Observed Degradation Rate Research Articles

Stability of azacitidine in sterile water for injection.

The product monograph for azacitidine states that once reconstituted, the drug may be held for only 30 min at room temperature or 8 h at 4°C. Standard doses result in wastage of a portion of each vial, and the cost of this wastage is significant, adding about $156 000 to annual drug expenditures at the authors' institution. To evaluate the stability of azacitidine after reconstitution. Vials of azacitidine were reconstituted with sterile water for injection. At the time of reconstitution, the temperature of the diluent was 4°C for samples to be stored at 4°C or -20°C and room temperature for samples to be stored at 23°C. Solutions of azacitidine (10 or 25 mg/mL) were stored in polypropylene syringes and glass vials at room temperature (23°C), 4°C, or -20°C. The concentration of azacitidine was determined by a validated, stability-indicating liquid chromatographic method in serial samples over 9.6 h at room temperature, over 4 days at 4°C, and over 23 days at -20°C. The recommended expiry date was determined on the basis of time to reach 90% of the initial concentration according to the fastest observed degradation rates (i.e., lower limit of 95% confidence interval). Azacitidine degradation was very sensitive to temperature but not storage container (glass vial or polypropylene syringe). Reconstitution with cold sterile water reduced degradation. At 23°C, 15% of the initial concentration was lost after 9.6 h; at 4°C, 32% was lost after 4 days; and at -20°C, less than 5% was lost after 23 days. More than 90% of the initial azacitidine concentration will be retained, with 97.5% confidence, if, during the life of the product, storage at 23°C does not exceed 2 h, storage at 4°C does not exceed 8 h, and storage at -20°C does not exceed 4 days. These expiry dates could substantially reduce wastage and cost where the time between doses does not exceed 4 days.

Photooxidation of benzene-structured compounds: Influence of substituent type on degradation kinetic and sum water parameters

The combined influence of substituent type and UV/H2O2 process parameters on the degradation of four aromatic water pollutants was investigated using modified 33 full factorial design and response surface methodology. Degradation kinetics was described by the quadratic polynomial model. According to the applied ANOVA, besides pH and [H2O2], model terms related with the pollutant structure are found to be significant. Different optimal operating conditions and values of observed degradation rate constants were determined for each of the pollutants indicating that the type of substituent influences the overall process effectiveness over structurally defined degradation pathway. Biodegradability (BOD5/COD) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals t1/2(P), t3/4(P), t1/4(OC) and t1/2(OC) corresponding to the real time required to reduce the concentration of parent pollutant and organic content for 1/2, 3/4, 1/4 and 1/2 of initial amount. The observed differences are correlated to the structural differences of studied aromatics.

Remediation of 4-nonylphenol in aqueous solution by using free radicals generated by the oxidative reactions.

IntroductionThis study relates to use of zerovalent iron to generate hydroxyl free radicals and undergo subsequent oxidation to destroy 4-nonylphenol (NP) by mild process in aqueous solution and activation of oxygen gas (O2) at room temperature. This technology is based on a novel oxidative mechanism mediated by zerovalent iron rather than commonly used reduction mechanism.Materials and methodsA laboratory scale device consisting of a 250 ml pyrex serum vials fixed to a Vortex agitator was used. Different amounts of zerovalent iron powder (ZVI; 1, 10, and 30 g/l) at pH 4 and room temperature with bubbling of oxygen gas were investigated.Results and conclusionExperiments showed an observed degradation rate k (obs) directly proportional to the amount of iron. 4-Nonylphenol degradation reactions demonstrated first-order kinetics with a half-life of about 10.5 ± 0.5 and 3.5 ± 0.2 min when experiments were conducted at [ZVI] = 1 and 30 g/l respectively. Three analytical techniques were employed to monitor 4-nonylphenol degradation and mineralization: (1) spectrofluorimetry; (2) high-performance liquid chromatography; (3) total organic carbon meter (TOC meter). Results showed a complete disappearance of 4-nonylphenol after 20 min of contact with ZVI. The intermediate by-products of the reaction were not identified but the disappearance of NP was monitored by the three above-mentioned techniques.

