Packed-column supercritical fluid chromatography of artemisinin (qinghaosu) with electron-capture detection

Lipidomics by Supercritical Fluid Chromatography

This review enlightens the role of supercritical fluid chromatography (SFC) in the field of lipid analysis. SFC has been popular in the late 1980s and 1990s before almost disappearing due to the commercial success of liquid chromatography (LC). It is only 20 years later that a regain of interest appeared when new commercial instruments were introduced. As SFC is fully compatible with the injection of extracts in pure organic solvent, this technique is perfectly suitable for lipid analysis and can be coupled with either highly universal (UV or evaporative light scattering) or highly specific (mass spectrometry) detection methods. A short history of the use of supercritical fluids as mobile phase for the separation oflipids will be introduced first. Then, the advantages and drawbacks of SFC are discussed for each class of lipids (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterols, prenols, polyketides) defined by the LIPID MAPS consortium.

Affordable and sensitive determination of artemisinin in Artemisia annua L. by gas chromatography with electron-capture detection

Artemisinin demand has increased sharply since the World Health Organization recommended its use as part of the artemisinin combination therapies in 2001. The area for the crop cultivation has expanded in Africa and Asia and simpler and affordable methods for artemisinin analysis are needed for crop quality control. This work presented a novel chromatographic method of artemisinin analysis using gas chromatography with electron-capture detection. The sample extraction and preparation involved a single-solvent one-step extraction, with samples being analyzed in the extraction solvent directly after extraction. This method was accurate and reproducible with over 97% recoveries. The limit of detection was less than 3 microg/mL and the limit of quantification was less than 9 microg/mL, allowing samples as low as 100mg dry weight to be analyzed for artemisinin. The method can be applied to quality control of commercial plant extracts and to artemisinin-derived pharmaceuticals.

Determination of artemisinin in human serum by high-performance liquid chromatography with on-line UV irradiation and peroxyoxalate chemiluminescence detection

Artemisinin is an antimalarial drug containing an internal endoperoxide linkage in its structure. A simple, selective and sensitive high-performance liquid chromatography (HPLC)-peroxyoxalate chemiluminescence (PO-CL) method for the determination of artemisinin was developed. This method is based on the fact that endoperoxide in artemisinin structure can be converted to hydrogen peroxide (H(2)O(2)) under ultraviolet (UV) irradiation and the generated hydrogen peroxide can be measured using PO-CL detection. The HPLC-PO-CL system was optimized on a mobile phase, post column chemiluminescence reagent, UV source and irradiation time. In addition, the system was combined with simple liquid-liquid extraction using n-hexane that allowed selective and sensitive determination of artemisinin in serum. The limit of detection using 0.5 mL of blood was 0.062 micromol/L (17.5 ng/mL) at a signal-to-noise ratio of 3. Calibration curve obtained for artemisinin in human serum 4-80 micromol/L (1.1-22.6 microg/mL) showed a good linearity (r = 0.999).

Effect of system variables involved in packed column SFC of nevirapine as model analyte using response surface methodology: Application to retention thermodynamics, solute transfer kinetic study and binary diffusion coefficient determination

A multifactor optimization technique is successfully applied to study the effect of simultaneously varying the system variables on feasibility of nevirapine analysis by packed column supercritical fluid chromatography (PC-SFC). The optimal conditions were determined with the aid of the response surface methodology using 3(3) factorial designs. The method is based on methanol-modified carbon dioxide as the mobile phase at flow rate of 3.0 ml/min with elution through a JASCO Finepak SIL-5, [C18 (5-micron, 25 cm x 4.6 mm, i.d.)] column using photodiode array detection. The method has been successfully used to analyze commercial solid dosage form to assess the chromatographic performance of SFC system. The present work briefs the thermodynamic applications of PC-SFC with an emphasis on the results of nevirapine. The foremost of such applications is the determination of solute diffusion coefficient in supercritical mobile phase by Taylor-Aris peak broadening technique.

