Perchloric Acid-methanol Research Articles

Chiral recognition mechanism studies of Tyr-Arg-Phe-Lys-NH2 tetrapeptide on crown ether-based chiral stationary phase.

Even though chiral recognition for crown-ether CSPs is generally understood, on a molecular level, exact mechanisms for the resolution are still unclear. Furthermore, short peptide analytes often contain multiple amino moieties capable of binding to the crown ether selector. In order to extend the understanding in chiral recognition mechanisms, polar organic mode separation of Tyr-Arg-Phe-Lys-NH2 tetrapeptide llll/dddd enantiomers on S- and R-(3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 stationary phases was studied with 50-mM perchloric acid in methanol as mobile phase. Deviation from the generally acceptable 1:1 stoichiometry was supported by mass spectroscopy analysis of the formed complexes between tetrapeptide enantiomer and crown ether selectors, which revealed adducts possessing 1:1, 1:2, and 1:3 stoichiometry. Further investigation of complexation induced shifts by NMR indicated on different binding mechanisms between llll/dddd enantiomers of Tyr-Arg-Phe-Lys-NH2 and crown ether selectors. Enantioselective proton shifts were observed in studied tetrapeptide tyrosine and phenylalanine residues exclusively for llll enantiomer upon binding with S-(3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 selector (and dddd enantiomer with R-(3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 selector), indicating that these two amino acid residues contribute to chiral recognition. The obtained results were in agreement with the LC data.

Electrochemical Polishing of Nitinol and Other Medical Alloys in Aqueous Electrolytes Using Pulse/Pulse Reverse Electric Fields

Nitinol is an important medical alloy, and its unique properties have allowed advancement of minimally invasive procedures for medical and orthodontic applications. Nitinol is a near equiatomic alloy of nickel and titanium whose properties, namely superelasticity, shape memory effect and self-passivity, are particularly important for medical applications. However, surface preparation plays a significant role in the surface properties of Nitinol and consequently influences corrosion behavior in a physiological environment. Surface treatments including mechanical polishing, chemical polishing, electropolishing, anodization and heat treatments have been investigated for corrosion behavior in physiological environments, especially in terms of nickel ion release from the device surface, which is an important consideration for medical applications owing to nickel’s toxicity. Electropolishing is attractive for the preparation of Nitinol surfaces due to improvements in corrosion resistance, biocompatibility and surface quality when compared with other surface preparation methodologies.[i] Traditionally, processing of these materials has been carried out in hazardous chemicals such as hydrofluoric acid, or fluoride salts that convert to hydrofluoric acid,[ii] to electropolish and passivate the device and achieve the surface finish required for insertion into the body. The inclusion of hydrofluoric acid, in addition to concentrated sulfuric-phosphoric acids, makes for an extremely hazardous working environment. Alternatively, non-aqueous electrolytes such as methanol-perchloric acid[iii] or methanol-sulfuric acid[iv] mixtures have been suggested, but these require low-moisture environments and low-temperatures (-10 °C) and industrial implementation is difficult. The current work demonstrates that Nitinol surfaces may be electropolished in simple, aqueous electrolytes using pulse and pulse/reverse electric fields. Electropolishing of Nitinol has been done in dilute sulfuric acid solutions (5-10%) as well as salt electrolytes using pulse/pulse reverse voltage fields under ambient conditions. This work has been demonstrated for Nitinol coupons, wires and shape sets; processing of these surfaces will be discussed. Implementation of a Nitinol wire manufacturing process is an important step in the fabrication of these devices for medical use. Scale up of Nitinol wire electropolishing in terms of apparatus is also currently underway and will be discussed. In the current work, a reel-to-reel apparatus will be utilized to facilitate scale-up activities. A schematic of the reel-to-reel apparatus is shown in the accompanying image. The apparatus design is straight-forward due to limited considerations needed for processing under ambient conditions in simple aqueous electrolytes. Important cell considerations such as cathode configuration and residence time will be discussed along with processing considerations. This method is applicable to other medical alloy wires, devices and implants. [i] R. Steegmueller, T. Fleckenstein, and A. Schuessler, Proceedings of the Materials and Processes for Medical Devices, 163-168 (December 1, 2006). [ii] Dr. James Carlson, Senior Metallurgical Engineer, Cook Medical, private communication, November 2010. [iii] W. Miao, X. Mi, M. Zhu and H. Li, J. Ceramic Processing Research, 7 (4), 367-370 (2006). [iv] K. Fushimi, M. Stratmann and A.W. Hassel, Electrochimica Acta, 52, 1290-1295 (2006). Figure 1

Determination of cephalomannine in rat plasma by gradient elution UPLC-MS/MS method.