The tissue response to photopolymerized PEG-p(HPMAm-lactate)-based hydrogels

Hydrogels are three-dimensional networks of crosslinked hydrophilic polymers widely used for protein delivery and tissue engineering. To be eligible for in vivo applications, the hydrogels should not evoke an adverse tissue response. In this study the angiogenic and inflammatory responses in vivo after implantation of photopolymerized thermosensitive poly(hydroxypropyl methacrylamide lactate)-poly(ethyl copolymer hydrogels are investigated. Hydrogels consisting of polymers with different crosslink densities were subcutaneously implanted in Balb/c mice and histological evaluation of the tissue response was performed. The implants showed an acute and localized inflammatory reaction upon implantation, mainly characterized by a strong infiltration of granulocytes. The acute inflammatory reaction was followed by a milder chronic inflammation which was characterized by infiltration of macrophages and persistent but decreasing levels of granulocytes. The number of macrophages and blood vessels was associated with the biodegradation and resorption of the biomaterial and increased in time as the degradation of the materials progressed. The observed degradation rates in vivo correlated well with previously observed in vitro degradation rates, which suggests that hydrolysis is the main mechanism governing the degradation.

A novel Electro-Fenton-Like system using PW 11O 39Fe(III)(H 2O) 4− as an electrocatalyst for wastewater treatment

A novel Electro-Fenton-Like (EFL) system was developed using the Keggin-type iron-substituted heteropolytungstate anion PW 11O 39Fe(III)(H 2O) 4− to substitute for Fe 3+ in the conventional Electro-Fenton (EF) system for treatment of water polluted with organic compounds. The EFL system overcomes the drawback of low pH in conventional EF approaches and can be directly applied to neutral water treatment without any pH adjustment. Experimental results for dimethylphthalate (DMP) revealed complete degradation in <80 min in pH 6.86 solution containing 0.1 mM DMP at a potential of −0.5 V and O 2 flow rate of 60 mL min −1. Total organic carbon removal of ∼56% was achieved at 120 min. Comparison with conventional EF oxidation revealed better efficiency of the present system for DMP degradation, suggesting its potential in treatment of water and wastewater with a relaxed pH requirement. The cumulative H 2O 2 concentration generated in situ at the electrode was monitored and the observed degradation rate constants k obs were determined for different initial DMP concentrations. The ligand exchange reaction of PW 11O 39Fe(III)(H 2O) 4− with H 2O 2 and the electron transfer resulting in hydroxyl radicals were examined using HPLC and electrochemical impedance spectroscopy. An electrocatalytic model involving inner-sphere electron transfer and a reaction mechanism for PW 11O 39Fe(III)(H 2O) 4− electrocatalytic reduction of H 2O 2 are proposed.

In Situ Chemical Oxidation of RDX‐Contaminated Groundwater with Permanganate at the Nebraska Ordnance Plant

Groundwater beneath the former Nebraska Ordnance Plant (NOP) is contaminated with the explosive hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX). The current pump and treat facility is preventing offsite migration but does not offer a short‐term solution. Our objective was to quantify the effectiveness of permanganate to degrade RDX in situ. This was accomplished by performing laboratory treatability experiments, aquifer characterization, and a pilot‐scale in situ chemical oxidation (ISCO) demonstration. Treatability experiments confirmed that permanganate could mineralize RDX in the presence of NOP aquifer solids. The pilot‐scale ISCO demonstration was performed using an extraction‐injection well configuration to create a curtain of permanganate between two injection wells. RDX destruction was then quantified as the RDX‐permanganate plume migrated downgradient through a monitoring well field. Electrical resistivity imaging (ERI) was used to identify the subsurface distribution of permanganate after injection. Results showed that RDX concentrations temporally decreased in wells closest to the injection wells by 70% to 80%. Observed degradation rates (0.12 and 0.087/d) were lower than those observed under laboratory batch conditions at 11.5 °C (0.20/d) and resulted from lower than projected permanganate concentrations. Both ERI and spatial electrical conductivity measurements verified that permanganate distribution was not uniform throughout the 6.1‐m (20 feet) well screens and that groundwater sampling captured both treated and nontreated groundwater during pumping. Although heterogeneous flow paths precluded a uniform permanganate distribution, pilot‐scale results provided proof‐of‐concept that permanganate can degrade RDX in situ and support permanganate as a possible remedial treatment for RDX‐contaminated groundwater.

