Risk evaluation of impurities in topical excipients:The acetol case

Pharmaceutical excipients for topical use may contain impurities, which are often neglected from a toxicity qualification viewpoint. The possible impurities in the most frequently used topical excipients were evaluated in-silico for their toxicity hazard. Acetol, an impurity likely present in different topical pharmaceutical excipients such as propylene glycol and glycerol, was withheld for the evaluation of its health risk after dermal exposure. 〈br〉 An ex-vivo in-vitro permeation study using human skin in a Franz Diffusion Cell set-up and GC as quantification methodology showed a significant skin penetration with an overall Kp value of 1.82 ？ 10 ？ 3 cm/h. Using these data, limit specifications after application of a dermal pharmaceutical product were estimated. Based on the TTC approach of Cramer class I substances, i.e. 1800 mg/（day？person）, the toxicity-qualified specification limits of acetol in topical excipients were calculated to be 90 mg/mL and 180 mg/mL for propylene glycol and glycerol, respectively.

Reversed-phase fused-core HPLC modeling of peptides

Different fused-core stationary phase chemistries（C18,Amide,Phenyl-hexyl and Peptide ES-C18） were used for the analysis of 21 structurally representative model peptides.In addition,the effects of the mobile phase composition（ACN or MeOH as organic modifier;formic acid or acetic acid,as acidifying component） on the column selectivity,peak shape and overall chromatographic performance were evaluated.The RP-amide column,combined with a formic acid-acetonitrile based gradient system,performed as best.A peptide reversed-phase retention model is proposed,consisting of 5 variables：log SumAA,log Sv,clog P,log nHDon and log nHAcc.Quantitative structure-retention relationship（QSRR） models were constructed for 16 different chromatographic systems.The accuracy of this peptide retention model was demonstrated by the comparison between predicted and experimentally obtained retention times,explaining on average 86% of the variability.Moreover,using an external set of 5 validation peptides,the predictive power of the model was also demonstrated.This peptide retention model includes the novel in-silico calculated amino acid descriptor,AA,which was calculated from log P,3D-MoRSE,RDF and WHIM descriptors.

Analysis of iodinated quorum sensing peptides by LC–UV/ESI ion trap mass spectrometry

Five different quorum sensing peptides(QSP) were iodinated using different iodination techniques. These iodinated peptides were analyzed using a C18 reversed phase HPLC system, applying a linear gradient of water and acetonitrile containing 0.1%(m/v) formic acid as mobile phase. Electrospray ionization(ESI)ion trap mass spectrometry was used for the identification of the modified peptides, while semi-quantification was performed using total ion current(TIC) spectra. Non-iodinated peptides and mono-and diiodinated peptides(NIP, MIP and DIP respectively) were well separated and eluted in that order. Depending on the used iodination method, iodination yields varied from low(2%) to high(57%).

A critical quality parameter in quantitative fused-core chromatography: The injection volume

As part of the method development, the injection volume as a critical quality attribute in fast fused-core chromatography was evaluated. Spilanthol, a pharmaceutically interesting N- alkylamide currently under investigation in our laboratory, was chosen as the model compound. Spilanthol was dissolved in both PBS and MeOH/H20 （70/30, v/v） and subsequently analyzed using a fused-core system hereby selecting five chromatographic characteristics （retention time, area, height, theoretical plates and symmetry factor） as responses. We demonstrated that the injection volume significantly influenced both the qualitative and quantitative performance of fused-core chromatography, a phenomenon which is confounded with the nature of the used sample solvent. From 2 ~tL up to 100 laL injection volume with PBS as solvent, the symmetry factor decreased favorably by 20%. Moreover, the theoretical plates and the quantitative parameters （area and height） increased up to 30%. On the contrary, in this injection volume range, the theoretical plates for the methanol-based samples decreased by more than 60%, while the symmetry factor increased and the height decreased, both by 30%. The injection volume is thus a critical and often overlooked parameter in fused-core method description and validation.