A rapid, sensitive and selective ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was developed and validated for the determination and pharmacokinetic investigation of cephalomannine in rat plasma. Sample preparation was accomplished through a simple one-step deproteinization procedure with 0.2 mL of perchloric acid-methanol (1:9, v/v) to a 0.1 mL plasma sample. Plasma samples were separated by UPLC on an Acquity UPLC BEH C18 column using a mobile phase consisting of acetonitrile-0.1% formic acid in water with gradient elution. The total run time was 2.0 min and the elution of cephalomannine was at 1.60 min. The detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction-monitoring (MRM) mode using the respective transitions m/z 832.8→264.1 for cephalomannine and m/z 812.6→286.0 for 10-DAT (internal standard), respectively. The calibration curve was linear over the range of 10-2,000 ng/mL with a lower limit of quantitation (LLOQ) of 10 ng/mL. Mean recovery of cephalomannine in plasma was in the range of 80.9-85.3%. Intra-day and inter-day precision were both <11.2%. This method was successfully applied in pharmacokinetic study after intravenous administration of 5.0mg/kg cephalomannine in rats.

Simultaneous determination of bendamustine and its active metabolite, gamma-hydroxy-bendamustine in human plasma and urine using HPLC-fluorescence detector: application to a pharmacokinetic study in Chinese cancer patients.

A simple, sensitive and cost-effective assay based on reversed phase high performance liquid chromatography (RP-HPLC) with isocratic mode for simultaneous determination of bendamustine (BM) and its active metabolite, gamma-hydroxy-bendamustine (γ-OH-BM) in human plasma and urine was developed and validated. Sample preparation involved protein precipitation by 10% perchloric acid-methanol solution. The peaks were recorded by using fluorescence detector (excitation wavelength 328 nm and emission wavelength 420 nm). The calibration curves were linear over concentration ranges of 8.192-10,000 ng mL(-1) and 5-1,000 ng mL(-1) for BM in human plasma and urine as well as 10-1,000 ng mL(-1) and 5-1,000 ng mL(-1) for γ-OH-BM in human plasma and urine, respectively. Intra- and inter-run precisions of BM and γ-OH-BM were less than 15% and the bias were within ± 15% for both plasma and urine. This validated method was successfully applied to a pharmacokinetic study enrolling 10 Chinese patients with indolent B-cell non-Hodgkin lymphoma and chronic lymphocytic leukemia administered a single intravenous infusion of 100 mg m(2) bendamustine hydrochloride.

Electropolishing behaviour of pure titanium in perchloric acid–methanol–ethylene glycol mixed solution

An electropolishing procedure for pure titanium in a methanol–perchloric acid–ethylene glycol electrolyte and the resulting surface characteristics are described. Based on the potential–current curves, and optical and atomic force microscopy examinations, it is shown that commercially available pure titanium can be electropolished well in methanol based solution containing 38 wt-% ethylene glycol and 10 wt-% perchloric acid. The optimum conditions for potentiostatic electropolishing of pure titanium in this solution are obtained by potentiostatic electropolishing under 20 V at 0°C under appropriate agitation. Surface properties of Ti after electropolishing under the optimum conditions were compared to those obtained after mechanical polishing. While this type of electropolishing solution is more durable and less toxic to the environment than most conventional solutions, it provides mirror-like titanium surface finishing.

4-Bromoanilinium perchlorate 18-crown-6 clathrate

The reaction of 4-bromo­aniline, 18-crown-6, and perchloric acid in methanol yields the title compound, C6H7BrN+·ClO4 −·C12H24O6, in which the protonated –NH3 + group forms three bifurcated N—H⋯O hydrogen bonds to the O atoms of the crown ether.

