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.

Photocatalytic reactive liquid microjunction surface sampling-mass spectrometry for rapid and selective in-situ analysis of alpha-unsubstituted amine metabolites or drugs in brain tissue.

In in-situ mass spectrometry (MS), different on-tissue derivatization methods have been developed to enhance the signals of poorly ionizable primary amines. However, those chemical derivatization methods are laborious and time-consuming, and are usually limited to detection of high-abundance amino acids which suppress the reaction of low-abundance monoamine neurotransmitters and drugs. Herein, A rapid and selective photocatalytic derivatization technique for alpha-unsubstituted primary amine was developed with 5-hydroxyindole as derivatization reagent and TiO2 as photocatalyst, and was introduced into liquid microjunction surface sampling (LMJSS)-MS system as online derivatization. The results showed that the photocatalytic derivatization method largely enhanced the signals of primary amines by 5-300 fold, and were selective to alpha-unsubstituted primary amines. Thus, the suppression effects from high-abundance amino acids to the reaction of monoamine neurotransmitters and benzylamine drugs proved to be largely reduced in the new method (matrix effect>50%) comparing with those in chemical derivatization method (matrix effect<10%). In addition, the optimal pH of the derivatization reaction was measured to be 7, which indicates the mild and physiologically compatible reaction conditions. By in-situ synthesis of TiO2 monolith in the transfer capillary of the LMJSS-MS system, rapid on-line photocatalytic derivatization was achieved and completed in 5 s during the transfer of sampling extract from the flow-probe to the MS inlet. With the new photocatalytic reactive LMJSS-MS method, detection limits of three primary amines on glass slides were in the range of 0.031-0.17 ng/mm2 with acceptable linearity (r=0.9815-0.9998) and relatively high repeatability (relative standard deviations <22.1%). Finally, endogenous tyramine, serotonin, two dipeptides and one doped benzylamine drug were identified and in-situ analyzed in the mouse cerebrum by the new method with largely enhanced signals comparing with LMJSS-MS without online derivatization. The new method provides a more selective, rapid and automated way to analyze alpha-unsubstituted amine metabolites and drugs in-situ comparing with traditional methods.

Liquid chromatographic method for the simultaneous determination of achiral and chiral impurities of dapoxetine in approved and counterfeit products.

A reversed-phase high performance liquid chromatographic method was developed and validated for the simultaneous determination of the related substances of S-dapoxetine, including R-dapoxetine, (3S)-3-(dimethylamino-3-phenyl-1-propanol), S-3-amino-3-phenyl-1-propanol, 1-naphtol, 4-phenyl-2H,3H,4H-naphtho[1,2-b]pyran and 1-(2E)-Cinnamyloxynaphthalene. During the screening experiments seven different polysaccharide-type chiral stationary phases (amylose-based Lux-Amylose-1, Lux-i-Amylose-1 and Lux-Amylose-2, as well as cellulose-based Lux-Cellulose-1, Lux-Cellulose-2, Lux-Cellulose-3 and Lux-Cellulose-4) were tested in polar organic mode using a mobile phase consisting of 0.1% diethylamine in methanol, ethanol, 2-propanol and acetonitrile with 0.5 mL min-1 flow rate at 20 °C. Best results were obtained on Lux Cellulose-3 column with the ethanol-based mobile phase. To increase the retention factor of two, early-eluting impurities, water was added to the mobile phase. In order to counterbalance the increased total analysis time, higher column temperature (40 °C) and gradient elution, combined with flow-programming` was applied. Using the optimized conditions baseline separations were achieved for all compounds within 30 min. The method was validated according to the International Council on Harmonization guideline Q2(R1) and applied to the analysis of an approved, tablet formulation and dapoxetine-containing products sold on the internet. As expected, in the case of the pharmacy-acquired product, all of the monitored impurities were below 0.1%. However, interesting results were obtained when internet-acquired samples were analyzed. These tablets contained racemic dapoxetine and/or high concentration of R-dapoxetine impurity. Based on this work polysaccharide-based chiral stationary phases can be successfully applied for the simultaneous determination of achiral and chiral impurities in reversed-phase mode applying gradient elution and flow-rate programs. The study further underlines the importance of not only achiral, but also enantiomeric quality control, whenever counterfeiting of a single enantiomeric agent is suspected.

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.

