欧洲药典中甘露醇铅盐镍盐采用液液萃取方法进行前处理，原子吸收火焰法采用标准曲线加入法测得样品中杂质含量，有人做过此类处理吗？做了两三次，线性非常差，想求助各位牛人，完全按照方法操作，还有什么要注意的呢？
方法如下：
Limit Test for Lead in Sugars 铅盐检查
 
(Ph. Eur. method 2.4.10)
 
Determine the lead by atomic absorption spectrometry (2.2.23, Method II).
Test solution  Dissolve 20.0 g of the substance to be examined in a mixture of  equal volumes of dilute acetic acid R and water R and dilute to 100.0 mL with the  same mixture of solvents. Add 2.0 mL of a clear 10 g/L solution of ammonium  pyrrolidinedithiocarbamate R and 10.0 mL of methyl isobutyl ketone R and then  shake for 30 s protected from bright light. Allow the layers to separate and use the  methyl isobutyl ketone layer.
Reference solutions . Prepare 3 reference solutions in the same manner as the  test solution but adding 0.5 mL, 1.0 mL and 1.5 mL respectively of lead standard  solution (10 ppm Pb) R in addition to the 20.0 g of the substance to be examined.
 
Set the zero of the instrument using methyl isobutyl ketone R treated as described  for the test solution without the substance to be examined. Measure the absorbance  at 283.3 nm using a lead hollow-cathode lamp as source of radiation and an air- acetylene flame.
Limit Test for Nickel in Polyols 镍盐检查
 
(Ph. Eur. method 2.4.15)
 
Determine the nickel by atomic absorption spectrometry (2.2.23, Method II).
Test solution? Dissolve 20.0 g of the substance to be examined in a mixture of  equal volumes of dilute acetic acid R and water R and dilute to 100.0 mL with the  same mixture of solvents. Add 2.0 mL of a saturated solution of ammonium  pyrrolidinedithiocarbamate R (about 10 g/L) and 10.0 mL of methyl isobutyl ketone R  and then shake for 30 s protected from bright light. Allow the layers to separate and  use the methyl isobutyl ketone layer.
Reference solutions?. Prepare 3 reference solutions in the same manner as the  test solution but adding 0.5 mL, 1.0 mL and 1.5 mL respectively of nickel standard  solution (10 ppm Ni) R in addition to the 20.0 g of the substance to be examined.
 
Set the zero of the instrument using methyl isobutyl ketone R treated as described  for preparation of the test solution omitting the substance to be examined. Measure  the absorbance at 232.0 nm using a nickel hollow-cathode lamp as source of  radiation and an air-acetylene flame.