An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method for the accurate and precise simultaneous measurement of the Mg/Ca and Sr/Ca content of carbonates was established. While a precision of <0.3% (1σ standard deviation (SD)) is easily obtainable for both Mg/Ca and Sr/Ca analysis, a Ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures. An alternative ratio calibration procedure is proposed which overcomes the Ca matrix effects and ensures the accuracy of the Mg/Ca and Sr/Ca analysis of marine carbonates to <0.3%, almost an order of magnitude better than conventional calibration methods. The longer-term precision is <0.1% if the batch run average values are corrected for longer-term drift. The method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples.