Multiple melting behaviour of poly(3-hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5V), 8 wt.% (PHB8V) and 12 wt.% (PHB12V)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by isothermal crystallisation kinetics. Thermal properties were investigated after isothermal crystallisation treatment. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting-recrystallisation-remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (C_p,IsoK, non-reversing signal). An increase in degree of crystallinity due to significant melt-recrystallisation was observed for isothermally crystallised polymers. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (C_p,ATD, reversing signal). PHB and PHBV showed different crystal morphologies for similar crystallisation condition. HSPOM results showed that the crystallisation rates reduced and sizes of spherulites were significantly increased as HV content increased.     

Development of a manual method for the determination of mineral oil in foods and paperboard

So far the majority of the measurements of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) were obtained from on-line high performance liquid chromatography–gas chromatography–flame ionization detection (on-line HPLC–GC–FID). Since this technique is not available in many laboratories, an alternative method with more easily available tools has been developed. Preseparation on a small conventional liquid chromatographic column was optimized to achieve robust separation between the MOSH and the MOAH, but also to keep out the wax esters from the MOAH fraction. This was achieved by mixing a small portion of silica gel with silver nitrate into highly activated silica gel and by adding toluene into the eluent for the MOAH. Toluene was also added to the MOSH fraction to facilitate reconcentration and to serve as a keeper preventing loss of volatiles during solvent evaporation. A 50 μl volume was injected on-column into GC–FID to achieve a detection limit for MOSH and MOAH below 1 mg/kg in most foods.     

Isothermal crystallisation kinetics of poly(3-hydroxybutyrate) using step-scan DSC

The crystallisation kinetics, melting behaviour and morphology, of bacterial poly(3-hydoxybutyrate) (PHB) have been investigated by using differential scanning calorimetry (DSC), step-scan DSC (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). DSC imparted isothermal crystallisation thermal history. The subsequent melting behaviour revealed that all PHB materials experienced secondary crystallisation during heating and the extent of secondary crystallisation varied depending on the crystallisation temperature. PHB samples were found to exhibit double melting behaviour due to melting of SDSC scan-induced secondary crystals, while considerable secondary crystallisation or annealing took place under the modulated heating conditions. The overall melting behaviour was rationalised in terms of recrystallisation and/or annealing of crystals. Interestingly, the PHB materials analysed by SDSC showed a broad exotherm before the melting peak in the non-reversing curve and a multiple melting peak reversing curve, verifying that the melting-recrystallisation and remelting process was operative. HSOM studies supported the conclusions from DSC that the radial growth rate of the PHB spherulites was significantly varied upon the crystallisation conditions. One form of crystals was shown by WAXRD from isothermally crystallised PHB.     

Determination of oxidation parameters by DSC for polypropylene stabilized with hydroxytyrosol (3,4-dihydroxy-phenylethanol)

Oxidation thermal parameters on samples of polypropylene (PP) stabilized with hydroxytyrosol were determined. For comparison purposes, α-tocopherol and a synthetic phenolic commercial antioxidant (Irganox 1076), were also analyzed. Oxidation induction time (OIt) and oxidation induction temperature (OIT) were determined by differential scanning calorimetry (DSC). The addition of hydroxytyrosol 0.1 mass% to PP was enough to obtain efficient stabilization during processing. Certain decrease in stabilizing properties of natural antioxidants was observed for compression moulded materials at high temperatures. However, these samples were still efficiently stabilized in comparison to the pure material. Hydroxytyrosol showed good performance as polypropylene antioxidant and it might be considered as promising alternative to the use of phenolic synthetic compounds.     

Thermal investigation of the crystallisation nucleant formed between 2,4,6 trinitrotoluene, (TNT) and 2,2′,4,4′,6,6′ hexanitrostilbene (HNS)

Hexanitrostilbene (HNS), is added to trinitrotoluene (TNT), in order to improve the grain structure of cast munitions. The formation and composition of the nucleant material has been investigated by thermal methods using mixtures of HNS and TNT, with composition in the range 0.5%, the normal casting level, to 50% w/w HNS to TNT. These were cycled between ambient and upper temperatures in the range 160 to 235°C. Endotherms in the DSC traces, due to nucleant decomposition, have been observed in situ without the need for separation and purification. DSC enthalpy measurements, before and after thermal decomposition, were used to determine the composition of separated nucleant. Nucleant regeneration after decomposition, was investigated by thermal methods. Nucleant could not be recrystallised from solvents. Results have been interpreted on the basis of the formation of a, solid solution of TNT in HNS, rather than a complex of formula TNT₂HNS.     

Calculation of smoothing factors for the comparison of DSC results

Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T _gs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most useful for the analysis of the derivative of the heat capacity, dC _p/dt or dC _p/dT, plots which best highlight overlapping T _gs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dC _p/dt vs. dC _p/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided for the analysis of bitumen, a complex mixture of natural origin.     

