HPLC and ESI
The compatibility of ESI with HPLC has resulted in LC/MS being extensively used for carbohydrate analysis as described later on in the section on total methods for analysis. LC/MS  and microseparation methods suitable for glycan analysis, particularly when coupled with MS, have recently been reviewed [172, 173]. Normal-phase (NP) separations provide good correlation between structure, molecular weight, and retention time , allowing some structural information to be obtained directly from the elution profile. Reversed-phase HPLC systems have also been used as illustrated by a study of the 2-AB derivatives of small oligosaccharides and N-linked glycans . Porous graphitized carbon is also popular for carbohydrate separations [176,
177], and graphitized carbon nanoflow columns (0.6 pL/min) have been reported to increase sensitivity by 10-fold over conventional columns with a detection limit in the low femtomole range for N-linked glycans ; cyclodextrin-based columns have also been used . The somewhat limited resolving power of earlier HPLC columns has now largely been overcome by the use of ultra-high-pressure column chromatography and monolithic silica- based capillary HILIC columns [180, 181]. “Chip-based” methods employing arrays of small sprayers built into silicon chips enable the ESI techniques to be automated and have been exploited in the carbohydrate field [182-184].