Dimethylammonium perchlorate 18-crown-6 monohydrate clathrate

The reaction of dimethyl­amine, 18-crown-6, and perchloric acid in methanol yields the title compound, C2H8N+·ClO4 −·C12H24O6·H2O. The dimethyl­ammonium cation and the water mol­ecule inter­act with the 18-crown-6 unit: N—H⋯O hydrogen bonds are formed between the ammonium NH2 + group and four O atoms of the crown ether, while the water mol­ecule on the other side of 18-crown-6 ring forms O—H⋯O hydrogen bonds with two other O atoms of the crown ether. All conventional donors and acceptors in the cations are thus engaged in hydrogen bonding. The ClO4 − anion is disordered over two sites, and occupancies for the disordered O atoms were fixed at 0.5. In the crystal, the cations and anions are arranged in alternating layers.

UPLC-ESI-MS-MS Determination of Three β2-Agonists in Pork

Matrix-induced ion suppression and different polarity usually interfere with extraction, purification and drug analysis, therefore a method was developed for determination of three β2-agonists namely, salbutamol, ractopamine and clenbuterol in pork. After enzymatic hydrolysis, a 2.0 g homogenized pork sample was extracted, with perchloric acid–methanol (9:1, v/v) to precipitate protein, and then cleaned by mixed-mode Bond Elut Plexa PCX solid phase extraction (SPE) cartridges. Finally, the evaporated extract was reconstituted to 2 mL with initial mobile phase. The analytes were determinated by ultra performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS-MS). Results indicate that the method is effective to reduce ion suppression phenomena. Recoveries of the three β2-agonists in most cases were better than 85% with relative standard deviations between 2 and 11%. The limits of detection (LOD) were 0.07–0.12 μg kg−1. The limits of quantitation (LOQ) ranged from 0.22–0.38 μg kg−1.

Spectroscopic and computational studies on a new Pd(II)-bis(pyrazol-1-yl)methane aqua-complex

Abstract By reacting a stoichiometric amount of BPM or Me 2 BPM (BPM = bis(pyrazol-1-yl)methane, Me 2 BPM = bis(3,5-dimethylpyrazol-1-yl)methane) with Pd(OAc) 2 (OAc = acetate) in CH 2 Cl 2 , the new neutral complexes [Pd(OAc) 2 (BPM)] ( 1 ) and [Pd(OAc) 2 (Me 2 BPM)] ( 1 Me ) were isolated and characterized by NMR and IR spectroscopy. Acidolysis of one Pd-OAc bond of compound 1 by using aqueous perchloric acid in methanol led to the formation of the stable cationic aqua-complex [Pd(OAc)(H 2 O)(BPM)](ClO 4 ) ( 2-ClO 4 ). The [Pd(OAc)(H 2 O)(BPM)] + cation was obtained also by reacting 1 with trifluoromethanesulfonic acid. NMR studies on inter - and intra -molecular hydrogen bonding of the aqua-ligand have been carried out and the data obtained have been interpreted on the basis of the results of DFT calculations.

HPLC Method for the Determination of Bezafibrate in Human Plasma and Application to a Pharmacokinetic Study of Bezafibrate Dispersible Tablet

A sensitive and selective high-performance liquid chromatographic-UV (HPLC-UV) method for the determination of bezafibrate in human plasma has been developed. Sample treatment was based on protein precipitation with a perchloric acid-methanol solution 10:90 (v/v). Analytical determination was carried out by HPLC with UV detection at 235 nm. Chromatographic separation was achieved on a C18 column by isocratic elution with acetonitrile-ammonium acetate aqueous solution (10 mmol/L; pH 4.0) (44:56, v/v) at a flow rate of 1.0 mL/min. The method was linear in the concentration range of 0.1-15.0 microg/mL. The lower limit of quantitation was 0.1 microg/mL. The intra-and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 6.96%. The accuracy determined at three concentrations (0.2, 2.0, and 10.0 microg/mL for bezafibrate) was within +/- 10.0% in terms of accuracy. The method was successfully applied for the evaluation of pharmacokinetic profiles of bezafibrate dispersible tablet in 20 healthy volunteers. The results show that AUC, C(max), and T(1/2) between the testing formulation and reference formulation have no significant difference (P > 0.05). Relative bioavailability was 105.0 +/- 15.7%.

