Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE credits
In this project we have been working with two different instruments home-made AMA 254 and Hydride Generator. Home-made AMA 254 was coupled to a fluorescence detector. The Hydride Generator was coupled to atomic absorption spectroscopy (AAS), by an optical path.
Calibration of mass-flow controller by applying a suitable gas in the inlet and a bubbles calibration unit at the outlet. All date was saved by labview program was used
The first configurations, carrier gas was fed into the middle of the catalyzer tube
and the gold-trap by a T-shape connector to carry mercury to the detector.
Condensation of mercury vapour when the gas-stream collided to the silicon walls, at the T-shape connection leads to failing.
Second configuration, two positioned-switching valve was introduced between the oxygen and argon tanks, allowing only one gas to reach MFC depending on the switching position.
There are four different parameters memory effects, repeatability, accuracy and sensitivity, have to investigated to know that the machine gives reliable result when running real samples.
Memory effect is one reason for deviation of the analysis. It is obvious that some mercury still remains within the tube after running. Memory effect is not significant at high concentration of the analyte, but could be troublesome at lower concentration.
Repeatability was tested by running 3 replicates with the same concentration of the analyte. This is important for knowing the precision of the analysis.
Reference material MESS-92 (92ppb) was used to evaluate the accuracy of the analysis . Triplicate was running and the mean value was calculated to 98.3 ppb, the deviation was 6.86%.
By comparing the mercury fluorescence detector and atomic absorption (AAS) it
become evident that the fluorescence detector is much more suitable for analysis with
AMA 254 as it gave an overloaded signal whereas the atomic absorption only
appeared as noise.
Minor Field Study in Chemistry – Autumn 2010 Page 4
The comparison between the mercury fluorescence detector and atomic absorption (AAS) was done with 0.05 gram(g) tuna fish samples. Mercury fluorescence detector gave an overloaded signal, whereas the AAS signal appeared as noise. It is evident that the fluorescence detector is much more sensitive than the AAS detector.
Hydride generation is one common method for determining mercury in water. Three different channels are used for pumping the solutions and forming hydride, they are
Hydrochloric acid, NaBH4and sample (blank, standards). The hydride form of mercury was flushed and collected into the gold trap by nitrogen gas. After that the gold-trap is heated up to release mercury optical cell where the absorption as a peak was measured in the same manner as normal flame AAS without using of flame.
In our project we also made up a temperature controller to control the temperature. The real temperature was measured by thermocouple and was designed like a small box.
2011. , 19 p.