Comparison of LC–UV, LC–ELSD and LC–MS Methods for the Determination of Sesquiterpenoids in Various Species of Artemisia

Simple and specific analytical methods for the quantitative determination of sesquiterpenoids from various species of Artemisia plant samples were developed. By LC–UV, LC–ELSD, the separation was achieved by reversed-phase chromatography on a C18 column with water and acetonitrile both containing 0.025% trifluoroacetic acid as the mobile phase. In the LC–MS system, trifluoroacetic acid was replaced by 0.1% formic acid. The wavelength used for quantification of sesquiterpenoids with a diode array detector was 205 nm. The limits of detection by LC–MS was found to be 5, 10, 25, 50, 50 ng mL^?1. The limits of detection by LC–UV and LC–ELSD were found to be 5.0, 3.0, 100, 100, 7.5 μg mL^?1, by LC–UV and 50, 25, 30, 100 and 75 μg mL^?1 by LC–ELSD. LC–mass spectrometry coupled with electrospray ionization (ESI) interface is described for the identification and quantification of sesquiterpenoids in various plant samples. This method involved the use of the [M + H]⁺ ions of sesquiterpenoids in the positive ion mode with extractive ion monitoring.     

Electrospray ionization-voltage sweep-Ion mobility spectrometry for biomolecules and complex samples

Voltage Sweep Ion Mobility Spectrometry (VSIMS) has been applied to complex samples using electrospray ionization (ESI). The usable range of VSIMS has been extended from that obtained in previous studies where only volatile compounds were investigated. Using ESI, VSIMS was evaluated with compounds with reduced mobility values as low as 0.3 V²cm^?1 s^?1. The primary advantage of VSIMS is to enable a drift time ion mobility spectrometer (DTIMS) to detect both fast and slow moving ions at optimal resolving power, thus improving the peak capacity. In this work ESI-VSIMS was applied to a series of small peptides and drugs spanning a large range of reduced mobility values in order to demonstrate ESI-VSIMS to separation. To demonstrate improved peak capacity of IMS with voltage scan operation, oligomers of silicone oil provided a series of evenly-spaced peaks, ranging in reduced mobility values from 0.85 to 0.3 V²cm^?1 s^?1. The peak capacity of 61 for a standard IMS was improved to 102 when voltage sweep operation was employed. In addition, VSIMS increased the average resolving power of the DTIMS from 66 to 106 for silicone oil.     

Electrochemical Determination of Pentachlorophenol Using a Glassy Carbon Electrode Modified with a Film of CuS Nanocomposite-Chitosan

A new electrochemical sensor was fabricated by modifying the glass carbon electrode surface with CuS nanocomposites and chitosan for the determination of pentachlorophenol. CuS nanocomposites obtained by a solvothermal method were composed primarily of CuS with hexagonal phase and Cu₂Cl(OH)₃ with a tetragonal phase. The results indicated that CuS nanocomposites possessed good electrochemical activity. After optimizing the experimental conditions, the linear dependence of current vs. pentachlorophenol concentration was reached in a range from 1.88 × 10^?6–7.50 × 10^?5 mol/L pentachlorophenol, and the detection limit was 6.25 × 10^?7 mol/L. The electrode displayed a high degree of stability and reproducibility. A new, simple, rapid, and highly sensitive electrochemical detection method of pentachlorophenol was established.     

A Sensitive LC–ESI–MS Method for Pharmacokinetic Studies of Picroside II in Dog Plasma

A high-performance liquid chromatography-electrospray ionization-mass spectromentry (LC–ESI–MS) method has been developed for the determination of picroside II in dog plasma. Plasma samples were deproteinated with acetonitrile and a Hypersil ODS2 column was used with a mobile phase consisted of methanol-water. The determination was validated in the concentration range of 0.10–50 μg mL^?1 using 50 μL of plasma. The method was successfully applied to a pharmacokinetic study of picroside II.     

