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

SOP for ESTIMATION OF NITRITE NITROGEN

PRINCIPLE:

Nitrite Nitrogen is determined through formation of a reddish purple azo-dye produced at              pH 2 – 2.5 by coupling diazotized sulphanalic acid with NED dihydrochloride.

MINIMUM DETECTION LIMIT: 0.01 mg/l

REAGENTS:

1.    Sulphanilamide reagent: Dissolve 5gm of the material in a mixture of 50ml of conc. hydrochloric acid & 300ml of water. Dilute to 500ml with water. The reagent is stable for several months.

2.    Sodium oxalate (0.05N): Dissolve 3.35 g Sodium oxalate, primary standard grade in water and dilute to 1000ml.

3.    Ferrous Ammonium Sulphate (0.05N): 19.607 g FAS plus 20 ml Conc. Sulfuric acid dilute to 1000 ml

4.    Stock nitrite solution: Dissolve 1.232 g Sodium nitrite in 1000 ml (250 ppm). Preserve it with 1 ml of chloroform.

5.    Standardization of stock nitrite solution:

Pipette out 50 ml standard (0.05M) KmnO4, 5 ml Conc. Sulfuric acid and 50 ml stock nitrite solution into a glass stopper flask or bottle. Submerge pipette tip well below permanganate acid solution while adding stock nitrite solution. Shake gently. Discharge permanganate colour by adding sufficient 10 ml portion of standard 0.05M FAS. Wait for 5 min.

Titrate excess FAS with 0.05 M KmnO₄ to the faint pink end point. Carry a water blank through the entire procedure and make the necessary corrections in the final calculation as shown in the equation below.

Calculate nitrite content of stock solution

            [ (B x C) – (D x E)] x 7

 A =  ----------------------------------------

                                               F

           

Where,

                        A = mg nitrite nitrogen /L in stock solution

                        B = Total ml of standard KMnO₄ used

                        C = Normality of standard KMnO₄

                        E = Normality of standard reductant,

                        F = ml stock sodium nitrite solution taken for titration.

Each one ml potassium permanganate consume by sodium nitrite solution corresponds to 1750 g nitrite nitrogen.

           

6.    Intermediate nitrite solution: Calculate the volume G of stock nitrite solution required for the intermediate nitrite solution from G = 12.5/A. Dilute the volume G (approximately 50 ml) to 250 ml with water. (50 ppm). Prepared daily

7.    Standard nitrite solution: Dilute 10 ml intermediate nitrite solution to 1000 ml with water (0.5 ppm)

PROCEDURE:

Removal of suspended solids: If sample contains suspended solids remove it by passing sample through 0.45 mm membrane filter.

Colour development: If sample pH is not between 5 – 9, adjust to that range with 1 N HCl or NH₄OH as required. To 50 ml sample or to a portion diluted to 50 ml add 2 ml colour reagent and mix.

Photometric measurement: Bet. 10 min and 2 hr. after adding colour reagent to samples and standards, measure absorbance at 543 nm.

CALCULATION:

Prepare a standard curve by plotting absorbance of standards against nitrite nitrogen concentration. Compute the sample concentration directly from curve.

Nitrite Nitrogen (as NO2-N) /l  =  µg NO2-N (in 52 ml of Final volume)

                                                                                       ml of Sample

REFERENCE: IS : 3025   ( Part 34 ) – 1988

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