Determination of cyanide
There are two similar methods for determination of cyanide.Both methods are differ in some chemicals,volumes and nanometers.
They are
1)Determination of cyanide by Pyridine barbituric acid method.
2)Determination of cyanide by pyrazolone method.
1)Determination of Cyanide by pyridine barbituric acid method.
AIM:
To determine the amount of cyanide present in a given sample by pyridine barbituric acid method.
PRINCIPLE:
The cyanide ions present in the sample react with chloramine-T and pyridine barbituric acid at alkaline medium to form cyanogen chloride and pink to red colour.UV measure the maximum absorbance at 578nm.
NaCN + Chloramine-T + pyridine barbituric acid -----> CNCL(cyanogen chloride).
APPARATUS REQUIRED:
1)Distillation apparatus.
2)UV Spectrophotometer.
3)Standard volumetric flask(100ml capacity).
4)Vials(50ml capacity)
5)Beakers.
6)Pipettes.
CHEMICALS REQUIRED:
1)Pyridine barbituric acid.
2)Hydrochloric acid.
3)Chloramine - T.
4)Sodium acetate trihydrate.
5)Glacial acetic acid.
6)Reagent grade water.
7)Sodium hydroxide.
8)Pyridine.
9)Lead carbonate.
10)Magnesium chloride.
11)Sulfamic acid.
Determination of TDS and TSS in water.
REAGENTS AND PREPARATIONS:
1)Acetate buffer:
Dissolve 82g of sodium acetate trihydrate in 100ml reagent grade water.then add 100ml of glacial acetic acid.
2)Pyridine barbituric acid:
Weigh 6g of pyridine barbituric acid in 100ml standard volumetric flask.add a little reagent grade water to make paste.slowly add 6ml of hydrochloric acid and 30ml Pyridine.don't shake (This reagent is hard to prepare).slowly add the reagent grade water and shake very slowly. add water again and make up to mark.shake slowly to dissolve Pyridine barbituric acid.(prepare this reagent daily).
Caution(!):
Be careful when handling Pyridine which gives unwanted smell and cause serious damage of body parts.
3)Chloramine-T solution:
Dissolve 1g of chloramine-T in 100ml reagent grade water(prepare this reagent daily).
4)0.04N NaOH solution:
Dissolve 1.6g of sodium hydroxide in 1 liter distiller water.
DISTILLATION OF SAMPLE:
To remove interferences,distillation must have to apply.
Take 500ml of sample in distillation flask.fix condensor connected to inlet tube and receiver.receiving container should contain 10ml of 1N sodium hydroxide and 50mg lead carbonate (PbCO3) diluted to till receiver to dip.lead carbonate is added to remove the interference of sulphide (S2-).add 50ml of 1:1 H2SO4(sulphuric acid),20ml of magnesium chloride solution and 2g of sulfamic acid to sample through inlet tube.set the temperature to collect drop wise.in this process,cyanide present in the sample is converted to HCN (hydrogen cyanide) which is toxic gas.avoid inhalation or contact.
The following reactions will take place while distillation:
The iron complex form of cyanide react with sulphuric acid to form hydrogen cyanide(HCN).
Fe (CN)6 -4 + 6H+ ------> 6HCN + Fe+2
Hydrogen cyanide react with Sodium hydroxide to form sodium cyanide.
HCN + NaOH -------> NaCN + H2O.
Determination of acidity and alkalinity of water.
PROCEDURE:
Take required volume of 50ml voyals including blank.add 35ml of distilled sample as mentioned above.then add 15ml of 0.04N sodium hydroxide solution.continuously add 1ml of acetate buffer and 2ml of chloramine-T.after 5 minutes,add 5ml of pyridine barbituric acid.if cyanide present,the solution become pink to red depend upon cyanide concentration.after colour development,read the absorbance in UV Spectrophotometer at 578nm.
