Instrumental methods in analytical UE Past Papers Questions.

In a chromatographic analysis of lemon oil a peak for limonene has a retention time of 8.36 min with a baseline width of 0.96 min. -Terpinene elutes at 9.54 min with a baseline width of 0.64 min. What is the resolution between the two peaks?

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In a chromatographic analysis of low molecular weight acids, butyric acid elutes with retention time of 7.63 min. The column`s dead time is 0.31 min. Calculate the retention factor for butyric acid.

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The concentration of Polynuclear Aromatic Hydrocarbons (PAH) in soil are determined by first extracting the PAHs with methylene chloride. The extract is diluted , if necessary, and the PAHs separated by HPLC using a UV/Vis or Fluorescence detector. Calibration is achieved using one or more external standards. In a typical analysis a 2.013-g sample of dried soil is extracted with 20.00 mL of methylene chloride. After filtering to remove the soil, a 1.00-mL portion of the extract is removed and diluted to 10.00 mL with acetonitrile. Injecting 5  of the diluted extract into a PHLC gives a signal of 0.217 (arbitrary units) for the PAH fluoranthene . When 5  of 1 20.00-ppm fluoranthene standard is analyzed using the same conditions, a signal of 0.258 is measured. What is the concentration of fluoranthene in the soil in ppm.

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In fulfillment of the requirements for B.Sc. Education Degree programme, a 3^rd year Education student conducted a special project (SP) on “Determination of Cu and Zn in Tissue samples from fish collected from Msimbazi river estuary”, the river which receives waste water from industrial areas in Dar es Salaam City. Copper and Zinc were isolated by digesting tissue samples after extracting any fatty tissue. The concentration of copper and zinc in the supernatant were determined by atomic absorption using an air-acetylene flame as follows:

Fish tissue sample were obtained by a muscle needle biopsy and were dried for 24-30 hours at 105°C to remove all traces of moisture. The fatty tissue in the dried samples was removed by extracting overnight with anhydrous ether. After removing the ether , the sample was dried to obtain the fat-free dry tissue weight (FFDT). The sample was digested at 68°C for 20-24 h using 3 mL of 0.75 M . After centrifuging at 2500 rpm for 10 min, the supernatant was transferred to a 5mL volumetric flask. The digestion was repeated two more times, for 2-4 h each, using 0.9-mL aliquots of 0.75 M  . These supernatants were added to the 5-mL volumetric flast, which is diluted to volume with 0.75 M . The concentration of Cu and Zn in the diluted supernatant was determined by atomic absorption spectroscopy using an air -acetylene flame and external standards. COpper was analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc was analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction was used for zinc . Results were reported as micrograms of Cu or Zn per gram of FFDT.

The following absobances were obtained for a set of Cu calibration standards.

	Absorbance
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 1.000	0.000 0.006 0.013 0.020 0.026 0.033 0.039 0.046 0.066

What is the concentration of copper, in micrograms per gram FFDT, for a 11.23 mg FFDT tissue sample that yields an absorbance of 0.023?.

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