Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6 µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Ultraviolet cutoff area and predictive ability of partial least squares regression method: A pharmaceutical case study

UV cutoff area (COA) is known to be the wavelength band where solvents used for analysis can absorb radiation and accordingly affect the absorption spectra of drugs of interest being analyzed, even if blank experiments are done to eliminate solvent interference. However, this area may show peaks of significance for some drugs, and accordingly some researchers tend to include it in analysis. This study is presenting the importance of avoiding using COA, where it may represent significant negative effect on predictive ability of some linear chemometric methods like partial least squares regression PLSR. The presented study is using previously analyzed pharmaceutical mixtures of Dapoxetine Hydrochloride (DAP) and Tadalafil (TAD) as a case study, whether in pure forms or in dosage form, where the study uses two datasets for analysis, the first aims to include COA and the second dataset avoids it, then a statistical comparison is conducted for training sets, test sets and dosage form datasets to see how far COA may interfere with analysis results. Generally, the results show significant difference in datasets for t and F statistics for analysis of dosage form sets; which reflects changes in predictive ability of used chemometric method upon inclusion of COA in absorbance datasets, and accordingly unsuitability of using COA especially for routine quality control analysis of pharmaceutical mixtures.

Stability indicating HPLC method for simultaneous quantification of sildenafil citrate and dapoxetine hydrochloride in Pharmaceutical products

A stability-indicating HPLC-UV method for the simultaneous determination of sildenafil citrate and dapoxetine hydrochloride in solution and tablet was developed. The mobile phase was comprised of acetonitrile and 0.2M ammonium acetate buffer. The analyte was eluted at 3.392min and 7.255min for sildenafil citrate and dapoxetine HCl respectively using gradient system at a flow rate of 1.5mL/min. The theoretical plates count was>2000, tailing factor <.30, capacity factor 3.19-7.58 and peak asymmetry factor <.08.The method was linear from 5-180 and 1-40μg/mL with a correlation coefficient of 0.9999 and 0.9994 for sildenafil citrate and dapoxetine HCl respectively. The drug solution was stable at ambient room temperature (26˚C) for 48hours.Both drugs were found susceptible to oxidation and the drug content dropped slightly in acid and alkali condition but stable under UV light and heat. No interference from tablet excipients and degradation products was found.

Comparative Study of PVC-Free All-Solid-State, PVC Membrane, and Carbon Paste Ion-Selective Electrodes for the Determination of Dapoxetine Hydrochloride in Pharmaceutical Formulation

The potentiometric response characteristics and analytical applications of a poly(vinyl chloride) (PVC)-free all-solid-state ion-selective electrode for dapoxetine hydrochloride (DAP) are examined. The Nernstian response of the electrode was evaluated by comparison with PVC-based liquid membrane and carbon paste electrodes. The PVC-free electrode is prepared by direct incorporation of dapoxetine-tetraphenyl borate (DAP-TPB) as a sensing element into a commercial nail varnish containing cellulose acetate propionate. The composite was applied onto a 3 mm diameter graphite disk electrode. The electrode exhibited a Nernstian slope of 56.0 mV/decade in the concentration range of 1 × 10-4 to 1 × 10-2 mol/L with an LOD of 2 × 10-5 mol/L. The electrode is independent of pH in the range of 2 to 6 and showed good selectivity for DAP with respect to a large number of inorganic cations and amino acids. Comparable Nernstian slope, sensitivity, pH range, and selectivity pattern were obtained with a PVC membrane and a carbon paste incorporating DAP-TPB as a sensing element and dioctylphthalate as a solvent mediator. The electrodes were used for the determination of DAP in pure solution and in tablets without extraction with high accuracy and precision (RSD ≤ 2%). The nail varnish solid-state electrode is simple, economical, and rapid when compared with PVC membrane and carbon paste electrodes.

