Correlation Study Between Particle Size Effect Of Samples And Accuracy Of Analytical Detection

Particle size, which is an important characteristic parameter, not only affects the physical properties such as friction coefficient and conductivity coefficient, but also can cause material surface changes and produce particle size effect, then further affect the spectrum in measurement. In particular, the size effect produced by Nano-size particles can greatly change the surface properties of the materials, which has been concerned and confirmed by analysts. At present, many theories have been developed to explain the size effects on experimental results. However, except for the development and improvement of these theories in the level of electronic structure, the particle size effect in macroscopic conditions also cannot be ignored. All analysis work is related to the samples, the sample collection and its preparation fully reflects the sample is representative or not. In the actual analysis, the smaller the sample size is, the stronger representative it is; surface enhancement technology has been widely used in Raman spectroscopy, fluorescence spectroscopy, infrared spectroscopy and other fields, most of them use nano-colloidal gold and colloidal silver as a reinforcing agent, and relative studies have shown that surface enhancement are related to particle size.From the theory of surface enhanced Raman spectroscopy and surface enhanced Infrared spectroscopy, we can see that the particle size has a great influence on the spectrum, however, the deeper explanations are mainly focused on the probe effect, while only few explanations are relative to the size correction theory of dielectric function, and they can't be accurately interpreted; and there is almost no relevant research reports on the size effect behind the probe effect. The calculation of the particle size of the sample has been reported already in the theory of shrinkage, but because there is a large difference between the estimation results and the actual results, how to calculate accurately needs further study and discussion.Herein, using the mathematic statistics and chemometrics, based on the hypothesis of binary system, two particle size effect models (Tan-Xie-S/L model) are proposed,(1) Tan-Xie-S model: It is determined that when the sample weight is constant, the third power of particle diameter is positively correlated with the square of relative standard deviation. At the same time, the particle diameter is positively correlated with the relative standard deviation, the sample weight and the content of the test substance.(2) Tan-Xie-L model: Assuming that in addition to the solvent, the system contains two kinds of particles and one is the test object. Combining with the local concentration effect, the relationship between the detection limit and the standard deviation is deduced. It can be seen that the larger the particle diameter is, the smaller the standard deviation is.Under the guidance of this theory, following applications are proposed,(1) Using the particle size reduction effect, the quantitative relationship between the particle diameter, the sample amount, the relative standard deviation and the sample content obtained by the sample preparation was proposed. It was found that the relative standard deviation was determined by the sample particle diameter when the sample amount is determined.Considering that the diameter and the shape of the particles are not consistent,the model is modified. The minimum sampling volume of several substances was calculated by constructing the model. The uncertainty assessment method of cadmium content determination in soil samples was discussed, including the uncertainty of sampling amount, sample preparation, measuring instruments, environmental conditions, personnel operation and so on. From the comparison of the uncertainty sources, it can be seen that the order of the factors affecting the uncertainty of the final content determination is sampling is the largest, and the detection method is the smallest. The importance of sample collection and the prepared sample's particles size during the analysis of solid samples is confirmed.(2) Using the effects of large particles, scattering intensity of Raman spectroscopy was increased, and the testing method for toxic substances was built based on surface-enhanced Raman spectrum. Based on the surface-enhanced spectroscopy technique of colloidal gold nanoparticles, the surface quality of surface-enhanced Raman spectroscopy in environmental water and food was studied by optimized pretreatment technique to monitor and detect illegal food additives, a simple and efficient surface-enhanced Raman spectroscopy based on the three rapid detection methods was established. The relationship between the size of the colloidal gold particles and the signal is discussed using a shielded probe, indicating the correctness of this argument as the particle size increases. Molar absorption coefficient and fluorescence coefficient were strengthened, and the testing method for thiols was built based on surface-enhanced fluorescence spectrum. The detection of thiols in body fluids was carried out by using the fluorescent europium tetracycline complex as the fluorescent probe and enhancing the fluorescence intensity of the complex by hydrogen peroxide molecules and thiols. A simple and rapid method for the determination of thiols in biological fluids has been established, which is of great significance for the study of important biological functions of thiols. After the addition of hydrogen peroxide, the original europium tetracycline complex molecules and hydrogen peroxide combined to form EuTc- H2O2 complex, so that the fluorescence intensity increases. When the thiols is present in the system under test, the thiols form a disulfide bond under the action of the hydrogen peroxide molecules to reduce the fluorescence intensity of the compound. At the same time, the change of the signal after the addition of the surfactant was discussed. The fluorescence signal on the surface was enhanced again on the basis of the original signal,and the signal size of the component to be measured was enhanced after the surfactant was adsorbed by the surfactant.(3) Using the adsorption effect of particles, the detection efficiency of heavy metals in the atmosphere was increased, and the testing method for cadmium is built to estimate the pollution and migration of cadmium in the atmosphere. In the atmosphere, heavy metals exist in atmospheric aerosols,and the smaller the particle size, the higher the content of heavy metals, the heavier metal content in large particles of aerosols can be detected by physical sedimentation method, small particles of aerosol through the plant pores or lenticels for adsorption. By studying the particle effect, the content of cadmium in the atmosphere was monitored by Moss-bag technique and TSP,the results were in agreement with the actual results. The results show that the multi-hairy and branch structure of moss, the relative surface area is large, and the existence of a large number of cation exchange points can solve the heavy metal problem caused by the particle size effect in the atmosphere.