Performance of ion pairing chromatography and hydrophilic interaction liquid chromatography coupled to charged aerosol detection for the analysis of underivatized amino acids

The charged aerosol detector (CAD) is frequently employed in liquid chromatography for the analysis of small polar and ionizable compounds such as amino acids and amino sugars, which provide a weak chromophore only. Separation of these compounds is achieved by means of ion pair chromatography (IPC), and, more recently, hydrophilic interaction chromatography (HILIC) techniques. However, as the CAD's response is highly dependent on the mobile phase composition, the substantial differences in the mobile phase composition of IPC and HILIC have a distinct impact on the detector's performance. This study was aimed at systematically comparing the performance of IPC and HILIC when coupled to the CAD. Therefore, the separation techniques characterized by their specific mobile phase compositions were evaluated for their influence on the CAD response and the signal-to-noise ratio (S/N) of the amino acids L-alanine, L-leucine, and L-phenylalanine applying the response surface methodology (RSM). The RSM results derived from flow injection analysis (FIA) indicated that the CAD response and thus the obtainable S/N are significantly higher in HILIC compared to IPC where the S/N decreased with the chain length of the applied ion-pairing reagent. In addition, an IPC and a HILIC method, respectively, were developed for the impurity profiling of the branched-chain amino acids (BCAAs) L-leucine, L-isoleucine, and L-valine. The beneficial effects of the HILIC conditions on the S/N observed under FIA conditions were partly offset by moderate column bleed effects when using an amide functionalized column, which facilitates the separation in the HILIC method. Satisfactory LOQs (3-10 ng on column) were obtained with both methods; however, the HILIC method was found to be slightly superior in terms of sensitivity and separation efficiency.

Validated ion pair chromatographic method for simultaneous determination and in vitro dissolution studies of indacaterol and glycopyrronium from inhaled capsule dosage form

A rapid, and highly sensitive analytical method were developed for the simultaneous determination of indacaterol maleate (IND) and glycopyrronium bromide (GLY) in their inhaler capsules. Valid ion-pairing chromatographic (IPC) method was performed for separation of GLY in presence of IND using C₁₈ column and mobile phase consisting of acetonitrile: acidified deionized water (60:40% v/v) containing 0.02% sodium dodecyl sulfate (SDS) adjusted to pH 3.0 using OPA (orthophosphoric acid) isocratically eluted at 2.0 mL/min. Quantitation was achieved with UV detection at 210 nm. Cyproheptadine was used as an internal standard. The retention times were 1.9 and 2.5 min for IND, and GLY, respectively. For the IPC method, the calibration graphs were linear in the range of 0.66-66.0 μg/mL for IND and 0.3-30.0 μg/mL for GLY. The proposed method are rapid, reproducible (R.S.D. <2.0%) and achieves satisfactory resolution between IND and GLY (resolution factor = 4.23). The mean recoveries of the analytes in their inhaler capsule were satisfactory. It was applied successfully to in vitro dissolution testing using Franz diffusion cell and extended to a content uniformity test consistent with the United States Pharmacopoeia (USP) guidelines and were found to be precise and accurate for the capsules studied with acceptance value of 4.53 and 1.39 for IND and GLY, respectively.