Validation of a Method of Determination of Apparent Diffusivity Versus Composition in Solids

Abstract

A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values.     

Rapid Method of Determination of Sorption Isotherms and Water Apparent Diffusivity

In the context of a research on the quality of pasta made from soft wheat, reaction kinetics had to be measured at definite temperatures and water contents. It was chosen to realize such experiments in a pilot dryer. To be able to fix temperature and water content of product for a definite period of time, it was first necessary to determine sorption curves of pasta and a drying model including the values of apparent diffusivity of water at elevated temperatures.

This paper presents a method to meet these objectives. It consists in realizing a sequence of plateaux of air relative humidities of decreasing values, at constant temperature, in the dryer. Air-product equilibrium at the end of each plateau would have been too long to attain, therefore equilibrium product water content was calcultated using an exponential model. Apparent water diffusivity was determined by adjustement of a diffusive model, taking in account that the air humidity change from one plateau to the next one was a linear ramp and not a step-wise change.

The average relative repeatability of equilibrium water Content is 0.1% water/dry basis. There is more dispersion on apparent diffusivity.     

Rapid Method of Determination of Sorption Isotherms and Water Apparent Diffusivity

ABSTRACT

In the context of a research on the quality of pasta made from soft wheat, reaction kinetics had to be measured at definite temperatures and water contents. It was chosen to realize such experiments in a pilot dryer. To be able to fix temperature and water content of product for a definite period of time, it was first necessary to determine sorption curves of pasta and a drying model including the values of apparent diffusivity of water at elevated temperatures.

This paper presents a method to meet these objectives. It consists in realizing a sequence of plateaux of air relative humidities of decreasing values, at constant temperature, in the dryer. Air-product equilibrium at the end of each plateau would have been too long to attain, therefore equilibrium product water content was calcultated using an exponential model. Apparent water diffusivity was determined by adjustement of a diffusive model, taking in account that the air humidity change from one plateau to the next one was a linear ramp and not a step-wise change.

The average relative repeatability of equilibrium water Content is 0.1% water/dry basis. There is more dispersion on apparent diffusivity.     

水中可溶性总固体的快速测定法

介绍了用“总溶固快速测定仪”测定水中的可溶性总固体量的分析方法。方法快速、简便、准确。     

A Method of Determination of Concentration Dependent Effective Moisture Diffusivity

ABSTRACT

A method based on Fourier series solution to Fick's diffusion equation has been proposed to evaluate effective diffusivity (D) as a function of moisture content in agricultural materials undergoing shrinkage during drying process. The shrinkage kinetics of the particulate was used to correlate its instantaneous size (spherical equivalent diameter) as a function of material moisture content A computer program was used to evaluate D based on shrinkage kinetics and experimental drying data and relate it to moisture content. The method was used to obtain moisture diffusivity data for thin layer drying of grape and corn.     

加巴喷汀原料中残留溶剂测定方法验证

加巴喷汀是美国Warner-Lanbert公司首先开发的抗癫痫药,是γ-氨基丁酸（GABA）的衍生物,于1993年首次在英国上市。其生产中的残留溶媒包括二氯甲烷、甲醇、乙醇、乙酸乙酯和异丙醇应进行严格控制。使用气相色谱法,采用顶空进样,参照ICH中Q3C对残留溶剂的要求,对加巴喷汀中的残留溶媒分析方法进行验证。验证结果表明,本方法精密度高,线性良好,能够满足药品质量控制的需要。     

橡胶中扩散和渗透的测定

介绍了在橡胶中各种物质传递过程的基本原理,以及在各种条件下测定扩散和渗透性能的试验方法。     

管内振荡流中轴向有效扩散系数的确定

将管内振荡流中物质扩散系统近似地作为一维非稳态系统，分析了用脉冲注射法确定振荡流中轴向物质扩散系数时，扩散物初始分布的两种形态?正态分布和矩形分布对有效扩散系数测定精度的影响. 分析结果表明，如果浓度测定点与注入点间的距离大于扩散物初始分布宽度的10倍，计算误差将小于1%. 实验所用圆管长2.5 m，内径6 mm，扩散系统的Schmidt数3590，流体振动幅度30~200 mm，Womersley数2.38~10.64. 实验结果与理论计算结果具有良好的一致性.     

一元弱酸表观离解常数pKa的测定

本文依据Ｈｅｌｍｋａｍｐ和Ｊｏｈｎｓｏｎ所提出的实验方法，通过选择易溶于水的弱酸，采用电位滴定法准确测定滴定ＨＡ至一半时溶液的氢离子浓度，得到表观离解常烤ｐＫａ，并通过数学方法计算出经对ｐＫａ，该方法不仅能用于ｐＫａ〈１１．３弱酸，也可以用于ｐＫａ≥１１．３的极弱酸离解常数的测定，具有简单，快速，准确的特点。     

生物材料有效水分扩散系数的模型与测定

对振动流化床干燥过程中含有白蛋白的多孔混合颗粒的有效水分扩散系数进行了实验观察,建立了基于费克第二定律的数值模型。此模型可通过颗粒水分含量、体积孔隙率和温度预测有效水分扩散系数。结果表明,颗粒水分含量和孔隙结构特性对水分扩散系数有显著影响。在热力干燥过程中,特别是在干燥气流速度较高的情况下,一些生物材料的外部传质阻力很小以致水分传递只受物料内部的水分扩散控制,此时不应该忽略颗粒水分含量和孔隙结构对有效水分扩散系数的影响。     

乳油型农药中多种禁止使用农药成分的同时检测

[目的]建立气相色谱法对乳油型农药制剂中多种禁止使用农药成分分析的方法.[方法]样品采用丙酮稀释,经大口径毛细管分离,气相色谱FID检测,双柱定性,内标法定量检测.[结果]6种乳油型农药中添加回收率在91.4％～105.6％之间,相对标准偏差为0.53％～3.75％.[结论]该方法可以高效、准确的对多种禁止使用农药成分同时检测.     

