Column selectivity comparison

The major parameter for column selection is the intended application. A balance of mobile-phase polarity in comparison with the polarity of the stationary... 

It is of much interest to compare polymer monoliths with monolithic silica columns for practical purposes of column selection. Methacrylate-based polymer monoliths have been evaluated extensively in comparison with silica monoliths (Moravcova et al., 2004). The methacrylate-based capillary columns were prepared from butyl methacrylate, ethylene dimethacrylate, in a porogenic mixture of water, 1-propanol, and 1,4-butanediol, and compared with commercial silica particulate and monolithic columns (Chromolith Performance). 

FIGURE 2.16 Influence of an organic modulator on selectivity. Comparison between acetonitrile and methanol. Isoelutropic conditions for ethyl benzene. Column Symmetry C8, 150 x4mm. Mobile phase methanol-water. 55-45, v-v. Acetonitrile-water, 42-58, v-v. Solntes 1, thiourea 2, aniline 3, phenol 4, o-toluidine 5, m-toluidine 6, -tolnidine 7, V,V-dimethyl aniline 8, benzoic acid ethylester 9, tolnene 10, ethyl benzene. 

Fast separations of 16 PAHs were achieved within 6-7 min using packed columns. A comparison study of the PAH molecular shape recognition properties of liquid-crystal-bonded phases in packed-column SFC and HPLC found that the selectivity was enhanced in SFC. The result of an interlaborotory round-robin evaluation of SFC for the determination of PAHs also shows that SFC possesses distinct advantages over GC-mass spectrometry (MS) and nuclear magnetic resonance (NMR) including speed, cost, and applicability. 

Figure 1. Conversion (top) and selectivity (bottom) of as milled PdsGay (100 mg) and chemically etched Pd3Ga7 (1 mg, pH = 10.5) (left column) and of as milled PdGa (40 mg) and chemically etched PdGa (1.5 mg, pH = 9.8) (right column). For comparison the data of commercial Pd/Al203 (0.15 mg) is also shown.

Figure 3.66 Selectivity comparison between lonPac AS16 and AS20 for the separation of polarizable anions. Separator columns (a) lonPac AS16 and (b) lonPac AS20 column dimensions 250 mm x 2 mm i.d. column temperature 30 °C eluent 35 mmol/L KOH (EG) flow rate 250 pL/min detection ...

Figure 6.61 Selectivity comparison between ion-exchange chromatography (a), ion-pair chromatography (b), and the combination of both on a mixed-mode phase (c). Separator columns OmniPac PAX-100, lonPac NS1, and OmniPac PAX-500 eluent 42 mmol/L NaOH...

Figure 6.69 Selectivity comparison between an ODS phase and an OmniPac PCX-100 exemplified with the separation of choline and acetylcholine, (a) Separator column Lichrosorb RP-18 eluent 5 mmol/L heptanesulfonic add (pH 4)/MeCN (99 1 v/v) flow rate 1 mU/min ...

Figure 6.95 Selectivity comparison between the 3 pm Acclaim Trinity PI and P2 columns. Column dimensions 50 mm x 3 mm i.d. column temperature 30 °C eluent MeCN/ 100 mmol/L ammonium formate, pH 3.65...

Figure 7.26 Selectivity comparison between various HILIC phases exemplified with the separation of selected nucleobases and nucleosides. Columns and column dimensions see Table 7.7 column temperature 30 °C eluent 90 10 (v/v) MeCN/IOOmmol/L ammonium acetate flow rates 1 mlVmln for 4.6mm...

Figure 11.6 Selective capture of glycoproteins on the boronate affinity monolithic column and comparison with non-glycoproteins. Mobile phase 250 mM ammonium acetate (pH 8.5), switched to 100 mM HAc (pH 2.7) at 10 min sample 0.5 mg mL protein dissolved in 250 mM ammonium acetate (pH 8.5). (Reproduced from ref. 7 with permission. Copyright 2009, Elsevier BV.)...

TABLE 13.2 Comparison of C6+ Hydrocarbon Types in Reformates and Methanol-Derived Gasoline as Determined by Open Ibbular Column Selective Olefin Absorption GC... 

Fig. 2. Comparisons of column selectivity for a given sample and RP-LC procedure. Sample (I) N,N-diethylacetamide (2) nortriptyline ...

Table 3. A comparison of average column selectivities by column type. Values of at pH 2.8 for the various column types ofTable 2 (Eq. 15).

An imderstanding of column selectivity is important for various reasons, but mainly when it is necessary to replace one column by another with either similar or very different selectivity. Column selectivity can be accurately characteri2 ed by five measurable properties of the column H, Hydrophobidty S, Steric resistance to insertion of bulky solute molecules into the stationary phase A, column hydrogen-bond Acidity B, column hydrogen-bond Basicity C, column Cation-exchange activity. Values of these column parameters (H, S, etc.) have now been measured for a large number of different RP LC columns. Given values of H, S, etc., it is possible to compare two columns in terms of selectivity by means of a column-comparison function F. Commercial software is available (Column Match Rheodyne LLC, Rohnert Park, CA, USA) that facilitates the convenient comparison of any two columns in terms of selectivity the software also includes values of H, S, etc. for about 300 different columns. 

The major parameter for column selection is the intended application [7, 8]. A balance of mobile phase polarity in comparison with the polarity of the stationary phase and sample polarity is important for pure SEC separations. In general, users will select their columns according to the mobile phase they need to use. Stationary phase materials can be either silica or polymeric based. Table 9.4 shows an overview of stationary phases with different polarities typically used in SEC. 

The analysis of cigarette smoke for 16 different polyaromatic hydrocarbons is described in this experiment. Separations are carried out using a polymeric bonded silica column with a mobile phase of 50% v/v water, 40% v/v acetonitrile, and 10% v/v tetrahydrofuran. A notable feature of this experiment is the evaluation of two means of detection. The ability to improve sensitivity by selecting the optimum excitation and emission wavelengths when using a fluorescence detector is demonstrated. A comparison of fluorescence detection with absorbance detection shows that better detection limits are obtained when using fluorescence. 

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