Application of clear polymethylmethacrylate dosimeter Radix W to a few MeV electron in radiation processing

Characteristics of clear PMMA dosimeter (Radix W) were studied for electron irradiation and compared with the response for gamma irradiation. The dose–response curves were nearly linear up to 30 kGy and become sublinear at higher doses. The radiation-induced absorbance was reduced with 6% within 4 h after irradiation. Dose comparisons were performed for 2, 3, 4 and 5 MeV electron irradiation using cellulose triacetate dosimeter (CTA) (FTR-125) and Radix W dosimeters which were independently calibrated for 2 MeV electrons and ⁶⁰Co gamma-rays using calorimeter and ionizing chamber, respectively. The doses estimated by CTA and Radix W were different by about 20%. The magnitude of this difference was, however, independent of electron energy.     

Rapid online equilibration method to determine the D/H ratios of non-exchangeable hydrogen in cellulose

An improved method for the determination of deuterium-to-hydrogen (D/H) ratios of non-exchangeable hydrogen in cellulose is presented. The method is based on the equilibration reaction of the hydroxyl hydrogen of cellulose and water vapour of known isotopic composition. The equilibrated cellulose is pyrolysed and the total D/H ratio determined by subsequent online isotope ratio mass spectrometry (IRMS). With a mass balance system the D/H ratio of non-exchangeable hydrogen is recalculated after an empirical calibration has been performed, yielding a mean exchangeability of 0.239 and an equilibrium fractionation factor of 1.082 between the hydroxyl hydrogen of cellulose and water hydrogen at 110 degrees C. Equilibration takes 10 min per sample. Results obtained by this online equilibration method agree very well with values obtained by the nitration technique (R2 = 0.941). The uncertainty of the equilibration method is +/-4 per thousand resulting from a single standard deviation of +/-2.8 per thousand for the equilibration determined by standard cellulose and 2.8 per thousand from the variable exchangeability of the hydroxyl hydrogen in cellulose due to crystalline areas. The latter uncertainty may be lowered by minimising the crystallinity of the cellulose. Advantages of this new technique are (i) the considerably reduced sample amount required (as low as 0.2 mg, ideally 0.5 mg compared with 20 mg for the conventional nitration technique); (ii) an approximately 100-fold reduced process time; and (iii) no need for the hazardous chemicals used in the nitration technique.     

Heat conduction effects during the calorimetric determination of absorbed dose to water in radiotherapy beams

A transportable water calorimeter for the determination of the quantity of absorbed dose to water in radiotherapy beams has been developed at the PTB and is presented in detail in this investigation. Heat conduction effects occurring in the calorimeter are studied for different lateral sizes of high-energy photon beams, for different depth dose distributions of electron beams and for a scanned-beam irradiation with a heavy ion beam. The corresponding correction factors are calculated and arguments are given under which conditions these can adequately be applied.     

Calculation of proton stopping power in the region of its maximum value for several organic materials and water

The stopping powers (SP) for 10 solid organic materials and water have been calculated in the range of proton energies 50–500 keV. Most of the presented results are new and are in good agreement with existing experimental data. The calculated data might be useful for applications in radiobiology and space research.     

A simple rapid method to precisely determine 13C/12C ratios of plant methoxyl groups

Stable isotope ratios of individual plant components have become a valuable tool for the determination of the geographical origin and authenticity of foodstuff. A recently published method with considerable potential in this context is the measurement of the deuterium/hydrogen (D/H) isotope ratios of plant matter methoxyl groups. The method entailed cleavage of methyl ethers or esters with hydriodic acid (HI) to form gaseous methyl iodide (CH₃I) and then measurement of the δ²H value of this gas. Here, as a follow up to a previous study, we describe a method for the rapid and precise δ¹³C analysis of plant matter methoxyl groups using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Conditions for sample preparation were investigated for isotope discrimination effects, the GC conditions optimized, the reproducibility of the measurement of standards undertaken, and the precision of the method defined. The reproducibility of the δ¹³C value determined for a CH₃I standard on 20 consecutive measurements was found to be 0.17‰. The method was also tested on four methoxyl‐rich plant components: vanillin, lignin, wood and pectin. The analytical precision obtained, expressed as the average standard deviation, for these compounds was found to be better than 0.13‰. The described procedure which is simple and rapid, allowing preparation and analysis of a sample within 1 h, produces accurate and reproducible isotopic measurements. We suggest that this validated δ¹³C method when employed together with the recently published δ²H method for two‐dimensional stable isotope studies of organic matter containing methoxyl groups will be of considerable value, e.g. for proving the authenticity of foodstuff. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermogravimetric method used to determine the saturated vapor pressure in a wide range of values

Thermogravimetric method was used to study the evaporation of a number of solvents. The evaporation coefficients in the Langmuir equation were calculated in relation to the conditions of a thermogravimetric experiment (atmospheric pressure, carrier-gas) and nature of a substance under study.     