Determination of phenolic preservatives in gelatin and vacant capsules for medicine use by ion-suppression reversed-phase high performance liquid chromatography

A reliable method for the simultaneous determination of phenolic preservatives parahydroxybenzoic acid, methyl, ethyl, propyl, butyl and pentyl parahydroxybenzoates in gelatin and vacant capsules for medical use has been developed by ion-suppression reversed-phase high performance liquid chromatography. Separation was carried out on a Kromasil C 18 column by isocratic elution using methanol–perchloric acid (pH 2.0; 10 mM) (60:40, v/v) at a flow-rate of 1.0 ml min −1, and detection by UV absorbance at a wavelength of 254 nm. This method has been successfully applied to the routine analyses of these preservatives in the real samples.

LC–MS/MS determination in rabbit plasma of the main photoproduct of RLP068/Cl, a cationic sensitizer proposed for photodynamic therapy (PDT) of microbial infections

The clinical development of a sensitizer for photodynamic therapy (PDT) requires the structural identification of the photoproducts and their quantification in biological fluids and tissues. We describe the LC–MS identification of the most important photoproducts of a cationic phthalocyanine sensitizer (RLP068/Cl) and a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the determination of the main photoproduct (the cationic phthalimide derivative 3-[(1,3-dioxo-2,3-dihydro-1 H-isoindol-4-yl)oxy]- N, N, N-trimethylbenzenaminium chloride) in rabbit plasma. The tri-deuterated product was used as co-eluting internal standard. The cationic photoproduct was isolated from plasma samples by protein precipitation with perchloric acid in methanol (7%, v/v). HPLC step was performed on a Phenomenex Synergi Hydro-RP column (20 mm × 2.0 mm, 2 μm particles) with a mobile phase of 0.5% (v/v) aqueous TFA/methanol (85:15, v/v). Flow rate was 0.2 mL/min and 40 μL injection were performed. Run time was 10 min. Detection was achieved by means of a Bruker Esquire 3000+ ion trap mass spectrometer equipped with an ESI source working in positive mode. A multiple reaction monitoring method following the transitions 297.1 → 282.1 for the analyte and 300.1 → 282.1 + 285.1 for the internal standard was used. The analytical method was validated over the concentration range 0.46–91.2 ng/mL and lower limits of detection (LLOD) and quantification (LLOQ) respectively of 0.2 and 0.5 ng/mL were found.

Ergosteroids VII: perchloric acid-induced transformations of 7-oxygenated steroids and their bio-analytical applications—a liquid chromatographic-mass spectrometric study

Sulfate esters of 7-oxo- Δ 5-steroids can be selectively and quantitatively hydrolyzed to the corresponding free steroids in the presence of carboxylic acid esters by solvolysis with perchloric acid in ethyl acetate at room temperature. Sulfates as well as carboxylic acid esters, methyl ethers, and ketals can be quantitatively converted to the corresponding 3,5-diene-7-one derivatives by heating with perchloric acid in methanol at 65 °C. The dienes have a strong UV absorption with maximum centered around 284 nm. These reactions have been used for the characterization and structural elucidation of 7-oxygenated- Δ 5-steroids that are present in complex biomatrices and can also be used for the quantitative estimation of total 7-oxo- Δ 5-steroids (free as well as conjugated) in biological matrices.