Separation and trace estimation of benzidine and its macromolecular adducts using supercritical fluid chromatography

A sensitive, rapid, selective and reproducible method has been developed to measure blood plasma levels of benzidine (BZ) and its acetylated metabolite, N-OH-N,N'-diacetylbenzidine (N-OH-DABZ), using supercritical fluid chromatography (SFC) for the first time. Benzidine and N-OH-N,N'-diacetylbenzidine were extracted from the plasma using ether. Separation was done on a Nucleosil (250 mm x 4.6 mm) 10 microm, Nucleosil-RP-C18 column with 7.4% (v/v) methanol-modified supercritical fluid carbon dioxide (2.5 ml min(-1)) as mobile phase. The column temperature was 45 degrees C and the outlet pressure was set at 8.83 MPa. The detection was done using a UV-Vis detector set at 280 nm. The limit of quantification was 0.10 ng ml(-1) (BZ) and 0.14 ng ml(-1) (N-OH-diacetylbenzidine) using 1 ml plasma specimen. The mean extraction recovery of BZ was found to be 98.6%. The SFC method was directly compared to a published HPLC-UV method. With respect to speed, organic solvent usage, sensitivity, specificity and accuracy, SFC was found to be superior. The method has been successfully used to estimate the BZ, N-OH-diacetylbenzidine levels in blood plasma of the animals who were administered 15 microg kg(-1) body weight of benzidine.Further, this method has been also applied for the detection and quantification of benzidine DNA and hemoglobin adducts from the blood and tissue samples of the benzidine dosed animals.

Liquid chromatographic-mass spectrometric method for the determination of alpha-,beta-arteether in rat serum

This study reports the development and validation of a sensitive and selective assay method for the determination of alpha-,beta-arteether in rat serum by liquid chromatography-mass spectrometry. The mobile phase was composed of methanol-0.1 mM sodium acetate (pH 5) (80:20%) at a flow-rate of 1 ml min(-1) and chromatographic separations were achieved on a Ultracarb, 5 ODS 20, Phenomenex column (5 micrometer, 30 mmx4.6 mm I.D.). The total effluent from the column was split so that one-tenth was injected into the electrospray LC-MS interface. ESI-MS analysis was carried out using a Micromass Quattro II Triple Quadrupole Mass Spectrometer equipped with an electrospray source. The MS analysis was carried out at a cone voltage of 52 V with a scan range of 100-400 Da. The analytes were quantified from the [M+Na](+) ion chromatograms of alpha-,beta-arteether at m/z 335 and artemisinin at m/z 305. A simple liquid-liquid extraction with 2x2 ml n-hexane was used to isolate alpha-,beta-arteether from rat serum. The method was validated in terms of recovery, linearity, accuracy and precision (within- and between-assay variation). The recovery from spiked control samples ranged from 88.41 to 96.17% with a maximum CV of 10.8% for alpha-arteether and 69.83-79.69% with a maximum CV of 17.06% for beta-arteether. Linearity in serum was observed over the range 20-320 ng ml(-1). Percent bias (accuracy) was well within the acceptable range. Within- and between-assay precision were less than 15%. The assay method described here is being applied to study the pharmacokinetics of CDRI developed intramuscular formulation Emal (alpha-/beta-arteether in the ratio of 30:70) in rats. The method is sensitive enough to monitor alpha-,beta-arteether up to 24 h after a single 30 mg kg(-1) i.m. dose.

Determination of sulfadoxine in human blood plasma using packed-column supercritical fluid chromatography

A sensitive, rapid, selective and reproducible method has been developed to measure plasma levels of sulfadoxine, 4-Amino-N-(5, 6-dimethoxy-4-pyrimidinyl) benzensulfonamide; in healthy, human volunteers using packed-column super-critical fluid chromatography. Omeprazole, 5-methoxy-2-[[(4-methoxy-3, 5-di-methyl-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole; was used as the internal standard (i.s.) at 15.0 microg/ml. The drug and the i.s. were extracted from plasma using dichloromethane. Separation of sulfadoxine and i.s. was done on a Nucleosil (250x4.6 mm) 10 microm, RP-C18 column with 7.4% (v/v) methanol-modified supercritical fluid carbon dioxide (2.5 ml/min) as the mobile phase. The column temperature was 40 degrees C and the outlet pressure was set at 8.83 MPa. The detection was done using a UV-Vis detector set at 265 nm. The limit of quantification was 0.50 microg/ml using 1 ml plasma specimen. The mean extraction recovery of the drug from plasma was found to be 94.9%. The SFC method was directly compared to a published HPLC/UV method. With respect to speed and use of organic solvents SFC was found to be superior; while in all other aspects the results were similar to the published technique. The method has been successfully used to estimate the sulfadoxine levels in healthy human volunteers from 0 to 240 h following an oral dose of 500 mg of sulfadoxine in combination with 25 mg of pyrimethamine.

