An APCI LC‐MS/MS method for routine determination of capecitabine and its metabolites in human plasma

The anticancer drug capecitabine and its metabolites [including the active metabolite 5‐fluorouracil (5‐FU)] display high pharmacokinetic inter‐patient variability. Such variability, which may lead to treatment failure or toxicity, could need drug concentration measurement to individualize dosing regimen. However, usual assay methods are often long and fastidious. A simultaneous and cost‐effective method was thus developed for the determination of the concentrations of these compounds in human plasma. Compounds were extracted via a classic liquid–liquid extraction. Chromatographic analysis was performed on a C18 reverse phase column with detection by atmosphere pressure chemical ionization LC‐MS/MS. Our method allows a good chromatographic separation of the compounds and was fully validated following Food and Drug Administration (FDA) recommendations (good selectivity, no carry‐over, linearity of the calibration curves without weighting, deviations from nominal concentrations of standard samples lower than 15%, intra‐ and inter‐assay precision and accuracy lower than 15%). Recovery and stability were also acceptable following the FDA guidelines. A matrix effect impairing the determination of 5‐FU was avoided by using a stable isotopic derivative of 5‐FU as internal standard. Interestingly, this method allows detection of TetraHydroUridine, an inhibitor of ex vivo degradation of metabolites, which is essential for the stability, the adequate conditioning of blood samples and for good laboratory practice, essential in routine determination. This method seems usable to routinely determine concentrations of capecitabine and its metabolites in blood and may be helpful in further studies aiming at performing therapeutic drug monitoring. Copyright © 2010 John Wiley & Sons, Ltd.     

Fast multidimensional localized parallel NMR spectroscopy for the analysis of samples

A parallel localized spectroscopy (PALSY) method is presented to speed up the acquisition of multidimensional NMR (nD) spectra. The sample is virtually divided into a discrete number of nonoverlapping slices that relax independently during consecutive scans of the experiment, affording a substantial reduction in the interscan relaxation delay and the total experiment time. PALSY was tested for the acquisition of three experiments 2D COSY, 2D DQF‐COSY and 2D TQF‐COSY in parallel, affording a time‐saving factor of 3–4. Some unique advantages are that the achievable resolution in any dimension is not compromised in any way: it uses conventional NMR data processing, it is not prone to generate spectral artifacts, and once calibrated, it can be used routinely with these and other combinations of NMR spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural elucidation of biologically active neomycin N‐octyl derivatives in a regioisomeric mixture by means of liquid chromatography/ion trap time‐of‐flight mass spectrometry

Structural elucidation of six regioisomers of mono‐N‐octyl derivatized neomycin is achieved using MSⁿ (up to n = 4) on an ion trap time‐of‐flight (IT‐TOF) instrument equipped with electrospray ionization. The mixture of six derivatized neomycin analogues was generated by reductive amination in a shotgun synthetic approach. In parallel to the liquid chromatography/mass spectrometry (LC/MS) detection, the antibacterial activity of the neomycin regioisomers was tested by post‐column addition of buffer and bacterial inocula, subsequent microfractionation of the resulting mixture, incubation, and finally a chemiluminescence‐based bioactivity measurement based on the production of bacterial ATP. The MS‐based high‐resolution screening approach described can be applied in medicinal chemistry to help in designing and producing new antibiotic substances, which is particularly challenging due to the high functionality of most antibiotic substances, therefore requiring advanced (hyphenated) separation and detection techniques for compound mixtures. Copyright © 2010 John Wiley & Sons, Ltd.     

The use of acetone as a substitute for acetonitrile in analysis of peptides by liquid chromatography/electrospray ionization mass spectrometry

The recent worldwide shortage of acetonitrile has prompted interest in alternative solvents for liquid chromatography/mass spectrometry (LC/MS). In this work, acetone was substituted for acetonitrile in the separation of a peptide mixture by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and in the positive electrospray ionization mass spectrometry (ESI‐MS) of individual peptides. On both C12 and C18 stationary phases, the substitution of acetone for acetonitrile as the organic component of the mobile phase did not alter the gradient elution order of a five‐peptide retention standard, but did increase peak width, shorten retention times, and increase peak tailing. Positive ESI mass spectra were obtained for angiotensin I, bradykinin, [Leu⁵]‐enkephalin, and somatostatin 14 dissolved in both acetonitrile/water/formic acid (25%/75%/0.1%) and acetone/water/formic acid (25%/75%/0.1%). Under optimized ESI‐MS conditions, the mass spectral response of [Leu⁵]‐enkephalin was increased two‐fold when the solvent contained acetone. The substitution of acetone for acetonitrile resulted in only slight changes in the responses of the remaining peptides. A higher capillary voltage was required for optimum response when acetone was used. Compared with acetonitrile/water/formic acid (50/50/0.1%), more interfering species below m/z = 140 were found in the ESI‐MS spectra of acetone/water/formic acid (50/50/0.1%). Copyright © 2009 John Wiley & Sons, Ltd.     

An Intermolecular Hydrogen Bridge between a Porphyrinoid μ‐Oxido Diiron(III) Host and a Guest Water Molecule

μ‐Oxido‐bis[(hexaethyldimethyl‐2,2′‐bidipyrrinato)iron(III)] ( 1 ) crystallizes as a mixed dichloromethane/water solvate as black plates in the triclinic system, space group Pbar{1} , with a = 14.536(3), b = 16.194(3), c = 25.883(5) Å, α = 98.89(3)°, β = 91.28(3)°, γ = 90.56(3)°, and Z = 2. In the crystal structure two distinct solvates 1· CH₂Cl₂ and 1· H₂O are present in equal ratio. In both cases the solvent is found in direct vicinity of the Fe–O–Fe subunit and is located within a binding pocket formed by the two helically distorted tetrapyrroles. Whereas the dichloromethane molecule is oriented within this pocket as a dipole with the positive end pointing towards the oxygen atom of the Fe–O–Fe subunit, the water molecule forms a hydrogen bond with this site, supported by additional weak interactions with adjacent N‐donor atoms.     

On‐line flow‐through extraction–preconcentration‐large volume injection‐RP LC for trace determination of pyrethroids in Slovak soil

A rapid micro‐analytical multiresidue method was developed for analysis of pyrethroids (kadethrin K, cypermethrin C and permethrin P) in soil micro‐sample (200 mg). It uses on‐line flow‐through extraction of soil micro‐samples (packed into a short glass column) with a methanol‐aqueous citric acid buffer mixture, successive on‐line SPE preconcentration of analytes from the extract and on‐line RP‐HPLC analysis with UV photometric detection. The separation of pyrethroids is performed on a Purospher RP‐18e column with methanol/water as mobile phase. Effects of sorbent placed at the bottom of a short column holding the soil sample and different kinds of on‐line SPE columns were tested. Besides, the influence of volume of the effluent on the pyrethroids recovery was also studied. Calibration curves were linear over the range assayed from 0.01 to 0.2 μg/mL with correlation coefficients of linear regression (least‐squares method) in the range 0.998–0.999. Recovery studies were carried out at 0.25–1.00 μg/g dry soil fortification level and obtained recoveries were for K 81–84%, C 56–59% and for P 58–63%. Achieved LOD (confidence band) of studied pyrethroids were for large‐volume injection (1 mL) 4.5 ng K, 3.7 ng C, 3.6 ng P or 27 ng/g K, 32 ng/g C and 29 ng/g P in dry soil “solid sampling HPLC”.