The present techniques are directed to a method for microprobe analyses of isotope ratios in inhomogeneous matrices. The method includes selecting matrix standards that have matrices that resemble a target matrix. A bulk isotope analysis is run on each of the matrix standards to determine a bulk isotope ratio value. A microprobe analysis is run on each of the matrix standards to determine a microprobe isotope ratio values for each of the plurality of matrix standards. Spurious values are eliminated from the microprobe isotope ratio values. The microprobe isotope ratio values are averaged for each of the matrix standards to create an average microprobe isotope ratio value associated with each of the matrix standards. The bulk isotope ratio value for each of matrix standards is plotted against the average microprobe isotope ratio value associated with each of the matrix standards to create a matrix corrected calibration curve.
