3.3. Analysis of samples
Free ibuprofen concentration in human urine corresponding to
healthy volunteers after the administration of usual oral dose were
in the low mg L−1 concentration range [12,26], as it was previously
reported in the literature. In the case of oral administration of ketoprofen
(two doses of 25 mg) provided urine concentration values in
the order of 0.5–1.0 mg L−1 [27]. So, it is clear that sensitivity would
not be a critical issue for NSAIDs determination in human urine.
Because of that, LC-DAD was employed for the determination of
NSAID concentration in urine of prescribed individuals. Trueness
and precision of the MIP method was established by the assessment
of recoveries using a urine blank sample spiked with NSAIDs
at different concentration levels from 0.05 to 10 mg L−1 and analyzed
by LC-DAD. The obtained recovery values ranged from 89 to
114%, as it can be seen in Table 2. A high precision for the complete
procedure was obtained with RSDs lower than 20% in all cases.
Urine of healthy volunteers was sampled before and after the
ingestion of a tablet of 600 mg ibuprofen, 25 mg ketoprofen and
500 mg naproxen in independent experiments, being 10 mL of sample
extracted and cleaned-up by using MIPs. Fig. 4 shows the
excretion profile of each evaluated compound. Free NSAIDs concentration
found in these experiments were in the 0.02–1.09 mg L−1
range. Thus, as it was expected LC-DAD provided enough sensitivity
to evaluate the urine levels of the evaluated NSAIDs in
prescribed subjects. The maximum excretion peaks for each study
corresponded to: 0.680 mg L−1 ibuprofen at 130 min for subject 1
and 0.603 mg L−1 ibuprofen at 75 min for subject 2; 0.88 mg L−1
ketoprofen at 400 min for individual 1 and 0.98 mg L−1 ketoprofen
at 210 min for individual 2; being determined a maximum elimination
of 1.09 mg L−1 naproxen at 1130 min for subject 1. The