Sonolytic Decomposition of Aqueous Bioxalate in the Presence of Ozone

Ultrasonic irradiation in the presence of ozone is demonstrated to be effective for the rapid oxidation of oxalic acid, bioxalate, and oxalate (H(2)C(2)O(4)/HC(2)O(4)(-)/C(2)O(4)(2-)) in aqueous solution to CO(2) and H(2)O. The degradation rate of bioxalate exposed to "sonozone" (i.e., simultaneous ultrasonication and ozonolysis) was found to be 16-times faster than predicted by the linear addition of ozonolysis and ultrasonic irradiation rates. The hydroxyl radical (*OH) is the only oxy-radical produced that can oxidize oxalate on a relevant time-scale. Thus, plausible *OH production mechanisms are evaluated to explain the observed kinetic synergism of ultrasonication and ozonolysis toward bioxalate decomposition. *OH production via decomposition of O(3) in the cavitating bubble vapor and via the reaction of O(3) and H(2)O(2) are considered, but kinetic estimations and experimental evidence indicate neither to be a sufficient source of *OH. A free-radical chain mechanism is proposed in which the HC(2)O(4)(-) + *OH reaction functions as a primary propagation step, while the termination occurs through the O(3) + CO(2)(*-) reaction via an O-atom transfer mechanism. Kinetic simulations confirm that ozone reacts efficiently with the superoxide (O(2)(*-)) ion that is produced by the reaction of O(2) and CO(2)(*-) to form *OH radical, and that the reaction of O(3) + CO(2)(*-) must be chain terminating. Oxalate is also readily oxidized by "peroxone" treatment (i.e., H(2)O(2) and O(3)). However, the addition of H(2)O(2) during the course of the sonolytic ozonation of oxalic acid does not appear to increase the observed degradation rate and decreases rates at millimolar levels.

Analysis of the stability and degradation products of triptolide.

Triptolide is the major active ingredient of the Chinese herbal remedy Tripterygium wilfordii Hook F. (TwHF). As triptolide content is used to estimate the potency of preparations of TwHF, assessment of its stability is warranted. The accelerated stability of triptolide was investigated in 5% ethanol solution in a light-protected environment at pH 6.9, within a temperature range of 60-90 degrees C. The observed degradation rate followed first-order kinetics. The degradation rate constant (K25 degrees C) obtained by trending line analysis of Arrhenius plots of triptolide was 1.4125 x 10(-4) h(-1). The times to degrade 10% (t1/10) and 50% (t1/2) at 25 degrees C were 31 and 204 days, respectively. Stability tests of triptolide in different solvents and different pH conditions (pH4-10) in a light-protected environment at room temperature demonstrated that basic medium and a hydrophilic solvent were the major factors that accelerated the degradation of triptolide. Triptolide exhibited the fastest degradation rate at pH 10 and the slowest rate at pH 6. In a solvent comparison, triptolide was found to be very stable in chloroform. The stability of triptolide in organic polar solvents tested at both 100% and 90% concentration was greater in ethanol than in methanol than in dimethylsulphoxide. Stability was also greater in a mixture of solvent:pH6 buffer (9:1) than in 100% solvent alone. An exception was ethyl acetate, which is less polar than the other solvents tested, but permitted more rapid degradation of triptolide. Two of the degradation products of triptolide were isolated and identified by HPLC and mass spectroscopy as triptriolide and triptonide. This suggested that the decomposition of triptolide occurred at the C12 and C13 epoxy group and the C14 hydroxyl. The opening of the C12 and C13 epoxy is an irreversible reaction, but the reaction occurring on the C14 hydroxyl is reversible. These results show that the major degradation pathway of triptolide involves decomposition of the C12 and C13 epoxy group. Since this reaction is very slow at 4 degrees C at pH 6, stability is enhanced under these conditions.

Fuel cell micro-CHP techno-economics: Part 2 – Model application to consider the economic and environmental impact of stack degradation

This article presents a literature review regarding the mechanisms of fuel cell degradation, accompanied by the reported range of observed degradation rates in experimental, demonstration and early commercial systems. It then synthesises and exploits this information to investigate the influence of degradation on the economic and environmental credentials of fuel cell micro-combined heat and power (micro-CHP) for the UK residential sector. The investigation applies a techno-economic model developed in the companion article designed to demarcate the key characteristics of commercially successful systems. Two distinct modes of degradation are examined; one proportional to power density in the stack, and the other proportional to thermal-cycling rate of the stack. It is found that limiting the power-density related degradation rate is very important from economic and environmental viewpoints, but thermal-cycling related degradation is less important when thermal energy storage is available because cycling can be avoided. Furthermore it is noted that techno-economic studies that ignore degradation can overestimate the marginal value of a micro-CHP system with respect to the conventional alternative by up to 45% and the CO 2 emissions reduction potential by up to 57%, for performance degradation rates of 2% per MW eh output. This conclusion is noteworthy because most techno-economic analyses of fuel cells ignore degradation, potentially providing misleading results. Finally it is concluded that existing commercial degradation targets, such as the SECA targets, are appropriate for achieving marketable systems.

