lOMoARcPSD|47389193
Question 1 [10]
A mining company presented an analyst with five acid mine effluent (water) samples
collected from a pond close to the mining site. The analyst is asked to determine the
concentration of chromium (Cr) in the effluent sample. According USEPA, the maximum
allowable level for Cr is 50.00 μg/L but higher concentrations are expected. The
physicochemical properties of the effluent samples are presented in the Table below.
The following instruments are available in your laboratory: AAS, HG-AAS, GF-AAS
and ICP-OES. All working standard solutions must be prepared in 1% nitric acid
solution.
From the available instruments, choose the most suitable instrument/s for the analysis. In
your answer, you need to comment on the suitability of each given instrument explaining
why it is suitable or not suitable. Also mention if special precautions are needed. (10)
Question 2 [9]
2.1. Describe the preparation of six working standards for Cr in your suggested calibration
range using 1000 mg/L stock solution. (5)
2.2. In analytical instrumental analysis, noise reduction is crucial. Explain, briefly, the most
common techniques for reducing noise. (4)
Question 3 [10]
3.1. (i) Describe the differences between a linear ToF mass spectrometer and an orthogonal
ToF instrument. (2)
(ii) What are the advantages and limitations of these two geometries? (3)
3.2. Describe three ways of introducing a sample into an ICP torch. (3)
3.3. A chromatogram of a mixture of compound X and Y provided the following data (see
Table 3.1):
Table 3.1: Chromatographic data for U and V
3
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, lOMoARcPSD|47389193
Mobile phase peak Compound X Compound Y
Retention time (min) 0.81 9.35 10.76
Peak width (at base) 0.01 1.13 1.19
(i) For compound X, calculate (correct to 3 sig figs) its retention factor. (1)
(ii) Calculate (correct to 3 sig figs) the selectivity factor for compound X and Y. (1)
Question 4 [12]
4.1. You are tasked to analyse the content of organic compounds from each of these sources,
air freshners, shampoo, upholstery, and lotion. Which chromatographic technique or
techniiques (HPLC, GC, or SFC) would you choose for this analysis and why? Consider
factors such as the nature of the sample, the properties of the compounds, and the
advantages and limitations of each technique in your explanation. (3)
4.2. A capillary zone electrophoresis was used for the electrophoretic separation of
chlorophenol red and indigo carmine dyes. A solution containing known concentrations of
chlorophenol red and indigo carmine dyes was prepared in a 100mL beaker. After the
addition of other necessary reagents, the capillary (40 cm) was deepened into the sample
solution. A potential of 30 kV was applied, which resulted in the migration of the analytes
towards the detector side, which was placed 30 cm from the injection end of the capillary.
The migration rate of chlorophenol red was 0.85 mm s-1 and electrophoretic mobility was
3.83 x 10-4 cm2 s-1 V-1. How long will it take for the chlorophenol analyte to reach the
detector? (4)
4.3. A solution of I2 in ethanol had a density of 0.947 g/cm3. A 1.25 cm layer was found to
transmit 23.3% of the radiation from a Mo Ka source. Mass absorption coefficients for I,
C, H, and O are 39.2, 0.70, 0.00, and 1.50, respectively. Calculate the percentage of I2
present in sthis solution. (5)
Question 5 [9]
5.1. Calculate the relative number of 19F nuclei in the higher and lower magnetic states at 25
°C in magnetic fields of 7.05 T magnet. (4)
5.1. How do the spectra for electron ionisation and chemical ionisation sources differ from one
another? (2)
4
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, lOMoARcPSD|47389193
5.2. List three (3) major disadvantages of LC-NMR. (3)
© UNISA 2024
5
Downloaded by Dorothy Reyes ()
, lOMoARcPSD|47389193
USEFUL DATA
Planck’s constanbt: 6.626 x 10-34 Js
6
Downloaded by Dorothy Reyes ()
Question 1 [10]
A mining company presented an analyst with five acid mine effluent (water) samples
collected from a pond close to the mining site. The analyst is asked to determine the
concentration of chromium (Cr) in the effluent sample. According USEPA, the maximum
allowable level for Cr is 50.00 μg/L but higher concentrations are expected. The
physicochemical properties of the effluent samples are presented in the Table below.
