Approximately 10 years later, Waters Corporation introduced the first instrument called a ‘liquid chromatograph’. The three most significant differences between this liquid chromatograph and the amino acid analysers of the time were:
• its ability to form continuous gradientsbetween two eluants;
• a single column temperature; and
• silica- or alumina-based stationary phases.
As instrument and column technology improved, liquid chromatography (LC) became increasingly popular as a method of separating and detecting a wide variety of organic compounds. In the early 1980s, Pickering Laboratories introduced the first isothermal, two-eluant gradient amino acid analysis based on the then available high-performance liquid chromatography (HPLC) technology of ternary gradient pumps and single temperature elution. Adding a specially designed post-column derivatisation system made it possible to analyse amino acids using contemporary HPLC equipment. Total analysis time was shortened. A little later, most HPLC manufacturers offered one of several pre-column derivatisation methods for amino acid analysis by reversed-phase chromatography.