ICP-OES is a widely applied technique for the certification of monoelemental solutions along with gravimetry and tritation. Therefore, it is essential to ensure traceability of measurements to the International System of Units (SI). In particular, an ICP-OES method developed by the National Institute of Standards and Technology (NIST)[1,2] is used by national metrology institutes and reference material producers due to its high accuracy and low uncertainty, typically in the order of 0,1% (relative expanded uncertainty). This method requires the determination of the instrumental response drift pattern, and its modeling by an equation. However, in sequential ICP-OES instruments this approach cannot be applied because analyte and internal standard signals are not measured simultaneously and consequently a drift pattern cannot be determined. In the proposed method both sample and calibrant were diluted with the internal standard solution six times to yield equal concentration of analyte and equal concentration of internal standard and signal ratios close to 1. After a comprehensive study, the instrumental parameters were optimized. Each sample was measured six times between two calibrants which were randomly selected and quantified using the average slope of each calibrant. This approach presents the benefits of both exact-matching and bracketing calibration given that the most accurate estimation of the response factor at that level is achieved and instrumental drift contributions are minimized. In the proposed method a probability density function can be assigned to each parameter of the equation, enabling uncertainty estimation through Monte Carlo[3] method by MCM Alchimia[4] software. The accuracy of the method was demonstrated by testing it with a monoelemental solution of sodium certified reference material from the Slovak Metrology Institute using a monoelemental solution certified reference material from NIST with a relative expanded uncertainty of 0,2% as a calibrant. An excellent agreement between the obtained and reference value was attained (normalized error En=-0,08) with a relative expanded uncertainty of 0,3%. In the near future, the proposed method will be further tested with other analytes.