Oligosaccharide-marker approach for qualitative and quantitative analysis of specific polysaccharide in herb formula by ultra-high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry: Dendrobium officinale, a case study.

•Oligosaccharide markers were prepared by hydrolysis and ABEE derivatization.•The specificity of two markers to Dendrobium polysaccharide was verified.•The linearity relationship between the markers and polysaccharide was established.•The quantitative use of these markers was systematically validated.