Peter Kootstra | Vrije Universiteit Amsterdam (original) (raw)
Papers by Peter Kootstra
Chemosphere, 1991
ABSTRACT Over 200 samples of cow's milk have been analysed for dioxins in a survey on the... more ABSTRACT Over 200 samples of cow's milk have been analysed for dioxins in a survey on the occurrence of dioxins in milk from the vicinity of municipal waste incinerators (MSWs) and other potential dioxin sources in The Netherlands. Levels in milk were found to vary considerably with time, depending on emission rates, the direction and distance to the source and the feeding and housing of cows. Highest levels of up to 13.5 pg TEQ/g of milk fat were found in the Lickebaert area and Zaandam near two incinerators with highest emission rates. The background level ranged between 0.7 and 2.5 pg TEQ/g of milk fat. Levels in winter were comparable to those found in summer and, in some areas, even higher, when cows were fed with hay and silage harvested on the same farm. After the closure of the MSW in Zaandam, cow's milk from neighbouring farms showed a significant decrease in dioxin levels to below the critical limit of 6 pg TEQ/g of milk fat. Dioxin levels in the vicinity of a metal reclamation plant were comparable to those in milk from the vicinity of a MSW with moderate emissions. Differences were observed in the ratio PCDF/PCDD, which was higher in milk near the metal reclamation plant. Principal component analysis has been applied on a large data set of patterns of the 2,3,7,8-chlorine substituted PCDDs and PCDFs in cow's milk. This technique has proved to be useful for distinguishing and identification of sources on the basis of the isomer pattern in milk.
This report describes the first results of Supercritical Fluid Extraction (SFE) as technique for ... more This report describes the first results of Supercritical Fluid Extraction (SFE) as technique for the extraction of organic components from soil. SFE is based on the extraction properties of supercritical fluids - in this case CO2 - having liquidlike as well as gaslike behaviour as their low viscosity and high solute diffusivities. The optimization of SFE of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. An experimental approach was set up to test the influences of different extraction parameters such as pressure, extraction time, state and dynamic extraction, restictor type and collection solvent for off-line SFE. Conditions obtained from these experiments with spiked samples were applied on real soil and optimized to gain maximum concentrations of components in comparison with conventional solvent extraction. The optimal conditions achieved for spiked samples did...
Journal of Chromatography A
The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real s... more The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. Optimal conditions obtained from experiments with spiked samples were applied on real soil and the influence of several extraction parameters was tested to gain maximum concentrations of components in comparison with solvent extraction.The optimal conditions achieved for spiked samples did not yield maximum concentrations for field samples. Stronger extraction conditions were necessary to overcome interactions between matrix and analytes. Longer dynamic extraction times were needed and the use of modifiers appeared to be essential for SFE of real samples. An increase in extraction pressure did not have any influence on extraction results. Comparable results were obtained for SFE and solvent extraction with an overall standard deviation between both methods of 25%.The stepwise approach is useful in meth...
MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards ... more MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards specific compounds, e.g. beta-agonists. The interactions between MIP particles and analytes are stronger than interactions obtained in conventional SPE. Bond Elut Certify columns show a bi-model non-polar and strong cation exchange and are generally used for basic and neutral drugs in urine and other biological samples. Both types of clean up methods were optimized for more than 30 different beta-agonists. After optimization, both methods were fully validated according to Commission Decision 2002/657/EC. Analysis is carried out by LC-MSMS, Ultima Triple Quad system. Results indicate that both sample preparation methods can be used for a range of beta- agonists. However, none of these methods can be used for all compounds, e.g. nine compounds cannot be extracted with either method in the selected concentration range (1-5 μg L-1). Sample preparation using MIP columns gives generally cleane...
This report describes the validation of the quantification and the identification of an analytica... more This report describes the validation of the quantification and the identification of an analytical method for the determination of low concentrations (0.1-1.0 micro g/kg) of chloramphenicol in samples of urine, shrimps and meat. The validation study was based on the criteria described in Decision 2002/657/EC of the European Commission. The analytical method consists of an enzymatic hydrolysis (urine) or enzymatic digestion (meat), followed by liquid-liquid extraction of chloramphenicol from the matrix with ethyl acetate. The extract is cleaned with Solid Phase Extraction (SPE), followed by LC fractionation. The SPE step can be omitted for shrimps. After derivatisation of the chloramphenicol, final separation and detection is performed with GC-MS with Negative Chemical Ionisation (NCI). Detection can also be carried out using Electron Impact (EI), which is a less sensitive technique. This method can be used for both screening and quantification. The limit of determination for all sam...
