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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. Tooth enamel consists mainly of the mineral calcium hydroxyapatite,. Trace elements in teeth of archeological specimens provide anthropologists with clues about diet and diseases of ancient people. Students at Hamline University used atomic absorption spectroscopy to measure strontium in enamel from extracted wisdom teeth. Solutions were prepared with a constant total volume of containing role="math" localid="1667792217398" of dissolved tooth enamel plus variable concentrations of added Sr.
(a) Find the concentration of Sr and its uncertainty in therole="math" localid="1667792593357" sample solution in parts per billion =.
(b) Find the concentration of Sr in tooth enamel in parts per million =.
(c) If the standard addition intercept is the major source of uncertainty, find the uncertainty in the concentration of Sr in tooth enamel in parts per million.
(d) Find the 95%confidence interval for Sr in tooth enamel.
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.
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.
How can you validate precision and accuracy?
Spike recovery and detection limit. Species of arsenic found in drinking water include (arsenite), (arsenate),role="math" localid="1655008942536" (dimethylarsinate), and (methylarsonate). Pure water containing no arsenic was spiked with arsenate/L. Seven replicate determinations gave 0.39,0.40,0.38, 0.41,0.36,0.35, and Find the mean percent recovery of the spike and the concentration detection limit .
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