Development of a headspace-solid phase microextraction-gas chromatography method to determine organohalogen contamination in drinking water

The formation of organohalogen compounds in waters treated by chlorination has drawn increasing scientific attention due to the potentially hazardous health effects of this class of substances. Today, chlorination is the most widely used technology for civil water disinfection. In this study, headspace-solid phase microextraction coupled with GC-electron capture detector was used to determine organohalogen compounds in drinking water sampled from aqueducts and artesian wells in Italy. Experimental parameters, such as sample volume, stirring, salting out, extraction temperature, and extraction time, were evaluated and optimized. The LODs ranged from 1 to 10 ng/L and LOQs from 5 to 50 ng/L. A linear response was confirmed by correlation coefficients ranging from 0.9443 to 0.9999. Quantifiable organohalogen residues were found in 11 water samples, with concentration up to 11.3 +/- 0.5 microg/L for the sum of all trihalomethanes and 0.66 +/- 0.03 microg/L for the sum of trichloroethylene and tetrachloroethylene. These concentrations are lower than the current regulatory limits in Italy.     

Calculation of detection limits for a single-laboratory ion-chromatographic method to determine parts-per-trillion ions in ultrapure water

This paper addresses the calculation of detection limits (DLs) for ion-chromatographic data at low part-per-trillion (w/w) levels. The main objectives are: (1) to explain two statistical techniques (the EPA or “3σ” approach and the Hubaux-Vos method), (2) to calculate DLs using each procedure, (3) to discuss the strengths and weaknesses of each statistical approach and (4) to decide if the analytical method is appropriate for quantifying anions at the 50-ppt level in deionized water. The analytes of interest are: fluoride, chloride, nitrite, bromide, nitrate, sulfate and phosphate. All work was performed on a Dionex DX500 microbore unit, using an AS11 column. Results indicate that the H-V method gives a more realistic (and higher) DL than does the 3σ. Assuming false-negative and false-positives probabilities of 10% or less, this analytical method is not acceptable for quantifying anions at the desired level.     

Use of SPME extraction to determine organophosphorus pesticides adsorption phenomena in water and soil matrices

Solid-phase micro extraction (SPME) coupled with GC enables rapid and simple analysis of organophosphorus pesticides in a range of complex matrices. Investigations were made into the extraction efficiencies from water of six organophosphorus insecticides (methamidophos, omethoate, dimethoate, parathion methyl, malathion, and parathion ethyl) showing a wide range of polarities. Three SPME fibres coated with different stationary phases, polydimethylsiloxane, polyacrylate, and carbowax-divinylbenzene (CW-DVB), were investigated. Water was spiked with the pesticides at concentrations from 1 to 0.01 µg mL-1, and the solutions used for optimization of the procedure. The CW-DVB fibre, with a 65 µm coating, gave the best performance. The optimized experimental conditions were sample volume 10 mL at 20°C, equilibration time 16 min, pH 5, and presence of 10% w/v NaCl. SPME analyses were performed on solutions obtained by equilibrating aqueous pesticide solutions with six certified soils with various physico-chemical characteristics. SPME data were also assessed by comparison with analyses performed by using conventional solid-phase extraction. Results indicate the suitability of SPME for analysis of pesticides in environmental water samples.     

Use of capillary electrophoresis with UV detection as a screening method to determine histamine in fish samples.

Histamine levels in fish, extracted with methanol, were determined by capillary electrophoresis (CE) using phosphate buffer pH 2.5 and U.V. detection at 210 nm. Histamine was well separated from the other co-extracted components under the given CE condition without any cleanup of the methanol extract. The average recovery of spiked histamine in various types of fish samples was 96%. Using the same methanol extracts from various fish samples, we then compared histamine concentration obtained by CE and fluorometric methods.     

