Characterization of a microparticulate strong anion-exchanger in the HPLC of acidic drugs

TY - JOUR

T1 - Characterization of a microparticulate strong anion-exchanger in the HPLC of acidic drugs

AU - Morgan, P E

AU - Hanna-Brown, M

AU - Flanagan, R J

PY - 2006/8

Y1 - 2006/8

N2 - The use of Waters Spherisorb S5SAX for the HPLC of acidic compounds, including a number of non-steroidal anti-inflammatory drugs (NSAIDs), has been investigated. Adequate retention, separation, and peak efficiency and symmetry were obtained for most analytes on a 250 x 4.6 mm i.d. column using methanol containing ammonium perchlorate (10 mmol L-1, pH 6.7 or pH 8.3) as eluent. The results of changes in (i) eluent pH (constant ionic strength); (ii) eluent ionic strength (constant pH); and (iii) adding water to the eluent (constant pH) were consistent with a retention mechanism dominated by ion-exchange with the bonded strong anion-exchange (SAX) moieties. However, there were some unexpected observations, including (i) a general decrease in retention at eluent pH values above 7.7; (ii) a marked increase in retention on adding 1% (v/v) water to the eluent; (iii) a subsequent marked decrease in retention on adding 5% (v/v) or more water; and (iv) decreased column activity with time. These observations may be due to (i) interaction between the charged SAX moieties and ionised surface silanols (with ionization increasing at higher eluent pH values) and (ii) influence of the solvation of silanols, analytes, SAX moiety, and counter-ion varying with both pH and water content. Nevertheless, the factors influencing separation of individual NSAIDs remain unclear especially as no relation between log k and pK(a) exists for these compounds. Hydrophobic interactions are unlikely to be important since basic and neutral compounds were hardly retained. Ease of accessibility of the counter-ion to the SAX moiety for analyte displacement may be a factor. Copyright (c) 2005 John Wiley & Sons, Ltd

AB - The use of Waters Spherisorb S5SAX for the HPLC of acidic compounds, including a number of non-steroidal anti-inflammatory drugs (NSAIDs), has been investigated. Adequate retention, separation, and peak efficiency and symmetry were obtained for most analytes on a 250 x 4.6 mm i.d. column using methanol containing ammonium perchlorate (10 mmol L-1, pH 6.7 or pH 8.3) as eluent. The results of changes in (i) eluent pH (constant ionic strength); (ii) eluent ionic strength (constant pH); and (iii) adding water to the eluent (constant pH) were consistent with a retention mechanism dominated by ion-exchange with the bonded strong anion-exchange (SAX) moieties. However, there were some unexpected observations, including (i) a general decrease in retention at eluent pH values above 7.7; (ii) a marked increase in retention on adding 1% (v/v) water to the eluent; (iii) a subsequent marked decrease in retention on adding 5% (v/v) or more water; and (iv) decreased column activity with time. These observations may be due to (i) interaction between the charged SAX moieties and ionised surface silanols (with ionization increasing at higher eluent pH values) and (ii) influence of the solvation of silanols, analytes, SAX moiety, and counter-ion varying with both pH and water content. Nevertheless, the factors influencing separation of individual NSAIDs remain unclear especially as no relation between log k and pK(a) exists for these compounds. Hydrophobic interactions are unlikely to be important since basic and neutral compounds were hardly retained. Ease of accessibility of the counter-ion to the SAX moiety for analyte displacement may be a factor. Copyright (c) 2005 John Wiley & Sons, Ltd

U2 - 10.1002/bmc.595

DO - 10.1002/bmc.595

M3 - Article

VL - 20

SP - 765

EP - 773

JO - Biomedical Chromatography

JF - Biomedical Chromatography

IS - 8

ER -