24 Jun 1. Shellfish are particularly good at
1. Shellfish are particularly good at concentrating heavy metals in seawater. A sample from scallops was analyzed for cadmium using atomic absorption spectroscopy and the following results were obtained: Cd Standard Concentration (ppm) Absorbance 0 0.00 2 0.10 4 0.20 6 0.30 8 0.40 10 0.50 a) Construct a Calibration Curve. b) One of the scallops was removed from its shell and chopped finely in a food processor. A 2.0g portion was digested on a hotplate with 10ml nitric acid. The mixture was then analyzed using AAS. An aliquot of this digest of scallops gave an absorbance of 0.42. Determine: i) The concentration of cadmium in the 10ml solution (in ppm) ii) The amount of cadmium in the 2.0 g sample of scallop iii) Express the amount of cadmium in mg per gram sample of scallop (ppt). 2. Explain (briefly! A few sentences ONLY!) why a continuous spectrum source lamp is a good source in molecular absorption spectroscopy, but not in atomic absorption spectroscopy. 3. Graphite furnace atomizers are renowned in Atomic Absorption Spectrometry for their exceptionally low detection limits (1012 g and lower for many elements). Why are detection limits so much better with graphite furnaces than with flame atom cells in AAS? 4. The Raman spectrum of SO2 has a peak at 1325 cm1. When excited by an argonion laser at 514.5 nm, at what wavelengths (nm) will the Stokes and antiStokes Raman lines for this spectral feature be measured? Which of these is more intense (include your reasoning!)? 5.Given the EI mass spectrum below, what organic compound is this? 6. Give the species from the fragmentations (labeled masses) in the mass spectrum of butanone. Make sure you indicate radical cations, cations or radicals where appropriate. Include the masses of all fragments in the scheme. 7. What are three advantages and three disadvantages to a DESI type ion source for a Mass Spectroscopy system?
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