Study On The Determination Of Lead In Cosmetics By Nitrogen Flotation

A nitrogen flotation spectrophotometry is a new technique which have to pump the air or N2 into the liquids so that the trace components(moleculars, ions, colloids or solid particles) to be determined can be separated and enriched by adsorbbing the tiny bubbles into the organic phase or suspend between the two unmixable phases.This topic have done some research on influencing factors of the RB system flotation efficiency, including the pH of solution, amount of KI & RB, different organic phase, different surfactant, velocity of N2, and time of flotation are the influencing factors. The result showed that the pH of solution, different surfactant, velocity of N2, and time of flotation have great effect on the flotation efficiency. We have gained the relative optimality conditions by both single factor analysis and orthogonal test : pH=2, VKI=1.5 mL, VRB=1.0 mL, VCPC=3.0 mL, the organic phase was 10 mL benzene, velocity of N2 was 30 mL/min for 20 min. Under this condition, the linear range of this method was 0～4.5 mg/L, the detection limit was 0.004 mg/L. This method have a better selectivity thus a RB flotation spectrophotometry method of the determination of lead has been established.This topic also preliminary studied on the flotation mechanism in the process of nitrogen flotation. Pb2+ and I- can form the complex anion of [PbI4]2- which can enter the RB+ molecular skeleton and the hydrophobic three-component can be quantificationally collected by adsorbbing the tiny bubbles in the organic phase. The efficiency of flotation is obviously higher than general extraction because flotation does not relate to the problem of equilibrium distribution. It was determined by wheather the measured substance was saturated in the organic phase or not. The bubble diameter cccould be adjusting by using G4/G5 sand core and adding tittle alcohol so that the surface area of the bubble could be controled and the adsorption of the component could be changed. Thus the flotation efficiency can be influenced. During the research in flotation dynamics, we found the dynamics of flotation system is accord with zero order reaction because the Pb2+ in the water phase changed with time iiin different pH and different velocity of N2. In addition, this topic has a preliminary discussion on the mathematic model of Valsaraj's group and Yujuan Lv's group and found that this mathematic model should be improved for the influencing factors hav a little discrepancy to experiment such as the flow rate, the mass transfer coefficient and the bubble diameter.The pretreatment of powder has been emphatically discussed. The methods such as dry ashing, wet digestion and pressure tank digestion has been contrasted by using ultrasonic and microwave as the assistant means. The result showed that the method of pressure tank digestion(using 3+1 HNO3 & HClO4) with the assistant of ultrasonic and microwave was much better than others with the recovery rate of 96%-104%. And there was no significant difference between the national standard method and the method we have established which also accorded with the result of ICP-OES.