In Vivo Evaluation of Blood Based and Reference Tissue Based PET Quantifications of [11C]DASB in the Canine Brain

This first-in-dog study evaluates the use of the PET-radioligand [¹¹C]DASB to image the density and availability of the serotonin transporter (SERT) in the canine brain. Imaging the serotonergic system could improve diagnosis and therapy of multiple canine behavioural disorders. Furthermore, as many similarities are reported between several human neuropsychiatric conditions and naturally occurring canine behavioural disorders, making this tracer available for use in dogs also provide researchers an interesting non-primate animal model to investigate human disorders. Five adult beagles underwent a 90 minutes dynamic PET scan and arterial whole blood was sampled throughout the scan. For each ROI, the distribution volume (V_T), obtained via the one- and two- tissue compartment model (1-TC, 2-TC) and the Logan Plot, was calculated and the goodness-of-fit was evaluated by the Akaike Information Criterion (AIC). For the preferred compartmental model BP_ND values were estimated and compared with those derived by four reference tissue models: 4-parameter RTM, SRTM2, MRTM2 and the Logan reference tissue model. The 2-TC model indicated in 61% of the ROIs a better fit compared to the 1-TC model. The Logan plot produced almost identical V_T values and can be used as an alternative. Compared with the 2-TC model, all investigated reference tissue models showed high correlations but small underestimations of the BP_ND-parameter. The highest correlation was achieved with the Logan reference tissue model (Y = 0.9266 x + 0.0257; R² = 0.9722). Therefore, this model can be put forward as a non-invasive standard model for future PET-experiments with [¹¹C]DASB in dogs.

Stability indicating HPLC-UV method for determination of dapoxetine HCl in pharmaceutical product

A stability-indicating HPLC-UV method for the determination of dapoxetine hydrochloride in solution and pharmaceutical product was developed. The mobile phase was composed of acetonitrile and 0.2 M ammonium acetate buffer at 50 : 50 ratio. The chromatographic parameters, theoretical plates (N), tailing factor (T), capacity factor (k') and peak asymmetry factor (As) were calculated. Stress degradation studies, namely, acid, alkali, oxidation, heat and UV light, were performed. The analyte was eluted at 5.8 min using gradient system at a flow rate of 1.5 mL/min. The theoretical plates count was > 2000, tailing factor < 1.54, capacity factor > 5.38 and peak asymmetry factor was < 1.10. The method was linear from 1 to 40 microg/mL with a correlation coefficient of 0.9994. The intraday precision and accuracy values were 0.14-1.54% and 0.63-1.83%, respectively. On the other hand, the interday precision and accuracy results were 0.49-1.83% and 1.15-1.85%, respectively. The drug solution was stable at ambient room temperature (26 degrees C) for 48 h. Dapoxetine HCI was found susceptible to oxidation and degraded slightly under acid and alkali conditions but was stable under UV light and heat. No interference from tablet excipiets and degradation products was found. Hence, the method can be employed as a stability-indicating method for the determination of dapoxetine HCl in pharmaceutical products.

Nonlinearity of cationic aromatic amine sorption to aluminosilicates and soils: role of intermolecular cation-π interactions

Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-π, π-π, and van der Waals interactions can increase aromatic cationic amine sorption to Na/Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3-2.3% of exchange sites occupied. Our experiments revealed the predominance of intermolecular cation-π interactions, which occurred between the π system of a compound retained on the surface via cation exchange and the cationic amine group of an adjacent molecule. Compounds with greater amine charge/area and electron-donating substituents that allowed for greater electron density at the center of the aromatic ring showed a greater potential for cation-π interactions on montmorillonite surfaces. However, benzylamine sorption to nine soils, at charge loadings comparable to the experiments with montmorillonite, revealed no significant cooperative interactions. It appears that cation-π interactions may be likely in soils with exceptionally high cation exchange capacities (>0.7 mol charge/kg) and low organic matter contents, abundant in montmorillonite and other expanding clay minerals.

Enantioselective analysis of melagatran via an LSPR biosensor integrated with a microfluidic chip

The impact of chiral compounds on pharmacological and biological processes is well known. With the increasing need for enantiomerically pure compounds, effective strategies for enantioseparation and chiral discrimination are in great demand. Herein we report a simple but efficient approach for the enantioselective determination of chiral compounds based on a localized surface plasmon resonance (LSPR) biosensor integrated with a microfluidic chip. A glass microfluidic chip with an effective volume of ~0.75 μL was fabricated for this application. Gold nanorods (AuNRs) with an aspect ratio of ~2.6 were self-assembled onto the surface of the inner wall of the chip to serve as LSPR transducers, which would translate the analyte binding events into quantitative concentration information. Human α-thrombin was immobilized onto the AuNR surface for enantioselective sensing of the enantiomers of melagatran. The proposed sensor was found to be highly selective for RS-melagatran, while the binding of its enantiomer, SR-melagatran, to the sensor was inactive. Under optimal conditions, the limit of detection of this sensor for RS-melagatran was found to be 0.9 nM, whereas the presence of 10,000-fold amounts of SR-melagatran did not interfere with the detection. To the best of our knowledge, this is the first demonstration of an LSPR-based enantioselective biosensor.