This report describes the results of a surveillance conducted in 2000. In total 70 animals were t... more This report describes the results of a surveillance conducted in 2000. In total 70 animals were tested for a range of anabolic compounds and beta-agonists. In two cases a compound was detected and confirmed, one case of stanozolol and one case of isoxsuprine, a registered veterinary drug. Dit rapport beschrijft de resultaten van een in 2000 uitgevoerd bewakingsonderzoek. Zeventig dieren werden onderzocht op de aanwezigheid van anabolica en beta-agonisten. In twee gevallen werd een stof aangetoond. Een geval betrof de groeibevorderende stof stanozolol, een andere betrof het geregistreerde geneesmiddel Isoxsuprine.
The Analyst, 2002
Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automate... more Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automated supercritical fluid extraction (SFE). After the addition of internal standards and sample pretreatment, the analytes are extracted from the matrix by supercritical CO2 and trapped directly in-line on alumina placed in the extraction vessel. The samples are analysed by liquid chromatography combined with ion-trap mass selective detection (LC-MSn). For quantification, deuterated internal standards are added and single ions of the analytes and internal standards are monitored. For confirmation of the identity of the analytes, two transition ions (one MS2 and one MS3) were monitored and the ratios between the ions were calculated and compared with those of standards. The detection capability for the multi-analyte LC-MSn analysis of megestrol acetate (MA), medroxyprogesterone acetate (MPA), chlormadinone acetate (CMA) and melengestrol acetate (MGA) is 0.5 microg kg(-1). The mean within-laboratory reproducibility ranges from 16-19% (%RSD) at a concentration level of 0.5 microg kg(-1) (n = 9). Running the SFE procedure overnight allows the analysis of 24 samples of fat per day.
The Analyst, 2002
Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automate... more Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automated supercritical fluid extraction (SFE). After the addition of internal standards and sample pretreatment, the analytes are extracted from the matrix by supercritical CO2 and trapped directly in-line on alumina placed in the extraction vessel. The samples are analysed by liquid chromatography combined with ion-trap mass selective detection (LC-MSn). For quantification, deuterated internal standards are added and single ions of the analytes and internal standards are monitored. For confirmation of the identity of the analytes, two transition ions (one MS2 and one MS3) were monitored and the ratios between the ions were calculated and compared with those of standards. The detection capability for the multi-analyte LC-MSn analysis of megestrol acetate (MA), medroxyprogesterone acetate (MPA), chlormadinone acetate (CMA) and melengestrol acetate (MGA) is 0.5 microg kg(-1). The mean within-laboratory reproducibility ranges from 16-19% (%RSD) at a concentration level of 0.5 microg kg(-1) (n = 9). Running the SFE procedure overnight allows the analysis of 24 samples of fat per day.
Biochemical Pharmacology, 1988
We have studied the effects of the recently reported two new metabolites of the antitumor agent V... more We have studied the effects of the recently reported two new metabolites of the antitumor agent VP-16-213, the ortho-dihydroxy derivative or catechol and the ortho-quinone, on the biological activity of single-stranded and double-stranded phi X174 DNA, the binding of the metabolites to calf thymus DNA and the conversion of the catechol into the ortho-quinone. Evidence was obtained for the oxidation of the catechol into the ortho-quinone and for the fact that the ortho-quinone is the metabolite of VP-16-213 responsible for its binding to rat liver microsomal proteins. The catechol and ortho-quinone of VP-16-213 were found to bind 7-9 times more strongly to calf thymus DNA than VP-16-213 itself. In contrast to the parent compound VP-16-213, the catechol as well as the ortho-quinone inactivated both single-stranded (ss) and double-stranded (RF) biologically active phi X174 DNA. The mean T37-values for inactivation of ss and RF phi X174 DNA by 2.2 x 10(-4)M catechol at 37 degrees and pH 7.4 were 96 and 640 min, respectively. Reduction of the ortho-quinone by NADPH cytochrome P-450 reductase resulted in formation of the catechol. The system ortho-quinone/NADPH cytochrome P-450 reductase inactivated ss phi X174 DNA with a mean T37-value of 454 min, and this inactivation was inhibited by DMSO. The mean T37-value for inactivation of ss phi X174 DNA by 1.8 x 10(-4) M ortho-quinone at 37 degrees and pH 4.0 was 24 min. The chemical stability of the ortho-quinone and the extent of inactivation of ss phi X174 DNA by the ortho-quinone were both pH-dependent: at higher pH the ortho-quinone was less stable and gave less inactivation of DNA. The aqueous decomposition product(s) of the ortho-quinone formed at pH 7.4 inactivated ss phi X174 DNA with a mean T37-value of 175 min. The rate of inactivation of RF phi X174 DNA by the ortho-quinone at pH 4.0 was twice as low as the rate of inactivation of ss phi X174 DNA: T37 = 49 min. When using excision repair deficient E. coli mutants (uvrA- or uvrC-), a higher inactivation of RF phi X174 DNA was found: T37 = 29 min for uvrA- E. coli, indicating that a part of the DNA damage introduced by the incubation with ortho-quinone is removed by excision repair.(ABSTRACT TRUNCATED AT 400 WORDS)
