2.7. HPLC-UV/DAD method validation
The validation of the HPLC-UV/DAD method was performed in
agreement with international guidelines for analytical techniques
for the quality control of pharmaceuticals (ICH guidelines).
The stock standard solution of each compound (quercetin-
3-O-rutinoside, quercetin-3-O-galactoside, 6-methoxyluteolin,
quercetin and isorhamnetin) was prepared as follows: an accu-
rately weighed amount of pure compound (1.9–2.8 mg) was
placed into a 10 mL volumetric flask; DMSO was added and the
solution was diluted to volume with the same solvent. The external
standard calibration curve was generated by using five data points,
covering the concentration ranges: 5.4–216.0 g/mL for quercetin-
3-O-rutinoside; 7.1–283.0 g/mL for quercetin-3-O-galactoside;
4.9–194.0 g/mL for 6-methoxyluteolin; 11.7–233.0 g/mL for
quercetin; 16.0–228.0 g/mL for isorhamnetin. 10 L aliquots of each standard solution were used for HPLC analysis. Injections were
performed in triplicate for each concentration level. The calibration
curve was obtained by plotting the peak area of the compound
at each level versus the concentration of the sample. The amount
of flavonoids in P. argentea extracts was determined by using the
calibration curves of the compounds with the same chromophore.
In particular, the calibration curve of quercetin-3-O-rutinoside
was used for compounds 1–3, that of quercetin-3-O-galactoside
for compounds 4–7, that of 6-methoxyluteolin for compounds 8
and 10. The quantification of compounds 9 and 11 was performed
by using their own calibration curves.
For reference compounds, the limit of detection (LOD) and the
limit of quantification (LOQ) were experimentally determined by
HPLC analysis of serial dilutions of a standard solution to reach a
signal-to-noise (S/N) ratio of 3 and 10, respectively.
The accuracy ofthe analytical procedure was evaluated by using
the recovery test. This involved the addition of a known quantity
of standard compound to half the amount of a P. argentea ethanolic
extract to reach 100% of the test concentration. The spiked samples
were then analyzed with the proposed method.
The precision of the chromatographic system was tested by per-
forming intra- and inter-day multiple injections of a P. argentea
ethanolic extract and then checking the %RSD of retention times
and peak areas. Six injections were performed each day for three
consecutive days.
The stability was assessed by using a P. argentea ethanolic
extract stored in amber glass flasks at 4 ◦C and at room temperature
(about 25 ◦C) and analyzed every 12 h for 72 h.
2.7. HPLC-UV/DAD method validationThe validation of the HPLC-UV/DAD method was performed inagreement with international guidelines for analytical techniquesfor the quality control of pharmaceuticals (ICH guidelines).The stock standard solution of each compound (quercetin-3-O-rutinoside, quercetin-3-O-galactoside, 6-methoxyluteolin,quercetin and isorhamnetin) was prepared as follows: an accu-rately weighed amount of pure compound (1.9–2.8 mg) wasplaced into a 10 mL volumetric flask; DMSO was added and thesolution was diluted to volume with the same solvent. The externalstandard calibration curve was generated by using five data points,covering the concentration ranges: 5.4–216.0 g/mL for quercetin-3-O-rutinoside; 7.1–283.0 g/mL for quercetin-3-O-galactoside;4.9–194.0 g/mL for 6-methoxyluteolin; 11.7–233.0 g/mL forquercetin; 16.0–228.0 g/mL for isorhamnetin. 10 L aliquots of each standard solution were used for HPLC analysis. Injections wereperformed in triplicate for each concentration level. The calibrationcurve was obtained by plotting the peak area of the compoundat each level versus the concentration of the sample. The amountof flavonoids in P. argentea extracts was determined by using thecalibration curves of the compounds with the same chromophore.In particular, the calibration curve of quercetin-3-O-rutinosidewas used for compounds 1–3, that of quercetin-3-O-galactosidefor compounds 4–7, that of 6-methoxyluteolin for compounds 8and 10. The quantification of compounds 9 and 11 was performedby using their own calibration curves.For reference compounds, the limit of detection (LOD) and thelimit of quantification (LOQ) were experimentally determined byHPLC analysis of serial dilutions of a standard solution to reach asignal-to-noise (S/N) ratio of 3 and 10, respectively.The accuracy ofthe analytical procedure was evaluated by usingthe recovery test. This involved the addition of a known quantityof standard compound to half the amount of a P. argentea ethanolicextract to reach 100% of the test concentration. The spiked sampleswere then analyzed with the proposed method.The precision of the chromatographic system was tested by per-forming intra- and inter-day multiple injections of a P. argenteaethanolic extract and then checking the %RSD of retention timesand peak areas. Six injections were performed each day for threeconsecutive days.The stability was assessed by using a P. argentea ethanolicextract stored in amber glass flasks at 4 ◦C and at room temperature(about 25 ◦C) and analyzed every 12 h for 72 h.
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