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Calibration of Instrument

The instrument was first calibrated before determinations of heavy metal concentrations were made with it. Calibration curves were made using the working standard solutions for the respective elements. The concentrations of the trace metals were determined using the Atomic Absorption Spectrophotometer ( AAS). The instrument was switched on and allowed to run for 10 minutes to equilibrate before the tests were commenced. The working conditions of the instrument were ascertained at this point , analysis made optimal, confirmed in respect of each element being analyzed.

Among the conditions include lamp current, correct band pass, flame type, resonance wavelength and fuel flow rate. With the working standard solutions aspirated into the

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flame with respective cathode lamps for each metal correctly in position, the corresponding absorbance for each concentration recorded. The calibration curve for each metal was thereby obtained. A blank test was ran immediately after each metal determination by carrying out the same processes with the omission of the sample.

When the sample was aspirated into the flame, the sample was reduced to free atoms that was able to absorb resonance radiation from its hallow cathode lamp.

The amount of light absorbed was related to the concentration of the analyte as given by Beer-Lamberts’ Law.

A = Ebc (3.1) Where,

A = absorbance; E =molar absorptivity; C = Concentration of the analyte

The corresponding concentrations of the metals in mg/L obtained versus the results of the absorbance for the working standard solution for metal were plotted. Sample concentrations were obtained from the standard graph for respective element.

Determination of manganesse, iron, lead, cadmium, zinc, chromium and copper by atomic absorption spectrophotometer.

Standard metal solution : A series of standard metal solutions were prepared by dilution of the following stock metal solution with water containing 1.5cm³ conc HNO3.

i. Manganese: 3.076g manganese sulphate (MnSO4.H2O) was dissolved in 200 cm³ distilled water,1.00 cm³ =1.00mg Mn

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ii. Lead : 1.598g lead nitrate was dissolved in about 200 cm³ of distilled water and 1.5 cm³ml of Conc HNO3 added, mixed and made up to 1000 cm³ with distilled water.1.0 cm³= 1.0mg Pb

iii. Cadmium: 1.00g cadmium metal was dissolved in a minimum volume of 1M HNO3.1.00 cm³=1.00mgCd

iv. Nickel : 1.273 nickel oxide(NiO)was dissolved in a minimum volume of 10%(v/v)HCl and then diluted with 1000 cm³ of distilled water,1.00 cm³= 1.00 mg Ni

v. Zinc: 1.00g zinc metal was dissolved in 20 cm³ml 1M HCl and diluted with 1000 cm³ of distilled water,1.00 cm³ =1.0mgZn

vi. Iron: 5.0503g of iron (ii)Ammonium Sulphate, Fe(NH4)2(SO4), was dissolved in distilled water and then made up to 1litre with distilled water[1ml = 1mgFe.

vii. Chromium: 2.8285g of anhydrous K2Cr2O7 was dissolved in distilled water and made up to 1litre.1 cm³= 1mgCr.

viii. Copper metal: 1.0gwas dissolved in 50 cm³ of 5M HNO3 acid. The solution was diluted to 1liter with de-ionized water in a 1dm³ volumetric flask.1 cm³=1mg Cu Standardization: At least five concentrations of each stock standard metal solution were prepared by diluting aliquots of the stock solution to 100 cm³.Each standard was aspirated in turn into the flame and the absorbance recorded. A calibration curve for each element to be determined was plotted on a linear graph paper, the absorbance of standards versus their concentrations in mg/L.

Analysis of samples : The nebulizer was rinsed by aspirating water containing 1.5 cm³ Conc HNO3.The instrument was zeroed by aspirating the blank. The samples werethen atomizedand the absorbance recorded.

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Calculation : The concentration of each metal ion in mg/L was calculated by referring to the appropriate calibration curve(this was obtained automatically from an attached software computer system).

3.10: Determination of Temperature

This was carried in-situ at all the sites. The apparatus used for measuring temperature was the mercury in glass centigrade thermometer. The thermometer was placed vertically and the bulb containing the mercury was immersed in the water/effluent.

This was allowed to stand still for about 2minutesfor the reading to be steady. This was taken and noted in⁰C. The readings were taken to the nearest half degree (Ademorati, 1996;

APHA, 1998).

3.11: Determination of Chloride in Water

This anion was determined by titration of the water sample with silver nitrate solution procedure. To 100 cm³ of the water sample was added 5% solution of potassium chromate (1.0 cm³) and was titrated with 0.1M silver nitrate solution to the first appearance of a buffer color(AOAC,2002);(APHA ,1998).

Calculation:

Chloride content (mg/l) =

𝑉𝑉𝐶𝐶𝑀𝑀𝐶𝐶𝐸𝐸𝐶𝐶1000

𝑉𝑉1

Where:

V=volume, M= Molarity, E=Equivalent weight of chloride, V1 = volume ofsample used.

66 3.12: Determination of pH

Thiswas taken in-situ at all the sites using Hannamicroprocessor pHmeter(HANNA 211).

The electrode was rinsed with distilled water and wiped dry. The pH electrode was rinsed in a beaker containing a little of sample. Sufficient volume of sample was poured into the beaker to allow the tips of the electrode to be immersed to a depth of about 2ml. The electrode was kept about 1ml from the sides of the beaker and the bottom of the beaker. The temperature adjustment dial was adjusted accordingly.

3.13: Determination of electrical conductivity

This was taken in-situ at all the sites using Hanna microprocessor Electrical Conductivity meter(HANNA EC 215). The conductivity cell was rinsed with at least three portions of the sample. The temperature of the sample was then adjusted to 26.01^oC and allowed to stabilize to temperature of the river . 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 (APHA, 1998).

Calculation,

First, the cell constant, K (cm⁻¹) was calculated.

K ═ R (kCl) x C

cm (3.3)

where:

R (kCl) isthe measured resistance of the standard potassium chloride solution.

C

═ conductivity (uScm

) of thestandard potassium chloride solution

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when t ═ 25

C.

C

conductivityof the sample which is given

C

𝑅𝑅𝐶𝐶

𝑅𝑅𝐶𝐶

. Siemen per meter(S/M) (3.4)

Where

R

measured resistance of the water sample.

3.14 Biological Oxygen Demand