Mohamed Yasin - Academia.edu (original) (raw)
Papers by Mohamed Yasin
International Journal of Environmental Analytical Chemistry, 1997
... DCBP was selected as the volumetric standard because of its wide employment and high reliabil... more ... DCBP was selected as the volumetric standard because of its wide employment and high reliability for sam-Page 6. 86 PM HANCOCK et al. TABLE I Characteristic fragmentation ions of the pyrethroids. mirex and DCBP Compound Characteristic ions Quantification ion ...
Rapid Communications in Mass Spectrometry, 1995
A gas chromatographic/mass spectrometric method was developed for the simultaneous determination ... more A gas chromatographic/mass spectrometric method was developed for the simultaneous determination of five synthetic pyrethroid insecticides in soil, moss and fish tissue. These pyrethroids were extracted with hexane-dichloromethane by ultrasonication and cleaned up on Florisil (soil and moss) and mixed acid/base alumina (fish) columns prior to determination by gas chromatography/negative-ion chemical ionization mass spectrometry in selected ion monitoring mode. All the pyrethroids were analyzed simultaneously in a single run on a DB5-MS 15 m capillary column. Recoveries of the pyrethroids from the three matrices at fortification levels of 10, 50 and 100 μg/kg ranged from 80 to 117%. Four determinations were made at each concentration level for each matrix. The practical determination limit of the method was in the range 0.5 to 5 μg/kg depending on the compound. This method was also applied to samples obtained from a contaminated ecosystem.
Journal of Chromatography A, 1996
An effective analytical method for the simultaneous determination of five synthetic pyrethroid in... more An effective analytical method for the simultaneous determination of five synthetic pyrethroid insecticides in soil is developed and method performance data presented. The pyrethroid residues were extracted with hexane-dichloromethane in an ultrasonic bath. The extract was cleaned up on a Florisil column prior to determination by gas chromatography-negativeion chemical ionization mass spectrometry (GC-NICI-MS) in selected-ion monitoring (SIM) mode. The highest detection sensitivities were achieved in the SIM mode where the instrument was adjusted to collect only a few ions which were indicative for the compound to be searched for, instead of scanning the entire spectrum over the whole mass range. The gain in sensitivity was the result of longer specific sampling times for each of the ions selected. Recovery studies were performed at 10, 50 and 100 ppb fortification levels of each pyrethroid and of the internal standard, mirex, and the percentage recoveries ranged from 81.7---4.2 to 108.2+-2.6%. Four determinations were made at each concentration level along with a procedural blank. The quantification limit of the method was in the range of 0.012 to 4.4 ppb, depending on the compound. This method was also applied to sediment samples collected from the environment of a River Catchment being currently monitored for the presence of target pyrethroids.
Biomaterials, 1990
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1990
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1992
The physical and degradative properties of polyhydroxybutyrate-hydroxyvalerate copolymer blends w... more The physical and degradative properties of polyhydroxybutyrate-hydroxyvalerate copolymer blends with polycaprolactone were investigated. Blends containing low levels of polycaprolactone (< 20%) were found to possess a considerable degree of compatibility, whilst those with higher levels of polycaprolactone were incompatible and showed phase separation behaviour. This incompatibility was most marked in blends containing approximately 50% of each component. In blends containing low levels of polycaprolactone, processing conditions governed the ease of crystallization of polycaprolactone in the polyhydroxybutyrate-hydroxyvalerate matrix and thus the mechanical property of the blend. The degradation rate of these blends was found to be influenced by a complex set of factors, including temperature, pH and polycaprolactone content of the blend. Although crystallinity affected the mechanical properties of the blends, its influence on the hydrolytic degradation rate was masked by the large difference in the molecular weight of the polyhydroxybutyrate-hydroxyvalerate copolymers (M, -300 000) and polycaprolactone (M, -50 000). The polyhydroxybutyrate-hydroxyvalerate/polycaprolactone blends were found to be much more stable to hydrolytic degradation than polyhydroxybutyrate-hydroxyvalerate/ polysaccharide blends previously studied. Here the combined techniques of goniophotometry and surface energy measurements proved extremely valuable in monitoring the early stages of degradation, during which surface, rather than bulk degradation, processes predominate.
Biomaterials, 1989
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1987
The hydrolytic degradation of poly(hydro~butyrate) together with a series of hydro~butyrate-hydro... more The hydrolytic degradation of poly(hydro~butyrate) together with a series of hydro~butyrate-hydro~valerate copolymers has been studied. The effects of copolymer composition and molecular weight are presented together with the results of varying pH and temperature on the degradation rate. ~eg~dation has been monitored by weight loss and water uptake measurements together with goniophotometric, surface energy and scanning electron microscopic studies. Some comparisons with the more widely used so-called 'biodegradable' polymers, poly(glycolic acid), poly(dioxanone) and the glycolic-lactic acid (90: 10) copolymers are presented together with the effect of blood plasma on the degradation process.
International Journal of Environmental Analytical Chemistry, 1997
... DCBP was selected as the volumetric standard because of its wide employment and high reliabil... more ... DCBP was selected as the volumetric standard because of its wide employment and high reliability for sam-Page 6. 86 PM HANCOCK et al. TABLE I Characteristic fragmentation ions of the pyrethroids. mirex and DCBP Compound Characteristic ions Quantification ion ...