Metal dusting: relationship between alloy composition and degradation rate

The authors have identified a compositional relationship between several commercially available wrought alloys, focussing only on the iron, nickel, chromium and aluminium content. The degradation rate due to metal dusting varies with the surface condition of each alloy: a ground surface condition corresponds to smaller mass losses than a pickled surface condition. The authors have derived a relationship between the maximum observed degradation rate due to metal dusting and the chromium plus aluminium content of each alloy. This relationship has been verified by comparing data from several exposures using different gas compositions and pressures. The results indicate that for the gas used in this exposure, the degradation rate strongly decreases up to a chromium plus aluminium content of 33 wt-%. Above this value, the mass loss rate is negligible. The current relationship is also found valid for aluminide diffusion coatings.

Aspects of Degradation Kinetics of Azithromycin in Aqueous Solution

The chemical stability of azithromycin (AZM) in aqueous solution has been investigated utilizing a stability-indicating LC assay with ultraviolet detection. The degradation kinetics were studied as functions of pH (4–7.2), buffer composition (phosphate, acetate, and citrate), buffer concentration, ionic strength, drug concentration and temperature. The observed rate obtained by measuring the remaining intact AZM was shown to follow pseudo-first-order kinetics. The maximum stability of AZM occured at an approximate pH 6.3 in 0.05 M potassium phosphate. The observed degradation rate increased with ionic strength, buffer concentration and obeyed the Arrhenius equation over the temperature range investigated (70–100 °C). The apparent energy of activation (E a) for AZM in solution was found to be 96.8 kJ mol−1 and by application of the Arrhenius equation the stability at 25 °C (k 25) and 40 °C (k 40) had been predicted. Moreover, the degradation rate of AZM was independent on its initial concentration. Trace metal ions are unlikely to be involved in the degradation of AZM in aqueous solution. The major degradation product of AZM in aqueous solution was isolated and identified by LC–MS–MS and 1H and 13C NMR spectra.

Hydrolysis of Flavanone Glycosides and Degradation of the Corresponding Aglycones from Dried ImmatureCitrusFruit by Human Fecal Florain vitro

The hydrolysis of the flavanone glycosides contained in dried immature Citrus fruit, originating from Citrus aurantium L (Family Rutaceae), and degradation of their aglycones in human fecal flora have been analyzed. High-performance liquid chromatography was used to determine the flavanone glycosides and their corresponding aglycones in human fecal flora. The separation of compounds was performed with an ODS column by isocratic and stepwise gradient elution with 0.5 % (v/v) acetic acid-acetonitrile. As a result, the hydrolysis rate of hesperidin and narirutin (flavanone rutinoside) was faster than that of naringin and neohesperidin (flavanone neohesperioside). When the half-life time of each flavanone glycoside was carefully calculated (under the mixed conditions with the human fecal flora), hydrolysis of the flavanone rutinoside turned out to be approximately two times faster than of flavanone neohesperioside. The observed degradation rates of both aglycones was found not to be different. Therefore, it seems that the hydrolysis rate of flavanone glycosides in dried immature citrus fruit with human fecal flora is closely related to the steric hindrance of the sugar. This finding might be effectively used for further pharmacokinetics research on the flavanone glycosides of dried immature Citrus fruit.

Reductive destruction and decontamination of aqueous solutions of chlorinated antimicrobial agent using bimetallic systems

Palladium, ruthenium and silver were investigated as catalysts for the dechlorination of dichlorophen (DCP, 2,2′-methylenebis(4-chlorophenol)), an antimicrobial and anthelmintic agent largely used as algicide, fungicide and bactericide. Experiments were undertaken under oxic and anoxic conditions for experimental durations up to 180 min (3 h). The anoxic conditions were achieved by purging the solutions with nitrogen gas. Reactions were performed in a 12 ± 0.5 mg L −1 DCP solution ( V = 20 mL) using 0.8 g of Fe 0 (40 g L −1). Along with micrometric Fe 0, five Fe 0-plated systems were investigated: Pd (1%), Ru (0.01%), Ru (0.1%), Ru (1%) and Ag (1%). Metal plating was controlled by atomic absorption spectroscopy. DCP degradation was monitored using: (i) two HPLC devices, (ii) ion chromatography, (iii) UV and fluorescence spectrophotometry. Results indicated: (i) total dechlorination with Fe/Pd, (ii) partial dechlorination (40%) with Fe/Ru, and no reaction with Fe/Ag. DCP is vanished completely after 90 min of contact with Fe/Pd following a first order kinetic. The observed degradation rate k obs was about (3.98 ± 0.10) × 10 −2 min −1, the calculated half-life t 1/2 about 17.4 ± 0.9 min and a t 50 about 10.1 ± 0.5 min. A DCP degradation pathway map was also proposed.

