Mahaveer B Melwanki

Soochow University, Taiwan, T’ai-pei, Taipei, Taiwan

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Publications (9)26.01 Total impact

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    ABSTRACT: Dispersive liquid-liquid microextraction (DLLME) and liquid chromatography-electrospray-tandem mass spectrometry (LC-ES-MS/MS) procedure was presented for the extraction and determination of 7-aminoflunitrazepam (7-aminoFM2), a biomarker of the hypnotic flunitrazepam (FM2) in urine sample. The method was based on the formation of tiny droplets of an organic extractant in the sample solution using water-immiscible organic solvent [dichloromethane (DCM), an extractant] dissolved in water-miscible organic dispersive solvent [isopropyl alcohol (IPA)]. First, 7-aminoFM2 from basified urine sample was extracted into the dispersed DCM droplets. The extracting organic phase was separated by centrifuging and the sedimented phase was transferred into a 300 microl vial insert and evaporated to dryness. The residue was reconstituted in 30 microl mobile phase (20:80, acetonitrile:water). An aliquot of 20 microl as injected into LC-ES-MS/MS. Various parameters affecting the extraction efficiency (type and volume of extraction and dispersive solvent, effect of alkali and salt) were evaluated. Under optimum conditions, precision, linearity (correlation coefficient, r(2)=0.988 over the concentration range of 0.05-2.5 ng/ml), detection limit (0.025 ng/ml) and enrichment factor (20) had been obtained. To our knowledge, DLLME was applied to urine sample for the first time.
    Talanta 05/2009; 78(2):618-22. · 3.50 Impact Factor
  • Mahaveer B Melwanki, Ming-Ren Fuh
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    ABSTRACT: Partitioned dispersive liquid-liquid microextraction (PDLLME) efficiency was demonstrated for the extraction of polar organic compounds (chlorophenoxyacetic acids) prior to high performance liquid chromatography (HPLC). The method was based on the formation of tiny droplets of an organic extractant in an aqueous sample (river water) by injecting a mixture of a water-immiscible organic solvent [tetrachloroethylene (TCE)] as extractant dissolved in a water-miscible organic dispersive solvent [tetrahydrofuran (THF)]. Based on their partition coefficients, polar compounds were extracted into the dispersed TCE droplets as well as into THF. Different parameters affecting the extraction efficiency were evaluated and precision, linearity, detection limit and an enrichment factor were determined.
    Journal of Chromatography A 09/2008; 1207(1-2):24-8. · 4.61 Impact Factor
  • Mahaveer B Melwanki, Ming-Ren Fuh
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    ABSTRACT: Dispersive liquid-liquid microextraction (DLLME) followed by a newly designed semi-automated in-syringe back extraction technique has been developed as an extraction methodology for the extraction of polar organic compounds prior to liquid chromatography (LC) measurement. The method is based on the formation of tiny droplets of the extractant in the sample solution using water-immiscible organic solvent (extractant) dissolved in a water-miscible organic dispersive solvent. Extraction of the analytes from aqueous sample into the dispersed organic droplets took place. The extracting organic phase was separated by centrifuging and the sedimented phase was withdrawn into a syringe. Then in-syringe back extraction was utilized to extract the analytes into an aqueous solution prior to LC analysis. Clenbuterol (CB), a basic organic compound used as a model, was extracted from a basified aqueous sample using 25 microL tetrachloroethylene (TCE, extraction solvent) dissolved in 500 microL acetone (as a dispersive solvent). After separation of the organic extracting phase by centrifuging, CB enriched in TCE phase was back extracted into 10 microL of 1% aqueous formic acid (FA) within the syringe. Back extraction was facilitated by repeatedly moving the plunger back and forth within the barrel of syringe, assisted by a syringe pump. Due to the plunger movement, a thin organic film is formed on the inner layer of the syringe that comes in contact with the acidic aqueous phase. Here, CB, a basic analyte, will be protonated and back extracted into FA. Various parameters affecting the extraction efficiency, viz., choice of extraction and dispersive solvent, salt effect, speed of syringe pump, back extraction time period, effect of concentration of base and acid, were evaluated. Under optimum conditions, precision, linearity (correlation coefficient, r(2)=0.9966 over the concentration range of 10-1000 ng mL(-1) CB), detection limit (4.9 ng mL(-1)), enrichment factor (175), relative recovery (97%) had been obtained. The applicability of this newly developed method was investigated for the analysis of CB in the water samples from river, lake and stream water.
    Journal of Chromatography A 08/2008; 1198-1199:1-6. · 4.61 Impact Factor
  • Mahaveer B Melwanki, Shang-Da Huang, Ming-Ren Fuh
