Speciation Analysis In Food By High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

There are many kinds of microelements contained in foods that are vital to human health. The toxicity and bioavailability of microelement depend upon their chemical forms which are essential to the food quality control and nutrition evaluation. The specific form in which an element was present appeared its physico-chemical properties, its behaviour and toxicity in the environment, physiological function and essentiality for humans, animals or plants. The elemental species are rather complicated in environmental and biological system, they are easy to change with the alteration of the conditions, and what is more, the concentration of specific form of an element in real sample is much lower than its total amount. Therefore, how to develop a simple, rapid and accurate method for the elemental species information in environmental and biological samples is always one of the most challenging tasks to analytical scientists.In the study the total elemental concentration in seafood and tea was studied using ICP-MS. By combining the separation capability of HPLC with the selectivity and sensitivity of ICP-MS, many elemental species of As, Hg, Cr can be separated in a single sample injection. The aim of the study was to develop a reliable and robust analytical method for elemental speciation analysis in a variety of samples.ICP-MS has become the dominant technique for the rapid, multi-element analysis of trace elements in environmental and biological samples. The total elemental concentration was determined by ICP-MS after microwave digestion with nitric acid and hydrogen peroxide under the microwave digestion program. Therefore ICP-MS was a trace element detector with strong elemental analytical capabilities. ICP-MS equipped with dynamic reaction cell （DRC） was an effective technique to remove polyatomic interferences to lower the detection limit using methane as reactive cell gas.ICP-MS was used as anion exchange chromatographic detector for speciation analysis of arsenic. The arsenic species studied include arsenite （As（III））, dimethyl arsenic acid （DMA）, arsenate （As（V））, Arsenocholine （AsC） and Arsenobetaine（AsB）. The choices of HPLC separation conditions were based on the selection and optimization of elutent concentration, methanol concentration and pH. Three extracting solutions had been studied for the purpose: CH₃OH/H₂O, pancreatin and pepsin. Better extraction efficiency of arsenic species can be obtained by using enzymatic extraction compared with CH₃OH/H₂O. Arsenic was determined as the adduct ion ⁷⁵As ¹²CHH at m/z 89, which is more sensitive than ⁷⁵As. The optimized AE-ICP-MS method was applied to determine arsenic species in seafood. The major speciation in seafood was AsB, and a small fraction of the extractable arsenic were DMA and As（V）. Several unknown peaks in seafood were not identified due to the lack of suitable standards. Mercury compounds were separated by reversed-phase high performance liquid chromatography using a C-18 column and aqueous 0.01M CH₃COONH₄ and 0.05%L-cysteine. The major Hg speciation was methylmercury. We found that vial material effected the stability of HgCl₂. The HPLC separation of chromium species in seafood and tea infusion were accomplished isocratically using tetrabutylammonium hydroxide as the ion-pair reagent. The high flow-rate permitted very rapid analysis times and reduced solvent consumption. The results suggested that vial material effected the stability of Cr（VI） over time.