Catalytic degradation of chlorothalonil in water using bimetallic iron-based systems

Modified zero valent iron (MZVI) was used to study the transformation of a chlorothalonil (CLT) solution and the variation of the observed degradation rate of the reduction reactions. This was carried out when transition metals e.g. Pd, Cu and Co plated on the surface of micrometric iron particles (<150 μm) were used as reducing catalytic agents for pesticide removal. Reactions were undertaken under both oxic and anoxic conditions in the presence and the absence of a phosphate buffer solution (PBS). Results of batch studies in nitrogen sparged solutions revealed that incomplete slow dechlorination merely occurred with zero valent iron (ZVI), however, complete rapid dechlorination reactions took place with MZVI especially Fe/Pd. Dechlorination was depicted by studying UV absorbance and MS spectra of CLT and all corresponding by-products. Typical blue shifts (Δ λ = 4–6 nm/chlorine atom) were observed at the same time as chlorine cluster isotopes disappeared. After the plating process, metal loading was controlled by analyzing the remaining metal in the solution by atomic absorption spectroscopy. Experiments showed that CLT degradation mechanism is faster in nitrogen sparged solutions in the absence of PBS. Time needed for complete removal of 2.08 ± 0.19 μM CLT solution was about 2 h when experiments were conducted with ZVI ( t 1/2 = 15.0 min) and about 10 min when the reaction was carried out under the same conditions with Fe/Pd 1% ( t 1/2 = 1.0 min). Degradation rates for all bimetallic systems were determined showing that Pd is the more exciting catalytic transition metal followed by Cu and Co. Furthermore, MZVI method showed obvious advantage to traditional CLT treatment methods.

Degradation of Tertiary Alkylamines during Chlorination/Chloramination: Implications for Formation of Aldehydes, Nitriles, Halonitroalkanes, and Nitrosamines

Drinking water utilities are exploring the use of waters impacted by wastewater effluents and agricultural runoff to meet the demands of growing populations. Due to the elevated organic nitrogen concentrations in these waters, the pathways responsible for transformation of organic nitrogen into toxic nitrogenous disinfection byproducts during chlorine and chloramine disinfection are of current concern. Tertiary alkylamines are important functional groups in human waste products and various consumer products that can be released to drinking water supplies via wastewater effluents. We investigated degradation pathways for model tertiary alkylamines during chlorination and chloramination. Our results indicate that tertiary alkylamines degrade nearly instantaneously during chlorination to form aldehydes and secondary alkylamines quantitatively, with no significant regioselectivity. Similar results were observed during chloramination, but the observed degradation rates were much slower, with lower yields of aldehydes. As these major products were fairly stable, these results explain why tertiary amines are significant precursors of secondary nitrosamines during chloramination. Trichloronitromethane formed at very low yields during chlorination, but was not observed during chloramination; monochloronitromethane and dichloronitromethane were never detected. Despite the significant yields of aldehydes during chloramination, our results indicated low nitrile yields bythe reaction between chloramines and aldehydes.

Rapid removal of flutriafol in water by zero-valent iron powder

A study of the effect of zero-valent iron (ZVI) powder is carried out for the first time on the degradation of flutriafol (( RS)-2,4′-difluoro-α-(1 H-1,2,4-triazol-1-ylmethyl)-benzhydryl alcohol, C 16H 13F 2N 3O), a bifluorinated soil and water persistent triazole pesticide using a laboratory scale device consisting of a 20 ml pyrex serum vials fixed to a Vortex agitator. Different amounts of ZVI powder (10–50 g l −1) at pH 6.6 and room temperature were investigated. Experiments showed an observed degradation rate k obs directly proportional to the surface of contact of flutriafol with ZVI. Flutriafol degradation reactions demonstrated first order kinetic with a half-live of about 10.8 ± 0.5 min and 3.6 ± 0.2 min when experiments were conducted at [ZVI] = 10 g l −1 into oxygenated and anoxic solutions, respectively. Three analytical techniques were employed to monitor flutriafol degradation and to understand solution and by-products behaviors: (1) A UV–Vis spectrophotometer; (2) a high performance liquid chromatography (HPLC) coupled with a photo diode array (PDA) and fluorescence detectors; (3) a similar HPLC coupled with a PDA and a mass spectrometer detectors equipped with an atmospheric pressure photoionization source. Results showed a complete disappearance of flutriafol after 20 min of contact with ZVI, the loss of fluorescence properties of the final by-products, the defluorination of the triazole pesticide via hydroxylation reaction and finally the hydrogenation of the triazole ring.

