Columns measurement

If the mobile phase is a liquid, and can be considered incompressible, then the volume of the mobile phase eluted from the column, between the injection and the peak maximum, can be easily obtained from the product of the flow rate and the retention time. For more precise measurements, the volume of eluent can be directly measured volumetrically by means of a burette or other suitable volume measuring vessel that is placed at the end of the column. If the mobile phase is compressible, however, the volume of mobile phase that passes through the column, measured at the exit, will no longer represent the true retention volume, as the volume flow will increase continuously along the column as the pressure falls. This problem was solved by James and Martin [3], who derived a correction factor that allowed the actual retention volume to be calculated from the retention volume measured at the column outlet at atmospheric pressure, and a function of the inlet/outlet pressure ratio. This correction factor can be derived as follows. 

Let us assume that we have collected a set of calibration data (X, Y), where the matrix X (nxp) contains the p > 1 predictor variables (columns) measured for each of n samples (rows). The data matrix Y (nxq) contains the q variables which depend on the X-data. The general model in calibration reads... 

Figure 1. A summary of water-column measurements of and Pa. Most of this data was compiled by Henderson et al. (1999a) and a full list of references is contained therein. More recent data have been added from Edmonds et al. (1998), Moran et al. (2001) and Vogler et al. (1998). Averages and the total number of measurements are shown on each panel for the various types of data. The average °Th concentration can be used to calculate the average ocean residence time for °Th (Yu et al. 1996) using the equation XTh=(" Th)/(234U) (l/ 230)...

The temperature difference between inlet and outlet temperature at the coil(s) of the refrigerant should be smaller than 1 °C (AT < 1 °C), to ensure a uniform condensation on the total coil. On warmer areas no ice will condense until the temperature at the ice surface has increased to the warmer temperature on the coil. For large surfaces it is necessary to use several coils or plates in parallel, each of which must be separately temperature controlled. If the condenser is operated in an overflow mode, the weight of the liquid column should not change the boiling temperature of the liquid at the bottom of the column measurably. 

Figure 7. Isopleths of phosphorus flux (micrograms per square meter per day) in the water column, measured hy using sediment traps. The values are the...

Measurements of sound velocity at ultrasonic frequencies are usually made by an acoustic interferometer. An example of this apparatus11 is shown in Fig. 2. An optically flat piezo-quartz crystal is set into oscillation by an appropriate electrical circuit, which is coupled to an accurate means of measuring electrical power consumption. A reflector, consisting of a bronze piston with an optically flat head parallel to the oscillating face of the quartz, is moved slowly towards or away from the quartz by a micrometer screw. The electrical power consumption shows successive fluctuations as the distance between quartz and reflector varies between positions of resonance and non-resonance of the gas column. Measurement of the distance between resonance positions gives a value for A/2, and if /... 

Both the liquid and gas products were analyzed by gas chromatography. The column for the liquid analysis was 20% Apiezon L on 60-80 mesh Chromosorb P. The column measured 1/4 inch by 7 feet. The gas analysis utilized a 1/4 inch by 10 foot column of 60-80 mesh Chromosorb 102. Temperature programming was required in both analyses. Identification of the GC peaks was based on retention time of pure compounds when these were available. In addition, two of the samples were analyzed by combined gas chromatography-mass spectrometry. By comparing the observed mass spectrometer fragmentation patterns with tabulated patterns it was possible to identify virtually every component in the product. Further details are available in the theses by Wu (23) and Early (J+). 

Figure 4-56. Overlay of the retention volumes of front (0.05 mM concentration of NH4PF6 in the solution) on all four columns measured from acetonitrile/water and methanol/water mixtures. (Reprinted from reference 169, with permission.)...

Particle-velocity profiles for several solid materials spouted in a 3.7-in. conical-cylindrical column, measured by the piezoelectric technique, have been reported by Mikhailik and Antanishin (M14, millet, silica gel, poly-... 

Table 8.8 Rates of ammonium (NH ) regeneration in the water column measured using N-isotope dilution C N ID) using distillation (Distill), solid phase extration (SPE), solvent extraction (SE). or diffusion (Diff)... 

Table 8.8 Rates of ammonium regeneration in the water column measured using N-isotope dilution C N ID) with isolated... 

Estimated for upper 50 m of the water column. Measured by both H-TdR and H-leu Assuming euphotic zone depth of 20 m. 

Fig. I.l. Evaluation of the releniion data from a chromatogram. EmfEo) column hold-up volume, i.e.. the volume of the mobile phase in the column measured as the elution volume of a non-relained solute imdo) column hold-up time VRiffRi) and VriUrj) retention (elution) volumes (times) of retained sample...

Hoff R. M. (1992) Differential SO2 column measurements of the Mt. Pinatubo volcanic plume. Geophys. Res. Lett. 19, 175-178. 

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