Solid-phase microextraction from small volumes of sample in a glass capillary.

A new sampling method is proposed for solid-phase microextraction (SPME), in which the extraction is carried out in a glass capillary containing a few microliters of sample. When an adsorption-type fiber is used for SPME, the equilibrium between aqueous sample and coating can be described by a Langmuir isotherm. Since the total amount of analytes and coexisting substances stays at a low level in a small volume of sample, the linear concentration range of analytes will be extended for SPME to be applied in quantification and the interference caused by sample matrix will be reduced. In addition, sampling in a capillary has a short diffusion distance and extraction equilibrium is established in 5-10 min. It is important in clinical analysis and therapeutic drug monitoring to be able to analyse sample volumes of samples. The feasibility of the new sampling method is demonstrated by the extractions of p-hydroxybenzaldehyde and a synthetic solution containing 1-naphthol, paeonol and 1-naphthylamine.