3.5.1 Apparatus:
• Conductivity meter
3.5.2 Method: Analysis was carried out according to APHA 2510 B guideline Model DDS- 307 (Laker and Dupreez, 1982)
35 3.5.3 Principles: It employs the magnitude of the total concentration of ionic solutes in solution and also the degree of dissociation.
3.5.4 Procedure:
10g of sample was dissolved in 10ml of distilled water
The conductivity cell was rinsed with at least three portions of the sample
The temperature of the sample was then adjusted to 20 ±0.10C
The conductivity cell containing the electrodes was immersed in sufficient volume of the sample
The conductivity meter was turned on and the conductivity of the sample recorded.
Resistivity is the inverse of electrical conductivity 3.6 METHODS FOR THE METAL ANALYSIS:
Heavy metal analysis was conducted using Varian AA240FS Atomic Absorption Spectrophotometer according to the method of APHA (American Public Health Association) described by (Laker and Dupreez, 1982).
3.6.1 Sample Digestion:
i. 2g of the dried sample were weighed into a digestion flask and 20ml of the acid mixture (650ml conc HNO3; 80ml Perchloric acid; 20ml conc H2SO4; ie Calgon) were added.
ii. The flask was heated until a clear digest was obtained.
iii. The digest was diluted with distilled water to the 250ml mark iv. Appropriate dilutions were then made for each element 3.6.2 Apparatus:
• Varian AA240FS Atomic Absorption Spectrophotometer
3.6.3 Working principle: Atomic absorption spectrometer's working principle is based on the sample being aspirated into the flame and atomized when the AAS's light beam is directed through the flame into the monochromator, and onto the detector that measures the amount of light absorbed by the atomized element in the flame. Since metals have their own characteristic absorption wavelength, a source lamp composed of that element is used, making the method relatively free from spectral or radiational interferences. The amount of energy of the characteristic wavelength absorbed in the flame is proportional to the concentration of the element in the sample.
36 3.6.4 Procedure: The sample was thoroughly mixed by shaking, and 100ml of it was transferred into a glass beaker of 250ml volume, to which 5ml of conc. nitric acid was added and heated to boil till the volume was reduced to about 20ml, by adding conc. nitric acid in increments of 5ml till all the residue was completely dissolved. The mixture was cooled, transferred and made up to 100ml using metal free distilled water. The sample was aspirated into the oxidising air-acetylene flame. When the aqueous sample was aspirated, the sensitivity for 1% absorption was observed.
Table 1; Preparation of reference solutions Standard Flame Emission Conditions for Ca
Wavelength (nm) Slit (nm) Flame
422.7 0.2 Nitrous oxide-acetylene
Stock Standard Solution Calcium, 500mg/l. to 1,249g of calcium carbonate, CaCO3, add 50ml of deionized water. Dissolve by adding dropwise 10ml of HCL. Dilute to 1 liter with deionized water.
Standard Flame Emission Conditions for Al
Wavelength (nm) Slit (nm) Flame
396.2 0.2 Nitrous oxide-acetylene
Stock Standard Solution Aluminium, 1000mg/l. Dissolve 1,000g of aluminium wire in a minimum amount of (1+1) HCL, adding a small drop of mercury as a catalyst. Dilute to 1 liter with 1%
(v/v) HCL. Filter the solution to remove the mercury.
Standard Flame Emission Conditions for Ag
Wavelength (nm) Slit (nm) Flame
328.1 0.2 Air-acetylene
Stock Standard Solution Silver, 500mg/l. Dissolve 787g of silver nitrate, AgNO3
in 50ml of deonized water. Dilute to 1 liter with 1%
(v/v) HNO3. Silver is sensitive to light. Store in an amber glass bottle. Prepare standards in 5% (v/v) HNO3
to keep the silver in solution.
Standard Flame Emission Conditions for Cd
Wavelength (nm) Slit (nm) Flame
326.1 0.2 Air-acetylene
Stock Standard Solution Cadmium, 100mg/l. Dissolve 1,000g of cadmium metal in a minimum volume of (1+1) HCL, Dilute to 1 liter with 1 % (v/v) HCL.
37 Standard Flame Emission Conditions for Co
Wavelength (nm) Slit (nm) Flame
315.4 0.2 Air-acetylene
Stock Standard Solution Cobalt, 1000 mg/l. Dissolve 1,000g of cobalt metal in a minimum volume of (1+1) HCL. Dilute to 1 liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Cr
Wavelength (nm) Slit (nm) Flame
425.4 0.2 Air-acetylene
Stock Standard Solution Chromium, 1000mg/L. Dissolve 3,735g of potassium chromate, K2CrO4, in deionized water and dilute to 1 liter with deionized water.
Standard Flame Emission Conditions for Fe
Wavelength (nm) Slit (nm) Flame
372.0 0.2 Air-acetylene
Stock Standard Solution Iron, 1000mg/l. Dissolve 1,000g of iron wire in 50ml of (1+1) HNO3. Dilute to 1 liter with deionized water.
Standard Flame Emission Conditions for Mn
Wavelength (nm) Slit (nm) Flame
403.1 0.2 Air-acetylene
Stock Standard Solution Manganese, 1000 mg/l, Dissolve 1,000g of manganese metal in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL,
Standard Flame Emission Conditions for K
Wavelength (nm) Slit (nm) Flame
766.5 0.2/0.4 Air – acetylene
Stock Standard Solution Potassium, 1000mg/l. Dissolve 1,907g of potassium chloride, KCL, in deionized water and dilute to 1 liter with deionized water.
Standard Flame Emission Conditions for Ni
Wavelength (nm) Slit (nm) Flame
341.5 0.2 Air-acetylene
Stock Standard Solution Nickel,1000 mg/l. Dissolve 1,000g of nickel in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Zn
Wavelength (nm) Slit (nm) Flame
213.9 0.2 Air-acetylene
Stock Standard Solution Zinc,1000 mg/l. Dissolve 1,000g of zinc metal in a
minimum volume of (1+1) HNO3. Dilute to 1 litre with 1%
(v/v) HCL.
Standard Flame Emission Conditions for Pb
38
Wavelength (nm) Slit (nm) Flame
403.1 0.2 Air-acetylene
Stock Standard Solution Lead, 1000mg/L. Dissolve 1,000g of lead metal in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Cu
Wavelength (nm) Slit (nm) Flame
324.8 0.2 Air-acetylene
Stock Standard Solution Copper,1000 mg/l. Dissolve 1,000g of copper metal in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Si
Wavelength (nm) Slit (nm) Flame
251.6 0.2 Air-acetylene
Stock Standard Solution Silicon,1000 mg/l, Dissolve 1,000g of standard silicon ion in a minimum volume of (1+1) HNO3. Dilute to 1liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Mg
Wavelength (nm) Slit (nm) Flame
285.21 0.2 Air-acetylene
Stock Standard Solution Magnesium,1000 mg/l. Dissolve 1,000g of magnesium in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL.
Standard Flame Emission Conditions for Na
Wavelength (nm) Slit (nm) Flame
589.6 0.2 Air-acetylene
Stock Standard Solution Sodium,1000 mg/l. Dissolve 1,000g of sodium in a minimum volume of (1+1) HNO3. Dilute to 1 liter with 1% (v/v) HCL.
3.7 REDUCING SAMPLES OF SOIL TO TESTING SIZE AASHTO T 248