Characterization of Nineteen Impurities in Roxithromycin by HPLC/TOF and Ion Trap Mass Spectrometry

Nineteen impurities in roxithromycin drug substance made in China were separated and identified by HPLC–MSⁿ (TOF and TRAP) for the further improvement of official monographs in Pharmacopoeias. The fragmentation patterns and structural assignment of these impurities were studied. The column was Shim VP-ODS (250 × 4.6 mm, 5 μm). The mobile phase was 10 m mol L^?1 ammonium acetate and 0.1 % formic acid aqueous solution-acetonitrile (62.5:37.5). In positive mode, full scan LC–MS was first performed to obtain the m/z value of the protonated molecules and formulas of all detected peaks on Agilent 6538Q TOF high resolution mass spectrometer. LC–MS-MS and LC–MS-MS–MS were then carried out on the compounds of interest on AB SCIEX 4000 Q TRAP? composite triple quadrupole/linear ion trap tandem mass spectrometer. The complete fragmentation patterns of nineteen impurities were studied and used to obtain information about the structures of these impurities. The structures of nineteen impurities in roxithromycin drug substance were deduced based on the HPLC–MSⁿ data, in which nine impurities were novel impurities.     

Mechanism of Oxidation of Ketorolac by Hexacyanoferrate(III) in Aqueous Alkali: A Thermodynamics and Kinetics Study

The kinetics of the oxidation of ketorolac by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.75 mol·dm^?3 was studied spectrophotometrically at 300 K. A plausible mechanism was proposed and the rate law was derived. The mechanism of oxidation of ketorolac (KET) in alkaline medium has been shown to proceed via a KET-HCF complex, which decomposes in a slow step followed by other fast steps to give the products. The main oxidative product was identified as (2,3-dihydro-1-hydroxy-1H-pyrrolizin-5-yl-)(phenyl)methanone and is characterized by its LC–ESI–MS spectrum. Thermodynamic parameters of various equilibria of the mechanism were calculated and activation parameters ΔH ^≠, ΔS ^≠, ΔG ^≠ and log₁₀ A were found to be 29.9 kJ·mol^?1, ?220 J·K^?1·mol^?1, 96 kJ·mol^?1 and 2.70 respectively.     

Enantiomeric Separation of Moxifloxacin and Its (R,R)-Isomer by Ligand-Exchange Chiral Chromatography

A new stereospecific LC method for the separation and quantification of moxifloxacin and its (R,R)-enantiomer in bulk drug was developed and validated by ligand-exchange liquid chromatography on a reversed phase column using aqueous mobile phase containing the chiral reagent l-isoleucine-Cu(II). The UV detector was operated at 293 nm. The flow rate of mobile phase was set at 0.9 mL min^?1. The achiral ODS column offers good separation of the two enantiomers in less than 20 min. The test concentration was 1,000 μg mL^?1 in the mobile phase. This method was capable of detecting the (R,R)-enantiomer of moxifloxacin up to 0.1 μg mL^?1 for a 20 μL injection volume. The drug was subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. There was no interference of degradants with the (R,R)-enantiomer in the developed method. The developed chiral RP-LC method was validated with respect to linearity, accuracy, precision and robustness. The percentage recovery for the (R,R)-enantiomer in bulk drug samples ranged from 98.1 to 104.4%. The test solution was found to be stable in the mobile phase for 48 h after preparation.     

LC–ESI-MS Determination of Hydroxycamptothecin in Rat Plasma

A rapid and sensitive method using liquid chromatography with electrospray ionization mass spectrometric detection (LC–ESI-MS) was developed and validated for the determination of hydroxycamptothecin in rat plasma. Plasma samples were extracted with ether and separated on a C₁₈ column interfaced with a single quadrupole mass spectrometer, with mobile phase consisting of 0.1% formic acid–methanol (45:55, v/v). Detection was carried out by positive electrospray ionization (ESI) in selected ion recording (SIR) mode at m/z 321 and 305 for hydroxycamptothecin and camptothecin (internal standard), respectively. The linearity was obtained ranged from 2.5 to 1,000 ng mL^?1 and the lower limit of quantification (LLOQ) was determined to be at 2.5 ng mL^?1. The intra- and inter-day precision (%RSD) was less than 5.5% and accuracy (% RE) ranged from 3.8 to 5.3%. This method was applied successfully to a preliminary pharmacokinetic study following the intravenous administration of hydroxycamptothecin to rats.     

LC Determination of Clindamycin Phosphate from Chitosan Microspheres

A simple, rapid and precise reverse phase LC method was adopted, modified and validated for the determination of clindamycin phosphate from chitosan microspheres prepared by spray drying method. Separation was performed using ACE5 C18 reversed phase column (150 mm × 4.6 mm, 5 μm) with acetonitrile:phosphate buffer at pH 2.5 (25:75 v/v) as mobile phase. The limit of detection was 46.43 × 10^?3 μg mL^?1, with UV detection at 210 nm. No interference from chitosan and other excipients was observed. Therefore an incorporation efficiency of microspheres could be determined accurately and specifically.     