Direct analysis of artemisinin in plasma and saliva using coupled-column high-performance liquid chromatography with a restricted-access material pre-column

A previously established HPLC system with post-column derivatization for the analysis of artemisinin was coupled to an ADS (alkyl-diol silica) pre-column, allowing direct and repetitive injection of protein-rich fluids such as plasma. The limit of quantitation for 100 microl of plasma was 10 ng/ml (CV=10.5%) while concentrations down to 2 ng/ml could be quantified for 1.00 ml saliva samples (CV=11.1%). The system was linear in the tested range of 10-2000 ng/ml for plasma and 2-240 ng/ml for saliva samples, respectively. This paper introduces coupled column HPLC as a simplified method for the routine analysis of artemisinin in biological fluids.

Separation and estimation of seven vasodilators using packed column supercritical fluid chromatography

This paper reports a method for an isocratic separation and simultaneous estimation of seven vasodilators: isosorbide mononitrate (ISMN), isosorbide dinitrate (ISDN), cyclandelate, nimodipine, amlodipine, pentifylline and pentoxifylline using packed column supercritical fluid chromatography (SFC). An arbitrary choice of vasodilatory compounds with respect to their chemical structures was made to examine the viability of this technique for analysis of drugs and pharmaceuticals. Elution was performed on a RP-C18 column. SFC offers several degrees of freedom: temperature, pressure and modifier concentration to attain optimum resolution and sensitivity. The effects of these parameters on retention time have been studied using methanol modified carbon dioxide. The analytes were identified and measured by UV-detection. The chromatographic points of merit have been listed. Detection limits appear to be similar to those found in liquid chromatography. Modifier concentration does generally make major changes in retention and selectivity. A full scale validation for the seven vasodilators has been attempted and the statistical quality evaluated.

Simple high-performance liquid chromatographic method with electrochemical detection for the simultaneous determination of artesunate and dihydroartemisinin in biological fluids

A simple, rapid, sensitive, selective and reproducible high-performance liquid chromatographic method with reductive electrochemical detection is described for the simultaneous quantification of artesunate (ARS) and dihydroartemisinin (DHA) in plasma. The procedure involved the extraction of ARS, DHA and the internal standard (artemisinin, ARN) with a mixture of dichloromethane and tert.-methyl butyl ether (8:2, v/v). Chromatographic separation consisted of the mobile phase (acetonitrile-water containing 0.1 M acetic acid, pH 4.8; 45:55, v/v) running through the column (Nova-Pak C18, 150 cm x 3.9 mm I.D., 5 microm particle size). The retention times of alpha-DHA, beta-DHA, ARS and ARN were 2.9, 4.2, 4.5 and 6.0 min, respectively. The average recoveries of ARS, alpha-DHA and ARN in the concentration range of 10-800 ng/ml were 81.9, 88.2, 101.1 and 84.3%, respectively. The coefficients of variation (precision and repeatability) were below 10% for all three compounds at concentrations of 50, 200, 400 and 800 ng/ml, and below 20% at a concentration of 10 ng/ml. The limits of quantification for both ARS and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for application to pharmacokinetic studies of both ARS and DHA.

Validation of an improved reversed-phase high-performance liquid chromatography assay with reductive electrochemical detection for the determination of artemisinin derivatives in man