Rapid Communications in Mass Spectrometry, 1995
A gas chromatographic/mass spectrometric method was developed for the simultaneous determination ... more A gas chromatographic/mass spectrometric method was developed for the simultaneous determination of five synthetic pyrethroid insecticides in soil, moss and fish tissue. These pyrethroids were extracted with hexane-dichloromethane by ultrasonication and cleaned up on Florisil (soil and moss) and mixed acid/base alumina (fish) columns prior to determination by gas chromatography/negative-ion chemical ionization mass spectrometry in selected ion monitoring mode. All the pyrethroids were analyzed simultaneously in a single run on a DB5-MS 15 m capillary column. Recoveries of the pyrethroids from the three matrices at fortification levels of 10, 50 and 100 μg/kg ranged from 80 to 117%. Four determinations were made at each concentration level for each matrix. The practical determination limit of the method was in the range 0.5 to 5 μg/kg depending on the compound. This method was also applied to samples obtained from a contaminated ecosystem.
Journal of Chromatography A, 1996
An effective analytical method for the simultaneous determination of five synthetic pyrethroid in... more An effective analytical method for the simultaneous determination of five synthetic pyrethroid insecticides in soil is developed and method performance data presented. The pyrethroid residues were extracted with hexane-dichloromethane in an ultrasonic bath. The extract was cleaned up on a Florisil column prior to determination by gas chromatography-negativeion chemical ionization mass spectrometry (GC-NICI-MS) in selected-ion monitoring (SIM) mode. The highest detection sensitivities were achieved in the SIM mode where the instrument was adjusted to collect only a few ions which were indicative for the compound to be searched for, instead of scanning the entire spectrum over the whole mass range. The gain in sensitivity was the result of longer specific sampling times for each of the ions selected. Recovery studies were performed at 10, 50 and 100 ppb fortification levels of each pyrethroid and of the internal standard, mirex, and the percentage recoveries ranged from 81.7---4.2 to 108.2+-2.6%. Four determinations were made at each concentration level along with a procedural blank. The quantification limit of the method was in the range of 0.012 to 4.4 ppb, depending on the compound. This method was also applied to sediment samples collected from the environment of a River Catchment being currently monitored for the presence of target pyrethroids.
Biomaterials, 1990
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1990
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1992
The physical and degradative properties of polyhydroxybutyrate-hydroxyvalerate copolymer blends w... more The physical and degradative properties of polyhydroxybutyrate-hydroxyvalerate copolymer blends with polycaprolactone were investigated. Blends containing low levels of polycaprolactone (< 20%) were found to possess a considerable degree of compatibility, whilst those with higher levels of polycaprolactone were incompatible and showed phase separation behaviour. This incompatibility was most marked in blends containing approximately 50% of each component. In blends containing low levels of polycaprolactone, processing conditions governed the ease of crystallization of polycaprolactone in the polyhydroxybutyrate-hydroxyvalerate matrix and thus the mechanical property of the blend. The degradation rate of these blends was found to be influenced by a complex set of factors, including temperature, pH and polycaprolactone content of the blend. Although crystallinity affected the mechanical properties of the blends, its influence on the hydrolytic degradation rate was masked by the large difference in the molecular weight of the polyhydroxybutyrate-hydroxyvalerate copolymers (M, -300 000) and polycaprolactone (M, -50 000). The polyhydroxybutyrate-hydroxyvalerate/polycaprolactone blends were found to be much more stable to hydrolytic degradation than polyhydroxybutyrate-hydroxyvalerate/ polysaccharide blends previously studied. Here the combined techniques of goniophotometry and surface energy measurements proved extremely valuable in monitoring the early stages of degradation, during which surface, rather than bulk degradation, processes predominate.
Biomaterials, 1989
The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in... more The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3,7.4and 10.6 and at 37°C and 70°C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up. Poly( hydroxybutyrate)-poly( hydroxyvalerate) copolymers represent a useful range of potential biodegradable polymers which offer advantage in the field of biomaterials. They are produced by a bacterial synthesis process', and are now available in a wide range of molecular weights and copolymer compositions. Although a substantial body of information exists relating to the thermal degradation and processability of the poly(hydroxybutyrate) homopolymer, published information relating to the behaviour of the copolymers and in particular their hydrolytic degradation is relatively limited. In the first part of this series2, we reviewed published information on the biodegradation and hydrolysis of esterbased polymers. It was clear from this that the hydroxybutyrate-hydroxyvalerate (H B-HV) copolymers provided a considerable extension to available materials of this type. I na subsequent paper3 we reported the results of an experimental study of the hydrolytic degradation of the hydroxybutyrate homopolymer together with a series of HB-HV copolymers.
Biomaterials, 1987
The hydrolytic degradation of poly(hydro~butyrate) together with a series of hydro~butyrate-hydro... more The hydrolytic degradation of poly(hydro~butyrate) together with a series of hydro~butyrate-hydro~valerate copolymers has been studied. The effects of copolymer composition and molecular weight are presented together with the results of varying pH and temperature on the degradation rate. ~eg~dation has been monitored by weight loss and water uptake measurements together with goniophotometric, surface energy and scanning electron microscopic studies. Some comparisons with the more widely used so-called 'biodegradable' polymers, poly(glycolic acid), poly(dioxanone) and the glycolic-lactic acid (90: 10) copolymers are presented together with the effect of blood plasma on the degradation process.