Resolution, increasing effective

Finally, temperature can have a profound effect on column performance. Tanaka et al. (48) studied the effects of temperature on the separation of hydrolyzed /3-cyclodextrin. In their studies, resolution increased with temperature on a Toyopearl HW-40S column. 

Photodiodes occur in many different varieties and are useful in both steady-state and time-resolved fluorescence studies. Photodiodes designed for use in steady-state or on microsecond time-scales are inexpensive and have effective areas up to a few square millimeters, and are capable of efficiently matching to simple focusing optics. However, as the temporal resolution increases so does the cost, and the effective area has to be reduced. For example, APDs with response times in the 50 psec region have effective diameters ofca. 10 /small active area of high-speed devices is currently the primary drawback in fluorescence studies. Also, photodiodes other... 

The magnification attended in the experiment with the photoelectron microscope was M = 10s, and the spatial resolution was around 30 nm, which proved sufficient for the visualization of individual color centers in a LiF crystal with the concentration of such centers less than 10l7cm 3. The results obtained in Ref. 9 may be considered the first successful implementation of laser resonance photoelectron microscopy possessing both subwavelength spatial resolution and chemical selectivity (spectral resolution). It will be necessary to increase the spatial resolution of the technique by approximately an order of magnitude and substantially improve its spectral resolution by effecting resonance multistep photoionization by means of tunable ultrashort laser pulses. 

Column temperature also has a significant effect on resolution. Increasing the column temperature from 30° to 50°C leads to inversion in selectivity. Therefore, increasing column temper-... 

Temperature and pressure are rarely optimized in HPLC, but these parameters are very important in SFC, hence can alter retention, selectivity, and resolution. Toribio et al. [149] presented the chiral separation of ketoconazole and its precursors on Chiralpak AD and Chiralcel OD CSPs. The authors also reported that alcohol modifiers provided better separation than acetonitrile. Further, Wilson [143] studied the effects of composition, pressure, temperature, and flow rate of the mobile phase on the chiral resolution of ibuprofen on a Chiralpak AD CSP. It was observed that temperature affords the greatest change in resolution, followed by pressure and composition. An increase in methanol concentration, pressure, and temperature has resulted in poor chiral resolution. At first chiral resolution increased with an increase of flow rate (up to 1.5 mL/min) but then started to decrease. Contrary to this, Biermann et al. [135] described the... 

Temperature is also an important parameter for controlling the resolution of enantiomers in HPLC. The enthalpy and entropy control of chiral resolution on antibiotic CSPs is similar to the case of polysaccharide-based CSPs (Chapter 2). Armstrong et al. [1] have studied the effect of temperature on the resolution behavior of proglumide, 5-methyl-5-phenylhydantoin and A-carbamyl-D-pheny-lalanine on the vancomycin column. The experiments were carried out from 0°C to 45°C. These results are given in Table 6 for three chiral compounds. It has been observed that the values of k, a, and Rs for the three studied molecules have decreased with the increase in temperature, indicating the enhancement of chiral resolution at low temperature. In another work, the same workers [22] have also studied the effect of temperature on the resolution of certain amino acid derivatives on the teicoplanin chiral stationary phase. They further observed poor resolution at ambient temperature, whereas the resolution increased at low... 

As in the case of other CSPs, the chiral resolution is effected by the structure of the solute. The chiral resolution of amino acids may be considered as the best example for this study. The work of Fukushima et al. [20] (i.e., the chiral resolution of amino acids) indicated the different behavior of the chiral resolution on (i8 )-/V-3,5-dinitrobcnzoyl-l -naphthylglycine CSP. Altomare etal. [142] studied the chiral resolution of a series of 3-phenyl-4-(l-adamantyl)-5-A-phcnyl-A2-1,2,4-oxadiazolines on A,Af,-(3,5-dinitrobenzoyl)-l(7 ),2( )-diaminocyclohcxanc CSP. The effect of the influence of aromatic ring substituents on enantioselectivity was studied by traditional linear free-energy-related equations and comparative molecular field analysis methods. The authors reported that an increase in retention was favored by the re-basicity and the hydrophilicity of the solutes. In... 

In addition to the mobile phase composition, the effect of other parameters such as temperature, flow rate, pH, and structure of the analytes were also studied, but only a few reports were available in the literature. In 1995, Lin and Maddox [66] studied the effect of temperature on the chiral resolution of amino acids and esters. The temperature was varied from 5°C to 25°C and it was reported that the resolution improved at low temperature. Hyun et al. [48-50,67] carried out the effect of temperature on the chiral resolution of amino alcohols, amines, fluoroquinolones, and other drugs. Again, lowering of temperature resulted in better resolution. The effect of temperature on the chiral resolution of phenylalanine, phenylglycine, and 2-hydroxy-2-(4-hydroxy-phenyl)-ethyl amine is shown in Table 5 [50], which indicates an increase in retention factors at lower temperature, but the best separation occurred at 20°C. These experiments indicated the exothermic nature of chiral resolution on CCE-based CSPs. Lin and Maddox [66] also studied the effect of flow rate on the chiral resolution of... 

The table below lists some common spectral interferences that are encountered in inductively coupled plasma mass spectrometry (ICP-MS), as well as the resolution that is necessary to analyze them.1 The resolution is presented as a dimensionless ratio. As an example, the relative molecular mass (RMM) of the polyatomic ion 15N160+would be 15.000108 + 15.994915 = 30.995023. This would interfere with 31P at a mass of 30.973762. The required resolution would be RMM/8RMM, or 30.973762/0.021261 = 1457. One should bear in mind that as resolution increases, the sensitivity decreases with subsequent effects on the price of the instrument. Note that small differences exist in the published exact masses of isotopes, but for the calculation of the required resolution, these differences are trivial. Moreover, recent instrumentation has provided rapid, high-resolution mass spectra with an uncertainty of less than 0.01%. 

It is evident that increasing the mobility simultaneously raises the EOF, and the relative velocity for each pair of zones is reduced along with the resolution. On the other hand, if the analyte migrates in an opposite direction to the EOF, the resolution increases because the residence time in the capillary is prolonged and the effective migration distance is lengthened, so that even components with very small differences in mobility can be separated from each other. 

---