Lanthanide-chelator combinatorial barcoding

A method of tracking reaction conditions in solutions, comprising:

• (a) labeling a first solution comprising a first enzyme with a first lanthanide-chelator complex to generate a first barcoded solution comprising the first enzyme labeled with the first lanthanide-chelator complex, wherein the first lanthanide-chelator complex comprises a first lanthanide chelated by a first chelator;
• (b) labeling a second solution comprising a first substrate with a second lanthanide-chelator complex to generate a second barcoded solution comprising the first substrate labeled with the second lanthanide-chelator complex, wherein the second lanthanide-chelator complex comprises a second lanthanide chelated by a second chelator,
• wherein the first enzyme is capable of carrying out an enzymatic reaction upon the first substrate under one or more conditions;
• (c) mixing the first barcoded solution and the second barcoded solution together to form two or more mixtures, wherein at least two of the two or more mixtures comprise different relative abundance of the first enzyme and/or the first substrate;
• (d) following the mixing in step (c), incubating the two or more mixtures under the one or more conditions for the first enzyme to carry out the enzymatic reaction upon the first substrate, wherein the enzymatic reaction generates one or more reaction products formed by the first enzyme acting upon the first substrate;
• (e) following the incubation in step (d), generating a mass spectrum of each of the at least two of the two or more mixtures, wherein the mass spectrum comprises the first lanthanide and the second lanthanide;
• (f) identifying the first lanthanide in the mass spectrum and the second lanthanide in the mass spectrum of each of the at least two of the two or more mixtures, wherein identifying the first lanthanide in the mass spectrum and the second lanthanide in the mass spectrum comprises determining a ratio of the peak intensity of the first lanthanide to the peak intensity of the second lanthanide in the mass spectrum of each of the at least two of the two or more mixtures;
• and
• (g) determining a relative abundance of the first enzyme and the first substrate in each of the at least two of the two or more mixtures formed in step (c), wherein the relative abundance of the first enzyme and the first substrate in each of the at least two of the two or more mixtures formed in step (c) is determined as linearly correlated to the ratio of the peak intensity of the first lanthanide to the peak intensity of the second lanthanide in the mass spectrum of each of the at least two of the two or more mixtures.