| Pearl powder, which is made by the shell of pteria martensii, Hyriopsiscumingii and cristaria plicata with physical methods, is good for sedative, eyesight,and detoxification, and widely used in many fields, such as medicine, healthprotection, cosmetology and so on. However, recently there have been much reportsabout the misconduct of mixing the shell powder in pearl powder, it is difficult todistinguish because both the appearance and the physical and chemical properties arevery close.THz (Terahertz) wave is generally defined as the frequency at0.1~10THz rangeof electromagnetic wave, between the microwave and infrared in the electrospectrum. In this frequency range, material’s THz spectrum contains a wealth ofphysical and chemical information, so investigating material’s THz spectrum is ofgreat significance for the exploration and analysis of material structure, buildingTHz database and the development of THz devices.In this paper, freshwater pearl powder, seawater pearl powder and shell powderhave been qualitatively analyzed by THz time domain spectroscopy, the results showthat the refractive indices of freshwater and seawater pearl powder with differentareas are the same in0.5~1.2THz, and slightly different in0.2~0.5THz and above1.2THz, because of the discrimination of some contents of the pearl powders.Besides, with the decreasing of the size of the particle, the refractive indices increasenearly linear with it. In this condition, we can get the refractive index2.236of the1000mu fresh water pearl powder in1.0THz, and2.306of the seawater pearlpowder. By comparing the two refractive indice, we can conclude that the refractiveindex of seawater pearl powder is obviously larger than the fresh water. This may becaused by the different concentration of trace metal elements, while the refractiveindex is sensitive with the metal elements.Recently, the national standard don’t distinguish the freshwater and seawaterpearl powder, and most of the pearl powder products are freshwater pearl powder.According to it, this paper focuses on the common freshwater water pearl powder,shell powder and their mixtures. They were measured with terahertz time-domainspectroscopy (THz-TDS), their absorption spectrum and refractive index spectrum within0.2-1.5THz were obtained. And we found that the two have the similarabsorption coefficient but the different refractive index. Simple linear regression(SLR) and partial least square (PLS) method were adopted for establishing theregression model between the refractive index and the content of the shell powder inthe mixtures. The results show that the content of shell powder obtained from thePLS regression model is better than the SLR model. And the largest prediction errorof the PLS regression model is2.1%, the root mean square error is1.2%. Then wehave done a error analysis according to the results, finally we found that the sourceof error mainly came from the length error of sample preparation and thedetermining accurate of refractive index of the THz-TDS system:1) in this paper, theerror of refractive index caused by the length error is~0.002, which browse~2%theerror of the concentration;2) the accurate of the refractive index is impacted bysignal to noise ratio (SNR) of the THz-TDS system, and it creat~1%error of theshell powder concentration. What’s more, PLS regression model is helpful toimprove the determination accrate of the concentration, though it is limited by thesize of sample particle. We have provided a new method for the quantitativelydetermination of pearl powder. And it also can be a reference method for the nationalstandard of pearl determination. |
PDF Full Text Request