高效液相色谱法快速测定水中的苯并(a)芘

本文建立了一种水中苯并(a)芘的快速测定方法。以环己烷萃取,过滤,浓缩,定容,用反相HPLC测定,方法的检出限为0.0025μg/L,RSD(n=8)为2.9%,加标回收率为98.9%—106.9%。     

基于可见分光光度法的食用油过氧化值检测

为了构建食用油过氧化值快速检测分析方法,以食用油为试验材料,利用可见分光光度计测定碘与淀粉的显色变化,建立食用油过氧化值的检测模型,探讨测定波长、饱和碘化钾添加量、反应时间、淀粉指示剂添加量、溶剂混合比例和油脂种类等因素对测定结果的影响。通过模型建立和验证、盲样验证及精密度分析,结果表明:检测条件对测定结果影响均不显著;当取样质量为(0.100±0.010)g,入射光波长为535nm时,食用油过氧化值模型为:y=28.856x+0.1331(y为过氧化值,mmol/kg,x为溶液吸光度),R2=0.9985。模型预测值与国标法测定值高度线性相关,盲样验证相对误差均10%,检出限为0.79mmol/kg,符合国家标准的相关要求,基于可见分光光度法的食用油过氧化值检测方法是可行的。     

Selective enumeration of viable Enterobacteriaceae and Pseudomonas spp. in milk within 7 h by multicolor fluorescence in situ hybridization following microcolony formation

Rapid and simultaneous enumeration of viable Enterobacteriaceae and viable Pseudomonas spp. in milk was achieved by using multicolor fluorescence in situ hybridization (FISH) with oligonucleotide probes based on 16S ribosomal RNA (rRNA) sequences in combination with a microcolony growth method (multicolor microcolony-FISH; MMC-FISH). The procedure of MMC-FISH method is rather simple; that is milk clearing, filtration of cells, incubation, hybridization and enumeration. Enumeration of targeted bacteria in logarithmic growth phase, stationary phase, or in a starved state in milk by MMC-FISH required 5-7 h, while it took 1-3 days to test for Escherichia coli and Pseudomonas putida by the conventional culture method. The numbers of E. coli and P. putida in each phase or in a starved state in milk determined by MMC-FISH were almost the same or greater than the number of colony forming units determined by the plate counting method. The MMC-FISH allows rapid examination of contamination in milk by viable Enterobacteriaceae and Pseudomonas spp. with growth potential.     

钢铁及合金中稀土总量快速测定方法研究

本文建立钢铁及其合金中稀土总量快速测定方法。试样用硫酸和硝酸的混合酸溶解,用草酸做掩蔽剂,偶氮氯膦mA与稀土生成蓝色络合物,于分光光度计波长670nm处测量其吸光度。样品的加标回收率为96.0%~101.8%,相对标准偏差(RSD)为3.0%。方法操作简便、快速、准确。     

基于图像处理的农药残留速测卡快速检测

目的通过图像处理的方法来快速检测农药残留。方法利用图像提取、中值滤波和分量定值等图像处理技术,建立了基于速测卡检测结果图像处理的半定量检测。结果农残样品与胆碱酯酶在37℃下经过4min预反应,与检测结果的红色分量均值与农药浓度呈显著的正相关关系,对西维因和乐果的检出限为0.1mg/kg。结论与目测法相比,图像处理的检出限更低,也更为客观准确,为农药残留的快速检测提供了一种新的技术手段。     

The electrochemical performance of melt-spun C14-Laves type TiZr-based alloy

The main objective of the present work is to study the effect of rapid solidification on the electrochemical performance of Zr-based Laves type alloy with a nominal composition Ti₁₂Zr_21.5V₁₀Cr_7.5Mn_8.1Co₈Ni_32.2Al_0.4Sn_0.3. The samples were prepared from the as-cast arc melted buttons by melt spinning at different copper wheel rotation speeds of 5, 16.5, 33, and 100 Hz, which are equivalent to linear speeds of 6.3, 21, 41, and 62.8 m s⁻¹ respectively using a cooling wheel with a diameter of 20 cm. The phase composition and morphology of the ribbons were analyzed by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The microstructural changes of the ribbons induced by the variations in the wheel rotation speed were found to be closely related to the electrochemical performances. High discharge capacities exceeding 400 mAh∙g⁻¹ were achieved for the melt spun samples during the measurements at low current densities. Furthermore, melt spun casting performed at the highest wheel rotation speed of 100 Hz resulted in the best rate performance of the alloy. As this alloy has the smallest crystallite size, this resulted in the shortest H atoms diffusion distances, and thus increased the efficient H diffusion rate and improved the electrochemical performance.     

汽车覆盖件快速模具原模加工机床的设计

设计了一套用于制造汽车覆盖件模具原模的数控机床,该机床的主机可以实现三坐标平动和两个坐标转动,工作台采用液压传动装置,可实现工作台的抬起、回转180°和回落,完成对车身的测量、原模的加工和模具的喷涂等工序.该机床具有加工测量精度高、柔性好、结构简单等优点,满足汽车覆盖件模具原模的加工要求.     