Effect of sodium and calcium cations on the ion-exchange affinity of organic cations for soil organic matter

Sorption of organic cations to soil organic matter was studied using dynamic column experiments with different compositions of electrolytes in aqueous eluents. The sorption affinity of the tested variety of charged compounds, including primary, secondary, and tertiary amines and quaternary ammonium compounds, all showed the same response to different medium compositions. The sorption affinity to Pahokee peat (i) strongly decreased with increasing electrolyte concentration, up to a factor 250 due to tested electrolyte compositions alone, (ii) was higher in NaCl solutions than in CaCl(2) solutions of similar ionic strength, and (iii) was more sensitive to a decrease in NaCl than to a decrease in CaCl(2), though the selectivity coefficients were not significantly different. For a weak base that was tested in eluent pH either above or below its pK(a), we demonstrated that the sorption affinity of (iv) the neutral base was hardly affected by different electrolyte compositions, comparable to a neutral reference compound, (v) the protonated weak base was strongly affected by different electrolyte compositions, and (vi) the protonated base was in the same range, or stronger, compared to the neutral base. Mass action law equations for ion-exchange reactions predicted similar trends in a qualitative but not in a quantitative way. More complex models are required to fully account for the contributions of ionic interactions to the sorption of organic cations. These results imply that risk assessment models for organic bases should take ion-exchange processes into account when estimating soil sorption coefficients and bioavailability.

RP-HPLC method for simultaneous determination of butenafine hydrochloride and betamethasone dipropionate in a cream formulation

An RP-HPLC method has been developed for the simultaneous determination of butenafine hydrochloride and betamethasone dipropionate on an Inertsil C18 column (250 x 4.6 mm id) using a mobile phase gradient consisting of methanol and water at a flow rate of 1 mL/min. Detection was carried out at 254 nm. Retention times of betamethasone dipropionate and butenafine hydrochloride were 4.82 (+/- 0.80) and 16.18 (+/- 0.17) min, respectively. The method was validated with respect to specificity, linearity, accuracy, precision, ruggedness, and robustness. This method is simple, precise, and sensitive, and applicable for the simultaneous quantification of butenafine hydrochloride and betamethasone dipropionate in a cream formulation.

Determination of carbamazepine and its impurities iminostilbene and iminodibenzyl in solid dosage form by column high-performance liquid chromatography

An accurate and precise RP-HPLC method was developed and validated for the determination of carbamazepine and its impurities iminostilbene and iminodibenzyl in a tablet formulation with fluphenazine as an internal standard. Buffer-methanol (50 + 50, v/v) was used as the mobile phase. During validation, specificity, linearity, precision, accuracy, LOD, LOQ, and robustness of the method were tested. The method was proven to be specific against placebo interference. Linearity was evaluated over the concentration range of 100-500, 0.05-0.25, and 0.1-0.5 microg/mL, and the r values were 0.9994, 0.9997, and 0.9979 for carbamazepine, iminostilbene, and iminodibenzyl, respectively. Intraday precision of the method was good, and RSD was below 2% for all analytes. The accuracy of the method ranged from 100.69 to 102.10, 99.76 to 102.66, and 99.26 to 100.08% for carbamazepine, iminostilbene, and iminodibenzyl, respectively. LOD was 0.0125, 0.025, and 0.05 microg/mL and LOQ was 0.05, 0.05, and 0.1 microg/mL for carbamazepine, iminostilbene, and iminodibenzyl, respectiviely. Robustness of the method was proven by using a chemometric approach. The method was successfully applied to the analysis of commercially available carbamazepine tablets and showed good repeatability, with RSD below 2%.

