Analytical Chem istry - DePauw University

Chapter 4 Evaluating Analytical Data73Table 4.7 Certified Concentrations for SRM 3246: Ginkgo biloba (Leaves) †Class of Analyte Analyte Mass Fraction (mg/g or ng/g)Flavonoids/Ginkgolide B Quercetin 2.69 ± 0.31(mass fractions in mg/g) Kaempferol 3.02 ± 0.41Constant and proportional determinate errors have distinctly differentsources, which we can define in terms of the relationship between the signaland the moles or concentration of analyte (equation 4.4 and equation 4.5).An invalid method blank, S mb , is a constant determinate error as it adds orsubtracts a constant value to the signal. A poorly calibrated method, whichyields an invalid sensitivity for the analyte, k A , will result in a proportionaldeterminate error.4B.2 Errors Affecting PrecisionIsorhamnetin 0.517 ± 0.099Total Aglycones 6.22 ± 0.77Selected Terpenes Ginkgolide A 0.57 ± 0.28(mass fractions in mg/g) Ginkgolide B 0.470 ± 0.090Ginkgolide C 0.59 ± 0.22Ginkgolide J 0.18 ± 0.10Biloabalide 1.52 ± 0.40Total Terpene Lactones 3.3 ± 1.1Selected Toxic Elements Cadmium 20.8 ± 1.0(mass fractions in ng/g) Lead 995 ± 30Mercury 23.08 ± 0.17† The primary purpose of this Standard Reference Material is to validate analytical methods for determining flavonoids,terpene lactones, and toxic elements in Ginkgo biloba or other materials with a similar matrix. Values are from theofficial Certificate of Analysis available at www.nist.gov.Precision is a measure of the spread of individual measurements or resultsabout a central value, which we express as a range, a standard deviation, ora variance. We make a distinction between two types of precision: repeatabilityand reproducibility. Repeatability is the precision when a singleanalyst completes the analysis in a single session using the same solutions,equipment, and instrumentation. Reproducibility, on the other hand, isthe precision under any other set of conditions, including between analysts,or between laboratory sessions for a single analyst. Since reproducibilityincludes additional sources of variability, the reproducibility of an analysiscannot be better than its repeatability.Errors affecting precision are indeterminate and are characterized byrandom variations in their magnitude and their direction. Because theyare random, positive and negative indeterminate errors tend to cancel,