For the determination of artemisinin (ART) and analogs, a reversed-phase high-performance liquid chromatography method using reductive electrochemical detection (ED) was set up with some important modifications as compared to previously published assays. A different technique of deoxygenating resulted in a factor 2-3 lower background current. A Spectroflow 400 liquid chromatograph in combination with a Triathlon autoinjector coupled to a Decade electrochemical detector was used. The detector was operated in the reductive mode as a closed system under chromatography grade helium to exclude any access of oxygen. The Decade has a glassy carbon electrode and a reference Ag/AgCl electrode. Infrequent electropolishing was required implicating a very stable system. By increasing acetonitril or lowering the pH of the mobile phase, the various derivatives could be determined in the same chromatogram. The assay was validated using artemether (ATM) and dihydroartemisinin (DHA) as test substances. In the concentration range seen in people after usual doses (5 to 220 ng/ml), the assay performs with adequate accuracy and precision. The interassay and intraassay precision are < 6% for ATM. For DHA, the interassay and intraassay precision are < 9%. The accuracy expressed as the deviation from the expected concentration varies from -1% to +4.5% for the intraassay ATM-determinations and from +1% to +6.3% for the interassay measurements. For DHA, the accuracy is somewhat less, varying from -0.3% to -9.5% for the intraassay measurements and -0.6% to +2.6% for the interassay measurements. The reproducibility of the assay, measured over a time period of 3 months, is good for ATM and DHA with an interassay precision of < 18% in 70 repetitive samples and an accuracy varying from -0.6% to +7.6%. In a cross-check with two other reference laboratories who used comparable methods of determination, a strong correlation (correlation coefficient > 0.98) was achieved. The method was applied in a study in which artemether was administered orally to healthy white subjects. We consider high-performance liquid chromatography with electrochemical detection an accurate and precise method for quantitative determination of artemisinin derivatives in pharmacokinetic studies.

Determination of artemether and its major metabolite, dihydroartemisinin, in plasma using high-performance liquid chromatography with electrochemical detection

A rapid, selective, sensitive and reproducible HPLC with reductive electrochemical detection for quantitative determination of artemether (ART) and its plasma metabolite, dihydroartemisinin (DHA: alpha and beta isomers) in plasma is described. The procedure involved the extraction of ART, DHA and the internal standard, artemisinin (ARN) with dichloromethane-tert.-methylbutyl ether (1:1, v/v) or n-butyl chloride-ethyl acetate (9:1, v/v). Chromatographic separation was performed with a mobile phase of acetonitrile-water (20:80, v/v) containing 0.1 M acetic acid pH 5.0, running through a microBondapak CN column. The method was capable of separating the two isomeric forms of DHA (alpha, beta). The retention times of alpha-DHA, beta-DHA, ARN and ART were 4.6, 5.9, 7.9 and 9.6 min, respectively. Validation of the assay method was performed using both extraction systems. The two extraction systems produced comparable recoveries of the various analytes. The average recoveries of ART, DHA and ARN over the concentration range 80-640 ng/ml were 86-93%. The coefficients of variation were below 10% for all three drugs (ART, alpha-DHA, ARN). The minimum detectable concentrations for ART and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for use in clinical pharmacokinetic study.

Clinical pharmacology and therapeutic potential of artemisinin and its derivatives in the treatment of malaria

Artemisinin and its derivatives are renowned for their potent antimalarial activity. They have found their way into clinical use in many areas where malaria is endemic. The in vitro concentration at which artemisinin can inhibit 50% of the growth of Plasmodium falciparum ranges from 3 to 30 micrograms/L. The fat-soluble derivatives artemether and arteether are approximately twice as active. The water-soluble dihydro-artemisinin and artesunate are 4 to 5 times more active in vitro. Artemisinin is available only for oral and rectal administration. Absorption is incomplete and elimination is fast, with and elimination half-life of 2 to 5 hours. Plasma concentrations after a single 500 mg oral dose most often exceed 200 micrograms/L. Artesunate and artemether can be considered as prodrugs. Biotransformation into the active metabolite dihydro-artemisinin occurs rapidly--almost immediately for artesunate. The reported elimination half-life of artesunate is less than 1 hour, and for artemether the figure is 3 to 11 hours. The pharmacokinetics of dihydro-artemisinin are not yet completely clear. Elimination is probably also rapid, with an elimination half-life of a few hours. Arteether, dissolved in oil for intramuscular administration, has a much longer elimination half-life of over 20 hours. The clinical efficacy of this group of drugs is characterised by an almost immediate onset and rapid reduction of parasitaemia, with complete clearance in most cases within 48 hours. Efficacy is high even in areas with multidrug-resistant parasite strains. To prevent recrudescence with monotherapy of these compounds, treatment needs to be extended beyond the disappearance of parasites. After 5 days of therapy the rate of recrudescence is approximately 10%. Alternatively, combination with other drugs can be used. Combination with mefloquine is recommended for areas with multidrug-resistant P. falciparum.