We have studied the effects of the recently reported two new metabolites of the antitumor agent V... more We have studied the effects of the recently reported two new metabolites of the antitumor agent VP-16-213, the ortho-dihydroxy derivative or catechol and the ortho-quinone, on the biological activity of single-stranded and double-stranded phi X174 DNA, the binding of the metabolites to calf thymus DNA and the conversion of the catechol into the ortho-quinone. Evidence was obtained for the oxidation of the catechol into the ortho-quinone and for the fact that the ortho-quinone is the metabolite of VP-16-213 responsible for its binding to rat liver microsomal proteins. The catechol and ortho-quinone of VP-16-213 were found to bind 7-9 times more strongly to calf thymus DNA than VP-16-213 itself. In contrast to the parent compound VP-16-213, the catechol as well as the ortho-quinone inactivated both single-stranded (ss) and double-stranded (RF) biologically active phi X174 DNA. The mean T37-values for inactivation of ss and RF phi X174 DNA by 2.2 x 10(-4)M catechol at 37 degrees and pH 7.4 were 96 and 640 min, respectively. Reduction of the ortho-quinone by NADPH cytochrome P-450 reductase resulted in formation of the catechol. The system ortho-quinone/NADPH cytochrome P-450 reductase inactivated ss phi X174 DNA with a mean T37-value of 454 min, and this inactivation was inhibited by DMSO. The mean T37-value for inactivation of ss phi X174 DNA by 1.8 x 10(-4) M ortho-quinone at 37 degrees and pH 4.0 was 24 min. The chemical stability of the ortho-quinone and the extent of inactivation of ss phi X174 DNA by the ortho-quinone were both pH-dependent: at higher pH the ortho-quinone was less stable and gave less inactivation of DNA. The aqueous decomposition product(s) of the ortho-quinone formed at pH 7.4 inactivated ss phi X174 DNA with a mean T37-value of 175 min. The rate of inactivation of RF phi X174 DNA by the ortho-quinone at pH 4.0 was twice as low as the rate of inactivation of ss phi X174 DNA: T37 = 49 min. When using excision repair deficient E. coli mutants (uvrA- or uvrC-), a higher inactivation of RF phi X174 DNA was found: T37 = 29 min for uvrA- E. coli, indicating that a part of the DNA damage introduced by the incubation with ortho-quinone is removed by excision repair.(ABSTRACT TRUNCATED AT 400 WORDS)
Journal of Chromatography A
The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real s... more The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. Optimal conditions obtained from experiments with spiked samples were applied on real soil and the influence of several extraction parameters was tested to gain maximum concentrations of components in comparison with solvent extraction.The optimal conditions achieved for spiked samples did not yield maximum concentrations for field samples. Stronger extraction conditions were necessary to overcome interactions between matrix and analytes. Longer dynamic extraction times were needed and the use of modifiers appeared to be essential for SFE of real samples. An increase in extraction pressure did not have any influence on extraction results. Comparable results were obtained for SFE and solvent extraction with an overall standard deviation between both methods of 25%.The stepwise approach is useful in meth...
MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards ... more MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards specific compounds, e.g. beta-agonists. The interactions between MIP particles and analytes are stronger than interactions obtained in conventional SPE. Bond Elut Certify columns show a bi-model non-polar and strong cation exchange and are generally used for basic and neutral drugs in urine and other biological samples. Both types of clean up methods were optimized for more than 30 different beta-agonists. After optimization, both methods were fully validated according to Commission Decision 2002/657/EC. Analysis is carried out by LC-MSMS, Ultima Triple Quad system. Results indicate that both sample preparation methods can be used for a range of beta- agonists. However, none of these methods can be used for all compounds, e.g. nine compounds cannot be extracted with either method in the selected concentration range (1-5 μg L-1). Sample preparation using MIP columns gives generally cleane...