Functional loss of pAMT results in biosynthesis of capsinoids, capsaicinoid analogs, in Capsicum annuum cv. CH-19 Sweet

Capsaicinoids are responsible for the spicy flavor of pungent peppers (Capsicum). The cultivar CH-19 Sweet is a non-pungent pepper mutant derived from a pungent pepper strain, Capsicum annuum CH-19. CH-19 Sweet biosynthesizes capsaicinoid analogs, capsinoids. We determined the genetic and metabolic mechanisms of capsinoid biosynthesis in this cultivar. We analyzed the putative aminotransferase (pAMT) that is thought to catalyze the formation of vanillylamine from vanillin in the capsaicinoid biosynthetic pathway. Enzyme assays revealed that pAMT activity catalyzing vanillylamine formation was completely lost in CH-19 Sweet placenta tissue. RT-PCR analysis showed normal mRNA transcription of the pAMT gene; however, SNP analysis of the cDNA sequence showed a T nucleotide insertion at 1291 bp in the pAMT gene of CH-19 Sweet. This insertion formed a new stop codon, TGA, that prevented normal translation of the gene, and the pAMT protein did not accumulate in CH-19 Sweet as determined using Western blot analysis. We developed a dCAPS marker based on the T insertion in the pAMT gene of CH-19 Sweet, and showed that the pAMT genotype co-segregated with the capsinoid or capsaicinoid fruit phenotype in the F(2) population. The T insertion was not found in other pungent and non-pungent Capsicum lines, suggesting that it is specific to CH-19 Sweet. CH-19 Sweet's pAMT gene mutation is an example of a nonsense mutation in a single gene that alters a secondary metabolite biosynthetic pathway, resulting in the biosynthesis of analogs. The dCAPS marker will be useful in selecting lines with capsinoid-containing fruits in pepper-breeding programs.

Bioassay of safinamide in biological fluids of humans and various animal species

This paper describes three methods to bioassay safinamide (CAS 133865-89-1) in biological fluids of humans and laboratory animals for pharmacokinetic, toxicokinetic and bioavailability studies. Two methods profited from liquid chromatography tandem mass spectrometry (LC-MS-MS) system, one (micro bioassay) working in the low dynamic range 0.5-20 ng/ml, the other in the range 20-6000 ng/ml. A third method used high-performance liquid chromatrography with fluorimetric detection (HPLC-FD), working in the dynamic range 20-1000 ng/ml. All the three methods were validated in compliance with the accreditated views on analytical bioassays. The shorter run time (5.5 min vs 16 min) has led the authors to prefer the two LC-MS-MS methods to the HPLC-FD bioassay, even if all the performances of the three methods were excellent. The methods described in this paper were and are still now extensively used to assay safinamide in more than 10,000 specimens of biological fluids from humans and laboratory animals in the development program of the drug. Main pharmacokinetic results obtained in various Phase I trials on healthy volunteers are briefly reported.

Using tandem mass spectrometry to predict chemical transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives in solution

Tandem mass spectrometry is used to predict the chemical transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives. Compound 1, N-2-2-4,6- dimethoxypyrimidin-2-yloxy benzylamino phenyl benzamide was selected as a model to present our idea. The CID reactions of protonated 1 include an intramolecular S(N)2 reaction and a cyclodehydration reaction. Under in-source CID conditions, deprotonated 1 undergoes a Smiles rearrangement reaction and then dissociates to the ion at m/z 349. Theoretical computations were invoked to shed light on the reaction mechanisms of 1 by the semiempirical PM3 method. These studies of gas-phase reactions show the reactivity of some potential reaction centers in this molecule, which inspired us to explore the solution phase analogous reactions of 1. Further experiments show that 1 has two analogous reactions in acidic solution: the acid-catalyzed cyclodehydration reaction and the acid-catalyzed Smiles rearrangement reaction. Moreover, 1 undergoes the base-catalyzed Smiles rearrangement under basic conditions. The present study demonstrates that mass spectrometry can play an important role in predicting the chemical solution phase transformations of 2-pyrimidinyloxy-N-arylbenzyl amine derivatives.

