مجله دانش آزمایشگاهی ایران
سال سوم شماره 2 (پیاپی 10، تابستان 1394)

DLS is a fast and simple tool to identify molecular weight. This instrument can be used to determine the molecular weight from the hydrodynamic radius for various types of specimens. It is possible to perform static light scattering as well with the software by measuring at several manually prepared concentrations. There is also a single-angle Debye Calculator that allows mathematical correction for angular effects. Typically the molecular weight measurements are performed using glass or quartz cuvettes due to their superior optical quality over plastic. and toluene are often selected as a standard sample and polystyrene will not hold up to toluene for a longer time.

Scanning Capacitance Microscope (SCM) is kinde of scanning probe microscope in which a thin electrode probe scan across the sample surface. In this way, the sample surface is characterized by data obtained from changing electrostatic capacitance between surface and probe. Scanning Capacitance Microscopy is non-destructive method and used to characterize and describe the semiconductors. One of the commercial applications of SCM is imaging the dopant in semiconductors. This microscope can also be used to to measure charge carrier density in nano-meter scale. The ability of SCM to image charge distribution with high resolution and sensivity cause that this is known as a valuable method to identify nano-materials.

The science, art, and practice of protein purification have been with us for more than a century. For purification of a specific a specific protein from a crude mixture the physical and/ or chemical properties of the individual protein must be utilized. There is no single or simple way to purify all kinds of proteins. Procedures and conditions used in the purification process of one protein may result in the inactivation of another. In this article, two types of conventional chromatographic methods, affinity chromatography and size exclusion chromatography are investigated; the advantages, disadvantages and the limitations of each method are discussed.

Studying of the materials properties is impossible without knowing the details of microstructures. In order to achieve this, using a scanning electron microscope (SEM) is very common and important. Due to the necessity of using electron beam in these microscopes and considering the fact that a wide variety of materials don’t have a good electrical conductivity, obtaining desired results with this microscope have some problems. For this purpose, a conductive coating on the surface of the non-conductive samples is applied, which is widely used. This article is an attempt to introduce a variety of coatings used on the samples in scanning electron microscope and the reasons we use them and then diffrent techniques of coating will be discussed.