离子色谱法同时测定奶粉中亚硝酸根、硝酸根、氯离子和磷酸根

Simultaneous Determination of Nitrite,Nitrate,Chloride and Phosphate in Milk Powder by Ion Chromatography

使用透析袋将溶解后的奶粉透析,用乙醚萃取,过C18柱分离后使用4.5 mmol.L-1Na2CO3--4.5 mmol.L-1NaHCO3作为淋洗液,用离子色谱法同时分离和测定了奶粉中亚硝酸根、硝酸根、氯离子和磷酸根。动态透析平衡时间只要1 h左右,四离子的离子色谱峰形较好,共存离子的干扰较小。峰面积与Cl-,PO43-,NO3-及NO2-4种阴离子浓度之间呈线性关系的相关系数依次为0.9982,0.9999,0.9997及0.9867,检出限(S/N=3)依次为9.36,15.0,0.1及0.02 mg.kg-1,测得4种离子测定结果的RSD值(n=7)分别为1.3%,2.6%,2.2%及7.3%。以3种奶粉为基体作加标回收试验,所得回收率均在92%以上。

The milk powder sample, after dissolution in water was dialyzed dynamically for 1 h. The dialyzate obtained was extracted with ethylether to remove fatty subsances and separated on C18 column to separate partially those non-polar organic compounds. Eluate from C18 column was filtered with filter membrane of 0. 45μm, and the filtrate was ready for IC determination. Ionpac AS9-HC was used as the chromatographic column and a mixed solution of 4.5 mmol·L^-1 Na2CO3 and 4. 5 mmol·L^-1 NaHCO3 was used as the mobile phase. Determination of the 4 anions was carried out by using conductivity detection. Linear relationships between peak area and concentration of the anions were obtained with correlation coefficients of 0. 998 2 （for Cl^-）, 0. 999 9 （for PO4^3-）, 0. 999 7 （for NO3^-） and 0. 986 7 （for NO2^-）, and detection limits （S/N=3, mg·kg^-1） of 9. 36 （Cl^-）, 15. 0 （PO4^3-）, 0. 1 （NO3^-） and 0. 02 （NO2^-）. Values of RSD＇s （n=7） found for Cl^-, PO4^3-, NO3^- and NO2^- were 1.3%, 2.6%, 2. 2% and 7. 3% respectively. Tests for recovery were made on 3 kinds of milk powder, giving values over 92%.