Transient Hot-Strip Method for Simultaneous Determination of Thermal Conductivity and Thermal Diffusivity of Refractory Materials

The transient hot-strip method has been used for determining thermal conductivity and thermal diffusivity of a refractory brick. The technique is based on recording the transient temperature increase of a 25-μm-thick, 8-mm-wide, and 70-mm-long iron strip clamped between two sample halves and heated with a constant direct current. The method is accurate to within 5% in the thermal conductivity and to within 10% in the thermal diffusivity in the temperature range 20° to 700°C.     

Validation of a UV Spectrophotometric Method for Determination of Proteolytic Activity of Enzymatic Detergents

Enzymatic detergents are widely used in health services. These products should be controlled to ensure their activity. In this paper, a UV spectrophotometric method for the determination of proteolytic activity in enzymatic detergents was validated. An artificial substrate (azocasein) was used to quantify the enzyme activity at 340 nm. The results showed that the method was satisfactory in respect to its specificity, linearity, precision, accuracy and robustness. This method fulfills both ICH’s and Brazilian criteria, demonstrating its suitability for routine analysis as well as its potential application for regulatory purposes.     

气相色谱法测定分子筛扩散系数

气相色谱法测定分子筛扩散系数是根据色谱VanDeemeter过程，将被测分子筛装人色谱柱中，以测得的色谱柱理论板高度（H）和相应的线速度（μ）作图，求得在高线速度部分的斜率（c），计算分子筛的扩散系数（D_p）。本文测定了8种5A型和4种13X型分子筛对氧和氛的扩散系数，证明用不同制各方法得到的产品其扩散系数有很大的差异，故其应用的工艺条件亦不应雷同。     

气相色谱法测定分子筛扩散系数

气相色谱法测定分子筛扩散系数是根据色谱VanDeemeter过程，将被测分子筛装人色谱柱中，以测得的色谱往理论板高度（H）和相应的线速度（u）作图，求得在高线速度部分的斜率（C），计算分子筛的扩散系数（Dp）。本文测定了8种5A型和4种13X型分子筛对氧和氛的扩散系数，证明用不同制各方法得到的产品其扩散系数有很大的差异，故其应用的工艺条件亦不应雷同。     

Determination of Moisture Diffusivity of Lentil Seed During Drying

The mechanism of drying and the diffusion of water in green (fresh), red and whole lentils (4.20-4.32 mm diameter and 2.20-2.30 mm thickness) were successfully interpreted and modelled by using Fick's law. The moisture content of fresh green lentil was 55 % and moisture content of the red and whole lentils was increased to 39-40 % and drying temperature (45-60°C) was varied, but the velocity and the humidity of the drying air was kept constant.

The effective diffusuvity was estimated from drying rate curves and expressed by an Arrhenius relation.     

含氧汽油中烃组成的分析比对

文章对含氧汽油组成进行分析,通过三种分析方法的比较中,发现芳烃的分析结果基本一致。烯烃的分析结果 SH/T 0741最高,ASTM D6839次之,GB/T 11132最低。含氧汽油的牌号和含氧量对三种分析方法的分析结果没有明显的影响。     

香菇多糖单糖组成及含量的测定方法研究

采用高压液相色谱、气相色谱、气相色谱一质谱联用等方法分析了香菇多糖中单糖组成及其含量。结果表明,用高压液相色谱测定由于葡萄糖和甘露糖的流出时间仅相差1min,在混合标样图中这两个单糖峰叠加在一起,没有分开。但是,据图能证明香菇多糖里含有木糖、阿拉伯糖、葡萄糖和半乳糖,并且其相关比例为：木糖：阿拉伯糖：葡萄糖：半乳糖=2：13：73：12;用气相色谱测定和气质联用测定都含有阿拉伯糖、木糖、半乳糖、葡萄糖和甘露糖,其比例分别为：阿拉伯糖：木糖：甘露糖：葡萄糖：半乳糖=13：2：29：39：17;阿拉伯糖：木糖：甘露糖：葡萄糖：半乳糖=12：4：24：45：15。     

螺旋霉素中蛋白含量的测定方法(Bradford法)及验证

建立螺旋霉素中蛋白含量的测定方法。用0.9%NaCl溶液为溶剂,采用Bradford法,于波长595nm处比色,螺旋霉素中蛋白含量的最小检测限:5μg/mL。     

水玻璃组成快速测定方法改进

水玻璃的用途十分广泛,几乎遍及到国民经济的各个行业。不同模数的硅酸钠有着不同的用处,而模数作为水玻璃的重要参数,目前其测量的通常方法是分别测出Na2O和SiO2的质量分数然后算出其模数。文章介绍了以溴百里酚蓝指示剂部分取代甲基红指示剂,实现快速测定水玻璃模数的一种新方法,该方法省去了氢氧化钠标准溶液的返滴过程,更加简便、快捷,并详细阐述了该方法的基本原理和实验步骤,计算方法以及相关数据。