European journal of cancer & clinical oncology, 1985
Covalent binding of 3H-labeled VP 16-213 to rat liver and HeLa cell microsomal proteins was studi... more Covalent binding of 3H-labeled VP 16-213 to rat liver and HeLa cell microsomal proteins was studied in vitro. Metabolic activation by cytochrome P-450 was found to play a role in the covalent binding of VP 16-213 to rat liver microsomal proteins, as shown by the need of NADPH cofactor, the increased binding after phenobarbital pretreatment and the inhibition by SFK-525A. Addition of ascorbic acid or alpha-phenyl-N-tert. butylnitrone to the incubation mixture depressed covalent binding by about 85%, suggesting that formation of a reactive metabolite from the phenolic structure may be involved in the binding process. VP 16-213 did not inhibit aminopyrine N-demethylase at the concentration used in the binding experiments (17 microM), indicating that metabolism of its methylenedioxy group does not play a role in binding to microsomal proteins. HeLa cell microsomes were found to possess aminopyrine N-demethylase activity. Covalent binding of radiolabeled VP 16-213 to HeLa cell microsomes...
ABSTRACT Biologically active phi X174 DNA is inactivated by the ortho-quinone derivative of the a... more ABSTRACT Biologically active phi X174 DNA is inactivated by the ortho-quinone derivative of the antitumor agent VP 16-213, but not by VP 16-213 itself, VP 16-213 phenoxy radical or aqueous decomposition product(s) of the ortho-quinone. Reduction of the ortho-quinone by cytochrome P-450 reductase and NADPH results in deactivation of the ortho-quinone towards anti-phi X174 DNA activity. However, compared with the parent compound VP 16-213, reduction of the ortho-quinone results in substantial damage towards DNA.
This report describes the validation of the quantification and the identification of an analytica... more This report describes the validation of the quantification and the identification of an analytical method for the determination of low concentrations (0.1-1.0 micro g/kg) of chloramphenicol in samples of urine, shrimps and meat. The validation study was based on the criteria described in Decision 2002/657/EC of the European Commission. The analytical method consists of an enzymatic hydrolysis (urine) or enzymatic digestion (meat), followed by liquid-liquid extraction of chloramphenicol from the matrix with ethyl acetate. The extract is cleaned with Solid Phase Extraction (SPE), followed by LC fractionation. The SPE step can be omitted for shrimps. After derivatisation of the chloramphenicol, final separation and detection is performed with GC-MS with Negative Chemical Ionisation (NCI). Detection can also be carried out using Electron Impact (EI), which is a less sensitive technique. This method can be used for both screening and quantification. The limit of determination for all sam...
This report describes the results of a surveillance conducted in 2000. In total 70 animals were t... more This report describes the results of a surveillance conducted in 2000. In total 70 animals were tested for a range of anabolic compounds and beta-agonists. In two cases a compound was detected and confirmed, one case of stanozolol and one case of isoxsuprine, a registered veterinary drug. Dit rapport beschrijft de resultaten van een in 2000 uitgevoerd bewakingsonderzoek. Zeventig dieren werden onderzocht op de aanwezigheid van anabolica en beta-agonisten. In twee gevallen werd een stof aangetoond. Een geval betrof de groeibevorderende stof stanozolol, een andere betrof het geregistreerde geneesmiddel Isoxsuprine.
Dit onderzoek werd uitgevoerd in opdracht en ten laste van de Voedsel en Waren Autoriteit in het ... more Dit onderzoek werd uitgevoerd in opdracht en ten laste van de Voedsel en Waren Autoriteit in het kader van het VWA/RBT project 310302 "Monitoring Dierbehandelingsmiddelen". RIVM, Postbus 1, 3720 BA Bilthoven, tel. 030-2749111; fax 030-2742971 RIVM rapport 310302002 Pag. 2 van 19
Journal of Chromatography A, 1995
ABSTRACT A new solid-phase extraction (SPE) method was developed for the analysis of 16 polyaroma... more ABSTRACT A new solid-phase extraction (SPE) method was developed for the analysis of 16 polyaromatic hydrocarbons (PAHs) on the US Environmental Protection Agency priority list, in soil samples. Different types of SPE columns were tested and conditioning and elution steps were optimised. In the final procedure, soil samples are extracted with acetone and, after dilution with HPLC-grade water, loaded on a C8 SPE column. After washing, all PAHs are eluted with tetrahydrofuran (THF). The final THF extract is analysed on an HPLC system for PAHs.Recoveries of the volatile PAHs, naphthalene, acephthylene and acenaphthalene were 80–90%. All other recoveries are comparable with standard liquid-liquid extraction (LLE) and range from 75 to 90%.The method is compared with the conventional LLE method for different types of real soil samples of a Dutch monitoring programme. Results indicate that SPE is a good method for the sample preparation for the analysis of PAHs in soil samples. Compared with LLE, correlation coefficients are better than 0.9 with relative standard deviations for SPE between 0.8 and 9.1%. LLE standard deviations ranged from 1.1 to 15.1%.