A simple HPLC method to determine urinary phenylmercapturic acid and its application to gasoline station attendants to biomonitor occupational exposure to benzene at less than 1 ppm

The objective of this study was to establish a hand-saving method to measure phenylmercapturic acid (PMA) and to examine urinary PMA as a marker of occupational exposure to benzene at levels less than 1 ppm. A simple HPLC method was developed to analyse PMA by monitoring absorption at 195 nm of the ef? uent from an ODS-3 column with acetonitrile–methanol–perchloric acid–water as a mobile phase. The detection limit of the method was 0.2 μg l−1 with sufficient reproducibility. The method was applied to end-of-shift urine samples from 70 gasoline station attendants exposed to up to 107 ppb benzene, and 20 non-exposed controls of both sexes. Time-weighted average (TWA) exposure to benzene was measured by diffusive sampling. A regression analysis was applied to examine the quantitative relationship between the intensity of exposure to benzene and PMA in the end-of-shift urine samples. Multiple regression analysis showed no effects of age, sex, smoking and co-exposure to toluene and xylenes on urinary PMA. There was a linear relationship between TWA benzene exposure and urinary PMA (r = 0.60–0.67, P < 0.01). Background PMA in urine of the non-exposed controls was low and scattering of PMA around the regression line was narrow so that those with 20 ppb benzene exposure can be separated from the non-exposed by urinalysis for PMA. Thus, urinary PMA is sensitive enough for biological exposure monitoring of those exposed to less than 1 ppm benzene.

Unusual Stabilities and Reactivities of Tris- and Bis(2,4,6-trimethoxyphenyl)carbenium Salts

Abstract 2,4,6-Trimethoxyphenyllithium, Φ′Li[Φ′ = 2,4,6-(MeO)3C6H2], reacted with diphenyl carbonate and with ethyl formate to give tris(2,4,6-trimethoxyphenyl)methanol, Φ′3COH (1), and bis(2,4,6-trimethoxyphenyl)methanol, Φ′2CHOH (2), respectively. Compound 1 reacted with a slight excess of perchloric acid in 2-propanol to give very dark-purple crystals of the triarylcarbenium salt, [Φ′3C]X (3, X = ClO4), which were inert even in hot ethanol. However, a treatment of 3 (X = Cl), prepared in situ in 1 M (1 M = 1 mol dm−3) hydrochloric acid, with 1 M sodium hydroxide resulted to give 4-bis(2,4,6-trimethoxyphenyl)methylene-3,5-dimethoxy-2,5-cyclohexadienone. Compound 2 also reacted with a slight excess of perchloric acid in methanol to give dark-red crystals of the diarylcarbenium salt, [Φ′2CH]X (5, X = ClO4). Compound 5 was considerably inert even in hot methanol, but was easily reduced in primary and secondary alcohols to give bis(2,4,6-trimethoxyphenyl)methane, Φ′2CH2. Measurements of the half-lives of 5 in these alcohols showed that 5 was more labile in secondary alcohols, such as 2-propanol and 2-butanol, than in primary alcohols. When a suspension of 5 (X = Cl), prepared in situ in 1 M hydrochloric acid, was heated, tris(2,4,6-trimethoxyphenyl)methane, Φ′3CH (7), was obtained. Analogous reactions to give 7 were observed in methanol containing a slight excess of hydrochloric acid or nitric acid in place of perchloric acid. The possible paths of these reactions are discussed.

Determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection

Sensitive high-performance liquid chromatographic assays have been develope to determine the levels of the lactone and lactone plus carboxylate (total) forms of the antitumor agent irinotecan (CPT-11) and its active metabolite SN-38, in human plasma. The related compound camptothecin was used as the internal standard. The selective sample pretreatment for the lactone forms involved a single solvent extraction with acetonitrile- n-butyl chloride (1:4,v/v), whereas the sample clean-up for the total forms was a simple protein precipitation with aqueous perchloric acid-methanol (1:1, v/v), which results in the conversion of the carboxylate to the lactone forms. Chromatography was carried out on a Hypersil ODS column, with detection performed fluorimetrically. The methods have been validated, and stability tests under various conditions have been performed. The lower limits of quantitation are 0.5 and 2.0 ng/ml for the lactone and total forms, respectively. The assays have been used in a single pharmacokinetic experiment in a patient to investigate the applicability of the method in vivo.

Determination of the lactone and lactone plus carboxylate forms of 9-aminocamptothecin in human plasma by sensitive high-performance liquid chromatography with fluorescence detection.

