Antibiotics are natural substances released by bacteria and fungi which are capable of killing, or inhibiting, competing microbial species. This phenomenon has long been known; but it was not until 1928 that penicillin, the first true antibiotic, was discovered by Alexander Fleming, Professor of Bacteriology at St. Mary's Hospital in London. However, it was 12 years later that penicillin was isolated and developed as a medicine by Howard Florey and Ernst Chain. Since this breakthrough in therapeutic medicine, derivates of penicillin were developed with increased efficacy levels. Amoxicillin is one of several such semisynthetic penicillin’s. First discovered in the 1960’s its patent has now expired. Consequently, amoxicillin and co-amoxiclav is now marketed under many different trade names worldwide. It is commonly used in the treatment of numerous infections including pneumonia, skin infections and Lyme disease. This application brief illustrates the rapid analysis of amoxicillin using the Quasar C18 column.