Heat Transfer in a Disc-Type DSC Apparatus IV. Applicability of the coupled cells model to periodic temperature modulation

The application of non-linear heating programs to a heat-flux DSC apparatus has attracted much attention. On the basis of thermodynamics, the change in enthalpy of a sample during a temperature change ΔT is due, on the one hand to the true heat capacity of the sample ΔT C_pξ and on the other, to the enthalpy of some transformation occurring in the sample Δ_rH Δξ. These contributions can be separated on the basis of the kinetics of the transformation. The coupled cells model of a disc type, heat flux DSC apparatus has been tested, using true heat capacities and a sine modulation of the temperature of the furnace around a constant temperature. In the range from 2 to 60 mHz, the amplitude and phase shift of the calorimetric signal were measured at several frequencies. Theoretical equations, based on the model, and using the thermal Ohm's law explains the results with a reasonable accuracy. A non-linear DSC experiment affords two ways of determination of the heat capacity of a sample making possible a distinction between the enthalpic effect and heat capacity. This revised version was published online in July 2006 with corrections to the Cover Date.     

New ta system for simultaneous determination of thermo-optical properties and DSC of different organic compounds

A new instrument for DSC in combination with thermomicroscopy in transmitted light is described, where a DSC device is in corporated within a commercially available hot stage.     

Melting and thermal history of poly(hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5HV), 8 wt.% (PHB8HV) and 12 wt.% (PHB12HV)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC) and hot-stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by SDSC. Thermal properties were investigated after different crystallisation treatments, fast, medium and slow cooling. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting–recrystallisation–remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (non-reversing signal). An increase in degree of crystallinity due to significant melt–recrystallisation was observed for slow-cooled copolymers. PHB5HV showed different crystal morphologies for various crystallisation conditions. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (reversing signal) HSPOM results showed that the crystallisation rates and sizes of spherulites were significantly reduced as crystallisation rate increased.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

Differential scanning calorimetry (DSC) and Raman spectroscopy study of poly(dimethylsiloxane)

Poly(dimethylsiloxane) was studied by laser Raman spectroscopy and differential scanning calorimetry. The Si O Si skeletal mode at 489 cm⁻¹ and the C Si C deformation bands at 188 cm⁻¹ and 158 cm⁻¹ were studied as functions of temperature from ambient to −130°C, and effects of temperature interpreted in accordance with results from thermal analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2805–2810, 1998     

Development and validation of a hydrophilic interaction liquid chromatographic method for determination of aromatic amines in environmental water

A simple, precise, and accurate hydrophilic interaction liquid chromatographic (HILIC) method has been developed for the determination of five aromatic amines in environmental water samples. Chromatography was carried out on a bare silica column, using a mixture of acetonitrile and a buffer of NaH₂PO₄–H₃PO₄ (pH 1.5, containing 10 mM NaH₂PO₄) (85:15, v/v) as a mobile phase at a flow rate of 1 mL min⁻¹. Aromatic amines were detected by UV absorbance at 254 nm. The linear range of amines was good (r² > 0.998) and limit of detection (LOD) within 0.02–0.2 mg L⁻¹ (S/N = 3). The retention mechanism for the analytes under the optimum conditions was determined to be a combination of adsorption, partition and ionic interactions. The proposed method was applied to the environmental water samples. Aromatic amines were isolated from aqueous samples using solid-phase extraction (SPE) with Oasis HLB cartridges. Recoveries of greater than 75% with precision (RSD) less than 12% were obtained at amine concentrations of 5–50 μg L⁻¹ from 100 mL river water and influents from a wastewater treatment plant (WWTP). The present HILIC technique proved to be a viable method for the analysis of aromatic amines in the environmental water samples.     

乙二醇和丙三醇水溶液冻结特性的研究

利用差示扫描量热仪（Pyris-Diamond DSC），研究了乙二醇（甘醇）和丙三醇（甘油）水溶液的过冷行为、水合性质和它们的玻璃化转变温度及反玻璃化温度，分析了它们与分子中羟基个数的关系.进行了12组共24种不同浓度(质量分数）的溶液的差示扫描量热实验.过冷度的实验结果表明，在浓度相等的情况下，两种低温保护剂水溶液冻结的过冷度有相同的变化规律.水合实验的结果表明，浓度相同时，二者结合水的能力大体相当.玻璃化转变的实验表明，二者玻璃化转变温度与反玻璃化温度存在明显差异.     

Development and validation of a rapid multiresidue method for pesticide determination using gas chromatography-mass spectrometry: a realistic case in vineyard soils

A rapid and simultaneous method for residue identification and quantification for seven pesticides in agricultural soils has been developed to study a realistic situation in vineyard. The target compounds are two insecticides, two herbicides and three fungicides, from different chemical families. The procedure is based on a pressurized liquid extraction (PLE) with acetone, before a multiresidue GC-MS analysis. The recovery of PLE is between 53.8 ± 2.4 and 99.9 ± 4.4% according to pesticide. A limit of detection (LOD) between 1.4 and 4.6 μg kg⁻¹ of dry soil was obtained for five analytes. This procedure for testing soil contamination is sensitive and easy to perform.     

