[Determination of fatty acids compositions and contents in Chinese mitten crabs by gas chromatography].

Determination of fatty acid compositions and contents in Chinese mitten crabs is of great significance to evaluate its nutritional value and quality. However, in the face of a wide range of fatty acid extraction and methyl esterification reagents, the measurement results are uneven, and it is difficult to accurately quantify the rich fatty acids in Chinese mitten crabs. In this paper, four kinds of oil extraction reagents and two kinds of methylating reagents, were investigated. Chloroform-methanol (1∶1, v/v) was used as the extraction solvent, and methanol containing 2% sulfuric acid was used as the derivatization reagent. A method for the determination of fatty acids in the muscle of Chinese mitten crabs by gas chromatography was established. The experiment was carried out under the condition of programmed temperature rise, 37 kinds of fatty acids were separated on a DM-2560 capillary column (100 m×0.25 mm×0.20 µm), detected by hydrogen flame ionization detector (FID) and quantified by external standard method. The linear relationships of the 37 fatty acids were good in the range of 0.5-100.0 µg/mL. The correlation coefficients (R2) were 0.9981-0.9999. The limits of detection (LODs) and limits of quantification (LOQs) were 0.01-0.02 mg/100 g and 0.04-0.06 mg/100 g, respectively. The methodology was validated by palmitic acid and stearic acid. The recoveries were 76.0%-97.5%, and the relative standard deviations (RSD, n=5) were 3.31%-7.90% at the spiked levels of 1, 2 and 10 mg/100 g. The method was applied to the determination of fatty acid compositions and contents in the muscle of Chinese mitten crabs. A total of 31 kinds of fatty acids were detected. The length of carbon chain ranged from 12 to 24, and the total content of fatty acids reached 281.03 mg/100 g. Oleic acid, docosahexaenoic acid and eicosapentaenoic acid were the main fatty acids in the muscle of Chinese mitten crabs. Thus, this method provided accurate and reliable theoretical data for the determination of fatty acids in Chinese mitten crabs. This method has the advantages of simple operation, small amount of reagent and sample, reliable qualitative, accurate quantitative, detection of more fatty acid types. It is suitable for the rapid detection of fatty acid compositions and contents in muscle tissue of Chinese mitten crabs.

Significantly enhanced base activation of peroxymonosulfate by polyphosphates: Kinetics and mechanism.

Base activation of peroxydisulfate (PDS) is a common process aiming for water treatment, but requires high doses of PDS and strongly basic solutions. Peroxymonosulfate (PMS), another peroxygen of sulfurate derived from PDS, may also be activated by a less basic solution. However, enhancing the base-PMS reactivity is still challenging. Here it is reported that pyrophosphate (PA) and tripolyphosphate (PB) can efficiently enhance PMS activation under weakly alkaline conditions (pH 9.5) via the formation of superoxide anion radical (O2•-) and singlet oxygen (1O2). The rate constant of Acid Orange 7 (AO7) degradation in PA/PMS system (kPA/PMS) was nearly 4.4-15.9 fold higher than that in PMS/base system (kPMS/base) without any polyphosphates. Increases in PA (or PB) concentration, PMS dose and pH favored the rapid dye degradation. Gas chromatograph-mass spectrometer (GC-MS) data confirmed AO7 and 2,4,6-trichlorophenol (2,4,6-TCP) were decomposed to a series of organic intermediates. The radical quenching and probe oxidation experiments indicate the degradation of organic compounds in the PA/PMS and PB/PMS processes was not reliant on sulfate radical (SO4•-) and hydroxyl radical (OH) species but on O2- and 1O2 reactive species. Comparison experiments show that the polyphosphate/PMS process was much more favorable than PDS/base process. The present work provides a novel way to activate PMS for contaminant removal using industrial polyphosphate wastewaters.

Distinct effects of oxalate versus malonate on the iron redox chemistry: Implications for the photo-Fenton reaction.

The dicarboxylic acids oxalate (Oxal) and malonate (Mal) are frequently detected as the final low-molecular-weight organic acids during oxidative degradation of aromatic compounds. Here a distinct effect of Oxal versus Mal on iron-based photocatalytic technologies was reported by testing the degradation efficiency of the dye rhodamine B. The rates of dye degradation in irradiated Fe(III) solutions depended on Fe(III/II) speciation, photoreactivities of Fe complexes and reactivities of Fe(II) complexes with H2O2. Photolysis of the Fe(III)-oxalato complex was favorable due to the formation of O2-, HO2 and OH for oxidizing the dye; however, an excess of H2O2 could quench the excited state of ferrioxalate, decreasing the degradation efficiency. In contrast, activities of UV/Fe(III) in the presence of Mal were significantly diminished because Fe(III)-Mal complexes, with much lower quantum yield of Fe(II) from photoreduction, dominated Fe(III) speciation. The results provide data for an understanding of the mechanism of iron redox (photo)chemistry mediated by diacids, which will aid in selecting appropriate Fe ligands, screening photo-Fenton conditions and designing UV/Fe(III) treatability.