Sample Caffeine (μg mL−1) RSD%, n = 3 Caffeine added (μg mL−1) Caffeine found (μg mL−1) Relative recovery (%) RSD%, n = 3
Green tea 120.5 3.2 50.0 169.8 98.5 3.7
Oolong tea 145.2 4.7 50.0 193.3 96.2 4.5
White tea 165.8 4.0 50.0 214.1 96.7 3.9
Black tea 149.5 3.0 50.0 198.9 98.8 3.6
Tea bag 171.7 4.5 50.0 220.4 97.4 4.8
Coffee 267.5 2.8 50.0 318.1 101.2 3.0
Nescafe coffee 246.8 3.2 50.0 295.6 97.6 3.8
Red bull 297.9 2.9 50.0 348.2 100.5 3.4
Hype 314.7 3.3 50.0 364.4 99.4 2.8
Coca cola 94.1 4.5 25.0 118.9 99.2 4.4
Coca-zero 83.1 2.6 25.0 107.7 98.8 3.1
Pepsi 55.5 3.1 25.0 80.6 100.3 3.7
Pepsi max 51.3 2.9 25.0 76.2 99.6 2.7
7up nd
a nd 25.0 24.5 98.0 4.2
Sprite nd nd 25.0 24.4 97.6 4.5
The relative recovery (RR) was calculated using the following equation:
equation2
where
Cfound,
Creal, and
Cadded are the concentrations of analyte after addition of known amounts of standard in the real sample, the concentration of analyte in real sample and the concentration of known amounts of the standard which was spiked to the real sample, respectively. The relative recovery values of 96.2–101.2% were obtained with three repeated measurements. The results demonstrated that the different sample matrices had no significant influence on the extraction efficiency of caffeine.
This is all relative as well, I like strong tea but weak coffee - so now thanks to reading research, I know my tea is higher in caffeine.