Analysis of pharmaceuticals and biomolecules using HPLC coupled to ICP-MS and ESI-MS
The work described within this thesis explores the use of HPLC coupled with ICPMS and ESI-MS in order to develop novel methods which overcome specific analytical challenges in the pharmaceutical industry. A membrane desolvation interface has been evaluated for coupling high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS). Desolvation of the sample prior to reaching the plasma was shown to facilitate a versatile coupling of the two instrumental techniques, enabling chromatographic eluents containing up to 100 % organic to be used. This interface also allowed gradient elution to be used with ICP-MS. Tris(2,4,6-trimethoxyphenyl)phosphonium propylamine bromide (TMPP) was used for the derivatisation of maleic, fumaric, sorbic and salicylic acids to facilitate determination by HPLC-electrospray ionisation tandem mass spectrometry (ESIMS/ MS) in positive ion mode. Improvements in detection limits post-derivatisation were achieved, and this method was successfully used for the determination of sorbic acid in a sample of Panadol™. HPLC coupled with sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) has been used for the determination of maleic, sorbic and fumaric acids after derivatisation with TMPP. This allowed 31P+ selective detection to be performed for these compounds, which are normally undetectable by ICP-MS. Optimal reagent conditions for the derivatisation of 0.1 mM maleic acid were: 1 mM TMPP; 10 mM 2-chloro-1-methylpyridinium iodide (CMPI); 11 mM triethylamine. The efficiency of the derivatisation reaction was estimated to be between 10-20%. Detection limits, estimated as 3 times baseline noise, were 0.046 nmol for TMPP and 0.25 nmol for derivatised maleic acid, for a 5 f.JL injection. Following on from this, a novel derivatising reagent, tris(3,5-dibromo-2,4,6- trimethoxyphenyl) phosphonium propylamine bromide (BrTMPP), was synthesised and subsequently characterised by proton NMR spectroscopy and ESI-MS. This was utilised to derivatise maleic acid, with a 9-fold increase in sensitivity gained when analysed by bromine selective detection as apposed to phosphorus selective ICP-MS. This derivatising reagent (BrTMPP) was also utilised to determine the degree of phosphorylation on phosphorylated peptides. A phosphorus containing carboxylic acid was successfully derivatised and the correct Br:P ratio was determined for this compound by ICP-MS. However, phosphorylated peptides were not successfully derivatised by BrTMPP. A combination of UV and phosphorus selective ICP-MS was also used to distinguish between phosphorylated and un-phosphorylated peptides after HPLC separation.