Mine Health and Safety Act, 1996 (Act No. 29 of 1996)RegulationsGuideline for a Mandatory Code of PracticeOccupational Health Programme (Occupational Hygiene and Medical Surveillance) on Personal Exposure to Airborne PollutantsAnnexuresAnnexure E : Background information, sampling and analysis on particulates10. Analysis |
The analysis and quality control must be in accordance with internationally recognised methods such as NIOSH or HSE standards.
A cellulose nitrate or a mixed ester of cellulose filter should be used if analysis is required. The sample must be forwarded to an accredited chemical analytical laboratory to determine the chemical composition of the collected sample.
Brief descriptions of the various analytical methods are included to help the occupational hygiene practitioner in discussions with the analyst and to make sure that the samples collected will be suitable for analysis - it is not to train the occupational hygiene practitioner in analytical techniques.
| 10.1 | Atomic absorption spectrometry (AAS) |
This is a common method used for analysis of metals such as:
| • | Lead. |
| • | Cadmium. |
| • | Nickel. |
| • | Copper. |
| • | Zinc. |
There are some 60-70 metallic elements, which can be analysed individually by this technique, which uses the fact that atoms in a vapour absorb light at specific wavelengths.
10.1.1 Basic operation of an AAS
The metal particulate is dissolved into a solution by immersing and heating the filter in a solvent (typically a diluted acid). Part of this solution is aspirated (sucked) into a flame, which vaporises first the solvent and then the metal. All vaporised atoms of solvent and metal pass into a chamber through which a beam of light passes. This beam is generated by a specific lamp, which produces a characteristic spectrum consisting of light specific wavelengths. For each specific metal, a lamp is chosen so that its light spectrum is compatible with the absorption characteristics of the metal.
As the atoms of the specific metal pass through the light, they absorb energy from the light and the intensity of the beam is reduced in proportion to the numbers of atoms present. The reduction in intensity is measured and by comparing this reduction (usually referred to as absorbance) with a calibration curve, a measure of the amount of element present can be obtained.
10.2 X-ray diffraction (XRD)
X-ray diffraction is an analytical technique used to identify and quantify the constituent compound in a substance. It works as follows:
| • | Many solids, and particular minerals, are crystalline (their atoms are arranged in a highly ordered three-dimensional lattice) and when x-rays are directed at them, this lattice acts as a diffraction grating. Every crystalline substance produces a unique diffraction pattern and in a mixture of substances each will produce its own pattern independently of the others. Therefore, different substances can be identified in a mixture. |
| • | The x-ray detector is swung round in an arc and a chart is produced showing lines of all the diffracted x-rays, which are picked up at different angles. The analyst will compare the patterns of the lines produced with standards and will be able to identify what is present in the sample. The more of a particular substance in the sample, the more intense will be the lines in the pattern. A calibrated x-ray diffractar will, therefore, give information not only on the type of crystalline substance in the sample, but how much there is. |
| • | X-ray diffraction only works for crystalline substances and is used particularly for analysing minerals such as quartz (a crystalline form of silica). |
10.3 X-ray fluorescence (XRF)
X-ray fluorescence is another method using x-rays, but it is used to identify and quantify elements rather than compounds. A beam of x-rays is directed at the sample, very much in the same way as XRD, but instead of the compounds in the sample diffracting the beam, the beam excites the atoms of the elements present causing them to emit their own radiation. This is a form of fluorescence. It is this secondary or fluorescent radiation, which is detected. Every element will produce radiation containing a characteristic set of wavelengths so that the trace obtained from a particular sample is compared to standard traces to determine the elements present in the sample. The intensity of the radiation given off is proportional to the amount of each element present, so if the instrument has been calibrated, it is possible to find out not only what elements are present but also how much there is.
XRF can be used to analyse elements from atomic number 9 (fluorine) upwards and is used particularly for metals.
10.4 Infra-red (IR)
Infrared can be used as an alternative method to XRD to analyse minerals. Light in the infrared region is directed onto a sample, which absorbs some of the light. A detector picks up the reflected rays of the remainder and a material is then identified and quantified according to how much light has been absorbed and in what regions of the IR spectrum.