360 Answers to 1997 December 360 Final Exam

2(i) FAAS

FAES

Furnace AAS

ICP

Spark Emission

Arc Emission

Hydride generation AAS

Cold Vapour Hg AAS

(ii) DPP:The sample is put in solution with a high concentration of electrolyte and the current is measured as a function of a changing applied voltage. A three electrode system is used, with a dropping mercury electrode as the working electrode. The voltage is changed steadily, with pulses(eg 50 mV) being applied towards the end of each drop.The current is actually measured before and after the application of the voltage pulse, and the current difference is plotted as a function of time.

Adv: Can analyse and identify several elements in one run

Dis: LOD higher than for furnace method. Only analyses easily reducible species.

Must be in soln.

FAAS:The sample is taken into solution and sucked through a nebuliser.. The sample is dispersed into an aerosol, and the smaller drops are carried to the flame where the solvent is evaporated and the sample atomized. The absorption of light (of characteristic wavelength) by these atoms is then used to quantify them.

Adv: Method is simple and reproducible.

Dis: High LOD, sample must be in solution.

5) nmr: CH2, CH3 by the C=O, CH3 by the CH2, and TMS.

Integral:2:3:3

Structure is CH3CH2OC=OCH3

IR:OH absorption, small, probably just from wet Kbr

overtone of C=O

C-H stretch

C=O stretch

C-H bend - asym CH3 and CH2 scissor

C-H bend - sym CH3 bend

C-O stretch

6) (a) give info on vibrations

(b) detector is at right angles to light source

stokes shift

(d) Beer’s law applies for quantitative analysis

7) Preconcentration -solvent extraction or solid phase

Use 15 mL aliquots instead of 5 mL

Use an organic solvent -from the initial solvent extraction, perhaps

Add strontium

Use a hotter flame

Use a furnace method

8) First order scattering

Fluorescence -with small contribution from Raman underneath

Light from source excites the pyrene. It gives off light in all directions, some reaching the detector which is at right angles to light beam from source.

Second order scattering - when the emission monochromator (in front of detector) is set to 680 during the emission scan, it will also let through light of 680/2 and thus we will see a small peak, because our excitation wavelength is 340 nm.

SDS Kbr pellet - grind 1 mg sample with 50 mg dry Kbr and press into a glassy disc

Dissolve the SDS in water and run in a liquid cell with BaF2 windows, or in a ZnSe ATR trough or circle cell.

Ibuprofen Dissolve 10 mg in 0.5 mL CDCl3 containing 1% TMS and put it in an nmr tube with a cap on.

Slime Cold Vapour Hg analysis will give the best LOD will the least sample prep. Take the Hg into soln, add SnCl2 to reduce the Hg to its elemental state, then blow the Hg vapour through a quartz cell by bubbling N2 through the solution. Quantitate by measuring the absortion of light from a Hg HCL.

Light Scattering

Turbidimetry

Nephelometry

Raman

Tyndall

Rayleigh

First and second order scattering (as described above) act as interferences in fluorescence methods

Raman is often considered to be a scattering method - where the wavelength has been changed

Light is absorbed then given off again - at a wavelength increased or decreased by an amount euivalent to a vibration.