Effect of Flow Rate

As the flow rate increases, the peak shifts to a lower elution angle (Fig. 1.3), due to a decrease in residence time. Mathematically, as the velocity increases, the first moment decreases, resulting in a lower elution angle. A decrease in flow rate leads to an increase in the solute band width due to eddy diffusion. This has been observed in practice [52]. 

As mentioned previously, the temperature settings and gas flow rates in the ion source will have to be adjusted to optimize ionization efficiency of a compound, depending on the solvent flow rates. 

5 EFFECT OF MOBIFE-PHASE COMPOSITION ON IONIZATION EFFICIENCY IN LC/MS 

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Elow rate determines the separation time and can significantly affect resolution and efficiency. The effect of flow rate on HETP for TSK-GEL SW and TSK-GEL SWxi analytical columns is shown in Fig. 4.6. Resolution is typically higher at slower flow rates, although results shown in Fig. 5B indicate that, with increasing sample load, the faster flow rates can give higher resolution. 

The effect of flow rate on resolution by Toyopearl HW-55F and Toyopearl HW-55S columns has been studied using a bovine serum albumin sample. Eor both columns, resolution decreased with increasing flow rate (46). Resolution is increased, however, with decreasing particle size (47). Resolution is proportional to the square root of the column length, as theoretically expected, and indicates that longer columns can be packed as well as shorter columns. Therefore, for samples difficult to resolve, the solution may be to increase the column length. 

Effect of Flow Rate and Temperature on Enantiomeric Separations... 

Fig. 2-10. The effect of flow rate on the resolution of methylphenidate enantiomers on vancomycin CSP (250 x 4.6 mm). The mobile phase was methanol 1.0 % triethyl-ammonium acetate (95/5 v/v) pH 4.1 at ambient temperature (23 °C).

Figure 9-79D. COg absorption from atmosphere effect of flow rates on Koa at elevated pressure. Reproduced by permission of the American Institute of Chemical Engineers, Spector, N. A., and Dodge, B. F., Trans. A.I.Ch.E., V. 42 (1946) p. 827 all rights resenred.

Figure 2 shows the effect of flow rate on column efficiency using the SW-2000 column with cytochrome C. The column efficiency expressed as the number of theoretical plates (N) was dependent on flow rate, a result typical of size exclusion chromatography. 

Figure 2. Effect of flow rate on the efficiency (N) of the Spherogel TSK-SW 2000 column. The conditions were as indicated in Figure 1 using cytochrome C as test solute.

Figure 5.12 Sorption breakthrough curves - effect of flow rate of breakthrough capacity (C0 = influent concentration C = effluent concentration).

Effect of flow rate on nickel deposition at 50 torr total pressure. [Reprinted with permission from... 

Flow rate and extraction time. Dynamic techniques for the extraction of carotenoids with SC-CO2 use flow rates that vary from 0.5 to 15 mL/min (measured at extraction temperature and pressure) with different effects depending on the matrix (Rozzi and others 2002 Subra and others 1998 Saldana and others 2006). Subra and others (1998) extracted (3-carotene from 1 to 2.5 g freeze-dried carrots and studied the effect of flow rates (0.4 and 1.2 liter/min) they obtained higher yields of (3-carotene at a flow rate of 1.2 liter/min. Sun and Temelli (2006) also evaluated the effect of flow rate (0.5 and 1.0 liter/min) on the extraction of (3-carotene with SC-CO2 + canola oil. The total carotenoids yield increased with flow rate, ranging from 934.8 to 1,973.6 pg/g dry carrot at C02 flow rates from 0.5 to 2 liter/min (measured at STP), respectively (Sun and Temelli, 2006). However, the lycopene yield decreased from 38.8% to 8% as flow rate was increased from 2.5 to 15 mL/min (measured at extraction temperature and pressure) (Rozzi and others 2002). 

Flow rate and extraction time. No report was found for the effect of flow rate in the extraction of phytochemicals from herbs. Extractions at lower pressures and/or temperatures required prolonged time and large amounts of CO2 to achieve the same yield as reported for the extraction of caffeine, theophylline, and theobromine from mate tea leaves (Saldana and others 1999,2002a). 

The actual design includes a second filament, within the same detector block. This filament is present in a different flow channel, however, one through which only pure helium flows. Both filaments are part of a Wheatstone Bridge circuit as shown in Figure 12.11, which allows a comparison between the two resistances and a voltage output to the data system, as shown. Such a design is intended to minimize effects of flow rate, pressure, and line voltage variations. 

