Sample preparation is still considered as the bottleneck of the whole analytical procedure, and efforts
has been conducted towards the automation, improvement of sensitivity and accuracy, and low comsuption
of organic solvents. Development of online sample preparation techniques (SP) coupled with liquid
chromatography (LC) is a promising way to achieve these goals, which has attracted great attention. This
article reviews the recent advances on the online SP-LC techniques. Various online SP techniques have
been described and summarized, including solid-phase-based extraction, liquid-phase-based extraction
assisted with membrane, microwave assisted extraction, ultrasonic assisted extraction, accelerated solvent
extraction and supercritical fluids extraction. Specially, the coupling approaches of online SP-LC
systems and the corresponding interfaces have been discussed and reviewed in detail, such as online
injector, autosampler combined with transport unit, desorption chamber and column switching. Typical
applications of the online SP-LC techniques have been summarized. Then the problems and expected
trends in this field are attempted to be discussed and proposed in order to encourage the further development
of online SP-LC techniques.