SAXS experiments on absolute scale with Kratky systems using water as a secondary standard
SAXS experiments on absolute scale with Kratky systems using water as a secondary standard
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DOI：
10.1107/s0021889899015216
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发表时间：
2000-04-01
影响因子：
6.1
通讯作者：
Glatter, O
中科院分区：
文献类型：
--
作者：
Orthaber, D;Bergmann, A;Glatter, O
对于x射线（SAXS）和中子（SANS）的小角度散射，自技术开始以来，绝对校准的重要性已被认识到。本文报道的工作重点是使用克拉特基狭缝系统进行SAXS测量。以前，只测定分子质量或每个粒子的散射，但今天的绝对校准意味着使用厘米（-1）作为散射曲线的单位。有必要测量所谓的绝对强度；即散射强度与主强度P-0之比。基本上有两种可能的方法来确定绝对强度。第一种方法是直接法，即通过旋转的圆盘或移动的狭缝对主光束进行机械衰减。第二种是间接法，采用二级标准。由于水具有与角度无关的散射特性，所以很适合作为校准标准。其本质优点是水的散射只取决于等温可压缩性的物理性质。在给出该方法的实际性能示例之前，总结了在绝对尺度上进行SAS实验的最重要的理论方程。利用狭缝准直系统，可以测量出具有较高统计精度的水散射曲线。作为第一个例子，给出了蛋白质溶菌酶在绝对尺度上的散射曲线。第二个示例是测定三嵌段共聚物P94 （EO17-PO42-EO17）的聚集数。考虑到至少10%的聚合物样品由双块组成，10%左右的聚集数确定的准确性是相当不错的。在粒子尺度上考虑P94的数据，得到径向散射-长度密度分布。(C) 2000年国际晶体学联合会在英国印刷-保留所有权利。
For small-angle scattering, of X-rays (SAXS) and neutrons (SANS), the importance of absolute calibration has been recognized since the inception of the technique. The work reported here focuses on SAXS measurements using Kratky slit systems. In former days, only molecular weights or scattering per particle were determined, but today absolute calibration implies the use of the unit of cm(-1) for the scattering curve. It is necessary to measure the so-called absolute intensity; which is the ratio of the scattering intensity to the primary intensity P-0. Basically there are two possible ways to determine the absolute intensity. The first one is the direct method, which involves the mechanical attenuation of the primary beam by a rotating disc or a moving slit. The second is the indirect method, using secondary standards. Water is well suited as a calibration standard because of the angle-independent scattering. The essential advantage is that the scattering of water only depends on the physical property of isothermal compressibility. Before presenting an example of the practical performance of this method, the most important theoretical equations for an SAS experiment on the absolute scale are summarized. With the slit collimation system, the scattering curve of water can be measured with high enough statistical accuracy. As a first example, the scattering curve of the protein lysozyme on the absolute scale is presented. The second example is the determination of the aggregation number of a triblock copolymer P94 (EO17-PO42-EO17). Taking into account that at least 10% of the polymer sample consists of diblocks, the accuracy of around 10% for the determined aggregation number is rather good. The data of P94 are also considered on the particle scale in order to obtain the radial scattering-length density distribution. (C) 2000 International Union of Crystallography Printed in Great Britain - all rights reserved.