Derivatization of aminoalkylphosphonic acids for characterization by gas chromatography mass spectrometry

An intramolecular benzyl rearrangement of 1-(N-benzyloxycarbonylamino)alkylphosphonate diesters under electrospray ionization conditions

The mass spectrometric behavior of eleven 1-(N-benzyloxycarbonyl(Cbz)amino)alkylphosphonate diesters was studied under positive ion electrospray ionization (ESI) conditions. Their fragmentation pathways are depicted and supported by tandem mass spectrometry. Besides the common eliminations of ether, benzyl alcohol, phosphite and an ether plus benzyl alcohol from molecular ions, the title compounds show a tendency to undergo an interesting intramolecular benzyl rearrangement to yield benzylphosphonate ions. The fragmentation patterns do not depend on the substituent attached to the alpha-carbon atom.

Chromatographic analysis of bisphosphonates

Chromatographic analysis of bisphosphonates in the past has been based primarily on reversed-phase liquid chromatography (RPLC) and ion-exchange chromatography. Gas chromatography (GC) and recently even capillary electrophoresis have also been employed. For bioanalysis, pre-treatment of the sample is a major part of the analysis; protein precipitation, calcium precipitation, solid-phase extraction (SPE) and derivatization have demonstrated to play an important role in bisphosphonate assays. For some of these treatments, for example SPE and derivatization, automation may be possible. Derivatization is a prerequisite for GC analysis of bisphosphonates; a volatile derivative has to be formed. For liquid chromatography, two types of derivatization are known for bisphosphonates. First, the bisphosphonate side chain can be modified by a chemical reaction to yield a derivative with advantageous chromatographic and spectroscopic properties. Secondly, by complexation of both phosphonate groups or of phosphate after decomposition of the analyte, a coloured complex can be formed. The most sensitive bioanalytical methods are based on RPLC and fluorescence detection, if necessary after derivatization. If low detection limits are not required, for example for analysis of pharmaceutical preparations, non-specific detection methods can be applied.

Determination of 4-amino-1-hydroxybutane-1,1-bisphosphonic acid in urine by automated pre-column derivatization with 2,3-naphthalene dicarboxyaldehyde and high-performance liquid chromatography with fluorescence detection

A sensitive (5 ng/ml) method for the determination of 4-amino-1-hydroxybutane-1,1-bisphosphonic acid in human urine is described. The procedure includes (1) the isolation of the drug from urine by co-precipitation of its calcium salt with endogenous phosphates in the presence of base, (2) a solid-phase anion-exchange sample clean-up and (3) automated pre-column derivatization of the primary amino group with 2,3-naphthalene dicarboxyaldehyde-cyanide reagent followed by fluorescence detection of the N-substituted cyanobenz[f]isoindole derivative. The derivative of the drug was synthesized and its spectral and fluorescence properties were evaluated. The fluorescence quantum efficiency was determined to be 0.82 in the mobile phase used for the assay. The derivative is also capable of accepting energy in an oxalate ester-hydrogen peroxide chemiluminescence system.

Analysis of (dichloromethylene) bisphosphonate in urine by capillary gas chromatography-mass spectrometry

An anion exchange extraction method of bisphosphonates from urine is described. More than 90% of the (dichloromethylene) bisphosphonate (Cl2MBP, clodronate) was recovered from urine. The extracted bisphosphonates were trimethylsilylated and analysed with capillary gas chromatography-mass spectrometry (GC/MS). The mass spectrometric techniques used were electron ionization (EI), ammonia chemical ionization (CI), ammonia CI tandem mass spectrometry and methane negative chemical ionization (NCI). The limit of detection of Cl2MBP was 25 pg/injection in the NCI/selective ion recording (SIR)-mode. At 100 ng ml-1 of Cl2MBP the precision of the whole assay method was 17.9% (N = 6). The NCI/SIR technique offers a sensitive and highly selective method for the quantitation of Cl2MBP in urine.

The determination of 4-amino-1-hydroxybutane-1,1-diphosphonic acid monosodium salt trihydrate in pharmaceutical dosage forms by high-performance liquid chromatography

A rapid, sensitive and specific high-performance liquid chromatographic (HPLC) assay is reported for the determination of 4-amino-1-hydroxybutane-1, 1-diphosphonic acid (AHBuDP) monosodium salt trihydrate, a new inhibitor of bone resorption. The compound does not demonstrate any intrinsic UV properties and thus pre-column derivatization of the primary amino group of the drug with 9-fluorenylmethyl chloroformate (FMOC) at pH 9 in the presence of sodium citrate is required to facilitate UV detection of the analyte. Excess derivatization reagent is extracted with methylene chloride and an aliquot of the aqueous portion is assayed on a polymeric phase (Hamilton PRP-1) at 35 degrees C by reversed-phase HPLC. A mobile phase of 0.05 M citrate and 0.05 M phosphate buffer (pH 8.0)-acetonitrile-methanol (75:20:5, v/v/v) is utilized with UV detection at 266 nm. Application of the method to the analysis of AHBuDP in I.V. solution, tablet and capsule formulations is presented.