Heterogeneous photocatalytic degradation of monochlorobenzene in water

This investigation evaluated the photocatalytic degradation of monochlorobenzene (MCB) in an aqueous TiO 2 suspension. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO 2 dosage. However, the solution pH had insignificant effect on the degradation efficiency. The heterogeneous photocatalytic degradation of MCB followed the Langmuir–Hinshelwood kinetics. The adsorption coefficient of MCB ( K) and the observed degradation rate constant ( k) were calculated as 13.4 mM −1 and 0.0054 mM min −1, respectively. In addition, a 0.255 dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e −–h + pair recombination. Both mineralization and dechlorination occurred during the photocatalytic degradation of MCB. Under the operating condition of initial MCB concentration of 0.1 mM, light intensity of 5.68 μEinstein s −1, TiO 2 dosage of 1.0 g L −1, and solution pH of 7, about 93.7% of MCB was mineralized after 240 min of irradiation. Nevertheless, 64.3% of the stoichiometric amount of Cl − ions was released into the bulk solution. The simulation results derived from the X-ray photoelectron spectroscopy (XPS) analysis was suggested that the interaction between Cl − ions and TiO 2 surface tended to lower the released amount of Cl − ions.

Effectiveness of Zerovalent Iron and Nickel Catalysts for Degrading Chlorinated Solvents and n‐Nitrosodimethylamine in Natural Groundwater

Laboratory batch experiments were performed to evaluate the effectiveness of nickel catalysts, nanoscale zerovalent iron (nZVI) doped with palladium, and microscale ZVI for treatment of tetrachloroethene, trichloroethene, and n-nitrosodimethylamine (NDMA) in soil-groundwater slurries. Results indicated that the presence of NDMA inhibited degradation of chlorinated solvents. Although both the nickel catalyst and nZVI were able to degrade NDMA in deionized water, neither of these metals was effective at degrading NDMA in the soil-groundwater system evaluated in this study. The effectiveness of the nickel catalyst and nZVI, with respect to treatment of the chlorinated solvents, also appeared to be highly dependent on the groundwater geochemical conditions. Overall results of this study suggest that the degradation mechanisms involving nickel catalysts and nZVI in natural soil/groundwater systems are not well-understood, and addition of metal catalysts to ZVI may not necessarily enhance observed degradation rates in natural systems.

Kinetic Study of the Acidic Hydrolysis of Oleuropein, the Major Bioactive Metabolite of Olive Oil

Abstract The hydrolytic stability of Oleuropein (OE), the major bioactive molecule of olive oil was investigated under acidic conditions. For this purpose a reversed‐phase liquid chromatography (HPLC) method was developed and validated using a C8 column and a diode array detection system. Statistical evaluation of the proposed HPLC method showed good linearity, precision and accuracy so that it can be used for analytical purposes. The relative standard deviation (RSD) of the method was less than 3.76% and the LOQ was established to be 0.5 µg/mL. OE was hydrolyzed at three different HCl concentrations (1, 0.1, and 0.01 N) under different temperatures. The results obtained were treated as logarithms of concentration vs. time because it was realized that the hydrolysis followed first order kinetics. The observed degradation rate constants kobs were determined as well as the corresponding half‐lifes t1/2. Arrhenius plots were also constructed from the hydrolysis data. The results indicate that OE is stable un...

Discrete bond-weighted random scission of linear polymers

A discrete population balance model, where the probabilities of particular bonds breaking within a given mer are assigned individual weights, is studied. The model represents an extension of previous population balance models and provides a framework for the analysis of a number of different scission mechanisms including pure random scission, end-chain scission, simultaneous random and end-chain scission and break-at-a-point scission. The main thrust of the work is aimed at interpreting observed degradation rates of PMMA. The model suggests that both random and end-chain scission must occur in order to reproduce the observed dependence of degradation rate with initial degree of polymerisation at low temperatures. However, at high temperatures it was found that molecule size dependence must also be incorporated in order to explain the observed behaviour.