We have previously reported analytical methods for the quantification of catecholamines (norepinephrine, epinephrine, and dopamine) via simple pretreatment using a monolithic silica disk-packed spin column with an attached phenylboronate moiety. However, under certain conditions, splitting in the dopamine peak was observed. In this study, we investigated the reason for this peak splitting and found that anions in the basic buffer solution used in the extraction influenced the peak shape. The extraction could be improved via additionally washing the column with a low-concentration buffer. The extraction recoveries of the catecholamines via the improved method were in the range of 95.9–100.8%. Thus, the improved method is expected to be more reliable for the quantification of catecholamines in biological samples.
In ultralow-temperature HPLC, analyte retention is often enhanced, inhibiting elution. To solve this problem, we have investigated the use of low-molecular-weight hydrocarbons, methane and ethane, as the mobile phase in a monolithic ODS column. Analyte retention was successfully reduced by the use of these mobile phases, and elution of mono- and di-chloromethane and n-octane, which were not eluted in our previous work using a liquid nitrogen based mobile phase, was achieved. The analysis of octane structural isomers revealed that, in cryogenic HPLC, the retention of branched octanes was significantly reduced compared to the retention of n-octane, i.e., the retention factor of iso-octane (2,2,4-trimethylpentane) was almost negligible. The retention factors of branched octanes were distributed between those of n-pentane and n-heptane in HPLC at -176°C, whereas, in gas chromatography at 50°C, these values were between those of n-heptane and n-octane.