Two sensitive reversed-phase high-performance liquid chromatographic fluorescence methods, with simple sample handling at the site of the patient, are described for the determination of the lactone and lactone plus carboxylate forms of 9-aminocamptothecin (9AC). For 9AC lactone, the sample preparation was a liquid-liquid extraction with acetonitrile-n-butyl chloride (1:4, v/v), whereas the sample preparation for 9AC total (lactone plus carboxylate) was a simple deproteinization with 5% perchloric acid-methanol (1:1, v/v), which results in the conversion of the carboxylate into the lactone form. The lower limits of quantitation were 50 pg/ml and 100 pg/ml for 9AC lactone and 9AC total, respectively. The within-run precisions at four tested concentrations were < or = 6.3% for 9AC lactone and < or = 5.3% for 9AC total. The between-run precisions were < or = 8.9% and < or = 5.6%, respectively. The assays were developed to enable pharmacological analysis of 9AC in a bioavailability and oral phase I study in patients with solid tumors.

High-performance liquid chromatography with electrochemical detection of aspartame with a post-column photochemical reactor

Aspartame (N- l-α-aspartyl- l-phenylalanine 1-methyl ester) was determined by high-performance liquid chromatography with electrochemical detection. Aspartame, which is electrochemically inactive, was made oxidizable in the range 0.1–1.1 V after post-column irradiation at 254 nm. A detection limit of 0.5 mg/l (signal-to-noise ratio 3:1) was attained using a coulometric detector with the working cell set at 0.8 V and a C 6 column (150 × 4.6 mm I.D.) operated under isocratic conditions with 0.1% perchloric acid-methanol (85:15, v/v) as the eluent at a flow-rate of 1 ml/min. A linear response for aqueous solutions of aspartame in the range 1–20 mg/l and a 5% standard deviation for five replicate injections were obtained. The method was applied to the determination of aspartame in two diet colas and a pharmaceutical product. Chromatograms and a hydrodynamic voltammogram are shown.

Optimization of the determination of 4-aminopyridine in human serum and urine by column liquid chromatography

Two convenient reversed-phase column liquid chromatographic procedures are described for the determination of 4-aminopyridine in human serum and urine. A 0.5-ml aliquot of serum after the addition of a 0.5-ml solution of 4-(aminomethyl)pyridine in 0.1 M Na 2HPO 4 as the internal standard is passed through a 1-ml BondElut C 18 silica extraction column. The column is selectively washed to remove acidic, neutral and weakly basic compounds. The desired compounds are eluted with a 0.3-ml aliquot of 35% perchloric acid-methanol (1:100, v/v). A 10-μl aliquot of the eluate is infected onto a 150 × 4.6 mm I.D. column packed with 5-μm C 18 silica particles that is eluted at ambient temperature with a mobile phase containing octanesulfonic acid as the ion-pairing agent. The peaks are monitored at 263 nm. A 0.25-ml aliquot of urine or 0.5 ml of serum is mixed with N-propionylprocainamide as the internal standard and subjected to benzoylation by Schotten Baumann reaction. The reaction mixture is adjusted to pH 5.5–6 and extracted with a BondElut C 18 extraction column. An aliquot of the eluate is chromatographed at ambient temperature with a mobile phase containing tetramethylammonium perchlorate. The peaks are monitored at 278 nm.

Column liquid chromatographic determination of clozapine and N-desmethylclozapine in human serum using solid-phase extraction

A 0.5-ml aliquot of a serum sample, after the addition of a 50-μl aliquot of a 5 μg/ml solution of amoxapine as the internal standard, is vortex-mixed with 0.5 ml of acetonitrile and centrifugated. The supernatant is applied to a 1-ml BondElut C 18 silica extraction column-conditioned with subsequent washings with 1 M HCl, methanol and water. After passing the sample at a slow rate, the column is washed twice with water and once with acetonitrile. The desired compounds are then eluted with a 0.25-ml aliquot of 35% perchloric acid-methanol (1:100, v/v). A 15-μl aliquot of the eluate is injected onto a 150 × 4.6 mm I.D. column packed with 5-μm C 8 silica particles and eluted at ambient temperature with a mobile phase of 0.1% tetramethylammonium perchlorate-acetonitrile (73:27, v/v) adjusted to pH 4.2 with 10% perchloric acid. The peaks are detected with an absorbance detector at 245 nm.