A Validated Green HPTLC Method for Quantitative Determination of Dapoxetine Hydrochloride and Tadalafil in Bulk and Pharmaceutical Formulations.

Dapoxetine hydrochloride (DAP) and Tadalafil (TAD) were separated and determined quantitatively using a validated green high-performance thin layer chromatographic (HPTLC) method in their binary mixtures either as raw materials or in pharmaceutical formulations. The concentration ranges were 0.1-1.6 and 0.2-2.5 µg/band for dapoxetine and tadalafil, respectively, with accuracies of 98.93% ± 0.62 and 99.26% ± 1.39, respectively. Silica gel HPTLC F254 plates were used to carry out the separation. The mobile phase used was a mixture of ethanol-ethyl acetate (1:9 by volume), which is environmentally green and harmless. Densitometric scanning with UV detector was used to detect the separated peaks at 222 nm. ICH guidelines were followed to validate the suggested method, and the results prove that they can be used for regular analysis in quality control laboratories with compatible results.

Multimodal imaging of hallucinogens 25C- and 25I-NBOMe on blotter papers.

Due to the much lower production costs but similar effects to lysergic acid diethylamide (LSD), phenethylamine derivatives are sold as a cheaper replacement or deceptively as LSD itself. These potent hallucinogenic substances can lead to severe intoxication, thus a more profound understanding of their use is required. This includes the elucidation of the manufacturing processes for the commonly used blotter papers and the assessment of the risk of overdosing because of a heterogeneous distribution on the blotter papers. Besides the rapid detection of the analytes, the manufacturing process was elucidated by three different imaging techniques and liquid chromatography-mass spectrometry (LC-MS). A blotter paper sample, containing the two hallucinogenic phenethylamine derivatives 25I-NBOMe and 25C-NBOMe, was analyzed by complementary techniques such as micro x-ray fluorescence (µXRF), laser ablation (LA)-inductively coupled plasma-optical emission spectroscopy (ICP-OES), matrix assisted laser desorption ionization (MALDI)-MS, and with LC-MS after extraction. Using the signal from chlorine and iodine within the compounds, µXRF proved to be the fastest, cheapest and easiest method for identification, requiring no sample preparation at all. LA-ICP-OES provided three-dimensional information of the elements in the blotter paper. These results helped to confirm the assumption that manufacturers spray the compounds onto the paper. Whereas µXRF and LA-ICP-OES detected signals for chlorine and iodine, MALDI-MS-imaging showed the molecular distribution of both analytes. LC-MS analyses as a complementary method support the imaging results. Quantitative results for different drug hotspots revealed a heterogeneous distribution of the drugs on the blotter paper implying an inherent risk of overdosing for consumers.

Cross-interaction of tau PET tracers with monoamine oxidase B: evidence from in silico modelling and in vivo imaging.

PURPOSE: Several tracers have been designed for tracking the abnormal accumulation of tau pathology in vivo. Recently, concerns have been raised about the sources of off-target binding for these tracers; inconclusive data propose binding for some tracers to monoamine oxidase B (MAO-B). METHODS: Molecular docking and dynamics simulations were used to estimate the affinity and free energy for the binding of several tau tracers (FDDNP, THK523, THK5105, THK5317, THK5351, T807 [aka AV-1451, flortaucipir], T808, PBB3, RO-948, MK-6240, JNJ-311 and PI-2620) to MAO-B. These values were then compared with those for safinamide (MAO-B inhibitor). PET imaging was used with the tau tracer [18F]THK5317 and the MAO-B tracer [11C]DED in five patients with Alzheimer's disease to investigate the MAO-B binding component of this first generation tau tracer in vivo. RESULTS: The computational modelling studies identified a binding site for all the tau tracers on MAO-B; this was the same site as that for safinamide. The binding affinity and free energy of binding for the tau tracers to MAO-B was substantial and in a similar range to those for safinamide. The most recently developed tau tracers MK-6240, JNJ-311 and PI-2620 appeared, in silico, to have the lowest relative affinity for MAO-B. The in vivo investigations found that the regional distribution of binding for [18F]THK5317 was different from that for [11C]DED, although areas of suspected off-target [18F]THK5317 binding were detected. The binding relationship between [18F]THK5317 and [11C]DED depended on the availability of the MAO-B enzyme. CONCLUSIONS: The developed tau tracers show in silico and in vivo evidence of cross-interaction with MAO-B; the MAO-B component of the tracer binding was dependent on the regional concentration of the enzyme.

