. Both ends should be fitted with a 3-way chromatography valves(11) to facilitate sample injection and effluent distribution operations. After purging the... 

To calibrate the coulometric system, including the response factor of the coulometer, a gas loop calibration system can be used. In principle it consists of a chromatography valve with sample loops of different sizes that can be filled with a calibration gas of high purity (> 99.99 % pure CO2). Prior to injection of the caUbration gas into the system, the temperature and pressure have to be measured accurately, as they have a significant impact on the amount of CO2 in the gas loop. 

Liquid water and liquid benzene have very small mutual solubilities. Equilibria in the binary water-benzene system were investigated by Tucker, Lane, and Christian as follows. A known amount of distilled water was admitted to an evacuated, thermostatted vessel. Part of the water vaporized to form a vapor phase. Small, precisely measured volumes of liquid benzene were then added incrementally from the sample loop of a hquid-chromatography valve. The benzene distributed itself between the hquid and gaseous phases in the vessel. After each addition, the pressure was read with a precision pressure gauge. From the known amounts of water and benzene and the total pressure, the liquid composition and the partial pressure of the benzene were calculated. The fugacity of the benzene in the vapor phase was calculated from its partial pressure and the second viiial coefficient. 

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). 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

Figure 2.20 Schematic representation of the set-up used for on-line exti action-GC VI and V2, valves PI and P2, syringe pumps L, sample loop CC flow, countercunent flow CT, cold ti ap. Reprinted from Journal of High Resolution Chromatography, 16, H. G. J. Mol et ai, Use of open-tubular tapping columns for on-line exti action-capillary gas cluomatography of aqueous samples , pp. 413-418, 1993, with permission from Wiley-VCH.

Figure 5.4 Schematic diagrams of a heait-cut valve configuration system. Reprinted from Journal of Chromatography, 602, S. R. Villasenor, Matrix elimination in ion cliromatography by heart-cut column switching techniques , pp. 155-161, copyright 1992, with permission from Elsevier Science.

Figure 10.3 Gas cliromatograms of a cold-pressed lemon oil obtained (a) with an SE-52 column in the stand-by position and (b) with the same column showing the five heart-cuts (c) shows the GC-GC chiral chromatogram of the ti ansfeired components. The asterisks in (b) indicate electric spikes coming from the valve switcliing. The conditions were as follows SE-52 pre-column, 30 m, 0.32 mm i.d., 0.40 - 0.45 p.m film tliickness cairier gas He, 90 KPa (stand-by position) and 170 KPa (cut position) oven temperature, 45 °C (6 min)-240 °C at 2 °C/min diethyl-tert-butyl-/3-cyclodextrin column, 25 m X 0.25 mm i.d., 0.25 p.m film thickness cairier gas He, 110 KPa (stand-by position) and 5 KPa (cut position) oven temperature, 45 °C (6 min), rising to 90 °C (10 min) at 2 °C/min, and then to 230 °C at 2 °C/min. Reprinted from Journal of High Resolution Chromatography, 22, L. Mondello et al, Multidimensional capillary GC-GC for the analysis of real complex samples. Part IV. Enantiomeric distribution of monoterpene hydrocarbons and monoterpene alcohols of lemon oils , pp. 350-356, 1999, with permission from Wiley-VCH.

Figure 10.4 Schematic representation of the multidimensional GC-IRMS system developed by Nitz et al. (27) PRl and PR2, pressure regulators SV1-SV4, solenoid valves NV— and NV-I-, needle valves FID1-FID3, flame-ionization detectors. Reprinted from Journal of High Resolution Chromatography, 15, S. Nitz et al, Multidimensional gas cliro-matography-isotope ratio mass specti ometiy, (MDGC-IRMS). Pait A system description and teclinical requirements , pp. 387-391, 1992, with permission from Wiley-VCFI.

Figure 11.3 Typical configuration for the on-line coupling of an achiral and chiral cliro-matograpliic system by means of a switching valve. The non-enantio-resolved solute is isolated on the achiral phase and then stereochemically separated on the chiral phase. Reprinted from G. Subramanian, A Practical Approach to Chiral Separation by Liquid Chromatography, 1994, pp. 357-396, with permission from Wiley-VCH.

Figure 12.23 SFC-SFC analysis, involving a rotaiy valve interface, of a standard coal tar sample (SRM 1597). Two fractions were collected from the first SFC separation (a) and then analyzed simultaneously in the second SFC system (h) cuts a and h are taken between 20.2 and 21.2 min, and 38.7 and 40.2 min, respectively. Peak identification is as follows 1, tii-phenylene 2, chrysene 3, henzo[g/ i]perylene 4, antliracene. Reprinted from Analytical Chemistry, 62, Z. Juvancz et al, Multidimensional packed capillary coupled to open tubular column supercritical fluid chromatography using a valve-switcliing interface , pp. 1384-1388, copyright 1990, with permission from the American Chemical Society.

Figure 12.24 Schematic diagram of the multidimensional packed capillary to open tubular column SFC-SFC system. Reprinted from Analytical Chemistry, 62, Z. Juvancz et al., Multidimensional packed capillary coupled to open tubular column supercritical fluid chromatography using a valve-switching interface , pp. 1384-1388, copyright 1990, with permission from the American Chemical Society.

Figure 13.5 Schematic presentation of the procedure involved in coupled-column RPLC AS, autosampler C-1 and C-2, first and second separation columns, respectively M-1 and M-2, mobile phases S-1 and S2, interferences A, target analytes HV, high-pressure valve D, detector. Reprinted from Journal of Chromatography, A 703, E. A. Hogendoom and R van Zoonen, Coupled-column reversed-phase liquid cliromatography in environmental analysis , pp. 149-166, copyright 1995, with permission from Elsevier Science.

The dimensions of the exit tube from the detector are not critical for analytical separations but they can be for preparative chromatography if fractions are to be collected for subsequent tests or examination. The dispersion that occurs in the detector exit tube is more difficult to measure. Another sample valve can be connected to the detector exit and the mobile phase passed backwards through the detecting system. The same experiment is performed, the same measurements made and the same calculations carried out. The dispersion that occurs in the exit tube is normally considerably greater than that between the column and the detector. However, providing the dispersion is known, the preparative separation can be adjusted to accommodate the exit tube dispersion and allow an accurate collection of each solute band. 

High Performance Liquid Chromatography. All separations were performed using an Altex Scientific (1780 Fourth Street, Berkeley, CA 94710) Model 320 Advance Research Chromatograph, consisting of a model lOOA dual piston analytical pump, a Model 153 UV detector, a Model 210 injection valve, and a Model 155 recorder. The columns (600 x7.5mm) evaluated were the Spherogel TSK-SW-2000 and SW-3000 (Altex). Unless otherwise stated, all separations were carried out at 23 - 25 . 

---