Direct Determination Of Metal In Dairy Products With Water-based Microemulsion By ICP-OES

ObjectiveIt is proposed to establish a fast ? green and non-pollution water-based microemulsion direct injection Inductively Coupled Plasma Optical Emission Spectrometry(ICP-OES)for the determination of metal elements in dairy products.MethodsSample collection : The samples were from five supermarket chains in Zhengzhou,including: Dennis?Carrefour?Jiashi? Century Hualian?Wal-Mart and other supermarkets.The four types of products were analyzed,which included stereotyped packaged milk,milk powder,milk tablets and cheese.A total of 60 samples were used to detect the contents of eight metal elements such as potassium,sodium,calcium,magnesium,lead,manganese,copper and chromium.Sample perparation: A certain amount of sample were weighed,the 0.1%polyethylene glycol surfactant was added and crushed beads for 240 s.The particle size of the prepared water-based microemulsion was characterized by Scanning Electron Microscopy,Transmission Electron Microscopy and Potential and Panometer Particle size analyzer.The particle size was from 100 nm to 200 nm.The optimizing surfactant was 0.1% PEG as emulsifiers,it could get satisfactory results.It was apparent from the observation by biofluorescence microscopy that the prepared water-based microemulsions belong to W-O-S-O-W(Oil-in-water,with solids)type vesicles.The prepared water-based microemulsion direct injection(ICP-OES)would be used to simultaneously determine the content of eight metal elements such as lead,manganese,copper,chromium,potassium sodium,calcium and magnesium.ICP-OES condition: The flow rate was 0.9L/min and auxiliary gas flow rate was1.5 L/min and reflection coil power was 1550 w and observation height for axial was9 mm and each reading was 5s and repeat times were three and the instrument settling time was 15 s and the sample lifting peristaltic pump speed was 20r/min and theinjection pump speed was 15r/min and the flushing time was 20 s.A “robust plasma”could well overcome the error caused by the matrix effect.ResultsThe lowest detection lead for eight metal elements were K 0.0009mg/L,Ca0.0030mg/L,Na 0.0066mg/L,Mg 0.0009mg/L,Cr 0.0015mg/L,t Cu 0.0024mg/L,Mn 0.0012mg/L and Pb 0.0009mg/L.Calibrations were carried out using aqueous standard solutions,the linear correlation coefficient(r)for K was 0.9993,for Ca was0.9996,for Na was 0.9991,for Mg was 0.9995,for Cr was 0.9999,for Cu was 0.9994,for Mn was 0.9999,for Pb was 0.9999 in this experiment.The standard reference material of GBW08509 skim milk powder was added with 8 kinds of metal elements with different contents,the spike recovery was between 92% and 108%,and relative standard deviation was less than 3%.The standard substances of GBW10017 milk powder and GBW08509 skimmilk powder were taken as the measurement indexes of accuracy and precision of the method,and the measured value completely fell within the standard range of the recommended value,and the relative standard deviation(RSD)was less than 3% for six times.ConclusionA water-based microemulsion direct inductively coupled plasma optical emission spectrometer(ICP-OES)analysis has been developed for the determination of metal element content in milk and dairy products.The samples are crushed and emulsified by adding a certain amount of surfactant.a certain amount of the preparation liquid takes to a constant volume.Than the metal element content can be directly determined by ICP-OES.The sample pretreatment is simple and fast,non-pollution,the limit of detection was low,the precision is good,the measurement results are accurate and reliable.So the method could be suitable for the determination of metal elements in dairy products.