Pump, analytical

Tandem mass spectrometer with HPLC pump, analytical column (LC-18S, 200 x 4.6 mm Supelco 59630), autosampler and data-handling system. 

The method of Thurnham etal. (1988) was modified for the quantification of plasma j3C and retinol. Plasma extracts were dissolved in 40 /il of dimeth-ylforamide and vortexed and then 210 pil of acetonitrile/methanol/chloro-form (47/47/6, v/v/v) was added. Reconstituted samples were vortexed and sonicated for 40 sec prior to being transferred to autosampler vials and sealed under nitrogen. The HPLC system consisted of a photodiode array detector (Waters 9%, Miliipore Corp., Milford, MA) with Millennium software, a Waters 717 plus autosampler, and a Hewlett-Packard Model 1050 pump. Analytes of interest were separated using acetonitrile/methanol/ chloroform (47/47/6, v/v/v), with 0.05 M of ammonium acetate and 1% triethylamine at a flow rate of 1.2 ml/min and a 4.6 X 15-cm Spherisorb ODS-2 column (LKB Instruments Ltd., Surrey, UK) maintained at 26°C using a column heater (Timberline Instruments Ltd., Boulder, CO). This analysis does not discriminate between C-enriched and nonenriched analytes, but rather measures the total concentration of each isotopomer. The retention times of retinol, retinyl acetate (internal standard), and /3-carotene were 2.1, 2.6, and 16.9 min, respectively. Plasma concentrations of retinol and /3C were calculated using a standard curve for each analyte and an internal standard to correct for volume recovery. 

As shown in Figure 1, an SFA system consists of five basic components sample changer, peristaltic pump, analytical manifold, detector, and data output system. The manifold contains the mixing coils, dial-yzer, heater, and other components through which sample and reagents are pumped and where sample clean-up and reaction takes place. The data output... 

This experiment describes the construction of an air sampler using an aquarium pump, a flow meter, a filter holder, and bottles that serve as traps for analytes. Applications include the determinations of SO2, NO2, HCHO, and suspended particulate matter. 

Ion-selective electrodes can be incorporated in flow cells to monitor the concentration of an analyte in standards and samples that are pumped through the flow cell. As the analyte passes through the cell, a potential spike is recorded instead of a steady-state potential. The concentration of K+ in serum has been determined in this fashion, using standards prepared in a matrix of 0.014 M NaCl. ... 

Selectivity in FIA is often better than that for conventional methods of analysis. In many cases this is due to the kinetic nature of the measurement process, in which potential interferents may react more slowly than the analyte. Contamination from external sources also is less of a problem since reagents are stored in closed reservoirs and are pumped through a system of transport tubing that, except for waste lines, is closed to the environment. 

For conventional electrospray, a solution of an analyte is sprayed from a narrow tube into a region where the solvent and other neutral molecules are pumped away and residual ions are directed into the analyzer of a mass spectrometer. 

Since 1970, new analytical techniques, eg, ion chromatography, have been developed, and others, eg, atomic absorption and emission, have been improved (1—5). Detection limits for many chemicals have been dramatically lowered. Many wet chemical methods have been automated and are controlled by microprocessors which allow greater data output in a shorter time. Perhaps the best known continuous-flow analy2er for water analysis is the Autoanaly2er system manufactured by Technicon Instmments Corp. (Tarrytown, N.Y.) (6). Isolation of samples is maintained by pumping air bubbles into the flow line. Recently, flow-injection analysis has also become popular, and a theoretical comparison of it with the segmented flow analy2er has been made (7—9). 

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

Important auxiliary equipment in a flotation plant includes feeder and controls, sampling and weighing devices, slurry pumps, filter and thickeners for dewatering solids, reagent storage and makeup equipment, and analytical devices for process control. 

The maximum and minimum flow rate available from the solvent pump may also, under certain circumstances, determine the minimum or maximum column diameter that can be employed. As a consequence, limits will be placed on the mass sensitivity of the chromatographic system as well as the solvent consumption. Almost all commercially available LC solvent pumps, however, have a flow rate range that will include all optimum flow rates that are likely to be required in analytical chromatography... 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

FIGURE 10< 108 The procedure to measure the capture efficiency by the tracer gas method, aj The measurement of the reference concentration in the duct, when the tracer is released direcdy into the duct, fb) The measurement of the concentration in the duct, when the tracer is released from the source, / -= sampling point, 2 = pump, J = analyter, 4 - injection of tracer, 5 = tracer gas flow meter, 6 = tracer gas cylinder. 

In most cases these flow markers are species that are mixed with the sample and coinjected with the analyte onto the GPC column. The retention time of this marker is used to adjust the time axis to compensate for any moderate pump variability during the running of the standards and the samples. 

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.

Trace enrichment or preconcentration by LC-LC methods are based on the possibility that the analytes will be retained as a narrow zone on the top of the first column when a large volume of sample is pumped trough the column. Good reproducibility can be achieved when the column capacity is not exceeded and the column is not overloaded. Trace enrichment is usually performed when relatively non-polar... 

Step 4) Precolumn clean-up not shown in Figure 5.4. After the heart-cut analytes have been transferred to the analytical column, a step-gradient programme is used to flush the precolumn of the more strongly retained compounds. An additional pump configuration makes precolumn clean-up possible while the analysis is running. 

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