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Objective: This study aimed to optimize the determination conditions of pantothenic acid content in infant milk powder by microbiological method and provide test data for the subsequent revision of the national standard method for pantothenic acid detection. Methods: The issues covering the determination of pantothenic acid by the national standard method were analyzed, and the key steps in the detection process, including bacterial solution preparation, pretreatment, and absorbance determination, were emphatically studied. Results: Lactobacillus plantarum from ATCC and CICC can be used to determine pantothenic acid. The best results were obtained by directly inoculating 80% bacterial solution concentration into the test tube, or adding 5 mL bacterial solution to 400 mL sterilization test medium. The results of direct extraction were higher than that of hydrolysis. The relative deviation of enzymole-plate and UV spectrophotometry was less than 5%. The recovery rate was 96.9%, and the relative standard deviation (RSD) was 4.95%. Conclusion: The optimization of the key steps in the determination of pantothenic acid by microbiological method can simplify the operation process and improve the accuracy of the samples, and the optimized conditions can be used as a reference for the subsequent revision of the National standard method for pantothenic acid determination.

Objective: A high performance liquid chromatography method was established for determination of four artificial sweeteners in syrups, i.e., acesulfame, saccharin sodium, aspartame and advantame. Methods: Acetonitrile was used as mobile phase A, and 0.02 mol/L ammonium dihydrogen phosphate (pH value adjusted to 5.5 by triethylamine) was used as mobile phase B. The gradient elution was conducted, with flow rate at 1.0 mL/min, and the column temperature was at 35 ℃; the detection wavelength was 214 nm, and sample size was 10 μL was loaded on the was Shiseido AQ-C18 column (4.6 mm×250 mm, 5 μm) A total of 45 batches of children's cough syrup samples from 21 manufacturers were determined by the established method. Results: The linear calibration curve of the four kinds of artificial sweeteners were obtained over the range of 2~100 mg/L. The average recoveries of acesulfame, saccharin sodium, aspartame and advantame were 98.65%, 104.09%, 100.96% and 102.30% respectively, with RSDs less than 2% (n=9). The actual sample test results showed that 3 batches of samples were found to be advename, and 2 batches of samples were found to be aspartame and advename. Conclusion: The established method is specific, simple, and reliable, and can be used to monitor the illegal addition of artificial sweeteners in syrups.

Inappropriate irrigation could trigger migration of heavy metals into surrounding environments, causing their accumulation and a serious threat to human central nervous system. Traditional site remediation technologies are criticized because they are time-consuming and featured with high risk of secondary pollution. In the past few years, the microbial-induced carbonate precipitation (MICP) is considered as an alternative to traditional technologies due to its easy maneuverability. The enzyme-induced carbonate precipitate (EICP) has attracted attention because bacterial cultivation is not required prior to catalyzing urea hydrolysis. This study compared the performance of lead (Pb) and copper (Cu) remediation using MICP and EICP respectively. The effect of the degree of urea hydrolysis, mass and species of carbonate precipitation, and chemical and thermodynamic properties of carbonates on the remediation efficiency was investigated. Results indicated that ammonium ion (NH4+) concentration reduced with the increase in lead ion (Pb2+) or copper ion (Cu2+) concentration, and for a given Pb2+ or Cu2+ concentration, it was much higher under MICP than EICP. Further, the remediation efficiency against Cu2+ is approximately zero, which is way below that against Pb2+ (approximately 100%). The Cu2+ toxicity denatured and even inactivated the urease, reducing the degree of urea hydrolysis and the remediation efficiency. Moreover, the reduction in the remediation efficiency against Pb2+ and Cu2+ appeared to be due to the precipitations of cotunnite and atacamite respectively. Their chemical and thermodynamic properties were not as good as calcite, cerussite, phosgenite, and malachite. The findings shed light on the underlying mechanism affecting the remediation efficiency against Pb2+ and Cu2+.

Due to the complicated working conditions of the ship stern-shaft mechanical seals, it is very difficult to evaluate and optimize the temperature on the sealed end faces. In the paper, one FEA model of the small taper convergent stern-shaft mechanical seals was put forward, and the nonlinear end-face liquid film pressure distribution was derived from different end-face gaps based on the simplified Reynolds equation as the end-face input parameters in FEA model. To prove the correction of the FEA results, one experiment was designed and completed. At the same time, combined with a parametrically coupled FEA model and an orthogonal experimental design, one PSO-BP-GA method based on the combination of particle swarm optimization (PSO), BP neural network and genetic algorithm (GA) was proposed to optimize the temperature of the sealed end faces. The results show that aiming at the prediction accuracy of the temperature on the sealed end faces, the PSO-BP algorithm is higher than BP algorithm and GA-BP algorithm, which error interval is shortened about 40% and 29%, respectively. Subsequently, PSO-BP-GA algorithm is obviously better than BP-GA algorithm and GA-BP-GA algorithm, which validates its effectiveness and feasibility. It will help to lay a theoretical foundation for temperature evaluation on the sealed end faces.