于在线固相萃取分离-紫外分光光度法测定乳制品中三聚氰胺(ML)含量的FIA系统中,引入了双柱结构(自制的PCX1柱和PCX2柱),并采用异步注射分析模式。调节乳制品样品酸度为pH 4.5。样品进入FIA系统后先后经过如下过程:流经PCX柱富集ML;用甲醇-水(75+25)溶液清洗150 s,除去吸附在柱上的其他杂质;用氨水-甲醇-水(1+25+74)混合液洗脱ML(洗脱时间PCX1柱为36 s,PCX2柱为34 s);洗脱液经采样环(体积60 μL)采样,0.3 mol·L-1氯化铵溶液作载流,推动采样环中“样品塞”流至流通池,于237 nm处进行光度检测。测得ML的质量浓度在0.50~40.0 mg·L-1内与相应的吸光度呈线性关系,检出限(3s/k)为0.21 mg·L-1。加标回收率在98.1%~108%之间,测定值的相对标准偏差(n=11)依次为4.2%,0.87%。

A dual-column (the self-made PCX column 1 and 2) construction was introduced into the FIA system for UV-spectrophotometric determination of melamine (ML) in dairy products with on-line SPE enrichment, and asynchronous injection mode was adopted in the analysis. The dairy sample was adjusted pH 4.5 and introduced into the FIA system. In flowing through the PCX column ML was retained on the column by ion-exchange. The column was cleaned up with a washing solution composed of CH3OH and H2O (75+25) for 150 s to remove adsorbed impurities, before elution of ML from the column with an eluant composed of aq. ammonia-CH3OH-H2O (1+25+74). Time of elution for PCX1 was set at 36 s and for PCX2 at 34 s. The eluate was carried over to the sample loop (vol. of this loop 60 μL) and its “sample plug” was carried over by 0.3 mol·L-1 NH4Cl solution acting as carrier to the flow-through cell where UV-detection was made at the wavelength of 237 nm. Linear relationship between values of absorbances and mass concentration of ML was obtained in the range of 0.50-40.0 mg·L-1 with detection limit (3s/k) of 0.21 mg·L-1. Values of recovery found by stardard addition method were in the range of 98.1%-108%, and values of RSD′s (n=11) were 4.2% and 0.87%, respectively.