润滑油或其添加剂试样置于瓷坩埚中燃烧完全后加入硝酸并蒸发至干,移入高温炉中,在650 ℃灼烧4.5 h,残渣中加硝酸并蒸发至近干,加适量水溶出,移入于250 mL容量瓶中,加水定容后供5-Br-PADAP分光光度法测定其钙含量.显色反应系在pH 9.0磷酸盐缓冲介质中并在Triton X-100存在下进行.在络合物的最大吸收波长(λmax) 555 nm处所测得的吸光度与相应钙(Ⅱ)的质量浓度在20.0 mg·L-1以内呈线性关系.应用此方法测定了润滑油和磺酸钙(一种添加剂)试样中钙含量,并以此两种试样为基体用标准加入法作回收率和精密度试验,测得其平均回收率依次为99.2%和100.7%,相对标准偏差(n=6)依次为3.8%及2.6%.

Samples of lubricating oil or its additive were burned completely in porcelain crucibles,treated with conc.HNO3 and evaporated to dryness,then ignited in muffle furnace at 650 ℃ for 4.5 h.The residues were treated with HNO3 and evaporated to near dryness.After taking up with water,the solutions were diluted to 250 mL in volumetric flasks and used for photometric determination of calcium with 5-Br-PADAP as color reagent.The color reaction of Ca2+ with 5-Br-PADAP was carried out in a phospate buffer medium of pH 9.0 in the presence of Triton X-100.Linear relationship between values of absorbance taken at λmax of 555 nm and mass concentration of Ca2+ was obtained in the range within 20.0 mg·L-1.The proposed method was used for the determination of calcium in samples of lubricating oil and synthetic calcium sulfonate,values of average recovery found by standard addition method using these 2 samples as matrixes were 99.2% and 100.7%,with RSD′s (n=6) 3.8% and 2.6% respectively.