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    ABSTRACT: Three-phase solvent bar microextraction (TPSBME) technique is described for the quantitative determination of trace amounts of clenbuterol (CB) in urine samples using liquid chromatography (LC) and electrospray tandem mass spectrometry (ES-TMS). CB was extracted from a basified urine sample (donor phase) into the organic solvent residing in the pores of a freely moving hollow fiber and then back extracted into an acidic solution (acceptor phase) inside the lumen of the hollow fiber. The ends of the fiber were pressure-sealed. Here, forward and back extraction took place spontaneously. We studied various parameters affecting the extraction efficiency viz. type of organic solvent (octanol, nonanol and dihexyl ether) used for immobilization in the pores of the hollow fiber, i.e. extraction time (10-40 min), stirring speed (0-1,000 rpm), effect of sodium chloride (0-25%, w/v) and concentration of the donor (0.25-3M NaOH) and the acceptor (0.5-5M formic acid) phases. After extraction, CB was analyzed by injecting the analyte enriched acceptor phase into LC combined with ES-TMS. Enrichment factor (79), repeatability (R.S.D.=5.1%), correlation coefficient (0.9972, for the range of 0.1-4 ng mL(-1)), detection limit (7 pg mL(-1)) were also investigated. The present technique is compared with the reported solid phase microextraction techniques in terms of selectivity, analysis time per extraction, cost of analysis per extraction, and precision. Among all microextraction techniques reported, this technique is the most economical sample preparation/preconcentration technique to our knowledge. The method was applied for the analysis of CB in human urine.
    Talanta 05/2007; 72(2):373-7. · 3.50 Impact Factor
  • Hong-Li Sheu, Yu-Hsiang Sung, Mahaveer B Melwanki, Shang-Da Huang
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    ABSTRACT: Solid-phase microextraction (SPME) coupled to LC for the analysis of five diphenylether herbicides (aclonifen, bifenox, fluoroglycofen-ethyl, oxyfluorfen, and lactofen) is described. Various parameters of extraction of analytes onto the fiber (such as type of fiber, extraction time and temperature, pH, impact of salt and organic solute) and desorption from the fiber in the desorption chamber prior to separation (such as type and composition of desorption solvent, desorption mode, soaking time, and flush-out time) were studied and optimized. Four commercially available SPME fibers were studied. PDMS/divinylbenzene (PDMS/DVB, 60 microm) and carbowax/ templated resin (CW/TPR, 50 microm) fibers were selected due to better extraction efficiencies. Repeatability (RSD, < 7%), correlation coefficient (> 0.994), and detection limit (0.33-1.74 and 0.22-1.94 ng/mL, respectively, for PDMS/DVB and CW/TPR) were investigated. Relative recovery (81-104% for PDMS/DVB and 83-100% for CW/TPR fiber) values have also been calculated. The developed method was successfully applied to the analysis of river water and water collected from a vegetable garden.
    Journal of Separation Science 11/2006; 29(17):2647-52. · 2.59 Impact Factor
  • Mahaveer B Melwanki, Shang-Da Huang
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    ABSTRACT: Liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase technique is described for the extraction of six hydroxyaromatic compounds in river water using a disposable and ready to use hollow fiber. Separation and quantitative analyses were performed using LC with UV detection at 254 nm. Analytes were extracted from the acidified sample solution (donor phase) into the organic solvent impregnated in the pores of the hollow fiber and then back extracted into the alkaline solution (acceptor phase) inside the lumen of the hollow fiber. The fiber was held by a conventional 10 microL LC syringe. The acceptor phase was sandwitched between the plunger and a small volume of the organic solvent (microcap). The acceptor solution was repeatedly moved in and out of the hollow fiber using a syringe pump. This movement provides a fresh acceptor phase to come in contact with the organic phase and thus enhancing extraction kinetics thereby leading to the improvement in enrichment of the analytes. The microcap separates the acceptor phase and the donor phase in addition to being partially responsible for mass transfer of the analytes from the donor solution to the acceptor solution. Under stirring, a fresh donor phase will enter through the open end of the fiber that will also contribute to the mass transfer. Various parameters affecting the extraction efficiency viz type of organic solvent, extraction time, stirring speed, effect of sodium chloride, and concentration of donor and acceptor phases were studied. RSD (3.9-5.6%), correlation coefficient (0.995-0.997), detection limit (2.0-51.2 ng/mL), enrichment factor (339-630), relative recovery (93.2-97.9%), and absolute recovery (33.9-63.0%) have also been investigated. The developed method was applied for the analysis of river water.
    Journal of Separation Science 09/2006; 29(13):2078-84. · 2.59 Impact Factor
  • Chung-Chiang Chen, Mahaveer B Melwanki, Shang-Da Huang
