关于食品中铅、镉的检测方法,目前已知的主要包括原子吸收光谱法、分光光度比色法、电感耦合等离子体质谱法等。由于石墨炉原子吸收光谱法具有仪器检测精密度和灵敏度高、样品检测限低、实际用样量少、仪器成本相对较低的优点,故采用这一方法对铅、镉进行检测。而像紫菜这种海洋产品又经过脱水加工的食品微量元素和重金属元素偏高,检测过程相互干扰特征谱线的吸收,造成检测结果偏差较大。Agilent AA 280Z 原子吸收光谱仪具有塞曼扣背景功能可校正结构化背景和光谱干扰,可覆盖全波长范围。同时,具备在线添加基体改性剂功能,可以用化学的方法改变样品的基体组成,以改变被分析元素的挥发性,降低干扰,或将被分析元素以特定形态隔离出来,从而分离出背景信号和被分析元素的原子吸收信号。对复杂基体,基体改性剂可在原子化阶段增强原子吸收信号和降低背景信号。可以稳定而准确地测定紫菜这种复杂基质食品的元素含量。
在部分混合日粮喂养的奶牛的1或2个放牧周期加8小时的苜蓿:对采食量、行为、消化、产奶量和成分的影响Including 8 hours of access to alfalfa in 1 or 2 grazing sessions in dairy cows fed a partial mixed ration Effects on intake, behavior, digestion, and milk production and composition奶牛TMR全混合日粮和苜蓿中蛋白质、非蛋白氮、可溶性氮使用格哈特VAPODEST 500 Carousel全自动凯氏定氮仪基于凯氏定氮法直接测定,中性洗涤不溶性氮、酸性洗涤不溶氮使用格哈特FT12纤维仪基于洗涤法进行样品前处理后再使用格哈特VAPODEST 500 Carousel全自动凯氏定氮仪基于凯氏定氮法测定。脂肪使用格哈特Soxtherm防爆级全自动索氏提取仪以乙醚做为溶剂在180摄氏度条件下提取2个小时测定,中性洗涤纤维和酸性洗涤纤维使用热稳定α淀粉酶及硫酸钠处理样品后按标准方法使用格哈特FT12纤维仪测定。
Geostrophic adjustment of an isolated axisymmetric lens was examined to better understand thedependence of radial displacements and the adjusted velocity on Burger number and the geometryof initial conditions. The behavior of the adjustment was examined using laboratory experimentsand numerical simulations, which were in turn compared to published analytical solutions. Threedefining length scales of the initial conditions were used to distinguish between various asymptoticbehaviors for large and small Burger number: the Rossby radius of deformation, the horizontallength scale of the initial density defect, and the horizontal length scale of the initial pressuregradient. Numerical simulations for the fully nonlinear time dependent adjustment agreed bothqualitatively and quantitatively with analogous analytical solutions. For large Burger number,similar agreement was found in laboratory experiments. Results show that a broad range of finalstates can result from different initial geometries, depending on the values of the relevant lengthscales, and the Burger number computed from initial conditions. For Burger number much largeror smaller than unity, differences between different initial geometries can readily exceed an order ofmagnitude for both displacement and velocity.