Microbore Liquid Chromatography Analysis of Monoamine Transmitters

Ion-pair reversed-phase liquid chromatography (LC), as introduced by Johansson et al. in 1978 (1 ) is still the most widely used separation technique for analysis of the biogenic amines. It is usually coupled with electrochemical detection (ECD). The use of microbore LC was introduced by Scott and Kucera in 1976 (2 ). These systems use columns with an internal diameter (id) of 1 mm or less. Microbore LC provides a significant advantage over conventional LC: The sample injected on to a microbore column is diluted by about 20-fold less than when injected on to a “normal” bore (e.g., 4.6 mm id) column. In this way, the compounds of interest become easier to detect. Microbore LC offers several other advantages:

1.	The lower flow rates employed lead to a reduction in mobile phase consumption;
2.	Microbore columns dissipate heat very rapidly and, therefore, are easily thermostatically controlled; and
3.	Microbore columns have a higher mass sensitivity than their larger diameter counterparts (mass sensitivity is inversely proportional to the square of the column radius) and require smaller sample volumes to achieve the same concentration sensitivity.