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Chapter 22: Q8P (page 600)

Bone consists of the protein collagen and the mineral hydroxyapatite,Ca10(PO4)6(OH)2. The content of archaeological humanskeletons measured by graphite furnace atomic absorption shedslight on customs and economic status of individuals in historicaltimes. 37 Explain why La3+is added to bone samples to suppressmatrix interference in Pbanalysis.

Short Answer

Expert verified

La3+ appears to be a releasing agent, as it preferentially reacts with PO42-, releasing Pb2+ .

Step by step solution

01

Define release agent.

A release agent (also known as a release coating, release agent, or mould release coating) is a substance that prevents other materials from adhering to surfaces. Mould release, die-cast release, plastic release, adhesive release, tyre and web release are all procedures where it can help.

02

Explain why  La3+ is added to bone samples to suppress matrix interference in   analysis.

To avoid the chemical matrix effect, La3+ is employed. By creating thermally stable compounds,PO42- prevents the atomization of Pb2+ . La3+ appears to be a releasing agent, as it preferentially reacts with PO42-, releasing Pb2+ .

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Most popular questions from this chapter

What resolving power is required to distinguishCH3CH2+fromHC=O+?

(This is a long exercise suitable for group work.) Relative intenities for the molecular ion region of several compounds are listed in arts (a)-(d) and shown in the figure. Suggest a composition for each nolecule and calculate the expected isotopic peak intensities.

a) m/z(intensity):94(999),95(68),96(3)

b)m/z(intensity):156(566),157(46),158(520),159(35)

c) m/z (intensity):224(791),225(63),226(754),227(60),28(264),229(19),230(29)

d)m/z(intensity):154(122),155(9),156(12)(Hint:Containssulfur.)

Phytoplankton at the ocean surface maintain the fluidity of their cell membranes by altering their lipid (fat) composition when the temperature changes. When the ocean temperature is high, plankton synthesize relatively more 37:2 than 37:364O⏟37:2=C37H70O(CH2)11(CH2)5CH)13CH3

After they die, plankton sink to the ocean fl oor and end up buried insediment. The deeper we sample a sediment, the further back into time we delve. By measuring the relative quantities of cell-membrane compounds at different depths in the sediment, we can infer the temperature of the ocean long ago. The molecular ion regions of the chemical ionization mass spectra of 37:2 and 37:3 are listed in the table. Predict the expected intensities of M, M11, and M12 for each of the four species listed. Include contributions from C, H, O, and N, as appropriate. Compare your predictions with the observed values. Discrepant intensities in these data are typical unless care is taken to obtain high-quality data.

Quantitative analysis by selected ion monitoring. Caffeine in beverages and urine can be measured by adding caffeine- D3as an internal standard and using selected ion monitoring to measure each compound by gas chromatography. The figure shows mass chromatograms of caffeine (m/z,194)and caffeine-DD3(m-z.197), which have nearly the same retention time.

Suppose that the following data were obtained for standard mixtures:

(a) Compute the mean response factor in the equation

role="math" localid="1664874599903" AreaofanalytesignalAreaofstandardsingle=F(concentrationofanalyteconcentrationofstandard)

(b) For analysis of a cola beverage, 1.000mL of beverage was treated with 50.0μLof standard solution containing 1.11 g/Lcaffeine-D3 in methanol. The combined solution was passed through a solid-phase extraction cartridge that retains caffeine. Polar solutes were washed off with water. Then the caffeine was washed off the cartridge with an organic solvent and the solvent was evaporated to dryness. The residue was dissolved in50μL of methanol for gas chromatography. Peak areas were 1144 for m/z197 and 1733 for m/z194. Find the concentration of caffeine (mg/L ) in the beverage.

Protein molecular mass from electrospray. The enzyme lysozyme 59exhibits MHnn+peaks at m/z = 1789.1, 1590.4, 1301.5 and 1 193.1. Follow the procedure of Table 22-3 to find the mean molecular mass and its standard deviation.
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