Thursday, 14 March 2019
SOP for ESTIMATION OF HEXAVALENT CHROMIUM
PRINCIPLE:
The
hexavalent chromium is determined calorimetrically by reaction with diphenylcarbazide in
acid
solution. A red-violet colored complex of unknown composition is produced. The
reaction
is very sensitive, the molar absorptivity based on chromium being about 40000 Lg –1 cm-1
at 540 nm.
MINIMUM
DETECTION LIMIT: 0.05
mg/l
REAGENTS:
1.
Stock chromium solution: Dissolve 141.4 mg K2Cr2O7
water and dilute to 100 ml;
1.00 ml = 500 µg Cr.
2.
Standard chromium solution: Dissolve 1.00 ml stock chromium
solution to 100 ml;
1.00 ml = 500 µg Cr.
3.
Phosphoric acid, H3PO4, conc.
4.
Diphenylcarbazide solution: Dissolve 250 mg 1,5-
diphenylcarbazide
(1,5-diphenylcarbazide) in 50 ml acetone. Store in a brown
bottle. Discard when solution
becomes discolored. Chromium solution (5 mg/L) ranging from 2.00
to 20.0 ml, to give
standards for 10 to 100 µg Cr, into 250-ml beakers or
conical flasks. Proceed with
subsequent treatment
PROCEDURE:
Preparation
of calibration curve:
To
compensate for possible slight losses of
chromium during digestion or other
analytical operations, treat standards by the
same procedure as the sample.
Accordingly, pipette measured volumes of standard
of standards as if they were
samples, also carrying out cupferron treatment of standards
if this is required
for samples. Develop color as for samples, transfer a suitable portion of
each
colored solution to a 1-cm absorption cell, and measure absorbance at 540 nm,
using reagent water as reference. Correct absorbance readings of standards by
subtracting absorbance of a reagent blank carried through the method.
Color
development and measurement: Add 0.25 ml (5 drops) H3PO4. Use
0.2 N
H2SO4 and a pH meter to adjust solution to pH 1.0 ±
0.3 the matter of pH range is
currently being considered by standard methods.
Transfer solution to a 100-ml volumetric
flask, dilute to 100 ml, and mix. Add
2.0 ml diphenylcarbazide solution, mix, and let stand
5 to 10 min for full
color development. Transfer an appropriate portion to a 1-cm
absorption cell
and measure its absorbance at 540 nm, using reagent water as reference.
Correct
absorbance reading of sample by subtracting absorbance of a blank through
the
method. From the corrected absorbance, determine micrograms chromium
present by
reference to the calibration curve.
CALCULATION
HEXAVALENT
CHROMIUM (mg/l) = ABS /
SLOPE
REFERENCE: APHA – 3500 Cr - B Colorimetric Method
SOP for ESTIMATION OF SOLIDS
PRINCIPLE:
TOTAL SOLIDS (TS) – The
sample is evaporated in a weighed dish on a steam
bath and is dried to a
constant mass in an oven either at 103 – 105°C or
179 to 181°C. Total residue
is calculated from increase in mass.
TOTAL DISSOLVED SOLIDS
(TDS) – the sample is filtered and the filtrate
evaporated
in tared dish on steam bath. The residue after evaporation is dried
to constant
mass at 103 – 105°C.
MINIMUM
DETECTION LIMIT(TDS): 5.0 mg/l
REQUIRMENT:
Filtration apparatus: Any
one of the following can be used.
1. Membrane filter funnel
2. Gooch crucible, 25 ml to 40
ml capacity with Gooch crucible adapter.
3. Filtration apparatus with
reservoir and coarse (40 – 60 mm) fritted disk as filter
support.
4. Suction flask of sufficient
capacity for sample size selected.
5. Drying oven for operation
at 180 ± 2 °C.
PROCEDURE:
PREPARATION:
Clean &
thoroughly wash all the glassware’s with dilute Sulphuric acid.
Rinse the
glassware’s several times with distilled water. Dry the glassware’s in oven
at
180oC for 1 hour. Keep them in desiccators for cooling. Weigh the
cooled
evaporating dishes (two nos.) initially. Note down the reading A (dish
for TS) &
B (dish for TDS).
Sample testing:
Select volume of the sample, which has residue, contains
approximately 100 to
200 mg. This value may be calculated from values of
specific conductance. To
obtain measurable residue if necessary, add successive
sample portions to the
same dish after evaporation.
Pipette this
sample to previously weighed evaporating dish A (for TS). Filter the sample
(20
ml /25 ml) using 0.45 m m membrane filter. Collect
the filtrate in a clean beaker.
Measure 10 ml or suitable aliquot of filtrate
& transfer it to second evaporating
dish B. Evaporate the water content
completely using water bath / oven. If oven is used
adjust the temp 103 – 105 oC. Cool the
dishes in desiccators.
Weigh the
cooled dishes. Again heat the samples at temperature 105oC for one
hour
and check the weight loss. If there is considerable difference in first
observation and
second one then repeat the heating till weight of dried sample
remains constant
in two consecutive observations & note down the reading
(C-for without filtration &
D-for filtrate).
OBSERVATIONS:
1. Initial weight of evaporating
dish for sample without filtration -------(A)
= g
2. Initial weight of evaporating
dish for sample with filtration---------(B)
= g
3. Final weight of evaporating
dish for sample without filtration -------
(C) =
g
4. Final weight of evaporating
dish for sample with filtration ----------
(D) = g
CALCULATIONS:
Total Solids (TS)
C - A
mg/L = ----------------------------- x 1000 x 1000
ml of sample taken
Total Dissolved Solids
(TDS)
D - B
TDS = --------------------------------- x
1000 x
1000
ml of sample taken
Total Suspended Solids (TSS) mg / l = TS mg / l – TDS mg / l
REFERANCE: IS : 3025 (Part 15 & 16) – 1984
DRY
RESIDUE, DVS AND TVS
PROCEDURE:
After noting down the final
weights of TS and TDS, keep the samples in muffled
furnace at temperature 550oC
for one hour.
Note down the final weights
of the evaporating dishes.
OBSERVATION:
Final weight of TS
evaporating dish (E) = g
Final weight of TDS
evaporating dish (F) =
g
CALCULATIONS:
1. TVS
(C - A) - E
TVS mg/L =
----------------------------------- x
1000 x 1000
ml of
sample taken
2. DVS
(D - B) - F
DVS mg/L =
------------------------------------- x 1000 x 1000
ml of
sample taken
REFERENCE: APHA –2540 Std. Methods for water and
wastewater analysis
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