Considering requirements for low sample volumes and trace level of analytes, capillary LC columns and sensitive detectors
are commonly used. Mass spectrometric detection has been employed for online MD-LC system, which becomes a major analytical tool for in vivo monitoring [35,36]. Moreover, the sensitivity of MD-LC method can be enhanced by further online concentration after MD sampling [37]. For example, nano-Au/TiO2 coated tubing has been used for the enrichment of Co and Ni between MD sampling and LC analysis [38].