The variations in nitrogen and oxygen stable isotopes of nitrate (δ15N and δ18O) are critical for identifying and quantifying nitrogen sources and their associated chemistry in the environment. Current techniques for nitrate isotope analysis, such as bacterial denitrification or Cd-azide reduction, require elongated procedures and careful handling of bacteria and toxic material. A recent study demonstrated that nitrate can be converted to N2O for isotopic analysis using a simple one-step chemical reduction with titanium (III) chloride. However, challenges remain in accurately quantifying δ18O due to its strong matrix effects. Moreover, both δ15N and δ18O values vary with the concentration of titanium used in the reduction solution. Here, we present an improved methodology for the Ti(III) reduction that employs the addition of potassium iodide to reduce the influence of solution matrix components on δ18O and identifies different optimized compositions for the reduction solution for a range of sample nitrate concentrations that minimize variation in both δ15N and δ18O due to matrix effects and dependence on TiCl3 concentration. Results from our new methodology yield uncertainties of ± 0.2‰ for δ15N and ±1.0‰ for δ18O, even in samples containing up to 1 mol/L chloride, demonstrating that this approach can be applied to complex environmental samples. Compared to other methods, the one-step chemical conversion of nitrate to N2O is faster, lower-cost, and easier to scale for routine measurements. Together, these improvements enhance the accessibility of high-precision nitrate isotope analysis and support broader applications in oceanography, hydrology, and atmospheric science.