Rapid and comprehensive impurity profiling of synthetic thyroxine by ultrahigh-performance liquid chromatography-high-resolution mass spectrometry.

Rapid and efficient quality control according to the public authority regulations is mandatory to guarantee safety of the pharmaceuticals and to save resources in the pharmaceutical industry. In the case of so-called "grandfather products" like the synthetic thyroid hormone thyroxine, strict regulations enforce a detailed chemical analysis in order to characterize potentially toxic or pharmacologically relevant impurities. We report a straightforward workflow for the comprehensive impurity profiling of synthetic thyroid hormones and impurities employing ultrahigh-performance liquid chromatography (UHPLC) hyphenated to high-resolution mass spectrometry (HRMS). Five different batches of synthetic thyroxin were analyzed resulting in the detection of 71 impurities within 3 min total analysis time. Structural elucidation of the compounds was accomplished via a combination of accurate mass measurements, computer based calculations of molecular formulas, multistage high-resolution mass spectrometry (HRMS(n)), and nuclear magnetic resonance spectroscopy, which enabled the identification of 71 impurities, of which 47 have been unknown so far. Thirty of the latter were structurally elucidated, including products of deiodination, aliphatic chain oxidation, as well as dimeric compounds as new class of thyroid hormone derivatives. Limits of detection for the thyroid compounds were in the 6 ng/mL range for negative electrospray ionization mass spectrometric detection in full scan mode. Within day and day-to-day repeatabilities of retention times and peak areas were below 0.5% and 3.5% R.SD. The performance characteristics of the method in terms of robustness and information content clearly show that UHPLC-HRMS is adequate for the rapid and reliable detection, identification, and semiquantitative determination of trace levels of impurities in synthetic pharmaceuticals.

Electro-catalytic oxidative cleavage of lignin in a protic ionic liquid.

Lignin is a component of lignocellulosic biomass and a promising matrix for recovering important renewable aromatic compounds. We present a new approach of electro-oxidative cleavage of lignin, dissolved in a special protic ionic liquid, using an anode with particular electro-catalytic activity. As appropriate ionic liquid triethylammonium methanesulfonate was identified, synthesised, explored for dissolution of alkali-lignin and used for electrolysis of 5 wt.% lignin solutions. As appropriate anode material, oxidation-stable ruthenium-vanadium-titanium mixed oxide electrodes were prepared and explored for their electro-catalytic activity. The electrolysis was performed at several potentials in the range from 1.0 V to 1.5 V (vs. an Ag pseudo reference electrode). A wide range of aromatic fragments was identified as cleavage products by means of GC-MS and HPLC measurements.

Comparing monolithic and microparticular capillary columns for the separation and analysis of peptide mixtures by liquid chromatography-mass spectrometry.

A mixture of ten proteins was trypsinized and injected onto poly-(styrene-divinylben-zene) monolithic columns (60 x 0.20 or 0.10 mm ID) and a column packed with C18 silica particles (75 x 0.075 mm ID), respectively. The columns were eluted at 200-2000 nL/min with gradients of ACN in 0.050% TFA. Eluting peptides were detected by ESI-MS/MS and subsequently identified by database searching. The 100 microm ID monolithic column showed the highest cumulative Mowse scores based on the highest ion scores for the peptides and the largest number of identified peptides. It is shown that the number of identified peptides strongly depends on the dynamic range within the peptide mixture. In consequence, all proteins were identified in a mixture of relatively balanced analyte amounts (12.5-80 fmol) whereas only peptides for six out of ten proteins were found in a sample of high-dynamic range (0.65-270 fmol). The 100 microm monolithic column showed the highest reproducibility for peptide identifications in three consecutive runs. Depending on sample amount, 57-72% of the identified peptides were detectable in each of the three runs of triplicate analyses. The results demonstrate the high suitability of 100 microm monolithic columns for high-resolution peptide separations in proteomic research.

Monolithic capillary-based ion-selective electrodes.

Poly(styrene-co-divinylbenzene)-based monolithic capillaries of an inner diameter of 200 mum and a length of 2-5 mm have been used to construct Ca2+-, Ag+-, and Na+-selective electrodes. The membranes consist of a solution of ionophore and ion exchanger in bis(2-ethylhexyl) sebacate or 2-nitrophenyl octyl ether, which are used as plasticizers in conventional PVC-based membranes. With capillaries of low porosity, the potentiometric responses down to 10(-8)-10(-9) M solutions do not depend on the composition of the internal solution, which indicates a strong suppression of transmembrane ion fluxes. Thus, no tedious optimization of the inner solution is required with monolith ISEs. The lower detection limits of Ag+- and Ca2+-ISEs are comparable to the best ones obtained earlier with optimized inner solutions. Additionally, a monolithic Na+-selective ISE has been obtained exhibiting a lower detection limit of 3 x 10(-8) M Na+. With monolithic capillaries of higher porosity and fused-silica GC capillaries, the transmembrane flux effects are noticeable but still significantly smaller than with conventional PVC membranes.