Determination of aminoheterocycle and azabicycle in gliclazide bulk by capillary zone electrophoresis with amperometric detection

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), was developed for simultaneous determination of 3-amino-3-azabicyclo[3,3,0]octane (aminoheterocycle) and 3-azabicyclo[3,3,0]octane (azabicycle) in gliclazide bulk drug. The optimal conditions of CZE-AD were 50 mM borate solution (pH 9.0) as running buffer, 14 kV as separation voltage and 0.95 V (versus SCE) as detection potential. Under the selected optimum conditions, the two analytes could be perfectly separated within 9 min. The linearity range of aminoheterocycle was from 1.0 x 10(-6) to 1.0 x 10(-3) M and that of azabicycle was from 2.0 x 10(-6) to 1.0 x 10(-3) M. Their detection limits were 5.0 x 10(-7) and 1.0 x 10(-6) M, respectively, (S/N=3). This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 2% for both migration time and peak current. It has been successively used for the determination of these two analytes in gliclazide bulk drug, and the assay results were satisfactory.

Determination of imipramine in presence of iminodibenzyl and in pharmaceutical dosage form

Two spectrophotometric methods for the determination of imipramine in presence of iminodibenzyl as an impurity are described. The first method is a ratio-spectra first derivative spectrophotometry, the signals were measured at 240.2 nm for imipramine. Calibration graph was found linear in the range 5-30 microg ml(-1). The second method is based on the reaction of imipramine base, being an electron donor, with p-chloranilic acid, being pi acceptor, to form a purple colored charge transfer complex. The absorbance was measured at 520.5 nm without interference with iminodibenzyl. Both methods are rapid, simple and do not require any preliminary separation or treatment of the samples. Furthermore, the two methods were applied to pharmaceutical dosage form.

Mixed-mode electrokinetic chromatography of aromatic bases with two pseudo-stationary phases and pH control

The electrokinetic chromatographic (EKC) separation of a series of aromatic bases was achieved utilising an electrolyte system comprising an anionic soluble polymer (polyvinylsulfonic acid, PVS) and a neutral beta-cyclodextrin (beta-CD) as pseudo-stationary phases. The separation mechanism was based on a combination of electrophoresis, ion-exchange interactions with PVS, and hydrophobic interactions with beta-CD. The extent of each chromatographic interaction was independently variable, allowing for control of the separation selectivity of the system. The ion-exchange and the hydrophobic interactions could be varied by changing the PVS and the beta-CD concentrations, respectively. Additionally, mobilities of the bases could be controlled by varying pH, due to their large range of pKa values. The separation system was very robust with reproducibility of migration times being <2% RSD. The two-dimensional parameter space defined by the two variables, [beta-CD] and %PVS, was modelled using a physical model derived from first principles. This model gave very good correlation between predicted and observed mobilities (r2=0.999) for the 13 aromatic bases and parameters derived from the model agreed with the expected ion-exchange and hydrophobic character of each analyte. The complexity of the mathematical model was increased to include pH and this three-dimensional system was modelled successfully using an artificial neural network (ANN). Optimisation of both the two-dimensional and three-dimensional systems was achieved using the normalised resolution product and minimum resolution criteria. An example of using the ANN to predict conditions needed to obtain a separation with a desired migration order between two of the analytes is also shown.

Identification of the degradation product of ezlopitant, a non-peptidic substance P antagonist receptor, by hydrogen deuterium exchange, electrospray ionization tandem mass spectrometry (ESI/MS/MS) and nuclear magnetic resonance (NMR) spectroscopy

The degradation product of ezlopitant was isolated from low specific activity material and identified by solution phase hydrogen/deuterium (H/D) exchange and electrospray ionization tandem mass spectrometry (ESI/MS/MS) to be an isopropyl peroxide analog of ezlopitant. The structure of the degradant was further confirmed by nuclear magnetic resonance (NMR) spectroscopy utilizing complete 1H and 13C assignments. Studies were also performed to identify the factors responsible for the oxidative degradation of ezlopitant, which included salt form, storage conditions and salt formation solvent. Of all the variable studies over a 3 weeks period, only a change in the salt form prevented this oxidative degradation.

Novel reagents for the sensitive spectrophotometric determination of flutamide, an anticancer drug in pharmaceutical preparations

Simple and sensitive spectrophotometric methods for the determination of flutamide (FLA) in either pure form or in its pharmaceutical preparations are described. The first method is based on the diazotisation of reduced FLA, followed by coupling with alcoholic iminodibenzyl (IDB) in acid medium to give a purple coloured product having a lambda(max) of 570 nm. In the second method, the diazotisation of reduced FLA followed by coupling with 4-amino-5-hydroxy-2,7-naphthalenedisulphonic acid monosodium salt (AHND) in a buffer medium of pH 12, gives a red coloured product having a lambda(max) of 520 nm. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed methods. Both the methods are highly reproducible and have been applied to a wide variety of pharmaceutical preparations and the results compare favourably with the reported method.

