The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
M W F Nielen - One of the best experts on this subject based on the ideXlab platform.
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Generic sample preparation combined with high-resolution liquid chromatography–time-of-flight mass spectrometry for unification of urine screening in doping-control laboratories
Analytical and Bioanalytical Chemistry, 2010Co-Authors: R. J. B. Peters, A A M Stolker, J E Oosterink, C. Georgakopoulos, M W F NielenAbstract:A unification of doping-control screening procedures of prohibited small molecule substances—including stimulants, narcotics, steroids, β2-agonists and diuretics—is highly urgent in order to free resources for new classes such as banned proteins. Conceptually this may be achieved by the use of a combination of one gas chromatography–time-of-flight mass spectrometry method and one liquid chromatography–time-of-flight mass spectrometry method. In this work a quantitative screening method using high-resolution liquid chromatography in combination with accurate-mass time-of-flight mass spectrometry was developed and validated for determination of glucocorticosteroids, β2-agonists, thiazide diuretics, and narcotics and stimulants in urine. To enable the simultaneous isolation of all the compounds of interest and the necessary purification of the resulting extracts, a generic extraction and hydrolysis procedure was combined with a solid-phase extraction modified for these groups of compounds. All 56 compounds are determined using positive electrospray ionisation with the exception of the thiazide diuretics for which the best sensitivity was obtained by using negative electrospray ionisation. The results show that, with the exception of clenhexyl, procaterol, and Reproterol, all compounds can be detected below the respective minimum required performance level and the results for linearity, repeatability, within-lab reproducibility, and accuracy show that the method can be used for quantitative screening. If qualitative screening is sufficient the instrumental analysis may be limited to positive ionisation, because all analytes including the thiazides can be detected at the respective minimum required levels in the positive mode. The results show that the application of accurate-mass time-of-flight mass spectrometry in combination with generic extraction and purification procedures is suitable for unification and expansion of the window of screening methods of doping laboratories. Moreover, the full-scan accurate-mass data sets obtained still allow retrospective examination for emerging doping agents, without re-analyzing the samples.
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multiresidue analysis of beta agonists in bovine and porcine urine feed and hair using liquid chromatography electrospray ionisation tandem mass spectrometry
Analytical and Bioanalytical Chemistry, 2008Co-Authors: M W F Nielen, J J P Lasaroms, Martien L Essers, J E Oosterink, Thijs Meijer, Marieke B Sanders, T Zuidema, A A M StolkerAbstract:The use of β-agonists as growth promoters in cattle breeding is forbidden in many countries for reasons of fair trade and consumer protection. In recent years the use of liquid chromatography (LC) tandem mass spectrometry (MS/MS) has been shown to be the method of choice for the control of β-agonists. In this study an LC-MS/MS multiresidue analysis method is presented for trace analysis of 22 β-agonists. A truly generic concept has been designed based on mixed-mode solid-phase extraction and positive electrospray ionisation LC-MS/MS operated in the multiple reaction monitoring mode. This method allows application to a wide variety of sample matrices such as urine, feed and hair, following minor modifications to the analysis procedure only. The method features fit-for-purpose sensitivity in urine as shown by CCα and CCβ values of less than 0.2 and less than 0.5 μg/l respectively, for all β-agonists studied (terbutaline and Reproterol, less than 0.3 and less than 1.0 respectively). Similar but semiquantitative application to feed and hair showed CCβ values of less than 10.0 and less than 5.0 μg/kg, respectively. A further simplification and improvement is demonstrated using Ultra Performance LC (UPLC™) and fast-switching MS/MS. The successful validation of this method following the latest EU requirements and its application to real samples demonstrate that a new versatile tool has been achieved for veterinary control of β-agonists.
A A M Stolker - One of the best experts on this subject based on the ideXlab platform.
