Guanidine is highly basic (pKa 12.5) and polar compound formed by oxidation of guanine. In human body guanine is a by-product of protein metabolism and can be found in urine. Guanine can be retained by cation-exchange mechanism on Primesep 100 column. Guanine is slightly UV active and can be observed at 200 nm. A better detection technique is ELSD, which allows you to see low concentrations of guanine. Temperature of ELSD must be maintained relatively low to insure proper sensitivity of the method. This method can be used for analysis of other guanidine-based compounds. If substituted guanidine has hydrophobic properties it will retain based on ion-exchange and reverse phase mechanisms.