Surface element compositions of the materials studied in this work^a.

Material	Element weight (%)			Element atom (%)
	Carbon	Nitrogen	Oxygen	Carbon	Nitrogen	Oxygen
WCG	26.10 ± 2.85	38.03 ± 0.57	35.88 ± 2.27	30.45 ± 3.09	38.09 ± 0.87	31.47 ± 2.23
FC WCG-3%b K30	33.70 ± 1.62	26.65 ± 1.28	39.66 ± 0.34	39.04 ± 1.75	26.45 ± 1.35	34.50 ± 0.39
FC WCG-6%b K30	45.27 ± 1.29	23.91 ± 1.66	30.83 ± 2.95	50.91 ± 1.17	23.05 ± 1.47	26.05 ± 2.65
FC WCG-9%b K30	52.21 ± 2.22	21.13 ± 1.45	26.66 ± 0.77	57.78 ± 2.20	20.07 ± 1.47	22.16 ± 0.73

^aWCG, wet-granulation citric acid granules; FC, fluid-bed coating; K30, PVP-K30.

^b% was the PVP content (w/w) and the PVP spray solution concentration (w/v) was 13%.