Suitability of Rapid Detection Methods for Salmonella in Poultry Slaughterhouses

In the perspective of an announced prohibition to bring Salmonella-contaminated fresh poultry meat on the retail market as of December 2010, requirements are postulated for rapid methods for detection of Salmonella in poultry meat. These rapid methods should deliver reliable results in time to make it possible to steer the finished products in poultry slaughterhouses into the direction of the fresh poultry market or into the direction of industrial treatment. The most important requirements are the detection limit (1 cfu/25 g), the time of analysis (within hours up to a maximum of 24 h), the sensitivity and specificity, and the validation of the rapid detection method. To determine a requirement for the number of samples to be analyzed per unit of time of the detection methods, a sampling plan for pooling of samples is suggested. Information of commercially available detection methods from literature and data provided by the suppliers was compared to the postulated requirements. The results showed that none of the commercially available detection methods meet all the suggested requirements. For all available methods, the time of analysis is too long to steer the production process in time. This implicates that faster methods should be developed before the announced prohibition can be sensibly introduced. Also, information about sensitivity and specificity, which is essential for the reliability of the rapid test method, should be examined in a more uniform way.     

Effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane

Experimental and numerical studies have been performed on the thermal and chemical effects of buffer gas composition on low temperature ignition of iso-octane and n-heptane. Experiments were conducted using a recently developed rapid compression machine in the temperature range of 600–850 K. Three buffer gases were studied including nitrogen (N₂), argon (Ar), and a mixture of Ar and carbon dioxide (CO₂) at a mole ratio of 65.1%/34.9%. Iso-octane was studied at 20 bar, ? = 1, and a dilution level of buffer gas to O₂ of 3.76:1 (mole ratio). n-Heptane was studied at 9 bar, ? = 1, and a dilution level of buffer gas to O₂ of 5.63:1 (mole ratio). For experiments where two-stage ignition was observed, the buffer gas composition had no impact on the first-stage ignition time but, as expected, it caused differences in the total heat release, pressure and temperature rise after the first-stage ignition. As a consequence, significant differences were observed for the total ignition delay time as a function of the buffer gas composition, with up to 40% and 42.5% faster total ignition time for iso-octane and n-heptane, respectively, by using Ar instead of N₂. The chemical effects of the buffer gas composition were studied experimentally by comparing the results of the N₂ and Ar/CO₂ (65.1%/34.9%) mixtures, recognizing that while the Ar/CO₂ mixture has the same heat capacity as N₂, its predicted combined third-body collision efficiency is about 76% higher than N₂. The experimental results showed negligible chemical effects on the first-stage and total ignition delay times. Numerical simulations were carried out over a wider range of temperatures for pure N₂, Ar, and CO₂ as buffer gases. Results showed that thermal effects are very pronounced and dominated at the negative temperature coefficient and two-stage ignition conditions, which is consistent with the experimental results and previous studies in the literature. However, the simulation results also showed at temperatures higher than 850 K, the chemical effects of CO₂ became more important than the thermal effects.     

Removing low ppb level perchlorate, RDX, and HMX from groundwater with cetyltrimethylammonium chloride (CTAC) pre-loaded activated carbon

Perchlorate contaminates vast amounts of groundwater throughout the United States which could potentially be used as potable water. Activated carbon pre-loaded with cetyltrimethylammonium chloride has been shown in this research to be an effective adsorbent for removing perchlorate from three low conductivity (50-66 microS/cm) groundwaters containing perchlorate (ClO(4)(-)) concentrations of 0.85, 1.0, and 5.6 parts per billion (ppb), respectively. In rapid small-scale column tests (RSSCTs), the virgin granular activated carbon (GAC) (used as a control) treated between 20,000 and 40,000 bed volumes (BV) of water. In contrast, the activated carbon that was pre-loaded with CTAC processed 170,000-270,000 BV before perchlorate was detected above 0.25 ppb in the effluent. Though this pre-loading significantly increased the capacity for perchlorate, it also diminished the GAC's capacity to remove organics. The groundwater containing 1 ppb ClO(4)(-) also contained the nitro-organics HMX (0.6 ppb) and RDX (5.5-6.6 ppb). RDX was detected in the effluent from the CTAC-pre-loaded bed after only 8000 BV had been processed whereas 308,000 BV could be processed through the virgin bed before RDX was detected. Likewise, HMX breakthrough was observed after 116,000 BV in the CTAC-pre-loaded bed while the virgin RSSCT exhibited no breakthrough of HMX during a test that was operated for 309,000 BV. However, by combining a CTAC-pre-loaded bed followed by a virgin GAC bed in series, both perchlorate and RDX could be removed for the same length of time.