Chemosphere, 1991
ABSTRACT Over 200 samples of cow's milk have been analysed for dioxins in a survey on the... more ABSTRACT Over 200 samples of cow's milk have been analysed for dioxins in a survey on the occurrence of dioxins in milk from the vicinity of municipal waste incinerators (MSWs) and other potential dioxin sources in The Netherlands. Levels in milk were found to vary considerably with time, depending on emission rates, the direction and distance to the source and the feeding and housing of cows. Highest levels of up to 13.5 pg TEQ/g of milk fat were found in the Lickebaert area and Zaandam near two incinerators with highest emission rates. The background level ranged between 0.7 and 2.5 pg TEQ/g of milk fat. Levels in winter were comparable to those found in summer and, in some areas, even higher, when cows were fed with hay and silage harvested on the same farm. After the closure of the MSW in Zaandam, cow's milk from neighbouring farms showed a significant decrease in dioxin levels to below the critical limit of 6 pg TEQ/g of milk fat. Dioxin levels in the vicinity of a metal reclamation plant were comparable to those in milk from the vicinity of a MSW with moderate emissions. Differences were observed in the ratio PCDF/PCDD, which was higher in milk near the metal reclamation plant. Principal component analysis has been applied on a large data set of patterns of the 2,3,7,8-chlorine substituted PCDDs and PCDFs in cow's milk. This technique has proved to be useful for distinguishing and identification of sources on the basis of the isomer pattern in milk.
This report describes the first results of Supercritical Fluid Extraction (SFE) as technique for ... more This report describes the first results of Supercritical Fluid Extraction (SFE) as technique for the extraction of organic components from soil. SFE is based on the extraction properties of supercritical fluids - in this case CO2 - having liquidlike as well as gaslike behaviour as their low viscosity and high solute diffusivities. The optimization of SFE of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. An experimental approach was set up to test the influences of different extraction parameters such as pressure, extraction time, state and dynamic extraction, restictor type and collection solvent for off-line SFE. Conditions obtained from these experiments with spiked samples were applied on real soil and optimized to gain maximum concentrations of components in comparison with conventional solvent extraction. The optimal conditions achieved for spiked samples did...
Journal of Chromatography A
The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real s... more The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. Optimal conditions obtained from experiments with spiked samples were applied on real soil and the influence of several extraction parameters was tested to gain maximum concentrations of components in comparison with solvent extraction.The optimal conditions achieved for spiked samples did not yield maximum concentrations for field samples. Stronger extraction conditions were necessary to overcome interactions between matrix and analytes. Longer dynamic extraction times were needed and the use of modifiers appeared to be essential for SFE of real samples. An increase in extraction pressure did not have any influence on extraction results. Comparable results were obtained for SFE and solvent extraction with an overall standard deviation between both methods of 25%.The stepwise approach is useful in meth...
MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards ... more MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards specific compounds, e.g. beta-agonists. The interactions between MIP particles and analytes are stronger than interactions obtained in conventional SPE. Bond Elut Certify columns show a bi-model non-polar and strong cation exchange and are generally used for basic and neutral drugs in urine and other biological samples. Both types of clean up methods were optimized for more than 30 different beta-agonists. After optimization, both methods were fully validated according to Commission Decision 2002/657/EC. Analysis is carried out by LC-MSMS, Ultima Triple Quad system. Results indicate that both sample preparation methods can be used for a range of beta- agonists. However, none of these methods can be used for all compounds, e.g. nine compounds cannot be extracted with either method in the selected concentration range (1-5 μg L-1). Sample preparation using MIP columns gives generally cleane...
This report describes the validation of the quantification and the identification of an analytica... more This report describes the validation of the quantification and the identification of an analytical method for the determination of low concentrations (0.1-1.0 micro g/kg) of chloramphenicol in samples of urine, shrimps and meat. The validation study was based on the criteria described in Decision 2002/657/EC of the European Commission. The analytical method consists of an enzymatic hydrolysis (urine) or enzymatic digestion (meat), followed by liquid-liquid extraction of chloramphenicol from the matrix with ethyl acetate. The extract is cleaned with Solid Phase Extraction (SPE), followed by LC fractionation. The SPE step can be omitted for shrimps. After derivatisation of the chloramphenicol, final separation and detection is performed with GC-MS with Negative Chemical Ionisation (NCI). Detection can also be carried out using Electron Impact (EI), which is a less sensitive technique. This method can be used for both screening and quantification. The limit of determination for all sam...