Iminodibenzyl as a novel coupling agent for the spectrophotometric determination of sulfonamide derivatives

A rapid, selective and simple spectrophotometric method for the determination of sulfa-drugs is described. The method is based on the formation of violet colored azo product by the diazotization of sulfonamides, viz. sulfathiazole (SFT), sulfadiazine (SFD), sulfacetamide (SFA), sulfamethoxazole (SFMx), sulfamerazine (SFMr), sulfaguanidine (SFG) and sulfadimidine (SFDd) followed by a coupling reaction with iminodibenzyl in alcohol medium. Absorbance of the resulting violet azo product is measured at 570-580 nm and is stable for 24 h at 27 degrees C. Beer's law is obeyed in the concentration range of 0.05-6.0 microg ml(-1) at the wavelength of maximum absorption. The method is successfully employed for the determination of sulfonamides in various pharmaceutical preparations and common excipients used as additives in pharmaceuticals do not interfere in the proposed method. The method offers the advantages of simplicity, rapidity and sensitivity without the need for extraction or heating. A reaction mechanism is proposed for the formation of the violet azo product.

Retention of ionizable compounds on HPLC. 8. Influence of mobile-phase pH change on the chromatographic retention of acids and bases during gradient elution

The relationships between retention and mobile-phase pH in gradient elution are studied for acids and bases. The apparent pH shift caused by the increasing amount of acetonitrile and methanol has been determined starting from a wide range of pH values. It is shown that good relationships between the retention of ionizable compounds and the pH of the aqueous buffer can be established if the same type of buffer (ammonium acetate in this work) is used for all pH points. Equations are proposed to fit the gradient retention data to the pH of the aqueous buffer. The proposed equation gives an account of the relative variation of the pKa of the compound in the reference to the variation of the pH of the buffer as both parameters change during gradient elution.

Assay of ezlopitant, a substance P receptor antagonist, and metabolites in biological matrices by gas chromatography with mass spectrometric detection: simultaneous analysis of a benzyl alcohol and alkene

A method for the analysis of the substance P antagonist ezlopitant and two active metabolites in serum using solid-phase extraction followed by GC-MS analysis is described. The linear dynamic range was 1.0 to 100 ng/ml and precision and accuracy over this range were within 15%. Upon injection of reconstituted sample extracts into the hot injector port of the gas chromatograph, the benzyl alcohol metabolite undergoes a small amount of spontaneous dehydration to the alkene metabolite. We have incorporated an additional hexadeuterated internal standard of the benzyl alcohol into the assay to permit measurement of the extent of dehydration in each sample. This novel approach should be generally applicable to the simultaneous determination of benzyl alcohols and corresponding alkenes by GC-MS when the possibility exists that the alcohol can undergo spontaneous dehydration to the alkene in the injector port of GC instrumentation.

Experimental human exposure to N,N-dimethylbenzylamine: generation of a controlled atmosphere and biological monitoring

The aim of the present study was to develop a method for generation of dimethylbenzylamine (DMBA) atmospheres in an exposure chamber and to investigate the possibility of using urinary DMBA metabolites for biological monitoring of exposure to DMBA. A DMBA atmosphere was generated by use of the gas-permeation principle. Six health male volunteers were exposed for 8 h to DMBA at air levels of 20, 45, and 80 microns/m3. Air levels of DMBA were analyzed by gas chromatography (GC). The total urinary amount of DMBA (U-SumDMBA; DMBA and metabolites that can be reduced to DMBA, e.g., DMBAO) was analyzed using GC-mass spectrometry (MS). The exposure chamber maintained very low (0-130 micrograms/m3) and steady concentrations for several weeks. DMBA uptake by inhalation was 76%. The amine was quickly distributed and biotransformed to nearly 100%. DMBA was eliminated in the urine with a half-time of 4.3 h. More than 50% was eliminated within 2 h of exposure. However, at all exposure levels the subjects continued to excrete DMBA the next morning. There was a significant correlation between the exposure to DMBA and the U-SumDMBA. Thus, U-SumDMBA may become an important biomarker for monitoring of industrial exposure to DMBA.