The following instruments are available in your laboratory: AAS, HG-AAS, GF-AAS
and ICP-OES. All working standard solutions must be prepared in 1% nitric acid
solution.
From the available instruments, choose the most suitable instrument/s for the analysis. In
your answer, you need to comment on the suitability of each given instrument explaining
why it is suitable or not suitable. Also mention if special precautions are needed. (10)
Question 2 [9]
2.1. Describe the preparation of six working standards for Cr in your suggested calibration
range using 1000 mg/L stock solution. (5)
2.2. In analytical instrumental analysis, noise reduction is crucial. Explain, briefly, the most
common techniques for reducing noise. (4)
Question 3 [10]
3.1. (i) Describe the differences between a linear ToF mass spectrometer and an orthogonal
ToF instrument. (2)
(ii) What are the advantages and limitations of these two geometries? (3)
3.2. Describe three ways of introducing a sample into an ICP torch. (3)
3.3. A chromatogram of a mixture of compound X and Y provided the following data (see
Table 3.1):
Table 3.1: Chromatographic data for U and V
3
Downloaded by Dorothy Reyes ()
, lOMoARcPSD|47389193
Mobile phase peak Compound X Compound Y
Retention time (min) 0.81 9.35 10.76
Peak width (at base) 0.01 1.13 1.19
(i) For compound X, calculate (correct to 3 sig figs) its retention factor. (1)
(ii) Calculate (correct to 3 sig figs) the selectivity factor for compound X and Y. (1)
Question 4 [12]
4.1. You are tasked to analyse the content of organic compounds from each of these sources,
air freshners, shampoo, upholstery, and lotion. Which chromatographic technique or
techniiques (HPLC, GC, or SFC) would you choose for this analysis and why? Consider
factors such as the nature of the sample, the properties of the compounds, and the
advantages and limitations of each technique in your explanation. (3)
4.2. A capillary zone electrophoresis was used for the electrophoretic separation of
chlorophenol red and indigo carmine dyes. A solution containing known concentrations of
chlorophenol red and indigo carmine dyes was prepared in a 100mL beaker. After the
addition of other necessary reagents, the capillary (40 cm) was deepened into the sample
solution. A potential of 30 kV was applied, which resulted in the migration of the analytes
towards the detector side, which was placed 30 cm from the injection end of the capillary.
The migration rate of chlorophenol red was 0.85 mm s-1 and electrophoretic mobility was
3.83 x 10-4 cm2 s-1 V-1. How long will it take for the chlorophenol analyte to reach the
detector? (4)
4.3. A solution of I2 in ethanol had a density of 0.947 g/cm3. A 1.25 cm layer was found to
transmit 23.3% of the radiation from a Mo Ka source. Mass absorption coefficients for I,
C, H, and O are 39.2, 0.70, 0.00, and 1.50, respectively. Calculate the percentage of I2
present in sthis solution. (5)
Question 5 [9]
5.1. Calculate the relative number of 19F nuclei in the higher and lower magnetic states at 25
°C in magnetic fields of 7.05 T magnet. (4)
5.1. How do the spectra for electron ionisation and chemical ionisation sources differ from one
another? (2)
4
Downloaded by Dorothy Reyes ()
, lOMoARcPSD|47389193
5.2. List three (3) major disadvantages of LC-NMR. (3)
© UNISA 2024
5
Downloaded by Dorothy Reyes ()
, lOMoARcPSD|47389193
USEFUL DATA
Planck’s constanbt: 6.626 x 10-34 Js
6
Downloaded by Dorothy Reyes ()
