¹³C incorporated internal standards (IS) are used less frequently than deuterated IS because they are typically more costly or are not commercially available. ¹³C IS are, however, considered to be superior for many applications, which is why Cayman scientists are working toward making more of them available. An ideal internal standard is one that is structurally similar (if not identical) to the analyte of interest, is not prone to exchange/loss of the isotopic label, and preferably has the same retention time and response factor as the analyte of interest. This allows the analyst to have confidence in quantifying analytes of interest that need to be isolated from complex biological matrices and normalize other sample handling and instrumentation conditions. ¹³C IS have the same retention time and response factors as the native analyte, and they are incapable of isotopic scrambling.