Question

How to calculate the mtabolic ratio of the entire experiment, when the concentration of caffeine and paraxanthine the urine sample is given ?

Answer 1

Caffeine and

paraxanthine standard solutions were analyzed as outlined in the experimental methods. A plot of the integrated peak areas versus the known concentrations of
paraxanthine and caffeine yielded calibration curves that
were used in the calculation of urinary concentrations of
caffeine and paraxanthine in Figure.

The calibration
curves were each linear with coefficients of correlation >
0.99 over a concentration range of 0.5–10 mg/mL. The
average retention times for paraxanthine and caffeine
were determined to be 2.5 min and 4.1 min, respectively.
Urine samples obtained from ten study participants
were analyzed using HPLC according to the procedures
described previously. Whole and expanded chromatograms of the raw urine samples identified multiple peaks
in the expected elution regions of paraxanthine and caffeine. Representative HPLC elution profiles.To confirm peak identity, each urine sample was
then spiked with caffeine and paraxanthine . Paraxanthine was

detected in all collected urine samples and ranged in
concentration from 1.93 to 51.98 mg/mL (Table I). Caffeine was detected in 23 of the 30 urine samples collected and ranged in concentration from 0.70 to 77.17
mg/mL (Table).

Detected caffeine concentrations were
normally smaller than those of paraxanthine and the lowest limit of detection of caffeine or paraxanthine in urine
samples was 0.5 mg/mL.
The metabolic ratio comparing the concentration of
paraxanthine to caffeine within each sample was determined using the relationship MR ¼ [paraxanthine]/[caffeine] as described by Kadulbar et al. (Fig).

The range for MR values found was 0.34 and 26.34.

and these values are within the ranges described in the
literature by many groups and with much larger sample
sizes (MR values between 0.27 to 21.24 are common
[30, 32, 33]).