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, H₃PO_4­, 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 

H₂SO_4­  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 180^oC 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 105^oC 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 550^oC 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

SOP for STANDARD WORKING PROCEDURE FOR ESTIMATION OF SILVER

SOP for STANDARD WORKING PROCEDURE FOR ESTIMATION OF SELENIUM

SOP for ESTIMATION OF PHOSPHORUS BY STANNOUS CHLORIDE METHOD

                PRINCIPLE:

Molybdophosphoric Acid is formed and reduced by stannous chloride to intensely

 coloured molybdenum blue.

                 MINIMUM DETECTION LIMIT:  3 µg P/l

                 REAGENTS:

1.    Phenolphthalein indicator aqueous solution.

2.    Strong acid solution: Slowly add 300 ml conc. H₂SO₄ to about 600 ml distilled 

water. When cool, add 4.0 ml conc. HNO₃ and dilute to 1000 ml.

3.    Ammonium molybdate reagent: Dissolve 25 g ammonium molybdate in 175 ml

 distilled water. Cautiously add 280 ml conc. H₂SO₄ to 400 ml distilled water. 

Cool, add molybdate solution and dilute to 1000 ml.    

4.    Stannous chloride reagent: Dissolve 2.5 g fresh SnCl₂. 2H₂O in 100 ml glycerol.

 Heat in a water bath and stir with a glass rod to hasten dissolution. This reagent is

 stable and requires neither preservatives nor special storage.  

5.    Standard phosphate solution: Dissolve 219.5 mg anhydrous KH2PO4 and 

dilute with distilled water to 1000 ml.  (1ml.= 50 mg PO₄) 

 PROCEDURE:

1.    Sample pretreatment: To 100 ml sample containing not more than 200 mg P and

 free from colour and turbidity. Add 0.05 ml (1 drop) phenolphthalein indicator. 

If sample turns pink add strong acid solution drop wise to discharge the colour. 

If more than 0.25 ml (5 drops) is required, take a smaller sample and dilute to 

100 ml with distilled water after first discharging the pink colour with acid. 

2.    Colour development: Add with through mixing after each addition, 

4.0 ml molybdate reagent and 0.5 ml stannous chloride. Rate of colour removal

 development and intensity of colour depend on temperature of the final solution.

 Each 1^o C increases producing about 1 % increase in colour. Hence hold samples,

 standards and reagents within 2 ^o C of one another and in the 

temperature range between 20 ^oC and 30 ^oC.

3.    Colour measurement: After 10 min., but before 12 min. using 

it specified interval for all determinations.

Measure colour photo metrically at 690 nm and compare with calibration curve.

  

           CALCULATION:

                                      A                    B

     mg/L of P  =   ------------------- x -----------

                             ml of sample            C

  

Where,

            A = mg P determined from plotted curve,

            B = final volume of diluted sample (ml)

            C = Volume of diluted sample used for colour development (ml)

            REFERENCE: APHA – 4500 P D. Stannous chloride method