A novel method to quantify the amount of surfactant at the oil/water interface and to determine total interfacial area of emulsions

We present a methodology to quantitatively determine the fraction of sodium dodecyl sulfate (SDS) that partitions to the oil/water interface in oil-in-water macroemulsions and calculate the total interfacial area (TIA) through the novel use of filtration through nanoporous membranes. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS (as monomers and micelles) that is in the bulk water phase (i.e., not at the interface) could pass through. The concentration of SDS in the filtrate was determined and used to calculate the TIA for each system. The mean droplet diameter of the emulsions was measured by light scattering. We analyzed the effects of total SDS concentration and oil chain length on the amount of SDS that partitions to the interface, the TIA, and the droplet diameter. The results showed that partitioning of SDS to the oil/water interface increases with increasing total SDS concentration in emulsion systems (i.e., the more SDS we add to the bulk solution, the more SDS partitions to the oil/water interface). However, the surface-to-bulk partition coefficient (i.e., the SDS concentration at the interface divided by the SDS concentration in the aqueous phase) remains the same over the entire concentration range (8-200 mM). The results showed a chain-length compatibility effect in that the minimum amount of SDS partitioned to the interface for C(12) oil. The droplet size measurements revealed a maximum size of droplets for C(12) oil. Penetration of oil molecules into SDS film at the interface has been proposed to account for the maximum droplet size and minimum partitioning of SDS at the oil/water interface for C(12) oil+SDS emulsion system. The TIA, as determined from our ultrafiltration method, was consistently two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.     

Use of a variably sensitive selected reaction monitoring method to extend the linear dynamic range for quantitative high-performance liquid chromatography/tandem mass spectrometry

A method has been devised with the capacity to extend the linear dynamic range of a triple quadrupole mass spectrometer operated in the selected reaction monitoring (SRM) mode of analysis. This extended range experiment can be realized by simultaneously acquiring variably sensitive data, via collision energy adjustment, for the same precursor-to-product ion transition within a single SRM method. While this method can be applied universally to many different study types without any detrimental effect to the analysis or throughput, it was applied herein to acquire and quantify, within a single analysis, the concentrations of GSK-A in a multiple-dose rodent study, that previously required a dilution scheme. Using this methodology, the linear dynamic range of GSK-A was increased over traditional methods by nearly two orders of magnitude, from 2.00-10,000 ng/mL to 0.500-100,000 ng/mL.     

Micellization to gelation of a triblock copolymer in water: Thermoreversibility and scaling

Aqueous solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer, Pluronic F108 (PEO₁₃₃PPO₅₀PEO₁₃₃), ranging from 1 to 35 wt %, were studied with differential scanning microcalorimetry and rheology. The thermoreversible micellization and gelation were examined through a heating process and a subsequent cooling process at a fixed rate of 1 °C/min. The critical micellization temperature (CMT), determined by the onset temperature of the endothermic peak in the heating process, was a decreasing function of the F108 concentration. A small secondary endothermic peak appeared only when the polymer concentration was 22.5 wt % or higher, indicating that there was a sol–gel transition but that the gelation was a nearly athermic process. Upon heating, an abrupt increase was observed in both the dynamic storage modulus (G′) and dynamic loss modulus (G″) within a narrow temperature range. T_G′, the temperature for the transition in G′, was a linear decreasing function of the polymer concentration and different from CMT. T_G′ tended to approach CMT with an increasing F108 concentration. Beyond this transition, G′ reached a plateau, and the plateau increased in height and broadened with the polymer concentration. The value of G′ at 70 °C (G′₇₀) could be approximately scaled with concentration c by G′₇₀ ∝ c^7.3. In addition, the definition for a gel to obey G′ > G″ was valid only when c was greater than 22.5 wt %, and this was in agreement with the secondary endothermic peak found with differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2014–2025, 2004     

Solid-state NMR spectroscopy of anionic framework aluminophosphates: a new method to determine the al/p ratio

A series of anionic framework aluminophosphates, with different Al/P ratios, have been investigated by various solid-state NMR techniques, including 27Al, 31P magic angle spinning (MAS), 27Al-->31P cross polarization (CP), 27Al{31P} rotational echo double resonance (REDOR), and 31P{27Al} transfer of population double resonance (TRAPDOR). Different Al coordinations (AlO4b, AlO5b, and AlO6b) and P coordinations (PO4b, PO3bOt, PO2bO2t, and PObO3t), where b represents bridging oxygens and t represents terminal oxygens, can be unambiguously determined based on the solid-state NMR spectroscopy. Furthermore, a new method to determine the Al/P ratio of open-framework aluminophosphates has been established, which is useful for the understanding of unknown aluminophosphate structures.     