HPLC–MS Analysis of Isoniazid in Dog Plasma

A simple, rapid, and sensitive liquid chromatography–mass spectrometric (LC–MS) method was developed and validated for the determination of isoniazid in dog plasma. Plasma samples were deproteined with methanol and separated on a C₁₈ column interfaced with a single quadrupole mass spectrometer, using 0.1% formic acid–acetonitrile (91:9 v/v) as mobile phase. Detection was performed by positive electrospray ionization with selected ion monitoring at m/z 138 for isoniazid and 152 for entecavir maleate internal standard. Linearity was obtained over the range of 25–5,000 ng mL^?1, with a lower limit of quantification of 25 ng mL^?1. The intra- and inter-day precision was less than 2.7% in terms of relative standard deviation. Accuracy, expressed as relative error, ranged from ?2.0 to 8.0%. Plasma samples were analysed within 5 min. The method was successfully applied to the evaluation of the pharmacokinetics of isoniazid in dog plasma.     

A Rapid Sample Preparation Procedure Using MonoSpin CBA and Amide Columns for Tetrodotoxin Detection in Serum and Urine Using LC–MS/MS Analysis

Clinical diagnosis of tetrodotoxin (TTX) poisoning can be difficult because of the lack of characteristic morphological findings and a screening test, such as an immunoassay. Here, we present a fully validated method for the analysis of TTX in serum and urine. In this method, serum and urine samples were extracted using MonoSpin CBA or amide columns, followed by LC–MS/MS analysis. The TTX was eluted from the column by 0.1 mL of 10 % acetic acid solution, and was directly injected into LC–MS/MS. An Agilent 1200 HPLC system equipped with a HILIC separation column (Zorbax HILIC Plus 2.1 × 100 mm, 3.5 μm) was used for isocratic elution, with a mobile phase of 10 mM ammonium formate with formic acid (95:5, v/v), along with 5 mM trifluoroacetic acid and 2 % acetonitrile. TTX was detected with an Agilent 6410 mass spectrometer utilizing positive electrospray ionization and multiple reaction monitoring. Limits of quantification for serum and urine were established to be 1 and 0.5 ng mL^?1, respectively. Limits of detection for serum and urine were 0.5 and 0.25 ng mL^?1, respectively. Intra-day and inter-day precision varied from 1.5 to 8.5 %. The recovery was >86.5 % for both matrices. In this method, the sample preparation process prior to injection into the LC–MS/MS takes approximately 10–15 min, which reduces the extraction time to one-tenth of that of previous methods. The application of this method was further verified by analysis of biological materials from a patient suffering from puffer fish poisoning.     

LC–MS Determination and Pharmacokinetic Study of Salidroside in Rat Plasma after Oral Administration of Traditional Chinese Medicinal Preparation Rhodiola crenulata Extract

A simple, rapid and sensitive liquid chromatography–mass spectrometry (LC–MS) method was developed for the quantification of salidroside in rat plasma and the study of its pharmacokinetics after oral administration of 15 g kg^?1 Rhodiola crenulata extract to Wistar rats. A 200 μL plasma sample was extracted by acetonitrile and performed on Kromasil C₁₈ column (150 mm × 4.6 mm, 5 μm) with the mobile phase of acetonitrile–water (11:89) within a run time of 8 min. The analyte was monitored with electrospray ionization (ESI) by selected ion monitoring (SIM) mode. The target ions were m/z 299.20 for salidroside and m/z 150.00 for internal standard (IS) paracetamol. A good linear relationship was obtained over the range of 100–20,000 ng mL^?1 and the lower limit of quantification was 100 ng mL^?1. The validated method was successfully applied for the pharmacokinetic study of salidroside in rat. After oral administration of Rhodiola crenulata extract, the main pharmacokinetic parameters T _max, T _1/2, C _max, AUC _0?t and AUC _0?∞ were 0.56 ± 0.21 h, 7.91 ± 4.42 h, 3,386 ± 2,138 ng mL^?1, 16,146 ± 6,558 ng h mL^?1 and 18,599 ± 6,529 ng h mL^?1, respectively.     

