SIGNAL STANDARDIZATION OF THE SECONDARY-ION MASS-SPECTROMETRY (SIMS) MICROSCOPE FOR QUANTIFICATION OF HALOGENS AND CALCIUM IN BIOLOGICAL APPLICATIONS

The secondary ion mass spectrometry (SIMS) microscope is able to map c hemical elements in tissue sections. Although absolute quantification of an element remains difficult, a relative quantitative approach is p ossible for soft tissue by using carbon (C-12) as an internal referenc e present at large homogeneous and constant concentration in specimen and embedding resin. In this study, this approach is used to standardi ze the signal of an SIMS microscope for the quantification of halogens (F-19(-), Cl-35(-) and Br-79(-)) and calcium (Ca-40(+)). Standard pre paration was determined based on homogeneity and stability criteria by molecular incorporation (halogens) or mixing (calcium) in methacrylat e resin. Standard measurements were performed by depth analysis on are as of 8 mu m (halogens) and 150 mu m (calcium) in diameter for 10-30 m in, under Cs+ (halogens) or O-2(+) (calcium) bombardment. Results obta ined from 100-120 measurements for each standard dilution show that th e relationship between the signal intensity measured and the elemental concentration (mu g/mg of wet tissue or mM) is linear in the range of biological concentrations. This quantitative approach was applied fir stly to bromine of the 5-bromo-2'-deoxyuridine (BrdU) used as nuclear marker of rat hepatocytes in proliferation. The second model concerns depletion of calcium concentration in cortical compartment in Parameci um tetraurelia during exocytosis. Then signal standardization in SIMS microscopy allows us to correlate quantitative results with those obta ined from other methods.