Spectroscopy Practical Work

Hazards relevant to the practical work are listed at the start of each set of instructions.

It is important that you read them carefully BEFORE starting any laboratory practical work!

1. State the best pipette to use (giving reasons) for measuring the following volumes:

55 ?L, 1.2 mL, 8.0 mL, 350 ?L

2. Outline the steps to take in dealing with a solvent spill eg hexane.

3. Discuss the applications and limitations (speed, particle size, volume) of each of the four types of filtration systems.

4. Explain why it is necessary to centrifuge two (2) tubes of equal mass.

Hazards particular to this practical

As well as observing normal laboratory precautions, please be aware of the following.

• AAS creates toxic gases (carbon monoxide, oxides of nitrogen);

Make sure the extractor fan is running before you ignite the flame.

• The FAAS burner is very hot;

Do not touch or attempt to remove the burner.

If you need to adjust the burner angle, use the handle provided.

• FAAS uses explosive gases;

Make sure that you wear safety glasses at all times in the instrument room (as well as the wet chemistry laboratory).

Make sure that the burner compartment door is closed whenever the flame is lit. Do not attempt to clear a blocked nebuliser when the flame is lit.

Calcium content is an important water quality parameter, and (along with magnesium) contributes to water “hardness”. Analysis is possible using a wide range of techniques, including traditional titrimetry, ion selective electrode, ion chromatography, and the various atomic spectroscopic methods (atomic absorption spectroscopy, atomic emission spectroscopy). In this experiment, we will use flame atomic absorption spectroscopy (FAAS). Rather than a simple calibration curve, we use the method of standard additions to control interference from oxyanions such as phosphate or nitrate.

Method

• Pipette 20 mL tap water into each of six 100 mL volumetric flasks, and add approximately 50 mL distilled water. Add 0.0, 0.25, 0.50, 0.75, 1.0, or 1.5 mL of 1000 mg L^-1Ca into each flask, and make to the mark.

• Analyse the solutions against a distilled water blank using an air-acetylene flame and the default instrument parameters.

• Plot the results on a computer-drawn graph as absorbance vs. concentration added (mg L^-1) and determine the unknown concentration.

Pre-reading

The basics of flame atomic absorption spectroscopy (hollow cathode lamp, monochromator, atomisation, compound formation interference, ionization interference)

Calculations used for preparation of standards Calibration curve, method of standard additions

Definitions of accuracy, precision, repeatability, reproducibility, bias Descriptive statistics (mean, standard deviation)

Hazards particular to this practical work

As well as observing normal laboratory precautions, please be aware of the following.

• AAS creates toxic gases (carbon monoxide, oxides of nitrogen);

Make sure the extractor fan is running before you ignite the flame.

• The FAAS burner is very hot;

Do not touch or attempt to remove the burner.

If you need to adjust the burner angle, use the handle provided.

• FAAS uses explosive gases;

Make sure that you wear safety glasses at all times in the instrument room (as well as the wet chemistry laboratory).

Make sure that the burner compartment door is closed whenever the flame is lit. Do not attempt to clear a blocked nebuliser when the flame is lit.

• The muffle furnace is extremely hot when running, and retains its heat for some time after switching off;

• 6 M HNO3is corrosive;

Make sure that you carry out all manipulations involving hot acid in a fume hood. Neutralise and clean up all spills.