Because of its advantages (high sensitivity and selectivity, low cost and miniaturization) amperometric detection has been frequently used in flow injection analysis (FIA) and RP-HPLC. However, it has been established that the peak area (detector response) considerably depends on the flow rate. A general approach has been proposed to predict the effect of flow rate on the peak area in FIA and RP-HPLC. The general form of the correlation describing the flow in a parallel plate cell with short rectangular electrodes is... 

Fig. 29. Effect of flow rate on number of sites and the hexagonal close packing arrangement for bubbles.

Fig. 7 Effect of flow rate in small rotameter on the 10 x pre-dilution factor...

FIGURE 21 Two HPLC gradient chromatograms (tryptic maps of lysozyme) illustrating the dramatic effect of flow rate (F), gradient time (t ), and void volume (Vg) on analysis time. Figure reprinted with permission from Reference 22. 

Figure 4.29 Effect of flow rate on the concentrations of Si and A in the basic system when operated as a CSTR (n = 1). The values of Q are indicated at the top of each section. Data for Q = 0.6 mL/h and Q = 6 mL/h are taken from Figures 4.14 and 4.17, respectively.

Figure 4.38 Effect of flow rate on the concentration of B in the basic system when operated...

Figure 4.76 Effect of flow rate on the concentration profile of B in the extended basic system when operated as a PER (n = 5). The values of Q are indicated, K = mM, and the values used for all other parameters are given in Table 4.12, set I.

Effect of Flow Rate Errors. The effect of flow rate errors on molecular-weight averages calculated from GPC data has been... 

While the effects of flow rate drift or noise at the one percent level over the duration of the separation are not nearly as disastrous as the case illustrated in Taible VI, the data serve to demonstrate the need for flow rate staibility and repeatcibility. The cibsolute accuracy of flow rate is of lesser importance, as this type of variation only manifests itself when comparing raw data obtained on different instruments, all of which should be calibrated independently of each other in any case. It should be pointed out that the GPC calibration should always be redetermined whenever any component of the system is changed this is simply good leiboratory practice. 

It is of interest to note in Figure 1 that there is a lag in the response of the LALLS with time caused by mixing in the cell. This is an artifact of the relatively higher viscosity and density of the solution flowing into the cell and displacing the less viscous solvent in the cell. This effect can be seen readily in this work because the solution concentrations were deliberately made high and the flow rate slow. Figure 2 shows the effect of flow rate and concentration on the time required for the cell to be completely emptied of polymer. In conventional SEC measurements this artifact could be of importance, but should not be observed unless very slow flow rates are used. 

Figure 1. Effect of flow rate on the baseline noise of the viscometer trace (Mobile Phase THF, Temperature 30 C)...

Meakin BJ, Ganderton D, Panza I, Ventura P. The effect of flow rate on drug delivery from the Pulvinal, a high-resistance dry powder inhaler. J Aerosol Med 1998 ll(3) 143-52. 

Facilitated transport of penicilHn-G in a SLM system using tetrabutyl ammonium hydrogen sulfate and various amines as carriers and dichloromethane, butyl acetate, etc., as the solvents has been reported [57,58]. Tertiary and secondary amines were found to be more efficient carriers in view of their easy accessibility for back extraction, the extraction being faciUtated by co-transport of a proton. The effects of flow rates, carrier concentrations, initial penicilHn-G concentration, and pH of feed and stripping phases on transport rate of penicillin-G was investigated. Under optimized pH conditions, i. e., extraction at pH 6.0-6.5 and re-extraction at pH 7.0, no decomposition of peniciUin-G occurred. The same SLM system has been applied for selective separation of penicilHn-G from a mixture containing phenyl acetic acid with a maximum separation factor of 1.8 under a liquid membrane diffusion controlled mechanism [59]. Tsikas et al. [60] studied the combined extraction of peniciUin-G and enzymatic hydrolysis of 6-aminopenicillanic acid (6-APA) in a hollow fiber carrier (Amberlite LA-2) mediated SLM system. 

Figure 2.11—(a) FID detector (b) NPD detector and (c) effect of flow rate on detector signal and difference between the mass flow detector and concentration dependent detector. 1, normal situation (constant flow) 2, mass flow detection (i.e. FID) with an interruption in the flow rate (the area remains constant) 3, TCD detection with an interruption in the flow rate (the area does not represent the mass of the compound flowing through the detector). 

Breakthrough-Flow Rate Studies. Because several of the acidic model compounds showed mixed results, it was decided to study the effect of flow rate and the presence of salts by establishing breakthrough curves. Primary emphasis was given to the evaluation of quinaldic acid, both with and without the presence of salts. The concentration of quinaldic acid was chosen high enough so that each eluant in the breakthrough study could be analyzed by direct injection HPLC. 

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