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Lecture Notes Monday April 2nd 2007

Answers to Quiz:

Questions	Answers
What is the concentration in mol L-1 of a 10 ppb solution of an element whose molar mass is 50 g mol-1?	2.0 x 10^-7^ M
What is the concentration in ppm of a solution containing 25 µmol L-1 of an element of molar mass 100 g mol-1?	2.5 ppm
You have a stock 100.0 ppm solution. You want to make 25 mL of a 200 ppb solution by dilution in one step. What volume (in µL) do you take?	50.0 µL

Separation.

Major topic in analytical chemistry. Can either be real (analyte(s) end up in one beaker and matrix end up in another) or figurative. That is the conditions are arranged so that only the analyte is detected. This can be done through selective reactions, of which the most selective are those of biological origin involving antibodies or enzymes.

Potentially interfering species can be masked, i.e. a masking agent is added to react with the unwanted sample component to prevent it from reacting with the analytical reagent. Many metals can be masked by the addition of a strong complexing agent such as EDTA.

Suggest procedures for the separation of the following mixtures.

Ground glass and wood fibers

Exploit differences in density, and float the wood on a solvent of density intermediate between that of wood and glass (water, maybe)

Iron filings and cornflakes

Use a magnet.

Water and ethanol

Distillation will work up to a point. The the final small amount water has to be removed by a solid-phase extractant such as silica gel, molecular sieve, sodium wire.

Silver and sodium (in solution as the nitrate salts).

Precipitate the silver. Could be done electrochemically to get silver metal. Or add halide to precipitate silver chloride (for example)

Carbon dioxide and oxygen

Cool and exploit differences in melting and boiling points.

Sand and gravel and salt.

Sieve, as gravel is big. Dissolve salt in water, filter to retain sand. Evaporate water to get salt.

Arsenic and phosphorus (in solution as the anions arsenate and phosphate as the sodium salts)

Hydride generation. As forms a gas, P does not. Trap arsine in absorbing solution.

Albumin and glucose (in solution)

Filtration at molecular level as albumin is big. Dialysis will partially separate. Affinity chromatography (solid-phase extraction with a material that binds the albumin), electrophoresis under conditions that make the albumin charged (pH control of addition of sodium decency), or even size exclusion (gel) filtration.