Capillary electrophoresis method for the determination of (R)-dapoxetine, (3S)-3-(dimethylamino)-3-phenyl-1-propanol, (S)-3-amino-3-phenyl-1-propanol and 1-naphthol as impurities of dapoxetine hydrochloride.

A capillary electrophoresis method was developed and validated for the determination of the purity of dapoxetine with regard to the related substances (3S)-3-amino-3-phenylpropan-1-ol, (3S)-3-(dimethylamino)-3-phenylpropan-1-ol, 1-naphthol and the enantiomer (R)-dapoxetine. The separation was based on a dual selector system, which was optimized by a fractional factorial resolution V + design followed by a central composite face centered design with star distance 1 and Monte Carlo simulations for defining the design space. The optimized background electrolyte consisted of a 50 mM sodium phosphate buffer, pH 6.3, containing 45 mg/mL sulfated γ-cyclodextrin and 40.2 mg/mL 2,6-dimethyl-ß-cyclodextrin. Separations were carried out in a 23.5/32 cm, 50 µm fused-silica capillary employing a separation voltage of 9 kV at 15 °C. Following robustness testing using a Plackett-Burman design the method was validated according to the International Council on Harmonization guideline Q2(R1) in the range of 0.05-1.0% relative to the dapoxetine concentration. The method was applied to the analysis of drug substance and a commercial tablet. Data regarding the enantiomeric purity of dapoxetine obtained by the capillary electrophoresis assay were comparable to the data obtained by an enantioselective HPLC method.

Validated spectrophotometric and spectrofluorimetric methods for determination of dapoxetine hydrochloride and dosulepin hydrochloride in their dosage forms using mercurochrome.

Validated, simple, rapid and sensitive spectrophotometric and spectrofluorimetric methods were developed for the determination of dapoxetine HCl and dosulepin HCl. The spectrophotometric method (I) was based on a binary complex formation between each drug and mercurochrome (MER) in acetate buffer (pH 3.5) with maximum absorbance at 557 nm. Calibration graphs were linear over the range 2.0-20.0 and 2.0-24.0 µg/ml, detection limits were 0.23 and 0.41 µg/ml and quantitation limits were 0.71 and 1.26 µg/ml for dapoxetine HCl and dosulepin HCl, respectively. Spectrofluorimetric method (II) was based on the measurement of the quantitative quenching effect of each drug on the native fluorescence of MER at the same pH. Fluorescence quenching of MER was measured at 538 nm after excitation at 470 nm. Calibration graphs were linear over the range 0.5-10.0 and 0.4-10.0 µg/ml, detection limits were 0.17 and 0.12 µg/ml and quantitation limits were 0.5 and 0.36 µg/ml for dapoxetine HCl and dosulepin HCl, respectively. Statistical comparison of results with those obtained by reported methods provided good agreement and revealed that there were no significant differences in accuracy and precision between methods. The proposed methods were applied successfully to analyse commercial tablets and capsules containing the studied drugs.

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.

A Validated Method for the Detection of 32 Bath Salts in Oral Fluid.

Workplace drug testing in Australia is usually adherent to one of two standards, AS/NZS 4308:2008 for urine or AS 4760:2006 for oral fluid. These standards prescribe the drugs tested, devices used and testing methodology followed by the testing agency. However, they are not comprehensive and for many years workers have been able to consume novel psychoactive substances to avoid detection and without consequences. Here, we present a validated method for the detection of 32 Synthetic Stimulant and Hallucogenic drugs, commonly sold as bath salts, in oral fluid. These drugs are cathinone, ephedrone, methylone, flephedrone, MDA, PMA, methedrone, TMA, MDMA, butylone, mephedrone, MDEA, MEC, pentedrone, MBDB, MTA, Alpha-PVP, MPBP, 2C-B, MDPV, DOB, 2C-T-2, TFMPP, DOET, 2C-T-7, naphyrone, MDAI, FMA, DMA, 25C-NBOMe, 25B-NBOMe and 25T4-NBOMe. Sample preparation was undertaken using a simple protein precipitation in acetonitrile. Chromatographic separation was achieved in 7.5 min on a Kinetex F5 column (50 mm × 3 mm × 2.6 µm) using 0.1% formic acid in water and acetonitrile as the mobile phases. The method was validated with limit of detection (1 ng/mL), limit of quantitation (2.5 ng/mL), selectivity, linearity (2.5-500 ng/mL), accuracy (85.3-108.4% of the target concentration) and precision (1.9-14%). This method was applied to 12 samples previously submitted for routine testing and two were found to contain 2-CB and DOB (5 and 4 ng/mL) and, MPBP and TFMPP (both at 4 ng/mL). This method provides for the rapid detection of a large number of compounds in oral fluid which is readily applicable to routine testing laboratories.

