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Chapter 5: Q29P (page 117)
State when standard additions and internal standards, instead of a calibration curve, are desirable, and why.
The cause of desirability is described in the below steps
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Standard addition graph. Allicin is a component in garlic with antimicrobial and possibly anticancer and antioxidant activity. It is unstable and therefore difficult to measure. An assay was developed in which the stable precursor alliin is added to freshly crushed garlic and converted to allicin by the enzyme alliinase found in garlic. Components of the garlic are extracted and measured by chromatography. The chromatogram shows standard additions reported as mg alliin added per gram of garlic. The chromatographic peak is allicin from the conversion of alliin.
(a)The standard addition procedure has a constant total volume. Measure the responses in the figure and prepare a graph to find how much alliin equivalent was in the unspiked garlic. The units of your answer will be mg alliin/g garlic. Find the confidence interval, as well.
(b) Given thatof alliin are converted toof allicin, find the allicin content of garlic (mg allicin/g garlic) including theconfidence interval.
Detection limit. A sensitive chromatographic method was developed to measure sub-part-per-billion levels of the disinfectant by-products iodate, chlorite, and bromatein drinking water. As the oxyhalides emerge from the column, they absorption at. For example, each mole of bromate makes by the reaction
Bromate near its detection limit gave the following chromatographic peak heights and standard deviations (s). For each concentration, estimate the detection limit. Find the mean detection limit. The blank is 0 because chromatographic peak height is measured from the baseline adjacent to the peak. Because blank =0, relative standard deviation applies to both peak height and concentration, which are proportional to each other. Detection limit is 3 s for peak height or concentration.
Internal standard calibration curve. Figure 5-10 is a graph of in Reaction 5-13.
(d) From the uncertaintyof the intercept, find theconfidence interval for the intercept. Does this interval include the theoretical value of zero?
Standard addition. An unknown sample of gave a current of in an electrochemical analysis. When of solution containing role="math" localid="1654761474124" was added to of unknown, the current increased to .
(a) Denoting the initial, unknown concentration as , write an expression for the final concentration, , after role="math" of unknown were mixed with of standard. Use the dilution factor for this calculation.
(b) In a similar manner, write the final concentration of added standard , designated as .
(c) Findin the unknown.
A solution containing(analyte) and(standard) gave peak areas ofand ,respectively, in a chromatographic analysis. Thenof was added toof unknown,and the mixture was diluted to. This solution gave peak areas ofandforand, respectively.
(a) Calculate the response factor for the analyte.
(b) Find the concentration of
(c) Find the concentration of
(d) Find the concentration of
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