Gradient tetraborate

Another CE method was developed and employed for the separation of the components of FD C Red No. 3 (erythrosine). The separations were also carried out by RP-HPLC and the efficacy of the methods was compared. The chemical structures of the main components of the dye are shown in Fig. 3.167. The components of erythrosine were separated in a fused-silica capillary (43 cm effective length X 75 /xm i.d.). The running buffer was 50 mM sodium tetraborate, 25 mM SDS (pH 9.3). Analytes were detected at 516 nm. HPLC measurements were realized in an octylsilica column (150 X 4.6 mm i.d. particle size 5 /xm) at 35°C. Solvent A was 0.1 M aqueous ammonium acetate and solvent B consisted of methanol. The gradient programme was 0 min, 55 per cent A 20 min 35 per cent A 21 min, 100 per cent B, final hold, 4 min. The flow rate was 1 ml/min. The separations of the components of the standard mixture (left) and those of a real sample (right) by CE are shown in Fig. 3.168. The electropherograms clearly illustrate that the method allows the baseline separation of the dye components even in real commercial samples. The main... 

Bertoldi and colleagues (2004) performed analysis of BAs in grape juice by automatic pre-column derivatization with OPA solution (45 mg OPA, 200 pX 2-mercaptoethanol, 1 mL methanol, sodium tetraborate decahydrate 0.1 M pH 10.5 buffer solution added up to final volume of 10 mL). Chromatographic separation of derivatives (see Figure 4.13) was achieved on a C18 (4.6 x 150mm, 5 pan) column kept at 40 °C at flow rate lmL/min. Eluent A was 0.05 M sodium acetate buffer/tetrahydrofuran 96 4 (v/v) and eluent B was methanol. The gradient program is reported in Table 4.1. 

Tetraborate ions exhibit a similar low affinity toward the stationary phase allowing for the separation of fluoride and short-chain aliphatic carboxylic acids. Since boric acid as the suppressor product is only weakly dissociated, sodium tetraborate is also suited for gradient elution to a limited extent. 

The urea concentration in the bulk media will affect the rate and quantity of ammonia produced and hence flie maintenance of the pH gradient within the co-immobilized enzyme pellet. The urea concentration will also determine the volume of the active XI core, and this will in turn influence the kinetics of the isomerization and the extent of isomerization. In Fig. 6, transient xylulose production is shown as a function of urea concentration. All pellets used were from the same co-immobilization batch and have the same urease and XI loadings. Experiments were conducted at 34 °C and pH 4.5 with either 0.01 M (curve A) or 0.1 M urea (curve B), 0.05 M sodium tetraborate, and an initial xylose concentration of 60 g/1. 

Figure 4. Dowex-l-X8 borate anion-exchange column chromatographic analysis of supernatants from 24 hour incubations of P. putida with 4-deoxy-4-fluoro-D-(U- C)glucose. 0 Radiolabeled metabolites internal non-radiolabeled carbohydrate standards. All compounds were eluted with a linear gradient of ammonium tetraborate.

To a limited extent, sodium tetraborate is also suited for gradient elution, because boric acid as the suppression product is only weakly dissociated. As an alternative to carbonate/bicarbonate systems, amino acids (a-aminocarboxylic acids) may be used as an eluent [90,91]. Their dissociation behavior is depicted in Figure 3.102. At alkaline pH, amino acids exist in the anionic form due to the dissociation of the carboxyl group and thus may act as an eluent ion. The product of the suppressor reaction is the zwitterionic form with a correspondingly low background conductance. This depends on the isoelectric point, pi, of the amino acid. 

Figure 3.204 Gradient elution of inorganic and organic anions with a sodium tetraborate eluent. Separator column lonPac ASM eluent Na2B407 gradient 2 mmol/L isocratically for 6 min and then linearly to 17.5 mmol/L flow rate 1.5 mL/min detection suppressed...

Figure 10.108 Trace anion analysis with an electolytically generated tetraborate eluent in a nuclear power plant water containing 2000 mg/L boron. Separator column lonPac AS14 column dimensions 250 mm x 2 mm i.d. eluent 50 mmol/L boric add/KOH gradient 4mmol/L KOH isocratically for 6 min and...

Fig. 3-150. Gradient elution of inorganic and organic anions with sodium tetraborate eluant. -Separator column lonPac AS14 eluant 2 mmol/L Na2B407 isocratically for 6 min, then linearly to...

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