LC–ESI–MS Determination of Flupentixol in Human Plasma

Flupentixol and an internal standard, loperamide were extracted from human plasma by liquid–liquid extraction and analyzed on a Thermo Hypersil HyPURITY C18 column, with 10 mM ammonium acetate–acetonitrile–methanol (26:62:12, v/v/v) as mobile phase, coupled with electrospray ionization mass spectrometry (ESI–MS). The protonated analyte was quantified by selected-ion monitoring (SIM) with a quadrupole mass spectrometer in a positive-ion mode. The calibration curve was linear (r = 0.9990) over the concentration range: 0.039–2.5 ng mL^?1. Intra-day and inter-day precision (RSD%) were less than 13.05%. The established method was successfully applied for the determination of pharmacokinetics of flupentixol in human plasma.     

Determination of Rutin in Plant Extracts and Emulsions by HPLC-MS

A method for the determination of rutin was developed from in an O/W emulsion with decyl oleate and Ceteareth-20 containing Ginkgo biloba L., Hedera helix L., and Thymus vulgaris L. extracts. Total quantification of rutin was performed by determination in the aqueous and oily phase. Rutin was extracted from the oily phase by ultrasonication for 30 min at 37°C in methanol and resolved by liquid chromatography on a column containing a Gemini 3 µ C18 110A stationary phase.

Chromatography was carried out using gradient elution with the mobile phase composed of water:formic acid and water:acetonitrile:formic acid, which was varied from 100:0.1 to 50:50:0.1 (v/v/v) over 80 min and delivered at a flow rate of 0.3 ml/min. The analytes were quantified using a UV-VIS absorption spectrometer at a wavelength of 254 nm and a single quadrupole mass spectrometer employing an ESI interface operated in the positive ion mode with single ion monitoring at m/z = 609.14.

Finally, a simple and rapid method for the extraction and determination of rutin in hydrophilic and lipophilic phases of an O/W emulsion with good precision and acceptable recovery was developed. This method might be of special importance for the analysis of rutin and other flavonoids in O/W or W/O emulsion matrices.     

Determination of trans-Resveratrol in Bio-Matrices for in Vitro,ex Vivo,and in Vivo Pharmacokinetic Studies by LC Spectrometric Analysis

A high-performance liquid chromatography-electrospray ionization-mass spectromentry (LC–ESI–MS) method has been developed for the determination of picroside II in dog plasma. Plasma samples were deproteinated with acetonitrile and a Hypersil ODS2 column was used with a mobile phase consisted of methanol-water. The determination was validated in the concentration range of 0.10–50 μg mL⁻¹ using 50 μL of plasma. The method was successfully applied to a pharmacokinetic study of picroside II.

     

Characterization of Nineteen Impurities in Roxithromycin by HPLC/TOF and Ion Trap Mass Spectrometry

Nineteen impurities in roxithromycin drug substance made in China were separated and identified by HPLC–MSⁿ (TOF and TRAP) for the further improvement of official monographs in Pharmacopoeias. The fragmentation patterns and structural assignment of these impurities were studied. The column was Shim VP-ODS (250 × 4.6 mm, 5 μm). The mobile phase was 10 m mol L⁻¹ ammonium acetate and 0.1 % formic acid aqueous solution-acetonitrile (62.5:37.5). In positive mode, full scan LC–MS was first performed to obtain the m/z value of the protonated molecules and formulas of all detected peaks on Agilent 6538Q TOF high resolution mass spectrometer. LC–MS-MS and LC–MS-MS–MS were then carried out on the compounds of interest on AB SCIEX 4000 Q TRAP™ composite triple quadrupole/linear ion trap tandem mass spectrometer. The complete fragmentation patterns of nineteen impurities were studied and used to obtain information about the structures of these impurities. The structures of nineteen impurities in roxithromycin drug substance were deduced based on the HPLC–MSⁿ data, in which nine impurities were novel impurities.