Mass spectrometric structure determination of metabolites of 3-[2-(N,N-dimethylaminomethyl)phenylthio]phenol

Metabolites of 3-[2-(N,N-dimethylaminoethyl)phenylthio]phenol (I) were isolated from the urine of rats, mice, rabbit and dog and from the faeces of rats by extraction and thin-layer chromatography. From the mass spectrum of I and using characteristics mass shifts in the spectra of metabolites, the structures of four metabolites were determined, whereas for two other isomeric metabolites the structures were resolved by means of IR spectra. Conclusions regarding the structures derived from the spectra were confirmed by comparing them with synthetic standards. Generally, metabolic changes of I can be characterized by demethylation, hydroxylation combined with methylation, S-oxidation and by a combination of these metabolic reactions.

Stereospecific deamination of benzylamine catalyzed by different amine oxidases

1. Stereospecific deuterated benzylamine enantiomers, R(alpha-2H1)-and S(alpha-2H1)-benzylamine, were synthesized by a combined chemical and enzymatic method. 2. The retention or cleavage of the deuterium atom during deamination of benzylamine catalyzed by amine oxidases from different sources was assessed by a GC-MS procedure and confirmed by HPLC separation of the products and by the observation of a deuterium isotope effect. 3. Three types of stereospecific abstraction of hydrogen atoms from the alpha-carbon of benzylamine during deamination were observed: (a) In the first type of deamination the pro-R hydrogen is removed from the alpha-carbon. Enzymes in this category are mitochondrial MAO from different tissues; (b) The second type of deamination involves the abstraction of pro-S hydrogen. Soluble enzymes such as rat aorta benzylamine oxidase or diamine oxidase from hog kidney and pea seedling have been found to belong to this group; and (c) Bovine plasma amine oxidase exhibits the third type of deamination where no absolute stereospecificity is required. 4. The kinetic deuterium isotope effect during the deamination of benzylamine by the different amine oxidase varies greatly, i.e. VH/VD ranged from 1.7 to 4.0.

GLC method for iminodibenzyl and desipramine impurities in imipramine hydrochloride and its formulated products

A GLC method is described for the determination of iminodibenzyl and desipramine impurities in imipramine hydrochloride and its formulated products. These impurities were extracted from an alkaline solution with a mixture of 30% methylene chloride in hexane for chromatography on a 3% OV-17 GLC column. Iminodibenzyl was determined using anthracene as an internal standard and desipramine was determined (after derivatization) using nortriptyline as an internal standard. Based on spiked excipient mixtures typically used to compound imipramine tablets, recoveries were 93-109% for iminodibenzyl and 93-107% for desipramine at 0.2-0.4% of the labeled claim of imipramine. Minimum detection levels were approximately 0.02% for each impurity, and procedural standards gave coefficients of variation of less than 1% for each impurity. The method was linear in the 0.05-0.5 microgram range and typically gave correlation coefficients greater than or equal to 0.999.

GLC determination of purity of Schiff bases bakrine and saddamine

GLC methods were developed for the investigation of impurities in bakrine and saddamine. The method used for bakrine was unsuitable for saddamine since two possible saddamine impurities, benzylamine and salicylaldehyde, reacted very readily in solution to form saddamine, thus giving a false low value for the original concentration of these impurities. The method devised for saddamine involved silylation, which greatly reduced the possibility of saddamine formation from its precursors and also enabled the detection of another possible impurity, salicylic acid. The method described has an obvious application to the determination of other Schiff bases.

High-performance liquid chromatographic assay of rat-brain dopamine and norepinephrine

A high-performance liquid chromatographic method for the assay of dopamine (DM) and norepinephrine (NE) in rat brain has been developed. 3,4-Dihydroxybenzylamine was added to the sample as an internal standard. The isolated amines and the internal standard were subjected to reaction with fluorescamine, separated liquid chromatographically on a glycol-type gel and determined fluorimetrically. The standard deviation of the method was +/-2.7% for DM and +/-5.3% for NE. The contents of DM and NE in rat brain, with or without administration of a tyrosine hydroxylase inhibitor, as measured by the proposed method were always lower than those obtained by the trihydroxyindole method.