Reliable and accessible methods for urea quantification in co-reduction of carbon-dioxide- and nitrogen-containing species

Electrocatalytic urea synthesis by the co-reduction of CO₂ and nitrogen sources under mild conditions offers an attractive alternative to the conventional protocol. However, the quantification of urea poses significant challenges because of low yields and diverse byproducts, thereby raising concerns regarding the reliability of catalyst performance. This study systematically assesses the commonly used methods (urease, diacetyl monoxime, and ¹H-NMR) in real electrochemical systems and identifies their potential limitations. We then propose an advanced analytical platform that uses ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) to quantify urea in electrolytes. This method exhibits high sensitivity, even at ultralow urea concentrations of 0.01 μg mL^-1, without compromising accuracy in the presence of byproducts. Its reliability is validated through a series of experimental cases, eliminating the occurrence of false positives. These findings contribute to establishing a benchmark for quantifying urea in electrosynthesis, facilitating the development of efficient electrocatalysts.