water analysis 2
DESCRIPTION
Water Analysis 2TRANSCRIPT
Spectrometry-principles
Additive property of absorbance
A = A1 + A2 + A3 + ….
It is essential to subtract absorbance of a blank from absorbance of samples
Determine the concentration of a sample - calibration curve
Concentration, ppm
Co C1 C2 C3 C4 C5
Ab
sorb
an
ce
Ax
Cx
Linear relationship
Determination of IRON in water by spectrometry
Total iron (Fe3+ and Fe2+) is determined
PRINCIPLE
• Fe3+ is reduced to Fe2+ by hydroxylamine (pH 3.3)
4Fe3+ + NH2OH 4Fe2+ + NO2 + H2O + 4H+
• Formation of Fe(II)-phenantroline complex (pH 3-9)Fe2+ + 3Ph [Fe(Ph)3]2+
redish-orange (510 nm)
Standard / Sample
Buffer
Reagent
Mix, dark place (15min)Measure at 510 nm
Reduce agentAcidtoC
PROCEDURE
Determination of IRON in water by spectrometry
Determination of nitrite - principles
Nitrite (NO2-) react with sulfanilic acid and N-(1-naphthyl)-ethylenediamine to form red azo dye (max
= 540nm)
Determination of nitrite -precautions
- NO2- can be converted to NO3- or NH3 by bacteria -> preserve samples at 2-5 oC for 1-2 days
- NO2- standard solution is not stable -> re-determine the concn. by KMNO4 / oxalic acid
(KMnO4 is standardized by oxalic acid)
Determination of nitrate - principles
- 220 nm: NO3- + organic compounds absorb light- 275 nm: organic compounds absorb light- ANO3- A220nm – 2A275nm
Chemical Oxigen Demand - COD
• An indicator of organic pollutant in water
• The quantity of oxidant consumed is expressed
in terms of its oxygen equivalence (mg O2/L)
Cr2O72- is used as oxidizing agent
In oxidation reaction 1 mole Cr2O72- equal to 1.5 mole O2
Principle
Cr2O72- + Organic matter Cr3+ + H2O + CO2 +
(known amount)
• Excess K2Cr2O7 is determined by titration with Fe2+
• Excess K2Cr2O7 or Cr3+ produced is determined by
spectrophotometry
K2Cr2O7 consumed
1 mole Cr2O7-2 reacts with 6 mole Fe2+
Chemical Oxigen Demand - COD
STRONG oxidizing and toxic chemicals!
- H2SO4 , 150oC (2hrs),
- Ag(SO4): catalyst
- HgSO4 : minimize Cl- interference (HgSO4:Cl– = 10:1)
Samples should be homogenized and analyzed without delay or preserved by acidification to pH ≤ 2
PRINCIPLE
Determination of SULFATE in water by turbidimetry
Ba2+ + SO42- BaSO4
Acetate buffer
420 nm
(1-40 mg SO42-/L)
Suspended particles must be removed by filtration before analysis!!!
MgCl2, KNO3
Log(I0/IT) = k.b.C
• C: concentration of the scattering particles (w/v),
• b: is the path length
• k: constant that depends on the size, shape of
the scattering particles and the wavelength of
the source radiation.
Determination of SULFATE in water by turbidimetry
It is necessary to maintain a UNIFORM distribution of
particle sizes throughout the sample and between
samples and standards
Procedure
Standard / Sample
Buffer BaCl2 (s)
Mixed
Mixed well (1 min)Measured (420 nm, in < 5 mins)
Determination of SULFATE in water by turbidimetry