This report describes the results of a surveillance conducted in 2000. In total 70 animals were t... more This report describes the results of a surveillance conducted in 2000. In total 70 animals were tested for a range of anabolic compounds and beta-agonists. In two cases a compound was detected and confirmed, one case of stanozolol and one case of isoxsuprine, a registered veterinary drug. Dit rapport beschrijft de resultaten van een in 2000 uitgevoerd bewakingsonderzoek. Zeventig dieren werden onderzocht op de aanwezigheid van anabolica en beta-agonisten. In twee gevallen werd een stof aangetoond. Een geval betrof de groeibevorderende stof stanozolol, een andere betrof het geregistreerde geneesmiddel Isoxsuprine.
The Analyst, 2002
Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automate... more Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automated supercritical fluid extraction (SFE). After the addition of internal standards and sample pretreatment, the analytes are extracted from the matrix by supercritical CO2 and trapped directly in-line on alumina placed in the extraction vessel. The samples are analysed by liquid chromatography combined with ion-trap mass selective detection (LC-MSn). For quantification, deuterated internal standards are added and single ions of the analytes and internal standards are monitored. For confirmation of the identity of the analytes, two transition ions (one MS2 and one MS3) were monitored and the ratios between the ions were calculated and compared with those of standards. The detection capability for the multi-analyte LC-MSn analysis of megestrol acetate (MA), medroxyprogesterone acetate (MPA), chlormadinone acetate (CMA) and melengestrol acetate (MGA) is 0.5 microg kg(-1). The mean within-laboratory reproducibility ranges from 16-19% (%RSD) at a concentration level of 0.5 microg kg(-1) (n = 9). Running the SFE procedure overnight allows the analysis of 24 samples of fat per day.
The Analyst, 2002
Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automate... more Acetyl gestagenic steroids are isolated from animal tissues such as bovine kidney fat by automated supercritical fluid extraction (SFE). After the addition of internal standards and sample pretreatment, the analytes are extracted from the matrix by supercritical CO2 and trapped directly in-line on alumina placed in the extraction vessel. The samples are analysed by liquid chromatography combined with ion-trap mass selective detection (LC-MSn). For quantification, deuterated internal standards are added and single ions of the analytes and internal standards are monitored. For confirmation of the identity of the analytes, two transition ions (one MS2 and one MS3) were monitored and the ratios between the ions were calculated and compared with those of standards. The detection capability for the multi-analyte LC-MSn analysis of megestrol acetate (MA), medroxyprogesterone acetate (MPA), chlormadinone acetate (CMA) and melengestrol acetate (MGA) is 0.5 microg kg(-1). The mean within-laboratory reproducibility ranges from 16-19% (%RSD) at a concentration level of 0.5 microg kg(-1) (n = 9). Running the SFE procedure overnight allows the analysis of 24 samples of fat per day.
Biochemical Pharmacology, 1988
We have studied the effects of the recently reported two new metabolites of the antitumor agent V... more We have studied the effects of the recently reported two new metabolites of the antitumor agent VP-16-213, the ortho-dihydroxy derivative or catechol and the ortho-quinone, on the biological activity of single-stranded and double-stranded phi X174 DNA, the binding of the metabolites to calf thymus DNA and the conversion of the catechol into the ortho-quinone. Evidence was obtained for the oxidation of the catechol into the ortho-quinone and for the fact that the ortho-quinone is the metabolite of VP-16-213 responsible for its binding to rat liver microsomal proteins. The catechol and ortho-quinone of VP-16-213 were found to bind 7-9 times more strongly to calf thymus DNA than VP-16-213 itself. In contrast to the parent compound VP-16-213, the catechol as well as the ortho-quinone inactivated both single-stranded (ss) and double-stranded (RF) biologically active phi X174 DNA. The mean T37-values for inactivation of ss and RF phi X174 DNA by 2.2 x 10(-4)M catechol at 37 degrees and pH 7.4 were 96 and 640 min, respectively. Reduction of the ortho-quinone by NADPH cytochrome P-450 reductase resulted in formation of the catechol. The system ortho-quinone/NADPH cytochrome P-450 reductase inactivated ss phi X174 DNA with a mean T37-value of 454 min, and this inactivation was inhibited by DMSO. The mean T37-value for inactivation of ss phi X174 DNA by 1.8 x 10(-4) M ortho-quinone at 37 degrees and pH 4.0 was 24 min. The chemical stability of the ortho-quinone and the extent of inactivation of ss phi X174 DNA by the ortho-quinone were both pH-dependent: at higher pH the ortho-quinone was less stable and gave less inactivation of DNA. The aqueous decomposition product(s) of the ortho-quinone formed at pH 7.4 inactivated ss phi X174 DNA with a mean T37-value of 175 min. The rate of inactivation of RF phi X174 DNA by the ortho-quinone at pH 4.0 was twice as low as the rate of inactivation of ss phi X174 DNA: T37 = 49 min. When using excision repair deficient E. coli mutants (uvrA- or uvrC-), a higher inactivation of RF phi X174 DNA was found: T37 = 29 min for uvrA- E. coli, indicating that a part of the DNA damage introduced by the incubation with ortho-quinone is removed by excision repair.(ABSTRACT TRUNCATED AT 400 WORDS)
