The thermal degradation mechanisms of random copolymers of methacrylonitrile (MAN) and styrene (St) have been investigated
by pyrolysis gas chromatography in the temperature range of 358 to 920‡C using a Curie point pyrolyzer (JHP-2) and comparing
results with the results from TG/DTA-FTIR apparatus (SII-6200, JASCO-320). The amount of St monomer from decomposition of
the copolymer is higher than that from P(St) alone; whilst that of MAN monomer from copolymer is lower than that from P(MAN).
This phenomenon reflects the boundary effect in the pyrolysis of copolymer. The thermal degradation mechanisms of copolymers
are discussed in terms of the competition between the depolymerization and the back biting reaction on the basis of bond dissociation
energies of C-C and C-H bonds in the copolymer chain.
The analysis of cantharidin, a potent antitumor yet highly toxic chemical, is reported in this article. In regions including the United States, Europe, and China, cantharidin is either a banned ingredient or being highly regulated in cosmetic products. In this article, a gas chromatographic-tandem mass spectrometric (GC-MS/MS) method has been established for the determination of cantharidin in cosmetic products. Cosmetic samples were divided into two groups according to whether they contained aqueous ethanol or not. Samples containing aqueous ethanol in the formulation were dried under an air flow prior to extraction by methanol. The multiple reaction monitoring (MRM) mode with the parent ion at m/z 128 and the product ions at m/z 55 and 85 was employed. The linear range covered from 0.1 to 30.00 μg mL−1 (R = 0.9996) for cantharidin. The detection limit (LOD) was 0.3 μg kg−1. The intraday and between-day relative standard deviations (RSDs) were <8.7%. The mean recoveries were within the range 101.5–110.5%. The developed GC-MS/MS method was applied on 12 commercial cosmetic product samples, and is shown to be simple and sensitive and can be used for the qualitative and quantitative analysis of cantharidin in cosmetic products.
The depth profile of phosphorus concentration in phosphorus-doped silicon was shown to be measureable with an accuracy of 1–3% by the use of liquid scintillation counting after neutron irradiation. Both the amount of Si and P are determined by neutron activation analysis followed by liquid scintillation counting for 1–5 hours after the end of irradiation and 5–10 days after irradiation, respectively. Concentrations as low as 10 ppm and thicknesses of 20 nm can be determined.
A method combining prior collection of gaseous products with subsequent neutron activation analysis has been developed for simultaneous determination of traces of arsenic, mercury, antimony and selenium in biological materials. The generation of hydrides of arsenic, antimony and selenium and cold vapor of mercury in the vapor generaion and collection system was investigated by the use of radiotracers of the respective elements. The result indicates that selenium and mercury can be completely evaporated from the digested sample solution in 5M HCl with the addition of 5% sodium tetrahydroborate solution, while additional reduction proces by potassium iodide and ascorbic acid is needed for complete evaporation of arsenic and antimony. The gaseous products were collected in a quartz tube for neutron irradiation. The detection limits of these elements were fount to be in the range of 10–7 to 10–8 g under the present experimental conditions. The reliability was checked with NBS standard reference materials.
Method for the isolation and radioactive cobalt /including58Co and60Co/ from a large volume of seawater and concentration in a small volume of chloroform as tris/pyrrolidine dithiocarbamato/cobalt/III/, Co/PDC/3, is described. The seawater was extracted first with Bi/PDC/3 in chloroform for removing parts of foreign metals like Hg, Ag, etc., and then added with ammonium pyrrolidindithiocarbamate, APDC, to complex with Co and possibly other ions and extracted into the organic phase. The final separation of Co from foreign ions in the organic phase was achieved by stripping with a Bi/III/ solution. The overall recovery of radiocobalt activity was found to be about 96%. The established method can be applicable for rapid and reliable determination of radiocobalt in seawater and other aqueous systems for environmental contamination.
A rapid adsorption method has been developed to determine the60Co content in sea water samples. The60Co activity is concentrated by filtering the water sample through an adsorption column of steel work. A 60-liter sample can be processed in 1 h with 95% adsorption efficiency.
The conductivities of binary mixtures of glycerine and water were measured at 20C by means of a transient method. The equation
describing the correlation between concentration and thermal conductivity was determined. The equation can be used for determining
concentrations in mixtures. The results show that (1) the error in the determination of the molar concentration of water in
mixtures is less than 1%, (2) the time of measurement is 1 s, (3) this method can be used for on-line analysis in production
The distributions of 210Po and 210Pb in the intermediate layer (400–2000 m) of the northwestern North Pacific were determined to elucidate the export flux of
particulate matter. 210Po generally showed depletion relative to 210Pb in the intermediate layer, suggesting that 210Po was scavenged by particles. Because the removal rate constants of 210Po in the western region were higher than those in the eastern region and this trend coincided with that of the particle fluxes
in the surface layer, the export production in the surface layer was assumed to influence the particle flux in the intermediate
layer of the northwestern North Pacific.
Authors:Y. Yang, X. Chen, Z. He, M. Röder and L. Xia
Genotypes with various
alleles perform different levels of pre-harvest sprouting (PHS) tolerance. In this study, 217 white-grained wheat cultivars, including 75 landraces, 39 historical cultivars, and 103 modern cultivars from five major regions of China, were examined to characterize the diversity of the Viviparous-1B (
) locus associated with PHS tolerance. Four
alleles were identified, three (
) of which were previously reported in Chinese wheat cultivars. A new allele,
, was identified in the PHS tolerant landrace Hongheshangtou. Sequence analysis showed that
had an insertion of a 4-bp fragment, two SNPs, and a deletion of an 83-bp fragment compared with the nucleotide sequence of
(AJ400713), all located in the third intron.
shared 97.80% similarity with the nucleotide sequence of AJ400713. The frequencies of
were 36.0%, 5.3%, and 57.3% in landraces; 23.1%, 7.7%, and 69.2% in historical cultivars; and 52.4%, 0%, and 47.6% in current cultivars, respectively.
In this study, the peach kernel proteins were extracted and treated with alkaline proteinase to generate peach kernel protein hydrolysate (PKH), which showed angiotensin converting enzyme (ACE) inhibition activity. The hydrolysate was separated into four fractions and their anti-ACE activities were investigated. Our results showed that all PKHs had anti-ACE activity, and the lowest molecular weight fraction PKH4 had the highest ACE inhibitory activity. Lineweaver–Burk plots illustrated that the inhibition types of PKH3 and PKH4 were non-competitive. The Ki of PKH4 was lower than Ki of PKH3; suggesting PKH4 had high affinity to ACE. Amino acid composition analysis showed that the best anti-ACE peptide PKH4 possessed high levels of hydrophobic amino acids, branched-chain amino acids, and aromatic amino acids. In summary, our findings demonstrated that high anti-ACE activity is negatively related to the size of the PKHs and possibly the composition of amino acids, and the PKH4 was the best ACE inhibitor. Further, peach kernel peptides can be developed as a functional food for patients with hypertension.