Solvent and stationary phase selectivity in capillary electrochromatography method development: Comparison of C18, C8, and phenyl‐bonded phases for the separation of a series of substituted barbiturates

Abstract

Abstract:The capillary electrochromatographic separation of six substituted barbiturates in the ion-suppressed mode was investigated on commercially available C18, C8, and, phenyl-bonded packing materials. The effect on the retention behavior of mobile phase composition, buffer pH, buffer ionic strength, and temperature was studied. Successful chromatography of the barbiturates was achieved with all three packing materials over a pH range from 2.3 to 7.8. It was Ž . notable that a significant electroosmotic flow EOF was generated with a pH 2.3 mobile phase for all the packing materials, suggesting that capillary electrochro-Ž . matography CEC in the ion suppression mode can be applied to a wide range of weakly acidic compounds of pharmaceutical interest. The C18, C8, and phenylbonded packing materials gave similar selectivities and retention times, and approximately linear relationships between percentage organic modifier in the mobile phase or temperature versus ln k were observed. Increasing the buffer ionic strength reduced the EOF but did not result in changes in selectivity. The use of methanol compared with acetonitrile had no effect on selectivity but resulted in a large increase in retention of the analytes. The experimental investigations have shown that the CEC separation of a series of weakly acidic compounds of pharmaceutical relevance can be achieved readily using a range of commercially available packed capillaries.

Investigation of the novel mixed-mode stationary phase for capillary electrochromatography

“…On the other hand, in CEC with ODS (Hypersil C 18 ), Euerby et al [12] demonstrated that the elution order of studied barbiturates was completely consistent with their hydrophobicity and phenobarbital eluted before secobarbital even using a phenyl-bonded stationary phase with the retention by − interaction. In CEC with NAIP [34,36], like ODS, the elution order of four barbiturates (barbital, phenobarbital, secobarbital, and thiopental) was according to their hydrophobicity (Fig.…”

“…After the first report on CEC in 1974 [4], the potential of CEC has been demonstrated by a burst of outstanding separations and applications [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Evaluation and comparison of tailor-made stationary phases based on spherical silica-based beads for capillary electrochromatography via peptide separation analysis

“…Since it is redundant to discuss hydrophobicity and hydrophobic selectivity in the absence of RP-temperament, as is the case with the MH OH material the reason behind the (decreased) rate of migration/retention must be sought elsewhere. Many phenomena have been associated with contributions to mechanisms occurring under CEC conditions by various authors [13,14,[33][34][35][36][37][38][39][40]. The only contributor that can be ruled out to be responsible for the observed elution of carbetocin with an increased positive κ CEC value so far is the RP-ligand.…”

Development and Pharmaceutical Applications of Functional Stationary Phases for Capillary Electrochromatography and Chiral Separation

“…On the other hand, in CEC with ODS (Hypersil C 18 ), Euerby et al demonstrated that the elution order of studied barbiturates was completely consistent with their hydrophobicity and phenobarbital eluted before secobarbital even using a phenyl-bonded stationary phase with the retention by S-S interaction [16]. In CEC with NAIP, the elution order of four barbiturates (barbital, phenobarbital, secobarbital, and thiopental) was according to their hydrophobicity ( Fig.…”