Development of an LC/MS/MS method in order to determine arctigenin in rat plasma: its application to a pharmacokinetic study

In this study, a simple and sensitive LC/MS/MS method was developed and validated for the determination of arctigenin in rat plasma. The MS detection was performed using multiple reaction monitoring at the transitions of m/z 373.2 → 137.3 for arctigenin and m/z 187.1 → 131.0 for psoralen (internal standard) with a Turbo IonSpray electrospray in positive mode. The calibration curves fitted a good linear relationship over the concentration range of 0.2–500 ng/mL. It was found that arctigenin is not stable enough at both room temperature and ?80 °C unless mixed with methanol before storage. The validated LC/MS/MS method was successfully applied for the pharmacokinetic study of arctigenin in rats. After intravenous injection of 0.3 mg/kg arctigenin injection to rats, the maximum concentration, half‐life and area under the concentration–time curve were 323 ± 65.2 ng/mL, 0.830 ± 0.166 and 81.0 ± 22.1 h ng/mL, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Conformational sampling with Poisson–Boltzmann forces and a stochastic dynamics/Monte Carlo method: Application to alanine dipeptide

We apply a combination of stochastic dynamics and Monte Carlo methods (MC/SD) to alanine dipeptide, with solvation forces derived from a Poisson–Boltzmann model supplemented with apolar terms. Our purpose is to study the effects of the model parameters, such as the friction constant and the size of the electrostatic finite difference grid, on the rate of conformational sampling and on the accuracy of the resulting free energy map. For dialanine, a converged Ramachandran map is produced in significantly less time than what is required by stochastic dynamics or Monte Carlo alone. MC/SD is also shown to be faster, per timestep, than explicit methods. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1750–1759, 1997     

Development of a headspace–SPME–GC/MS method to determine volatile organic compounds released from textiles

A method for determining the volatile organic compounds (VOCs) in textiles was developed, by the use of high capacity headspace, solid phase micro extraction (SPME) and gas chromatography–mass spectrometry (GC/MS). The detection targets contained total organic compounds (TVOCs) and six specific substances (toluene, vinylcyclohexene, styrene, 4-phenylcyclohexene, vinylchloride and butadiene), according to Oeko-Tex Standard 100. A designed experiment was used to optimize the headspace–SPME–GC/MS operation, and the method was validated in terms of linearity, limit of detection (LOD) and method precision. It was found that at a loading ratio of 10 m²/m³, the LODs for toluene, vinylcyclohexene, styrene and 4-phenylcyclohexene were 0.0002 mg/m², 0.01 mg/m², 0.01 mg/m² and 0.0001 mg/m² respectively, while for vinylchloride and butadiene they were both 0.08 mg/m². SPME exhibited better adsorption performance for toluene, vinylcyclohexene, styrene and 4-phenylcyclohexene, for which the extraction fractions were 10 times of those for vinylchloride and butadiene. The method developed was successfully applied to analyze several commercial textiles, and would be a simple, efficient and promising technique for the analysis of volatile compounds from textiles or other samples (such as polymer materials).     

HPLC-MS/MS method to determine genipin in rat plasma after hydrolysis with sulfatase and its application to a pharmacokinetic study

A sensitive high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the quantification of genipin in rat plasma after hydrolysis with sulfatase. Genipin could not be detected directly as it could be transformed into other forms such as conjugated‐genipin immediately after administration. The conjugated genipin could be hydrolyzed by sulfatase to genipin. The conditions of hydrolysis were investigated. Genipin and the internal standard, peoniflorin (IS), were separated on a reversed‐phase column by gradient elution and detected using an electrospray ion source on a 4000 QTrap triple‐quadrupole mass spectrometer. The quantification was performed using multiple reaction monitoring with selected precursor‐product ion pairs of the transitions m/z 225.0 → 122.7 and m/z 479.1 → 449.1 for genipin and peoniflorin. The assay was linear over the concentration range of 1.368–1368 ng/mL, with correlation coefficients of 0.9989. Intra‐ and inter‐day precisions and accuracy were all within 15%. The lower limit of quantification was 1.368 ng/mL. The recoveries of genipin and peoniflorin were more than 53.3 and 51.2%. The highly sensitive method was successfully applied to estimated pharmacokinetic parameters of genipin following oral and intravenous administration to rats. The absolute bioavailability of genipin was 80.2% in rat, which is the first report. Copyright © 2011 John Wiley & Sons, Ltd.