Death after 25C-NBOMe and 25H-NBOMe consumption.

A teenager male was found dead in a waterway after he was spotted jumping off into the water stream. The boy looked agitated and confused after a party with friends. At the gathering place, investigators seized packages of blotter papers. A complete autopsy and a histological evaluation of the main tissues were performed; although the death occurred by drowning, the prosecutor requested toxicological exams, in order to evaluate the potential role of drugs of abuse in the episode. Blood (both peripheral and central) and urine samples as well as seized blotter papers were collected and analyzed as follows. The blotter paper, analyzed through a GC-MS method, revealed the presence of 25-NBOMes. A liquid chromatography tandem mass spectrometric (LC-MS/MS) system was used to identify and quantify 5 different 25-NBOMes (namely 25B-NBOMe, 25C-NBOMe, 25D-NBOMe, 25H-NBOMe, 25I-NBOMe) in blood and urine. 25E-NBOMe was used as internal standard (IS). 1mL of urine and 1mL of blood (both peripheral and cardiac) were diluted in 2mL phosphate buffer at pH 6.0, containing IS and purified on a solid phase extraction (SPE) cartridge. LOD and LOQ for the five 25-NBOMes were calculated at 0.05 and 0.1ng/mL respectively. Linearity, accuracy, precision, ion suppression, carry over and recovery were tested and all parameters fulfilled the acceptance criteria. Blood and urine provided positive results for 25C-NBOMe and 25H-NBOMe. Eventually, the seized blotter papers were analyzed by means of LC-MS/MS and the presence of the two NBOMes was confirmed: 25C-NBOMe and 25H-NBOMe were measured at the concentration of 2.80 and 0.29ng/mL in peripheral blood, of 1.43 and 0.13ng/mL in central blood and of 0.94 and 0.14ng/mL in urine, respectively. THC and THCCOOH were also detected in biological fluids, at the concentration of 15.5 and 56.0ng/mL in peripheral blood, 9.9 and 8.5ng/mL in central blood, respectively. NBOMes can produce severe hallucination even at very low doses, and the 25C-NBOMe levels measured in the subject's blood are considered potentially toxic.

Application of a Urine and Hair Validated LC-MS-MS Method to Determine the Effect of Hair Color on the Incorporation of 25B-NBOMe, 25C-NBOMe and 25I-NBOMe into Hair in the Rat.

NBOMes are a group of new psychoactive substances derived from phenethylamines. Recreational abuse is thought to have begun in 2010 and they are commonly associated with the "club drug" scene. They are administered in liquid form or as blotters due to their high potency. An LC-MS-MS method was validated using Scientific Working Group for Forensic Toxicology parameters for the detection of 25B-, 25C- and 4-iodo-2,5-dimethoxy-N-[(2-methoxyphenyl)methyl]-benzeneethanamine (25I-NBOMe) using 4-bromo-2,5-dimethoxy-N-[(2-methoxyphenyl)methyl]-benzeneethanamine (25B-NBOMe)-D3 as internal standard for urine and hair. Calibration graphs with R2 values >0.99 were observed for urine and hair for concentrations ranging from 0.1 to 100 ng/mL and 0.025 to 2.5 ng/mg, respectively. Urine LODs ranged from 5 to 25 pg/mL and had an LOQ of 50 pg/mL. Hair LOD and LOQs ranged from 3 to 5 pg/mg and 6.25 to 12.5 pg/mg, respectively. Intra- and inter-day precision was <20% and accuracy was within ±20% for both matrices. The method was shown to be selective for both exogenous and endogenous compounds. No matrix effects were observed for either matrix. LLE recovery ranged from 90 to 103% for urine samples and solid phase extraction recovery ranged from 80 to 107% for hair samples. Long-Evans rats (n = 55) were administered 25B-, 25C- or 25I-NBOMe at doses ranging from 30 to 300 µg/kg over a period of 10 days. Rats were shaved prior to their first dose and re-shaved after the 10-day period. Hair was separated by color (black: n = 55 and white: n = 55) and analyzed using the validated LC-MS-MS method to assess the impact hair color has on the incorporation of these drugs. All drugs were successfully detected in black hair. 25B-NBOMe from rats receiving the highest dose and 25C-NBOMe from rats receiving the medium and high doses were quantified in white hair. 25I-NBOMe was detected but fell below the limit of quantification. A dose-dependent concentration increase was observed in the black hair. All pooled urine samples tested positive for their expected NBOMes.

