Determination And Speciation Of Harmful Elements In Milk

The various nutrients in milk are the most similar to human nutritional model. The elemental analysis of milk is important because of an indicator of environmental contamination and a significant pathway for toxic metal intake and a source of essential nutrients for humans.Inductively coupled plasma optical emission spectrometry/mass(ICP-OES/MS) is an powerful multi-elements trace analysis technology. It offers extending good advantages in terms of low detection limit, high precision, good selectivity, little matrix effect, wide linear range and simultaneous multi-elements determination, so it is widely used. But the routine determination of ICP-OES/MS couldn't meet the research demand with scientific development. The hyphenation of ICP-OES/MS with analytical instruments else would combine advantages of them to a certain extent and ulteriorly improves analytical capability.Hydride generation(HG) combined with modern atomic spectrometric detection has become one of the most powerful analytical tools for some elements determination because it has adopted chemical reaction and realized awaiting measuring component separated from a large number of matrix. It makes determination go on in a situation that there is no any basic spectrum interference. HG-ICP-OES enhance detection power of ICP-OES to hydride–forming elements. The detection limits of hydride-forming elements can be improved by one or two orders of magnitude over conventional nebulizer, and nearly elimination interference. Therefore, it provides a new way to solve complex matrix samples analysis.Capillary electrophoresis (CE) has many advantages: high efficiency, quick analysis speed, many analysis modes, little reagent consumption, wide application, easy automation, etc. It become the important components analysis method in a complex system. CE coupled with ICP-OES has the individual advantages of capillary electrophoresis and inductively coupling plasma spectrometry, it realized the combination of efficient separation and element alternative measurement. It was considered as a powerful analytical method.In this paper, the research has been carried on hyphenating of inductively coupled plasma optical emission spectrometry with hydride generation and capillary electrophoresis. The determination for hydride elements, mechanism of plumbane generation and speciation analysis of aluminum have been studied. The main contents and researched results of the paper are as follows:1. A simple and fast analytical method has been developed for the determination of As, Se, Sb and Bi in milk by microwave digestion hydride generation inductively coupled plasma optical emission spectrometry. Milk were firstly pre-reduced with 6 mol/L HCl for 40 min in a boiled water for Se determination after they were digested in microwave oven, and then were driven away acid and pre-reduced by hydroxylamine hydrochloride for determination of As and Sb. Interferences of concomitant elements were eliminated by tartaric acid and citric acid in the samples. The detection limits(3σ) were 0.24, 0.12, 0.06 and 0.02μg/L for As, Se, Sb and Bi, respectively. The average relative standard deviations were 5.0%, 5.7%, 4.3% and 3.8%, respectively.2. To clarify the mechanisms of the generation of plumbane in the Pb(II)-NaBH4-K3Fe(CN)6 system , the intermediates produced through the reaction of lead(II) and NaBH4 in the presence of K3Fe(CN)6 were studied. The plumbane generated was measured by a continuous flow hydride generator-inductively coupled plasma-optical emission spectrometer. Based on the experimental results, the mechanisms can be depicted in the following steps: 1) plumbane and black lead sediment (black Pb) were formed through the reaction of lead(Ⅱ) and NaBH4 ; 2) the black Pb was oxidized by K3Fe(CN)6 to form the Pb2[Fe(CN)6] complex which was then further reacted with NaBH4 to form more plumbane and black Pb; 3) another round started, i.e. the black Pb thus produced continued to be oxidized by K3Fe(CN)6 to form more Pb2[Fe(CN)6] complex to generate more plumbane. In short, the black Pb and the Pb2[Fe(CN)6] complex were the key intermediate products for the generation of plumbane in the Pb(II)-NaBH4-K3Fe(CN)6 system. 3. The speciation of aluminum in milk has been developed by capillary electrophoresis-inductively coupled plasma optical emission spectrometry. The forms of aluminum in milk have six species. The free aluminum and aluminum citrate were identified by spiked the standard of free aluminum and aluminum citrate. The concentration of aluminum citrate quantified by peaks area was 0.17 mg/L in milk. The relative standard deviation of migration time and concentration for aluminum species were less than 3% and 5%, respectively. The recovery and detection limit of aluminum citrate was in the range of 96.4% to 100.7% and 37μg/L, respectively.