Disclosed herein are methods for tracking solutions, (e.g., reaction conditions in solutions). In some embodiments, the method comprises: contacting a first lanthanide-chelator complex to a first solution to generate a first barcoded solution, wherein the first lanthanide-chelator complex comprises a first lanthanide chelated by a first chelator; contacting a second lanthanide-chelator complex to a second solution to generate a second barcoded solution, wherein the second lanthanide-chelator complex comprises a second lanthanide chelated by a second chelator; mixing the first barcoded solution and the second barcoded solution to form one or more mixtures; and identifying the first lanthanide ions in the mass spectrum and the second lanthanide ions in the mass spectrum to track the condition of each of the one or more mixtures.

Disclosed herein are methods for tracking solutions, (e.g., reaction conditions in solutions). In some embodiments, the method comprises: contacting a first lanthanide-chelator complex to a first solution to generate a first barcoded solution, wherein the first lanthanide-chelator complex comprises a first lanthanide chelated by a first chelator; contacting a second lanthanide-chelator complex to a second solution to generate a second barcoded solution, wherein the second lanthanide-chelator complex comprises a second lanthanide chelated by a second chelator; mixing the first barcoded solution and the second barcoded solution to form one or more mixtures; and identifying the first lanthanide ions in the mass spectrum and the second lanthanide ions in the mass spectrum to track the condition of each of the one or more mixtures.