DANGER(!):
Formation of cyanogen chloride(CNCL) while adding pyridine barbituric acid reagent is a "Toxic gas".avoid contact,inhalation or ingestion.wear apron,mask,handwear and eye wear.
CALCULATION:
If you take sample without distillation,follow the below calculation method.if you take sample after distillation,convert it to suitable calculation format.
CN- = A1 / A2 × S.C × M.V / S.V
Where,
A1 = Sample absorbance of cyanide.
A2 = Standard absorbance of cyanide.
S.C = Standard concentration of cyanide.
M.V = make up volume.
S.V = volume of sample taken.
EXAMPLE:
CN - = 0.010 / 0.013 × 0.010 × 50 / 35 = 0.01mg/l.
Determination of PH and conductivity in water.
2)Determination of cyanide by Pyrazolone method.
AIM:
To determine the amount of cyanide present in a given sample by pyrazolone method.
PRINCIPLE:
Principme of this method also same as pyridine barbituric acid method.but pyrazone replacing Pyridine barbituric acid here.At 620nm,UV Spectrophotometer measures the maximum absorbance for cyanide ions.Pyrazolone gives pink to blue colour when cyanide is present.
NaCN + Chloramine-T + pyrazolone -----> CNCL(cyanogen chloride).
APPARATUS REQUIRED:
1)Standard volumetric flasks(25ml capacity).
2)UV Spectrophotometer.
3)Distillation apparatus.
4)Pipettes.
CHEMICALS REQUIRED:
1)1-phenyl-3methyl-5 pyrazolone.
2)Bis pyrazolone.
3)Sodium hydroxide.
4)Pyridine.
5)Reagent grade water.
6)Acetic acid.
7)Chloramine-T.
Determination of sulphate and sulphite in water.
REAGENTS AND PREPARATIONS:
1)Pyrazolone reagent:
a) Dissolve 0.5g of 1-phenyl-3methyl-5 pyrazolone in 100ml reagent grade water.
b) Dissolve 0.025g of Bis-pyrazole in 25ml Pyridine.
Mix the a & b solution.(prepare this reagent daily).
2)0.2N NaOH solution:
Dissolve 8.0g of sodium hydroxide in 1 liter of sample.
3)Acetic acid solution:
Dilute 10ml of acetic acid with 40ml reagent grade water.
4)Chloramine-T solution:
Dissolve 1g of chloramine-T in 100ml reagent grade water.(prepare this reagent daily).
Determination of nitrate and nitrite in water.
PROCEDURE:
Take 15 ml of distillate or direct sample or an aliquot of sample diluted to 15ml with 0.2N sodium hydroxide solution.maintain its PH from 6 to 7 with acetic acid.then add 0.2ml of chloramine-T.after 5 minutes.add 5ml of Pyrazolone reagent.make up to the mark with 0.2N sodium hydroxide solution. Before colour faded to colourless,read the absorbance in UV Spectrophotometer at 620nm.
DANGER(!):
Formation of cyanogen chloride(CNCL) while adding pyrazolone reagent is a "Toxic gas".avoid contact,inhalation or ingestion.wear apron,mask,handwear and eye wear.
CALCULATION:
CN- = Abs1 / Abs2 × S.C × M.V2 / S.V2 × M.V1/ S.V1
Where,
Abs1 = Sample absorbance of cyanide.
Abs2 = Standard absorbance of cyanide.
S.C = Standard concentration of cyanide.
M.V = make up volume.
S.V = volume of sample taken.
EXAMPLE:
CN - = 0.040 / 0.040 × 0.040 × 25 / 15 × 250 / 500 = 0.03mg/l.
Determination of total hardness of water.
How to discard cyanide tested or cyanide present samples?
Collect totally tested cyanide sample in a container and add excess of 50% sodium hydroxide solution to reduce the toxic risk of cyanide.by adding sodium hydroxide,the highly toxic cyanogen chloride converted to cyanate ion (OCN-) which is less toxic.
CNCL + 2 NaOH -----> NaOCN + Nacl + H2O.
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