## 1 Introduction  
Monoclonal antibodies (mAbs) are the most promising sector in the pharmaceutical industry and five of the top ten best-selling drugs in 2023 were mAbs [1]. Due to their high target specificity, good clinical efficiency, long serum half-life, and the capability to be produced routinely with consistency, the annual growth rate of the global mAbs market is projected to be approximately 15% in the next decade [2; 3; 4]. N-glycan is one of the most common post-translational modifications (PTMs) of mAbs, and glycans can be attached to the asparagine conserved sequaton of Asn-Xaa-Ser/Thr (where Xaa is any amino acid except proline) at the CH2 domain of the Fc fragment [5]. N-linked glycans are classified into high-mannnose, hybrid, and complex types [6]. The mAbs from different host systems show different N-glycan profiles. Currently, the majority of mAbs are expressed in Chinese Hamster Ovary (CHO) cells, generally with complex type biantennary oligosaccharides as the major species. These glycans usually have a core fucose and a bisecting N-acetylglucosamine with variation in the galactose and sialic acid content of the antennae [7; 8]. N-glycan plays an essential role in effector functions and serum half-life. Atcosylation can enhance antibody-dependent cell cytotoxicity (ADCC) by increasing binding affinity to receptors present on the surface of leukocyte effector cells [9; 10]. Galactosylation may increase complement-dependent cytotoxicity (CDC) [11; 12]. Moreover, N-glycan plays a vital role in serum half-life. It is well known that high-mannose glycans accelerate clearance of mAbs from the blood, thereby shortening the circulating half-life in the bloodstream [13; 14]. N-glycan is considered a critical quality attribute (CQA) for its potentially important impact on the safety, efficacy, pharmacokinetics, and pharmacodynamics of mAbs [15; 16]. Therefore, N-glycan should be monitored and controlled at different stages, including cell line development, cell culture process, purification process, release testing, etc. The 2-aminobenzamide (2-AB) method is considered the gold standard for N-glycan analysis and is widely used in the mAbs industry for its high labelling efficiency and fluorescent response. However, the conventional 2-AB method is labor intensive and time consuming, usually taking several days to perform the whole testing, including glycan release by PNGase F, fluorescent labelling by 2-AB, subsequent purification, and testing [17]. There is an urgent demand for a rapid, accurate, and less sample-consuming method of N-glycan analysis to speed up the development of mAbs, especially in the process development steps that require plenty of N-glycan data. For instance, one of the most labor-intensive steps in the development of mAbs is the clone selection process of cell line development. To increase the likelihood of identifying rare clones with high titer and product quality attributes, hundreds of clones must be carried from single cell to relatively small-scale cell cultures [18], resulting in large workloads and a long time for quality attribute analysis, especially N-glycan analysis using the time-consuming conventional 2-AB method. Moreover, the cell culture scale is usually at the milliliter level per clone with low titer in the cell line development step [19]. Therefore, there are not enough protein samples for N-glycan analysis by means of the conventional 2-AB methods. In this situation, major N-glycans are the primary focus, and minor N-glycans should be removed from the CQA list. Analytical methods that provide major N-glycan data rapidly are key to the success of mAb development. To this end, methods have been developed for rapid N-glycan analysis. Based on the principle of the conventional 2-AB method, rapid N-glycan release, labelling and purification steps have been successfully optimized to reduce the testing time to less than one day [6].