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Generic sample preparation combined with high-resolution liquid chromatography–time-of-flight mass spectrometry for unification of urine screening in doping-control laboratories
Analytical and Bioanalytical Chemistry, 2010Co-Authors: R. J. B. Peters, A A M Stolker, J E Oosterink, C. Georgakopoulos, M W F NielenAbstract:A unification of doping-control screening procedures of prohibited small molecule substances—including stimulants, narcotics, steroids, β2-agonists and diuretics—is highly urgent in order to free resources for new classes such as banned proteins. Conceptually this may be achieved by the use of a combination of one gas chromatography–time-of-flight mass spectrometry method and one liquid chromatography–time-of-flight mass spectrometry method. In this work a quantitative screening method using high-resolution liquid chromatography in combination with accurate-mass time-of-flight mass spectrometry was developed and validated for determination of glucocorticosteroids, β2-agonists, thiazide diuretics, and narcotics and stimulants in urine. To enable the simultaneous isolation of all the compounds of interest and the necessary purification of the resulting extracts, a generic extraction and hydrolysis procedure was combined with a solid-phase extraction modified for these groups of compounds. All 56 compounds are determined using positive electrospray ionisation with the exception of the thiazide diuretics for which the best sensitivity was obtained by using negative electrospray ionisation. The results show that, with the exception of clenhexyl, procaterol, and Reproterol, all compounds can be detected below the respective minimum required performance level and the results for linearity, repeatability, within-lab reproducibility, and accuracy show that the method can be used for quantitative screening. If qualitative screening is sufficient the instrumental analysis may be limited to positive ionisation, because all analytes including the thiazides can be detected at the respective minimum required levels in the positive mode. The results show that the application of accurate-mass time-of-flight mass spectrometry in combination with generic extraction and purification procedures is suitable for unification and expansion of the window of screening methods of doping laboratories. Moreover, the full-scan accurate-mass data sets obtained still allow retrospective examination for emerging doping agents, without re-analyzing the samples.
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multiresidue analysis of beta agonists in bovine and porcine urine feed and hair using liquid chromatography electrospray ionisation tandem mass spectrometry
Analytical and Bioanalytical Chemistry, 2008Co-Authors: M W F Nielen, J J P Lasaroms, Martien L Essers, J E Oosterink, Thijs Meijer, Marieke B Sanders, T Zuidema, A A M StolkerAbstract:The use of β-agonists as growth promoters in cattle breeding is forbidden in many countries for reasons of fair trade and consumer protection. In recent years the use of liquid chromatography (LC) tandem mass spectrometry (MS/MS) has been shown to be the method of choice for the control of β-agonists. In this study an LC-MS/MS multiresidue analysis method is presented for trace analysis of 22 β-agonists. A truly generic concept has been designed based on mixed-mode solid-phase extraction and positive electrospray ionisation LC-MS/MS operated in the multiple reaction monitoring mode. This method allows application to a wide variety of sample matrices such as urine, feed and hair, following minor modifications to the analysis procedure only. The method features fit-for-purpose sensitivity in urine as shown by CCα and CCβ values of less than 0.2 and less than 0.5 μg/l respectively, for all β-agonists studied (terbutaline and Reproterol, less than 0.3 and less than 1.0 respectively). Similar but semiquantitative application to feed and hair showed CCβ values of less than 10.0 and less than 5.0 μg/kg, respectively. A further simplification and improvement is demonstrated using Ultra Performance LC (UPLC™) and fast-switching MS/MS. The successful validation of this method following the latest EU requirements and its application to real samples demonstrate that a new versatile tool has been achieved for veterinary control of β-agonists.
R P Garay - One of the best experts on this subject based on the ideXlab platform.
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Inhibition by Reproterol of cAMP PDE in intact mastocytoma P-815 cells
Pulmonary Pharmacology & Therapeutics, 2004Co-Authors: M Alvarez-guerra, H Libertus, R P GarayAbstract:In vitro studies in rat mastocytes and human monocytes suggested that Reproterol (a selective beta(2)-adrenoceptor agonist with a theophylline moiety) exerts anti-inflammatory actions through inhibition of cyclic AMP (cAMP) PDE activity. Thus, Reproterol was tested for its ability to inhibit cAMP PDE in cultured mouse mastocytoma P-815 cells. cAMP PDE activity was measured in intact cells by spectrofluorometry using the fluorescent substrate 2'-O-anthraniloyl cAMP. Reproterol was more potent than theophylline to inhibit cAMP PDE (pIC(50)=4.28+/-0.25 vs. 3.16+/-0.05). This contrasted with disrupted cells, where the PDE inhibitory potency of Reproterol was low (pIC(50)=2.85+/-0.03) and similar to that of theophylline (pIC(50)=2.66+/-0.19). No cAMP PDE inhibition was found with other beta(2)-agonists tested (fenoterol, salbutamol, salmeterol and formoterol). Finally, the selective PDE inhibitors calmidazolium (100 nM), milrinone (5 microM) and rolipram (50 microM) inhibited cAMP PDE activity by approximately 20, 30 and 25% respectively. In conclusion, Reproterol potently and non-specifically inhibited intracellular cAMP phosphodiesterases in intact mastocytoma cells. This can explain the previously reported beta(2)-adrenoceptor-independent anti-inflammatory actions of Reproterol in vitro. Further studies are required to define the anti-inflammatory potential of Reproterol in asthma.