Identification, Characterization, and Quantification of Impurities of Safinamide Mesilate: Process-Related Impurities and Degradation Products.

The characterization of process-related impurities and degradation products of safinamide mesilate (SAFM) in bulk drug and a stability-indicating HPLC method for the separation and quantification of all the impurities were investigated. Four process-related impurities (Imp-B, Imp-C, Imp-D, and Imp-E) were found in the SAFM bulk drug. Five degradation products (Imp-A, Imp-C, Imp-D, Imp-E, and Imp-F) were observed in SAFM under oxidative conditions. Imp-C, Imp-D, and Imp-E were also degradation products and process-related impurities. Remarkably, one new compound, identified as (S)-2-[4-(3-fluoro-benzyloxy) benzamido] propanamide (i.e., Imp-D), is being reported here as an impurity for the first time. Furthermore, the structures of the aforementioned impurities were characterized and confirmed via IR, NMR, and MS techniques, and the most probable formation mechanisms of all impurities proposed according to the synthesis route. Optimum separation was achieved on an Inertsil ODS-3 column (250 × 4.6 mm, 5 µm), using 0.1% formic acid in water (pH adjusted to 5.0) and acetonitrile as the mobile phase in gradient mode. The proposed method was found to be stability-indicating, precise, linear, accurate, sensitive, and robust for the quantitation of SAFM and its process-related substances, including its degradation products.

Cerebral 5-HT release correlates with [11C]Cimbi36 PET measures of 5-HT2A receptor occupancy in the pig brain.

Positron emission tomography (PET) can, when used with appropriate radioligands, non-invasively generate temporal and spatial information about acute changes in brain neurotransmitter systems. We for the first time evaluate the novel 5-HT2A receptor agonist PET radioligand, [11C]Cimbi-36, for its sensitivity to detect changes in endogenous cerebral 5-HT levels, as induced by different pharmacological challenges. To enable a direct translation of PET imaging data to changes in brain 5-HT levels, we calibrated the [11C]Cimbi-36 PET signal in the pig brain by simultaneous measurements of extracellular 5-HT levels with microdialysis and [11C]Cimbi-36 PET after various acute interventions (saline, citalopram, citalopram + pindolol, fenfluramine). In a subset of pigs, para-chlorophenylalanine pretreatment was given to deplete cerebral 5-HT. The interventions increased the cerebral extracellular 5-HT levels to 2-11 times baseline, with fenfluramine being the most potent pharmacological enhancer of 5-HT release, and induced a varying degree of decline in [11C]Cimbi-36 binding in the brain, consistent with the occupancy competition model. The observed correlation between changes in the extracellular 5-HT level in the pig brain and the 5-HT2A receptor occupancy indicates that [11C]Cimbi-36 binding is sensitive to changes in endogenous 5-HT levels, although only detectable with PET when the 5-HT release is sufficiently high.

Vehicle effects on human stratum corneum absorption and skin penetration.

This study evaluated the effects of three vehicles-ethanol (EtOH), isopropyl alcohol (IPA), and isopropyl myristate (IPM)-on stratum corneum (SC) absorption and diffusion of the [14C]-model compounds benzoic acid and butenafine hydrochloride to better understand the transport pathways of chemicals passing through and resident in SC. Following application of topical formulations to human dermatomed skin for 30 min, penetration flux was observed for 24 h post dosing, using an in vitro flow-through skin diffusion system. Skin absorption and penetration was compared to the chemical-SC (intact, delipidized, or SC lipid film) binding levels. A significant vehicle effect was observed for chemical skin penetration and SC absorption. IPA resulted in the greatest levels of intact SC/SC lipid absorption, skin penetration, and total skin absorption/penetration of benzoic acid, followed by IPM and EtOH, respectively. For intact SC absorption and total skin absorption/penetration of butenafine, the vehicle that demonstrated the highest level of sorption/penetration was EtOH, followed by IPA and IPM, respectively. The percent doses of butenafine that were absorbed in SC lipid film and penetrated through skin in 24 h were greatest for IPA, followed by EtOH and IPM, respectively. The vehicle effect was consistent between intact SC absorption and total chemical skin absorption and penetration, as well as SC lipid absorption and chemical penetration through skin, suggesting intercellular transport as a main pathway of skin penetration for model chemicals. These results suggest the potential to predict vehicle effects on skin permeability with simple SC absorption assays. As decontamination was applied 30 min after chemical exposure, significant vehicle effects on chemical SC partitioning and percutaneous penetration also suggest that skin decontamination efficiency is vehicle dependent, and an effective decontamination method should act on chemical solutes in the lipid domain.

