Peracetic Acid Titrative Assay

[methyl_ethyl]

In regards to: Does anyone have a ready reference to a titration method to determine the concentration of the peracetic solution.

Post 354166

(wacko_reaco: "stability of peracetic acid", Methods Discourse) I know it is an old question, however I do not think anyone has acutally answered this effectively.

This is the method I used to use:

Materials Needed:

Micropipettor/Tips
Analytical Balance
Glass Beaker 200mL
5%H₂SO₄
Cracked Ice/Bath
Magnetic Stirrer/Stir Bar
Burette
Ferroin Indicator
Ceric Ammonium Sulfate (.1N)
Potassium Iodide Solution (10%)
Sodium Thiosulfate (.1N)
Startch Indicator Solution

Method:

Pipette 200 µl of Peracetic Acid into a tared, clean, glass, beaker.  Record weight in grams, (i.e. .220g)

Add 50 mL of 5% H₂SO₄to beaker and place in ice bath and start magnetic stirring.

Add three drops of Ferroin indicator to beaker (this will turn the solution to a salmon color)

Titrate with .1N Ceric Ammoniun Sulfate until the disappearance of the salmon color.

Add 10mL of 10% Potassium Iodide Solution to beaker.

Add 3mL of Starch Indicator Solution to beaker.

Titrate with .1N Sodium Thiosulfate until the appearance of an orange solution (record volume of Sodium thiosulfate used)

I usually perform the assay in duplicate, (if you are anal enough to go this far you might as well do it correctly)

Calculation:

(mL of Sodium Thiosulfate)(Normality of Sodium Thiosulfate)(3.       =              %
                    grams of sample

Example:

Weight of 35% Commercial PAA: .220g

Burette reading at start: 8

Burette reading at finish: 28.5

Total mL of Sodium Thiosulfate used: 20.5

(20.5)(.1)(3.     = 35.4% Peracetic Acid
       .220

[terbium]

I don't understand the point of titrating with ceric ion. When I used to determine peroxides we would just add iodide and titrate the liberated iodine with thiosulfate and starch indicator.

[methyl_ethyl]

I don't understand the point of titrating with ceric ion. When I used to determine peroxides we would just add iodide and titrate the liberated iodine with thiosulfate and starch indicator.

Regarding the titration with Ceric Sulfate:  The point of titrating with ceric sulfate first  is the titration of H₂O₂.  Since we are interested in the percent peracetic acid, it is not pertinant to us how much free hydrogen peroxide is present.  If we we wanted to know how much Hydrogen Peroxide was present in the solution we could derive that from:

mL of Ce(SO₄)₂ X Normality X .017 X 100   =  % H₂O₂
                                     sample weight

The assay I describe originally is an assay for the iodometric determination of  percent peracetic acid.  I believe the method I described is the best method for accurately determining the % Peracetic Acid in Solution.

H₂O₂ + 2Ce(SO₄)₂ ------>  O₂ + Ce₂(SO₄)₃ + H₂SO₄

CH₃COOOH + 2 KI + H₂SO₄ -----> I₂ + K₂SO₄ + H₂O + CH₃COOH

I₂ + Na₂S₂O₃ -----> 2 NaI + Na₂S₄O₆

I hope this helps explain the need to titrate the free hydrogen peroxide first before quanitifying the percent peracetic acid.  If not please inquire further about the validity of the assay and I will try to explain / justify further. 

Unfortunately I have not had time to log onto the hive as often as I would like, therefore my response will more than lilkely not be in a timely manner.   Sorry....

regards,

m_e