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    ABSTRACT: A simple liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase (LLLME/AMADP) technique is described for the quantitative determination of five phenoxyacetic acids in water using a disposable and ready to use hollow fiber. The target compounds were extracted from the acidified sample solution (donor phase) into the organic solvent residing in the pores of the hollow fiber and then back extracted into the alkaline solution (acceptor phase) inside the lumen of the hollow fiber. The fiber was held by a conventional 10-microl syringe. The acceptor phase was sandwiched between the plunger and a small volume of the organic solvent (microcap). The acceptor solution was repeatedly moved in and out of the hollow fiber assisted by a programmable syringe pump. This repeated movement provides a fresh acceptor phase to come in-contact with the organic phase and thus enhancing extraction kinetics leading to high enrichment of the analytes. The microcap separates the aqueous acceptor phase and the donor phase in addition of being partially responsible for mass transfer of the analytes from donor solution (moving in and out of the hollow fiber from the open end of the fiber) to the acceptor solution. Separation and quantitative analyses were then performed using liquid chromatography (LC) with ultraviolet (UV) detection at 280 nm. Various parameters affecting the extraction efficiency viz. type of organic solvent used for immobilization in the pores of the hollow fiber, extraction time, stirring speed, effect of sodium chloride, and concentration of donor and acceptor phases were studied. Repeatability (RSD, 3.2-7.4%), correlation coefficient (0.996-0.999), detection limit (0.2-2.8 ng ml(-1)) and enrichment factors (129-240) were also investigated. Relative recovery (87-101%) and absolute recoveries (4.6-13%) have also been calculated. The developed method was applied for the analysis of river water.
    Journal of Chromatography A 03/2006; 1104(1-2):33-9. · 4.61 Impact Factor
  • Mahaveer B. Melwanki, Shang-Da Huang
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    ABSTRACT: In this article, a simple new solvent microextraction technique is described for the extraction of ionizable organic compounds. This involves performing simultaneous forward- and back-extraction across an organic film immobilized in the pores of a porous polypropylene hollow fiber. Four chlorophenoxyacetic acid herbicides were chosen as model compounds. The target compounds are extracted from the stirred acidic aqueous sample (adjusted to 0.5M HCl; donor phase) through a thin film of an organic solvent residing in the pores of a polypropylene hollow fiber; they are then finally extracted into another alkaline aqueous phase (1M NaOH; acceptor phase). Both ends of the fiber are pressure-sealed. The acceptor phase was analyzed by liquid chromatography (LC). This method gave good enrichment (by a factor of 438–553) of the analytes in 40min extraction time with reasonably good reproducibility. The analytical potential of the method was demonstrated by applying the method to spiked river water sample.
    Analytica Chimica Acta - ANAL CHIM ACTA. 01/2006; 555(1):139-145.
  • Mahaveer B. Melwanki, Wei-Hsun Hsu, Shang-Da Huang
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    ABSTRACT: Headspace solid phase microextraction (HS-SPME) and liquid–liquid–liquid microextraction with automated movement of the acceptor phase (LLLME/AMAP) techniques are described for the extraction of clenbuterol (CB) in urine. HS-SPME technique involves the extraction of the drug by SPME fibre in a headspace mode with a cooling device at the upper part of the vial to cool the headspace of the vial where the fiber is suspended. This cooling effect will enhance the absorption of analytes by the fiber. As the cooling system is surrounding the vial, the headspace will also be cooled in addition to the cooling of the fiber. After extraction the derivatization of the extracted drug with hexamethyldisilazane (HMDS) was performed by suspending the fiber in the headspace of another vial saturated with the vapor of HMDS. This derivatized compound was analyzed by gas chromatography with mass spectrometric detection (GC/MS). LLLME/AMAP technique involves the extraction of CB, a basic drug, from an alkaline solution into the organic solvent residing in the pores of the hollow fiber and then back extracted into the acidic acceptor solution inside the lumen of the hollow fiber. The acceptor solution was repeatedly moved in and out of the hollow fibre assisted by a syringe pump. This repeated movement provides fresh acceptor phase to come in-contact with the organic phase and thus improving the efficiency of extraction. Quantification was performed using high performance liquid chromatography with ultraviolet (HPLC/UV) detection. In both the techniques, experimental parameters have been studied to achieve greater sensitivity. Linearity was observed over the range of 1–1000 ng ml−1 (R2 = 0.9990) and 50–3000 ng ml−1 (R2 = 0.9956) with detection limits of 0.23 ng ml−1 and 3.9 ng ml−1, respectively, for HS-SPME-GC/MS and LLLME/AMAP-HPLC/UV method. R.S.D. values of 3.9% (HS-SPME-GC/MS) and 5.8% (LLLME/AMAP-HPLC/UV) indicated good precision of the techniques. Absolute recovery was found to be 0.007% and 18%, respectively, for HS-SPME-GC/MS and LLLME-HPLC/UV methods. Finally, the techniques have been applied for the analysis of CB in urine samples. No effort has been made to compare the method with official method.
    Analytica Chimica Acta. 01/2005;

Publication Stats

106 Citations
26.01 Total Impact Points

Institutions

  • 2008–2009
    • Soochow University, Taiwan
      • Department of Chemistry
      T’ai-pei, Taipei, Taiwan
  • 2005–2007
    • National Tsing Hua University
      • Department of Chemistry
      Hsinchu, Taiwan, Taiwan