The optimal conditions for acid hydrolysis are not well established
in the literature. Thus, in this work the most important
variables for this purpose were studied. The optimum values
were: time 90 min, 100–110 ◦C of temperature and 6M of HCl.
3.4. Optimization of variables
The hydrodynamic parameters of the system: injected reagent
volume, reactor length and flow rate, were optimized by univariate
method in order to achieve a compromise between sensitivity,
sample throughput and reproducibility. The studied ranges and
optimum values were showed in Table 2.
The only chemical variable optimized was the enzyme concentration.
This concentration was tested between 300 and
1200 UE ml−1, and the optimum value was 800 UE ml−1.
3.5. Analytical parameters
The calibration graph was linear between 11 and
132 mg l−1 of catechol. The regression line was A = (0.0039±
0.0001)C+ (0.1737±0.0080), where A is the absorbance and C
is the concentration in mg l−1 of cathecol, with a R2 = 0.998. The
detection limit [20] and the sample throughput were 7.7 mg l−1
of catechol and 49 h−1, respectively. The precision of the
method, represented by the repeatability (%R.S.D.) was 0.9%
and it was calculated from 10 independent measurement of a
standard containing 30 mg l−1 of catechol.
3.6. Analytical application to real samples
The proposed method was applied to determine total phenols
in urine samples. The concentrations of total phenols are shown
in Table 3, where these values were also expressed as a function
The optimal conditions for acid hydrolysis are not well establishedin the literature. Thus, in this work the most importantvariables for this purpose were studied. The optimum valueswere: time 90 min, 100–110 ◦C of temperature and 6M of HCl.3.4. Optimization of variablesThe hydrodynamic parameters of the system: injected reagentvolume, reactor length and flow rate, were optimized by univariatemethod in order to achieve a compromise between sensitivity,sample throughput and reproducibility. The studied ranges andoptimum values were showed in Table 2.The only chemical variable optimized was the enzyme concentration.This concentration was tested between 300 and1200 UE ml−1, and the optimum value was 800 UE ml−1.3.5. Analytical parametersThe calibration graph was linear between 11 and132 mg l−1 of catechol. The regression line was A = (0.0039±0.0001)C+ (0.1737±0.0080), where A is the absorbance and Cis the concentration in mg l−1 of cathecol, with a R2 = 0.998. Thedetection limit [20] and the sample throughput were 7.7 mg l−1of catechol and 49 h−1, respectively. The precision of themethod, represented by the repeatability (%R.S.D.) was 0.9%and it was calculated from 10 independent measurement of astandard containing 30 mg l−1 of catechol.3.6. Analytical application to real samplesThe proposed method was applied to determine total phenolsin urine samples. The concentrations of total phenols are shownin Table 3, where these values were also expressed as a function
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