We have studied the effects of the recently reported two new metabolites of the antitumor agent V... more We have studied the effects of the recently reported two new metabolites of the antitumor agent VP-16-213, the ortho-dihydroxy derivative or catechol and the ortho-quinone, on the biological activity of single-stranded and double-stranded phi X174 DNA, the binding of the metabolites to calf thymus DNA and the conversion of the catechol into the ortho-quinone. Evidence was obtained for the oxidation of the catechol into the ortho-quinone and for the fact that the ortho-quinone is the metabolite of VP-16-213 responsible for its binding to rat liver microsomal proteins. The catechol and ortho-quinone of VP-16-213 were found to bind 7-9 times more strongly to calf thymus DNA than VP-16-213 itself. In contrast to the parent compound VP-16-213, the catechol as well as the ortho-quinone inactivated both single-stranded (ss) and double-stranded (RF) biologically active phi X174 DNA. The mean T37-values for inactivation of ss and RF phi X174 DNA by 2.2 x 10(-4)M catechol at 37 degrees and pH 7.4 were 96 and 640 min, respectively. Reduction of the ortho-quinone by NADPH cytochrome P-450 reductase resulted in formation of the catechol. The system ortho-quinone/NADPH cytochrome P-450 reductase inactivated ss phi X174 DNA with a mean T37-value of 454 min, and this inactivation was inhibited by DMSO. The mean T37-value for inactivation of ss phi X174 DNA by 1.8 x 10(-4) M ortho-quinone at 37 degrees and pH 4.0 was 24 min. The chemical stability of the ortho-quinone and the extent of inactivation of ss phi X174 DNA by the ortho-quinone were both pH-dependent: at higher pH the ortho-quinone was less stable and gave less inactivation of DNA. The aqueous decomposition product(s) of the ortho-quinone formed at pH 7.4 inactivated ss phi X174 DNA with a mean T37-value of 175 min. The rate of inactivation of RF phi X174 DNA by the ortho-quinone at pH 4.0 was twice as low as the rate of inactivation of ss phi X174 DNA: T37 = 49 min. When using excision repair deficient E. coli mutants (uvrA- or uvrC-), a higher inactivation of RF phi X174 DNA was found: T37 = 29 min for uvrA- E. coli, indicating that a part of the DNA damage introduced by the incubation with ortho-quinone is removed by excision repair.(ABSTRACT TRUNCATED AT 400 WORDS)
Journal of Chromatography A
The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real s... more The optimization of supercritical fluid extraction (SFE) of organochlorine pesticides from real soil samples is performed, according to a general stepwise set-up for quantitative SFE. Optimal conditions obtained from experiments with spiked samples were applied on real soil and the influence of several extraction parameters was tested to gain maximum concentrations of components in comparison with solvent extraction.The optimal conditions achieved for spiked samples did not yield maximum concentrations for field samples. Stronger extraction conditions were necessary to overcome interactions between matrix and analytes. Longer dynamic extraction times were needed and the use of modifiers appeared to be essential for SFE of real samples. An increase in extraction pressure did not have any influence on extraction results. Comparable results were obtained for SFE and solvent extraction with an overall standard deviation between both methods of 25%.The stepwise approach is useful in meth...
MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards ... more MIPs are engineered cross-linked polymers that can exhibit high affinity and selectivity towards specific compounds, e.g. beta-agonists. The interactions between MIP particles and analytes are stronger than interactions obtained in conventional SPE. Bond Elut Certify columns show a bi-model non-polar and strong cation exchange and are generally used for basic and neutral drugs in urine and other biological samples. Both types of clean up methods were optimized for more than 30 different beta-agonists. After optimization, both methods were fully validated according to Commission Decision 2002/657/EC. Analysis is carried out by LC-MSMS, Ultima Triple Quad system. Results indicate that both sample preparation methods can be used for a range of beta- agonists. However, none of these methods can be used for all compounds, e.g. nine compounds cannot be extracted with either method in the selected concentration range (1-5 μg L-1). Sample preparation using MIP columns gives generally cleane...