Identification and characterization of a new dapoxetine impurity by NMR: Transformation of N-oxide by Cope elimination.

Unknown impurity associated with the degradation process of dapoxetine base was isolated. The structure elucidation of this new compound using accurate mass data, IR and NMR spectroscopy is presented herein. The unambiguous resonance assignment concluded to the formation of geometrical isomers of cinnamyloxynaphtalenes via Cope elimination of dapoxetin-N-oxide, the major oxidative and metabolic degradation product of dapoxetine. An efficient and simple synthetic approach has also been developed for the synthesis of dapoxetine-N-oxide for the first time and cinnamyloxynaphtalene in order to confirm the proposed degradation pathway and structures of the degradation products. It was observed that the main degradation product of dapoxetine base when exposed to air is 1-(2E)-cinnamyloxynaphthalene, while its Z isomer was also confirmed as a minor impurity.

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 Situ Generation and Consumption of H2O2 by Bienzyme-Quantum Dots Bioconjugates for Improved Chemiluminescence Resonance Energy Transfer.

Exploration of quantum dots (QDs) as energy acceptors revolutionizes the current chemiluminescence resonance energy transfer (CRET), since QDs possess large Stokes shifts and high luminescence efficiency. However, the strong and high concentration of oxidant (typically H2O2) needed for luminol chemiluminescence (CL) reaction could cause oxidative quenching to QDs, thereby decreasing the CRET performance. Here we proposed the use of bienzyme-QDs bioconjugate as the energy acceptor for improved CRET sensing. Two enzymes, one for H2O2 generation (oxidase) and another for H2O2 consumption (horseradish peroxidase, HRP), were bioconjugated onto the surface of QDs. The bienzyme allowed fast in situ cascaded H2O2 generation and consumption, thus alleviating fluorescence quenching of QDs. The nanosized QDs accommodate the two enzymes in a nanometric range, and the CL reaction was confined on the surface of QDs accordingly, thereby amplifying the CL reaction rate and improving CRET efficiency. As a result, CRET efficiency of 30-38% was obtained; the highest CRET efficiency by far was obtained using QDs as the energy acceptor. The proposed CRET system could be explored for ultrasensitive sensing of various oxidase substrates (here exemplified with cholesterol, glucose, and benzylamine), allowing for quantitative measurement of a spectrum of metabolites with high sensitivity and specificity. Limits of detection (LOD, 3σ) for cholesterol, glucose, and benzylamine were found to be 0.8, 3.4, and 10 nM, respectively. Furthermore, multiparametric blood analysis (glucose and cholesterol) is demonstrated.

Separation of polyethylene glycols and amino-terminated polyethylene glycols by high-performance liquid chromatography under near critical conditions.

The separation and characterization of polyethylene glycols (PEGs) and amino-substituted derivatives on common silica-based reversed-phase packing columns using isocratic elution is described. This separation is achieved by liquid chromatography under the near critical conditions (LCCC), based on the number of amino functional end groups without obvious effect of molar mass for PEGs. The mobile phase is acetonitrile in water with an optimal ammonium acetate buffer. The separation mechanism of PEG and amino-substituted PEG under the near LCCC on silica-based packing columns is confirmed to be ion-exchange interaction. Under the LCCC of PEG backbone, with fine tune of buffer concentration, the retention factor ratios for benzylamine and phenol in buffered mobile phases, α(benzylamine/phenol)-values, were used to assess the ion-exchange capacity on silica-based reversed-phase packing columns. To the best of our knowledge, this is the first report on separation of amino-functional PEGs independent of the molar mass by isocratic elution using common C18 or phenyl reversed-phase packing columns.