مجله دانش آزمایشگاهی ایران
سال سوم شماره 3 (پیاپی 11، پاییز 1394)

Dynamic light scattering DLS is a technique that can be used to determine the size distribution profile of small particles in suspension, Zeta potential and Molecular weight. In order to achieve the most reliable analysis of the parameters, it is necessary to choose validated procedures for sample preparation. The current study presents different techniques of sample preparation for size, zeta and molecular weight measurements in DLS.

Technical developments in high resolution low voltage scanning electron microscopy (LVHR-SEM) such as use of new detectors and reduced choromatic aberration corrector have made it possible to acquire invaluable information of nonconductive materials in electron microscopy with problems achieved. The advantages of low-voltage scanning electron microscopy reduced damage of fragile samples, reduced of interaction volume between electron and sample, reduced of sample charging for non-conductive materials, ,and reduced electron range. Thus, the practical optimum conditions in scanning electron microscopy, in order to achieve real details of surface samples are of considerable importance.

Scanning tunneling spectroscopy (STS) is a powerful technique which uses a scanning tunneling microscope (STM) to probe the local density of electronic states (LDOS) and the band gap of surfaces and materials on surfaces at the atomic scale. STS provides a plot of the current (I) as a function of the tip bias voltage (V) applied to a sample. Then, it can be used to local measurement of the tunneling current versus tip-sample bias (I-V curve) and measurement of the tunneling conductance "dI / dV". Also, the spectroscopy data can be used to find basic information on the distribution of electron systems.

Recently, more improvements have been done in the field of biomarker analysis. These improvements are mainly related to sample preparation and analytical methods of petroleum hydrocarbons. Better resolution, enhancing of signal to noise and structured chromatogram are three major features of comprehensive two dimensional gas chromatography. In this paper, applications of comprehensive two dimensional gas chromatography particularly in biomarker analysis such as hopanes and steranes are discussed.