     

Determination of Poricoic Acid A in Rat Plasma after Oral and Intravenous Administration by LC–MS–MS and Its Application to a Pharmacokinetic Study

A sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS–MS) method was developed and validated for the quantification of poricoic acid A (PAA) in rat plasma. The plasma samples were precipitated by protein precipitation with methanol. Glycyrrhetic acid was used as the IS. Chromatography was performed on a Dionex C₁₈ 120 Å (4.6 × 250 mm, 5 μm) column with the mobile phase composed of acetonitrile–water (90:10, v/v) at a flow rate of 0.8 mL min^?1. A tandem mass spectrometer equipped with an ESI source was used as the detector and was operated in the negative ion mode. Quantification was performed using multiple reaction monitoring (MRM) of the transitions m/z 497.4 → 423.3 and m/z 469.2 → 425.1 for PAA and IS, respectively. The calibration curves were linear over the range of 5–5,000 ng mL^?1 (r ² = 0.9966) and the lower limit of quantification (LLOQ) was 5 ng mL^?1. In this range, RSDs were <10% for intra-assay and inter-assay precisions. The accuracy expressed by deviation (DEV) was <6%, and the extraction recoveries of QC samples were >78%. The validated method was successfully used to study the pharmacokinetics of PAA in rats after intravenous administration at a dose of 1.0, 2.5 and 5.0 mg kg^?1 and oral administration at a dose of 25, 50 and 100 mg kg^?1, respectively. The relative bioavailability of PAA in rats following oral administration was achieved.     

Comparison of Ion-Pairing and Reversed Phase Liquid Chromatography in Determination of Sulfamethoxazole and Trimethoprim

Abstract

Two simple, rapid, and sensitive HPLC methods have been developed for the simultaneous determination of sulfamethoxazole and trimethoprim in their pure and dosage forms, one utilizing reversed phase HPLC and the other ion-pair HPLC. In the reversed phase HPLC method (A) the mobile phase consists of 0.05% aqueous solution of formic acid with pH adjusted to 4.5±0.2 with triethylamine : acetonitrile:tetrahydrofuran 50 : 49 : 1 (v/v), and the mobile phase pumped at flow rate of 1.0 ml min^?1. An Appolo LC18 column (5.0 µm), 250 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. In the ion-pair HPLC method (B) the mobile phase consisted of methanol : buffer 35 : 65 (v/v) with the buffer composed of potassium dihydrogen phosphate 0.3 M and sodium heptan sulfonic acid 5.0 mM. To 500 ml of buffer was added 2.0 ml triethylamine, and then the pH was adjusted to 5.0 with phosphoric acid, and the mobile phase was pumped at a flow rate of 1.2 ml min^?1. A Hypersil C₁₈ column (5.0 µm), 150 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. Linearity ranges for sulfamethoxazole and trimethoprim were 1.0–110 and 1.5–98 µg ml^?1, respectively, with method A and 0.5–100 and 1.0–125 µg ml^?1, respectively, with method (B). Minimum detection limits obtained were 0.1969 and 0.3451 µg ml^?1 for sulfamethoxazole and trimethoprim, respectively, with method A, and 0.1377 and 0.2454 µg ml^?1 with method (B). The proposed methods were further applied to the analysis of tablets containing the two drugs, and the results were satisfied.     

Sprayed liquid-gas extraction in combination with ion mobility spectrometry: a novel approach for the fast determination of semi-volatile compounds in air and from contaminated surfaces

We developed a fast, simple and highly-efficient enrichment procedure for trace levels of semi volatile organic compounds from air and surfaces and combined it with ion mobility spectrometry as field-deployable and rapid analytical technique. Our new technique, the sprayed liquid-gas extraction, was developed and optimized to allow the enrichment of semi volatile organic compounds. The air sample is pumped through a flow blurring nebulizer together with water. The sprayed liquid is collected and the organic compounds are transferred from the water phase to n-hexane via a miniscale liquid-liquid extraction. 50 μL of the n-hexane extract is applied to a fiber tape. After the n-hexane has evaporated, the fiber tape is transferred to the thermodesorber unit of a GDA-X ion mobility spectrometer (Airsense, Schwerin, Germany). The whole sampling and the sample preparation procedure takes no longer than 15 min and only requires 2.5 mL organic solvent. The method was optimized for Malathion, a widely used organophosphate insecticide and an accepted simulant for the nerve-agent, VX. Malathion provides defined ion mobility spectra in both, the positive and negative mode. The positive spectra show one major peak with a reduced mobility of 1.197 cm² Vs^?1 and an additional peak at 1.449 cm² Vs^?1 with lower intensity. A major product ion peak of 1.720 cm² Vs^?1 can be detected in negative mode together with an additional peak of low intensity at 1.403 cm² Vs^?1. The detection limit of the ion mobility spectrometer is approximately 20 ng absolute.