Development of a method for the rapid determination of pentachlorophenol in leather using supercritical fluid extraction with in situ derivatization

Pentachlorophenol (PCP) was extracted from leather with supercritical carbon dioxide and in situ acetylated under static SFE conditions in the presence of triethylamine. During the dynamic extraction step, the derivatives were removed from the matrix and collected with either a pure liquid (light petroleum) or a liquid-solid (light petroleum-solid sorbent (C18, alumina, Florisil or Celite)) trap. To prevent restrictor plugging, a suitable restrictor was designed. The clean-up of the extracts was optimized in this study. Different internal standards were tested and it was shown that not all of them were usable. The SFE results were compared with those obtained by Soxhlet extraction with methanol. With SFE instead of conventional Soxhlet extraction, the overall time required for determination of PCP in leather can be reduced from about 2 days to approx. 3 hours.     

Establishment and application of a new method for the determination of kinetic parameters by plug-plug kinetic capillary electrophoresis (ppKCE)

A novel plug-plug kinetic capillary electrophoresis method was established, which can be used to si-multaneously determine the kinetic parameters kon and koff in interaction systems. The method is comparatively simple and some restrictions in conventional ppKCE methods can be effectively avoided. The requirements for resolution and detection sensitivity in this method are much lower than those of conventional ppKCE. The successful determination of the kinetic parameters and the binding constant Kb between citalopram and BSA showed availability of this method. The results were confirmed by us-ing the time ratio method. The application field of kinetic capillary electrophoresis can be expanded with this new method.     

Development of a liquid chromatography–tandem mass spectrometry method for the determination of Grayanotoxins in rat blood and its application to toxicokinetic study

A sensitive and specific high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed for the determination of Grayanotoxin I (GTX I) and Grayanotoxin III (GTX III) in rat whole blood. Grayanotoxins (GTXs) and clindamycin as internal standard (IS) were extracted from rat blood via solid‐phase extraction using PEP solid‐phase extraction cartridges. Chromatographic separation of the analytes was achieved on a Kinetex C₁₈ (100 × 2.1 mm, 2.6 µm) reversed‐phase column using a gradient elution with the mobile phase of 1% acetic acid in water and methanol at a flow rate of 0.2 mL/min. Electrospray ionization mass spectrometry was operated in the positive ion mode with multiple reaction monitoring. The calibration curves obtained were linear over the concentration range of 1–100 ng/mL with a lower limit of quantification of 1 ng/mL for GTXs. The relative standard deviation of intra‐day and inter‐day precision was below 6.8% and accuracy ranged from 94.8 to 106.6%. The analytes were stable in the stability studies. The validated method was successfully applied to the quantification and toxicokinetic study of GTXs in rats for the first time after oral administration of 11.52 mg/kg mad honey and 0.35 mg/kg GTX III, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a sensitive thermal desorption method for the determination of trihalomethanes in humid ambient and alveolar air

A sensitive and reliable method has been developed for the determination of trihalomethanes (THMs) in air samples through adsorption in sorbent tubes and thermal desorption (TD) of the compounds, followed by gas chromatography (GC)–mass spectrometry (MS) analysis. Three commercial sorbent materials were compared in terms of adsorption efficiency and breakthrough volume, finding Chromosorb 102 to be the most appropriate adsorbent for air sampling. The method allows us to reach detection limits of 0.03 ng (0.01 μg m⁻³ for 3 l of air), linear ranges from 0.1 to 2000 ng and specific uncertainties of ca. 5.0 ± 0.2 ng for all THMs. Several salts were tested to reduce water retention (from the humid air of an indoor swimming pool) at the sampling stage, Na₂SO₄ being the one that provides optimum efficiency. The method was validated by a new recovery study in which several tubes with and without adsorbent were spiked with THMs and analyzed by TD-GC/MS, recoveries ranging from 92% to 97% for all the compounds. Finally, the performance of the method was evaluated through the analysis of ambient air samples from an indoor swimming pool and alveolar air samples from swimmers to assess their THM uptake. THMs were found to be stable in the sorbent tubes for at least 1 month when stored at 4 °C.     

Development of gas chromatographic method for determination of cholesterol oxides in meat products

Summary A method of extraction, purification and gas chromatographic analysis of five cholesterol oxidation products (COPs) (7β-hydroxycholesterol, 5α, 6α-epoxycholesterol, 25-hydroxycholesterol, 7-ketocholesterol and cholestane-3β, 5α, 6β-triol) has been developed. The method is aimed at the determination of COPs in meat and meat products, in particular dry sausages, where large differences in the content of cholesterol and its oxidation derivatives may occur. Linearity of response of trimethylsilyl ethers was defined. The minimum concentration tested was 2.5 μg g⁻¹ in the injected solution. The main feature of the present work is the addition of a purification step of unsaponifiables by SPE on silica cartridges. Extraction recoveries of COP standard mixtures, performed with or without the SPE step, are evaluated. The introduction of the clean-up step results in high purity samples without further losses in the entire process.