OmniPac PAX

FIGURE 18 Chromatographic identification of tabiet press contaminant. Coiumn 4x250 mm OmniPac PAX-i00. Eiuent i mM disodium phosphate in 40% methanoi. Fiow rate i mLmin. Injection voiume lOpL. Detection UV at 220nm. Ion I—dimethylbenzene sulfonate. 

Omnipac Pax-500 fitted with a Cis reversed-phase guard column 0.1 M sodium phosphate-methanol-acetonitrile (3 1 1) adjusted to pH 2.3 with 85%... 

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...

As can be seen from Figure 6.63, very small and symmetric peaks result when a salt gradient is applied. Separations of this kind are not possible with either the ion-suppression technique or with ion-pair chromatography. This is especially true for aromatic polycarboxylic acids, which elute from a mixed-mode phase such as OmniPac PAX-500 according to their valency (Figure 6.64b). When separating on chemically bonded silica under ion-suppression conditions (Figure 6.64a), a shorter analysis time is observed but not all components of the test mixture are separated. Moreover, penta- and... 

C,8 ion suppression separator coiumn chemically bonded silica (ODS) eiuent 20mmoi/L H3PO4-i-20mmol/L HOAc/MeCN gradient linear, 5% MeCN to 30% in 20 min (b) mixedmode separator column OmnIPac PAX-500 eluent KOH/KCl/MeCN (80 20 v/v) gradient linear, 0.5 mmol/L KOH + 50 mmol/L KCI to... 

Figure 6.65 (a and b) Comparison of ion-pair and mixed-mode selectivities exempiified with the separation of phenylphosphonate and aromatic sulfonic acids, (a) Cis ion-pair separator column chemically bonded silica (ODS) eluent 4 mmol/L H3PO4 -I-10 mmol/L tetrabu-tylammonium phosphate (pH 7.5)/MeCN gradient linear, 25% MeCN to 60% in 20 min (b) mixed-mode separator coiumn OmniPac PAX-500 eiuent KOH/KCi/MeCN (75 25 v/v) ... 

Figure 6.66 Simultaneous analysis of molecular and ionic organic compounds on OmniPac PAX-500. Eluent NaOH/NaCI/MeCN gradient MeCN/water (80 20 v/v) for 10 min isocraf-cally, then linearly from 0.2 mmol/L NaOH + 50 mmol/L NaCI/MeCN (80 20 v/v) to 1.6mmol/L NaOH -I-400 mmol/L NaCI/MeCN (80 20 v/v) in 10 min flow rate 1 mL/min detection UV...

Polymer-based mixed-mode phases with anion-exchange properties are suitable for the analysis of a number of polar and ionic organic species, including the compound class of barbiturates (see also Figure 6.30), which can be separated on an OmniPac PAX-500 with a combined sodium car-bonate/acetonitrile gradient and UV detection at 254 nm. Figure 6.67 shows a respective separation of various barbiturates. Their structures are summarized in Table 6.3. Compared to the separation under ion-suppression... 

Figure 6.67 Separation of barbiturates on OmniPac PAX-500. Eluent Na2C03/MeCN gradient linear, 5 mmol/L Na2C03/MeCN (91 ...

In addition, excellent separations of acidic azo dyes such as Methyl Orange, Methyl Red, /1-Naphthol Orange, Orange I, Orange II, and so on can be obtained on an OmniPac PAX-500. They can be eluted with acetonitrile in an alkaline environment and detected by measuring the light absorption at 254 nm (see also Figure 6.74). 

Figure 6.68 Separation of anti-inflammatory drugs on OmniPac PAX-500. Eluent Na2C03/ MeCN gradient linear, lOmmol/L Na2C03/ MeCN (84 16 v/v) to 50 mmol/L Na2C03/ MeCN (70 30 v/v) in 10 min flow rate 1 ml/...

Fig. 6-61. Separation of aliphatic and aromatic carboxylic acids on OmniPac PAX-lOO (250 X 2 mm i d.) with a NaOH concentration gradient. - Eluant NaOH -methanol (95 5 v/v) gradient linear,...

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