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The determination of peak purity in chromatographic methods used in pharmaceutical analysis is a vital step in evaluating specificity to ensure the safe production of medicines. Current peak purity assessments accomplished through diode array detectors (DAD) and mass spectrometry (MS) have some challenges that could lead to misinterpreted purity values when the sample under evaluation is susceptible to the limitations of these techniques. Two-dimensional liquid chromatography (2D -LC) has the ability to resolve difficult-to-separate mixtures, and has been widely adapted to biological compounds. This study proposes a 2D-LC screening method as a means of determining peak purity of active pharmaceutical ingredients (API) and their related substances. Results confirm that the 2D-LC screen was successful in separating API/impurity mixtures in all 10 test cases studied. Selection of screening conditions including mobile phase choice and column selection is discussed along with the effectiveness and idiosyncrasies of peak purity analysis by 2D-LC., The possible pitfalls of diode array detectors-ultraviolet region (DAD-UV) absorbance based peak purity determinations have been well documented (1,2). Some possible issues with DAD-UV based peak purity include: i) co-eluted [...]

In two recent installments of 'LC Troubleshooting,' I discussed the roles of mixers in liquid chromatography (LC) systems in a general sense (1,2). Mixers are often used in pumping systems [...]

A new decarbonylation reaction is observed for [(K2-acetate)Pd(K2-diphosphine)]+ complexes. Gas-phase IR experiments identify the product as [CH3Pd(OP(Ph2)CH2PPh2)]+. DFT calculations uncovered a plausible mechanism involving O atom abstraction by the diphosphine ligand within the coordination sphere to yield the acetyl complex, [CH3COPd(OP(Ph2)CH2PPh2)]+, which then undergoes decarbonylation. [ABSTRACT FROM AUTHOR]

A new decarbonylation reaction is observed for [(K 2 -acetate)Pd(K 2 -diphosphine)] + complexes. Gas-phase IR experiments identify the product as [CH 3 Pd(OP(Ph 2 )CH 2 PPh 2 )] + . DFT calculations uncovered a plausible mechanism involving O atom abstraction by the diphosphine ligand within the coordination sphere to yield the acetyl complex, [CH 3 COPd(OP(Ph 2 )CH 2 PPh 2 )] + , which then undergoes decarbonylation.

Intramolecular hydrogen atom transfer (HAT) was examined in homocysteine (Hcy) thiyl radical/alkali metal ion complexes in the gas phase by combination of experimental techniques (ion-molecule reactions and infrared multiple photon dissociation spectroscopy) and theoretical calculations. The experimental results unequivocally show that metal ion complexation (as opposed to protonation) of the regiospecifically generated Hcy thiyl radical promotes its rapid isomerisation into an α-carbon radical via HAT. Theoretical calculations were employed to calculate the most probable HAT pathway and found that in alkali metal ion complexes the activation barrier is significantly lower, in full agreement with the experimental data. This is, to our knowledge, the first example of a gas-phase thiyl radical thermal rearrangement into an α-carbon species within the same amino acid residue and is consistent with the solution phase behaviour of Hcy radical., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)