The present disclosure provide systems, compositions, methods, reagents, kits and products for extending a nucleic acid that includes incorporating a nucleotide residue at a terminus of a nucleic acid using a polymerase enzyme and at least one nucleotide, wherein the at least one nucleotide includes a thiophosphate moiety, and wherein the at least one nucleotide is resistant to hydrolysis by phosphatase. In some embodiments, the nucleotide incorporation can be conducted in the presence of a phosphatase. In some embodiments, the nucleotide incorporation can be conducted in the presence of at least on chelation moiety that is configured to bind an orthophosphate moiety.