Detectors two-column

High Performance Size Exclusion Chromatography (HPSEC) A Varian Model 5000 liquid chromatograph equipped with a variable wavelength UV detector, two columns in series (PL gel, 300 x7.5 mm, particle size 5/im, porosity of 50 and 500A), was used, THF being the eluent. 

NMR spectra were recorded, in CDCl with DRX-500MHz spectrometer (TMS as the reference). Size exclusion chromatography (SEC) was performed using a LDC Analytical refractoMonitor IV instrument [RI detector, two columns SDV 8x3(X) (5 pm and 104 A porosity) and SDV 8 x 300 (5 pm and 100 A porosity), eluent - toluene (0.7 ml/min)]. Parallel measurements were effected with Wyatt Optilab 903 apparatus... 

The inlet as well as the outlet streams were analysed by an on-line gas chromatography, equipped with a TCD detector. Two columns, one with TENAX (Alltech Associates, Inc.) for determination of MA and PA and other oxygenates products, and a Porapak Q (Alltech Associates, Inc.) for n-pentane were used, both stainless steel of about 2.5 m length and 1/8 in dieimeter. Heliiun was used as a carrier gas at a flow of 22 ml/min in both columns. Two loops of 1.69 and 9.50 ml were used for injection on the Porapak Q and the TENAX columns, respectively. Injection loops as well as the 6-port valve were kept at a temperature of about 175°C. A temperature program was used on both columns, i.e. 2 minutes at 70 °C and then increase of the temperature at a rate of about 20 C/min up to 190 °C for the column with Porapak Q and, for Tenax, 2 minutes at 120 °C, and then an increase up to 240 °C. 

FIGURE 5.1 Analysis of American Polymer Standards dextran standards, two columns AMGEL Linear 300 X 7.8 mm, eluant DMSO, flow rate I ml/min, temperature S0°C, detector (DRI). 

Application developed by using a Fisons GC 8000 chi omatogi aph where the two columns were installed and coupled via a moving capillary stream switching (MCSS) system. The chi omatogi aph was equiped with a flame-ionization detector on the MCSS system outlet and a Flame-photometric detector on the main column outlet, and a split/splitless injector. 

The use of extraction cartridges in the separation of azines, discussed in the last Section, is an example of on-column concentration using off-line column switching. A chromatogram can be cut off-line by collecting the zones of interest at the detector outlet followed by reinjection of the collected fraction onto a secondary column. The mobile phases used with the two columns should be compatible, eg they should be miscible and the mobile phase used with the first column should not have too high an eluting power in the second column. If the mobile phases are incompatible it may be possible to evaporate the primary mobile phase and redissolve the sample in a suitable solvent. 

A 12-port valve was used for the periodic sampling of the first column onto multiple second-dimension columns for the 2DLC analysis of aromatic amines and other species (Venkatramani and Zelechonok, 2003). The utility of the 12-port valve is that two columns can be utilized in the second dimension and flow is kept constant through both columns. This configuration requires three sample loops for implementation. The output of the second-dimension columns are connected so that both columns continuously feed the detector. 

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

It is well known that UV detectors used in liquid chromatographs are concentration-sensitive devices. Injection of the same mass of a particular compound onto two columns with identical plate number and length but different inner diameters, will result in a higher response from the column with the smaller inner diameter. The gain in the signal is inversely proportional to the square of the ratio of the inner diameters of the two columns. The situation is different for a mass spectrometer, which is a mass-flow sensitive detector. Under constant flow conditions,... 

GAS CHROMATOGRAPHIC ANALYSIS. The gas chromatograph was equipped (in the example used) with a flame ionization detector. Two stainless steel columns were packed with 5% SE-30 and 8% SE-52 on 60/80 mesh Chromasorb W-AW HMDS. The detector was maintained at 240°C and helium carrier was used at a flowrate of 3.5 cm3/min. Column temperature was programmed. The operator should determine the best rate of progression of temperature with the set-up in use. For example, one can start at 80°C and program at 4°/min up to 250°C. 

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