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enhancement by Reproterol of the ability of disodium cromoglycate to stabilize rat mastocytes
Pulmonary Pharmacology & Therapeutics, 1999Co-Authors: N Eleno, E Gajate, J Macias, R P GarayAbstract:The beta2-adrenoceptor agonist Reproterol and disodium cromoglycate (DSCG) are used in fixed combination for the treatment of asthma, because they act on bronchial smooth muscle and inflammatory cells, respectively. Here, we investigated if Reproterol can also act in rat mast cells in vitro to facilitate the inhibitory action of disodium cromoglycate (DSCG) on histamine secretion induced by compound 48/80. Reproterol was as potent as DSCG to inhibit histamine release in rat mast cells (32.8+/-6.0 vs. 36.7+/-6.2% at 1 microM of each compound, n=10 and n=8 respectively). Mast cell stabilization by DSCG (1-100 microM) was strongly and significantly enhanced in the presence of a fixed saturating concentration of Reproterol (100 microM). Conversely, the combination of DSCG (1-100 microM) with the beta2-agonist used as reference compound, salbutamol (100 microM) did not inhibit histamine release more than DSCG alone. In combination with a saturating concentration of DSCG (100 microM), Reproterol inhibited histamine release more than Reproterol alone. The potent adenylate cyclase stimulator forskolin (50 microM) was able to inhibit histamine release to a similar extent as DSCG and significantly (P<0.05) enhanced the inhibition of histamine release by DSCG. Finally, the phosphodiesterase inhibitor theophylline (100 microM) was equipotent to Reproterol and DSCG in stabilizing rat mast cells. In conclusion, Reproterol enhances the ability of disodium cromoglycate to stabilize rat mast cells. This effect is not shared by salbutamol and can be, at least in part, independent of beta2-adrenoceptor stimulation.
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Enhancement by Reproterol of the Ability of Disodium Cromoglycate to Stabilize Rat Mastocytes
Pulmonary Pharmacology & Therapeutics, 1999Co-Authors: N Eleno, E Gajate, J Macias, R P GarayAbstract:The beta2-adrenoceptor agonist Reproterol and disodium cromoglycate (DSCG) are used in fixed combination for the treatment of asthma, because they act on bronchial smooth muscle and inflammatory cells, respectively. Here, we investigated if Reproterol can also act in rat mast cells in vitro to facilitate the inhibitory action of disodium cromoglycate (DSCG) on histamine secretion induced by compound 48/80. Reproterol was as potent as DSCG to inhibit histamine release in rat mast cells (32.8+/-6.0 vs. 36.7+/-6.2% at 1 microM of each compound, n=10 and n=8 respectively). Mast cell stabilization by DSCG (1-100 microM) was strongly and significantly enhanced in the presence of a fixed saturating concentration of Reproterol (100 microM). Conversely, the combination of DSCG (1-100 microM) with the beta2-agonist used as reference compound, salbutamol (100 microM) did not inhibit histamine release more than DSCG alone. In combination with a saturating concentration of DSCG (100 microM), Reproterol inhibited histamine release more than Reproterol alone. The potent adenylate cyclase stimulator forskolin (50 microM) was able to inhibit histamine release to a similar extent as DSCG and significantly (P
J E Oosterink - One of the best experts on this subject based on the ideXlab platform.
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Generic sample preparation combined with high-resolution liquid chromatography–time-of-flight mass spectrometry for unification of urine screening in doping-control laboratories
Analytical and Bioanalytical Chemistry, 2010Co-Authors: R. J. B. Peters, A A M Stolker, J E Oosterink, C. Georgakopoulos, M W F NielenAbstract:A unification of doping-control screening procedures of prohibited small molecule substances—including stimulants, narcotics, steroids, β2-agonists and diuretics—is highly urgent in order to free resources for new classes such as banned proteins. Conceptually this may be achieved by the use of a combination of one gas chromatography–time-of-flight mass spectrometry method and one liquid chromatography–time-of-flight mass spectrometry method. In this work a quantitative screening method using high-resolution liquid chromatography in combination with accurate-mass time-of-flight mass spectrometry was developed and validated for determination of glucocorticosteroids, β2-agonists, thiazide diuretics, and narcotics and stimulants in urine. To enable the simultaneous isolation of all the compounds of interest and the necessary purification of the resulting extracts, a generic extraction and hydrolysis procedure was combined with a solid-phase extraction modified for these groups of compounds. All 56 compounds are determined using positive electrospray ionisation with the exception of the thiazide diuretics for which the best sensitivity was obtained by using negative electrospray ionisation. The results show that, with the exception of clenhexyl, procaterol, and Reproterol, all compounds can be detected below the respective minimum required performance level and the results for linearity, repeatability, within-lab reproducibility, and accuracy show that the method can be used for quantitative screening. If qualitative screening is sufficient the instrumental analysis may be limited to positive ionisation, because all analytes including the thiazides can be detected at the respective minimum required levels in the positive mode. The results show that the application of accurate-mass time-of-flight mass spectrometry in combination with generic extraction and purification procedures is suitable for unification and expansion of the window of screening methods of doping laboratories. Moreover, the full-scan accurate-mass data sets obtained still allow retrospective examination for emerging doping agents, without re-analyzing the samples.
