Chapter 18: Q17P (page 457)
What is the purpose of neocuproine in the serum iron analysis?
The purpose of neocuproine in the serum iron analysis is the it reacts with Cu(I), so it cannot form complex with ferrozine. Ferrozine gives false positive result in analysis.
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What is the difference between luminescence and Chemi-luminescence?
18-29. Biotin-streptavidin fluorescence titration. Biotin is a cofactor in enzymatic carboxylation reactions. Biotin activatesfor biosynthetic reactions.
Streptavidin is a protein isolated from the bacterium Streptomyces avidinii that binds biotin with a formation constant of . The biotin-streptavidin complex is widely used in biotechnology because the noncovalent complex is stable in the presence of detergents, protein denaturants, and organic solvents, and at extremes of pH and temperature.
The stoichiometry of the biotin-streptavidin complex was measured by a fluorescence titration. Fluorescein (page 453 ) covalently attached to biotin via the biotin carboxyl group fluoresces at 520 nm when irradiated at 493 nm. When biotin-fluorescein (BF) binds to streptavidin (SA), fluorescence decreases. The table gives emission intensity for addition of BF to SA and also for addition of SA to BF. Data are already corrected for dilution.
(a) Make a graph of fluorescence versus mole ratio for each titration and state the stoichiometry of binding of biotin to streptavidin.
(b) Explain the shape of each titration curve.
You have been sent to India to investigate the occurrence ofgoiter disease attributed to iodine deficiency. As part of your investigation, you must make field measurements of traces of iodide in groundwater. The procedure is to into an intensely colored complex with the dye brilliant green inthe organic solvent toluene.
(a)A solution of the colored complex exhibited an absorbance of 0.267 at 635nmin a 1.00 - cm cuvet. A blank solution made from distilled water in place of groundwater had an absorbance of 0.019 . Find the molar absorptivity of the coloredcomplex.
(b) The absorbance of an unknown solution prepared from groundwater was0.175. Find the concentration of the unknown.
If the observed absorbance is 0.200 and the blank absorbance is 0.049,
what is the concentration of Fe (mg/mL) in the serum?
Preparing standards for a calibration curve.
(a) How much ferrous ammonium sulfateshould be dissolved in a 500mL volumetric flask withto obtain a stock solution with?
(b) When making stock solution (a), you weighed out 3.627 g of reagent. What is the Fe concentration in?
(c) How would you prepare 250mL of standard containing containing infrom stock solution (b) using only 5- and 10-mL Class A pipets, only 250mL volumetric flasks, and only two consecutive dilutions of the stock solution? For example, to prepare a solution with , you could first dilute 15mL(=10+5mL) of stock solution up to 250 mL Then dilute 15mL of the new solution up to 250 mL again to get
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