The calibration range included nine levels of 10–3000 ng/mL and 1–300 mg/mL for terpenoids and nicotine, respectively ( Table 2). Repeatability ( n = 5 1250 ng/mL in vial or 125 ppm in plant sample), intermediate precision ( n = 17 over 3 days 1250 ng/mL in vial or 125 ppm in plant sample) and method recoveries ( n = 5 3500 ng/mL in vial or 350 ppm in plant sample) were also evaluated.įor vaping liquid (e-juice) method validation, each headspace vial included 5 mL glycerol, 25 μL internal standard (400 μg/mL linalool- d 3), 25 μL of the fortification (or solvent as method blank), and 50 μL glycerol:propylene glycol (1:1 v/v) as a surrogate vaping liquid where applicable. Carry-over was assessed by comparing the raw area response of each analyte in the high calibration sample (4000 ng/mL in vial) to that of a method blank analysed immediately after-an area response ratio < 0.1% in the method blank was accepted as suitable carry-over. MRLs were established at a fortification concentration of 25–200 ng/mL in vial ( n = 7). The method reporting limit (MRL) for each analyte was verified using precision and accuracy specifications as outlined by the United States Environmental Protection Agency. Method detection limits (MDL) were evaluated by determining the minimum measured concentration of an analyte at 25–200 ng/mL in vial (2.5–20 ppm in plant sample n = 7 over 3 days) that could be reported as distinct from the method blank with 99% confidence. Dynamic range was calculated as the logarithm of the high calibration concentration divided by the low calibration concentration for each analyte. Calibration functions for all analytes were fit to linear or quadratic curves, with inverse concentration weighting applied to all analytes. Nine calibration levels were prepared at final concentrations of 25–4000 ng/mL in vial ( Table 1). Each headspace vial included 5 mL glycerol, 25 μL internal standard (400 μg/mL linalool- d 3), 25 μL of the fortification (or solvent as method blank), and 50 mg ground, dry stinging nettle where applicable. Method validation in plant tissue was performed using plant material fortified with select terpenes and terpenoids ( vide infra). Matthew Noestheden, in Comprehensive Analytical Chemistry, 2020 2.4 Method validation
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