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multiresidue analysis of beta agonists in bovine and porcine urine feed and hair using liquid chromatography electrospray ionisation tandem mass spectrometry
Analytical and Bioanalytical Chemistry, 2008Co-Authors: M W F Nielen, J J P Lasaroms, Martien L Essers, J E Oosterink, Thijs Meijer, Marieke B Sanders, T Zuidema, A A M StolkerAbstract:The use of β-agonists as growth promoters in cattle breeding is forbidden in many countries for reasons of fair trade and consumer protection. In recent years the use of liquid chromatography (LC) tandem mass spectrometry (MS/MS) has been shown to be the method of choice for the control of β-agonists. In this study an LC-MS/MS multiresidue analysis method is presented for trace analysis of 22 β-agonists. A truly generic concept has been designed based on mixed-mode solid-phase extraction and positive electrospray ionisation LC-MS/MS operated in the multiple reaction monitoring mode. This method allows application to a wide variety of sample matrices such as urine, feed and hair, following minor modifications to the analysis procedure only. The method features fit-for-purpose sensitivity in urine as shown by CCα and CCβ values of less than 0.2 and less than 0.5 μg/l respectively, for all β-agonists studied (terbutaline and Reproterol, less than 0.3 and less than 1.0 respectively). Similar but semiquantitative application to feed and hair showed CCβ values of less than 10.0 and less than 5.0 μg/kg, respectively. A further simplification and improvement is demonstrated using Ultra Performance LC (UPLC™) and fast-switching MS/MS. The successful validation of this method following the latest EU requirements and its application to real samples demonstrate that a new versatile tool has been achieved for veterinary control of β-agonists.
R. J. B. Peters - One of the best experts on this subject based on the ideXlab platform.
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Generic sample preparation combined with high-resolution liquid chromatography–time-of-flight mass spectrometry for unification of urine screening in doping-control laboratories
Analytical and Bioanalytical Chemistry, 2010Co-Authors: R. J. B. Peters, A A M Stolker, J E Oosterink, C. Georgakopoulos, M W F NielenAbstract:A unification of doping-control screening procedures of prohibited small molecule substances—including stimulants, narcotics, steroids, β2-agonists and diuretics—is highly urgent in order to free resources for new classes such as banned proteins. Conceptually this may be achieved by the use of a combination of one gas chromatography–time-of-flight mass spectrometry method and one liquid chromatography–time-of-flight mass spectrometry method. In this work a quantitative screening method using high-resolution liquid chromatography in combination with accurate-mass time-of-flight mass spectrometry was developed and validated for determination of glucocorticosteroids, β2-agonists, thiazide diuretics, and narcotics and stimulants in urine. To enable the simultaneous isolation of all the compounds of interest and the necessary purification of the resulting extracts, a generic extraction and hydrolysis procedure was combined with a solid-phase extraction modified for these groups of compounds. All 56 compounds are determined using positive electrospray ionisation with the exception of the thiazide diuretics for which the best sensitivity was obtained by using negative electrospray ionisation. The results show that, with the exception of clenhexyl, procaterol, and Reproterol, all compounds can be detected below the respective minimum required performance level and the results for linearity, repeatability, within-lab reproducibility, and accuracy show that the method can be used for quantitative screening. If qualitative screening is sufficient the instrumental analysis may be limited to positive ionisation, because all analytes including the thiazides can be detected at the respective minimum required levels in the positive mode. The results show that the application of accurate-mass time-of-flight mass spectrometry in combination with generic extraction and purification procedures is suitable for unification and expansion of the window of screening methods of doping laboratories. Moreover, the full-scan accurate-mass data sets obtained still allow retrospective examination for emerging doping agents, without re-analyzing the samples.