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5、What is the principle of turbidity or particle size measurement by using conventional light scatteri

　　6.What is the principle of turbidity or particle size measurement by using conventional light scattering? What is the difference between NTU and FTU? How to measure them?(15 points)
　　使用常规光散射测量浊度或粒度的原理是什幺？NTU和FTU有什幺区别？如何衡量它们？
　　①The principle of turbidity or particle size measurement using conventional light scattering is based on the interaction of light with particles suspended in a liquid. When a beam of light passes through a suspension, the particles scatter the light in different directions. The intensity of the scattered light is then measured and used to infer information about the turbidity or particle size of the sample.
　　②There are two commonly used parameters in turbidity measurement:
　　【1】NTU (Nephelometric Turbidity Unit): NTU is a unit of measurement for turbidity and is typically used in environmental and water quality analysis. It quantifies the scattering of light at a 90-degree angle to the incident beam. The NTU scale is based on the scattering of light by a formazin standard suspension, which is a stable and well-defined turbidity standard.
　　【2】FTU (Formazin Turbidity Unit): FTU is another unit of measurement for turbidity that is also based on the scattering of light at a 90-degree angle. However, the FTU scale is based on the scattering of light by a formazin suspension that is prepared using formazin reagent. The FTU scale is used in industries such as pharmaceuticals and chemical manufacturing.
　　③To measure turbidity or particle size using light scattering, a turbidimeter or nephelometer is commonly used. The instrument emits a beam of light into the sample and measures the intensity of the scattered light at a specific angle (usually 90 degrees) using a detector. The detected intensity is then converted into turbidity units (NTU or FTU) using calibration curves established with known standards.
　　The main difference between NTU and FTU lies in the type of suspension used to establish the turbidity scale. NTU uses a formazin standard suspension, while FTU uses a formazin suspension prepared using formazin reagent. The choice of scale depends on the specific application and industry requirements.
　　6.
　　①传统光散射法测量浊度或粒径的原理基于光与悬浮在液体中的颗粒的相互作用。当一束光通过悬浮液时，颗粒将光在不同方向上进行散射。测量散射光的强度，然后用于推断样品的浊度或粒径信息。
　　②浊度测量中常用的两个参数有：
　　NTU（Nephelometric Turbidity Unit，浊度单位）和FTU（Formazin Turbidity Unit，浊度单位）是两种常用的浊度测量参数。
　　NTU是用于环境和水质分析中测量浊度的单位。它量化了光在与入射光线呈90度角散射时的散射强度。NTU的刻度基于一种称为formazin标准悬浊液的散射光。这种悬浊液是一种稳定且定义良好的浊度标准。
　　FTU也是用于测量浊度的单位，但它的刻度基于通过使用formazin试剂制备的formazin悬浊液的散射光。FTU通常在制药和化工制造等行业中使用。
　　③测量NTU或FTU的浊度通常使用浊度计或浊度计（nephelometer）进行。该仪器向样品中发射一束光，并使用探测器测量特定角度（通常为90度）处的散射光强度。通过使用已知标准建立的校准曲线，将检测到的强度转换为相应的浊度单位（NTU或FTU）。
　　NTU和FTU的区别在于用于建立浊度刻度的悬浊液类型。NTU使用formazin标准悬浊液，而FTU使用通过formazin试剂制备的formazin悬浊液。选择哪种测量刻度取决于具体应用和行业要求。