Rapid and Sensitive Determination of Methylxanthines in Commercial Brands of Tea Using Ultra-High-Performance Liquid Chromatography-Mass Spectrometry

Table 4

Ruggedness study of the proposed method.

Chromatographic conditions	Retention time of caffeine tR (sec) ± %RSD (n = 3)	Percentage change
Optimum conditions	28 ± 0.62	—
Effect of mobile phase flow rate
0.55 mL/min	23 ± 0.49	18
0.45 mL/min	35 ± 0.40	25
Effect of mobile phase composition
ACN: H2O (15 :  85, v/v)	24 ± 0.33	14
ACN: H2O (5 :  95, v/v)	33 ± 0.56	18
Effect of column temperature
75°C	26 ± 0.51	7
65°C	31 ± 0.37	11