European journal of cancer & clinical oncology, 1985
Covalent binding of 3H-labeled VP 16-213 to rat liver and HeLa cell microsomal proteins was studi... more Covalent binding of 3H-labeled VP 16-213 to rat liver and HeLa cell microsomal proteins was studied in vitro. Metabolic activation by cytochrome P-450 was found to play a role in the covalent binding of VP 16-213 to rat liver microsomal proteins, as shown by the need of NADPH cofactor, the increased binding after phenobarbital pretreatment and the inhibition by SFK-525A. Addition of ascorbic acid or alpha-phenyl-N-tert. butylnitrone to the incubation mixture depressed covalent binding by about 85%, suggesting that formation of a reactive metabolite from the phenolic structure may be involved in the binding process. VP 16-213 did not inhibit aminopyrine N-demethylase at the concentration used in the binding experiments (17 microM), indicating that metabolism of its methylenedioxy group does not play a role in binding to microsomal proteins. HeLa cell microsomes were found to possess aminopyrine N-demethylase activity. Covalent binding of radiolabeled VP 16-213 to HeLa cell microsomes...
ABSTRACT Biologically active phi X174 DNA is inactivated by the ortho-quinone derivative of the a... more ABSTRACT Biologically active phi X174 DNA is inactivated by the ortho-quinone derivative of the antitumor agent VP 16-213, but not by VP 16-213 itself, VP 16-213 phenoxy radical or aqueous decomposition product(s) of the ortho-quinone. Reduction of the ortho-quinone by cytochrome P-450 reductase and NADPH results in deactivation of the ortho-quinone towards anti-phi X174 DNA activity. However, compared with the parent compound VP 16-213, reduction of the ortho-quinone results in substantial damage towards DNA.
This report describes the validation of the quantification and the identification of an analytica... more This report describes the validation of the quantification and the identification of an analytical method for the determination of low concentrations (0.1-1.0 micro g/kg) of chloramphenicol in samples of urine, shrimps and meat. The validation study was based on the criteria described in Decision 2002/657/EC of the European Commission. The analytical method consists of an enzymatic hydrolysis (urine) or enzymatic digestion (meat), followed by liquid-liquid extraction of chloramphenicol from the matrix with ethyl acetate. The extract is cleaned with Solid Phase Extraction (SPE), followed by LC fractionation. The SPE step can be omitted for shrimps. After derivatisation of the chloramphenicol, final separation and detection is performed with GC-MS with Negative Chemical Ionisation (NCI). Detection can also be carried out using Electron Impact (EI), which is a less sensitive technique. This method can be used for both screening and quantification. The limit of determination for all sam...
This report describes the results of a surveillance conducted in 2000. In total 70 animals were t... more This report describes the results of a surveillance conducted in 2000. In total 70 animals were tested for a range of anabolic compounds and beta-agonists. In two cases a compound was detected and confirmed, one case of stanozolol and one case of isoxsuprine, a registered veterinary drug. Dit rapport beschrijft de resultaten van een in 2000 uitgevoerd bewakingsonderzoek. Zeventig dieren werden onderzocht op de aanwezigheid van anabolica en beta-agonisten. In twee gevallen werd een stof aangetoond. Een geval betrof de groeibevorderende stof stanozolol, een andere betrof het geregistreerde geneesmiddel Isoxsuprine.
Dit onderzoek werd uitgevoerd in opdracht en ten laste van de Voedsel en Waren Autoriteit in het ... more Dit onderzoek werd uitgevoerd in opdracht en ten laste van de Voedsel en Waren Autoriteit in het kader van het VWA/RBT project 310302 "Monitoring Dierbehandelingsmiddelen". RIVM, Postbus 1, 3720 BA Bilthoven, tel. 030-2749111; fax 030-2742971 RIVM rapport 310302002 Pag. 2 van 19
Journal of Chromatography A, 1995
ABSTRACT A new solid-phase extraction (SPE) method was developed for the analysis of 16 polyaroma... more ABSTRACT A new solid-phase extraction (SPE) method was developed for the analysis of 16 polyaromatic hydrocarbons (PAHs) on the US Environmental Protection Agency priority list, in soil samples. Different types of SPE columns were tested and conditioning and elution steps were optimised. In the final procedure, soil samples are extracted with acetone and, after dilution with HPLC-grade water, loaded on a C8 SPE column. After washing, all PAHs are eluted with tetrahydrofuran (THF). The final THF extract is analysed on an HPLC system for PAHs.Recoveries of the volatile PAHs, naphthalene, acephthylene and acenaphthalene were 80–90%. All other recoveries are comparable with standard liquid-liquid extraction (LLE) and range from 75 to 90%.The method is compared with the conventional LLE method for different types of real soil samples of a Dutch monitoring programme. Results indicate that SPE is a good method for the sample preparation for the analysis of PAHs in soil samples. Compared with LLE, correlation coefficients are better than 0.9 with relative standard deviations for SPE between 0.8 and 9.1%. LLE standard deviations ranged from 1.1 to 15.1%.