Representative absorbance scans obtained for total calcium and zinc determinations using the BAPTA method. See Results for additional explanation. This particular example is from rat soleus muscle tissue homogenate and yielded the following values for total calcium and zinc concentrations (2.738 mmole/kg Ca²⁺ without TPEN addition; 2.348 mmole/kg Ca²⁺ with TPEN addition). (A) Blank measurement solution. (B) Rat soleus muscle tissue homogenate. 0.15 mM BAPTA, 1 mM EGTA, 1 mM CaCl₂, and 0.2 mM TPEN were used in the corresponding trials. A vertical dotted line is used to help visualize the absorbance values at 292 nm.