Question on Nitrite Analysis in Coolants (boring topic, sorry)

[CoolantChemist]

We are trying to offer an alternative Nitrite test method through titration.

We found that Molybdate seems to interfere in the titration.

The titration involves using Ceric Sulfate - H4Ce(SO4)4 and a ferroin indicator.

Does anyone have any idea why the Moly would interfere?

Thanks for any ideas.

 

[lelakwoman]

are you with a specific company, because i might have a couple of contacts for you. i work for a utility company. one of our stations utilizes propane boilers prior to the propane vaporizers. the water side of the boiler is a glycol soultion. i had it tested for a ton of stuff, one thing of interest to you is: Moly corrosion inhibitor. i don't much about it, but i assume it's a chelant, and maybe that's what's botching the nitrate test. My test result sheet says it's ASTM D 6130 method of analysis.

 

[Stinky Peterson]

We do this all the time and have not noticed a problem. What strengths are you using? how much coolant? ferroin? etc. Are you sure it is the moly? what are you seeing that makes you question the results? Do you have any other oxidizable materials in the mix? they can cause screwy readings. If you get some 50:50 premixed Caterpillar ELC it has 550 ppm NO2 and 900 ppm MoO4 so you could use this as a standard. This is what we get when we test and also what we get when it is tested on the capillary electrophoresis instrument.

I'll be glad to try to help you.

 

[Stinky Peterson]

Well I don't have access to my database at home so I can't tell you the Moly or nitrite level in DCA4 but when we test additives we do a 1:10 dilution before we do the titration. When we do the titration we use use 1 mL coolant or additive into 9 ml water and use 2 drops of indicator.

 

[CoolantChemist]

quote:

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Originally posted by Stinky Peterson:
We do this all the time and have not noticed a problem. What strengths are you using? how much coolant? ferroin? etc. Are you sure it is the moly? what are you seeing that makes you question the results? Do you have any other oxidizable materials in the mix? they can cause screwy readings. If you get some 50:50 premixed Caterpillar ELC it has 550 ppm NO2 and 900 ppm MoO4 so you could use this as a standard. This is what we get when we test and also what we get when it is tested on the capillary electrophoresis instrument.

I'll be glad to try to help you.

---

It's DCA-4 that we are trying to use for the titration.

Method as follows:
1g of DCA-4
50g DI H2O
1 drop ferroin indicator
Add the titrant (ceric sulfate .1N)until the color change lasts for 30 seconds
Multiply by a factor and that gives you the %bw.

I know it's the moly because when I make it in the lab and exclude the moly, the titration works.

Application of the test is for a blender in Europe who is having trouble using the colorimetric method.

p.s. I'm not comfortable giving out concentrations etc... sorry sir.

[ December 30, 2004, 01:05 PM: Message edited by: CoolantChemist ]

 

[1 FMF]

going to take a stab,
just posted in the diesel coolant thread in this forum,

what I've read about the Fleetguard DCA-4 supplemental coolant additive (SCA), the molybdate in it in addition to the nitrite inhibits cavitation in diesel engines with cylinder liners by forming an oxide layer on the cast iron liner. How true that is I don't know, that's just what I've read. Maybe this oxide formation has something to do or is interfering with your testing? Chemistry isn't my strong suit, sorry.

I do know to test the pH and concentration of nitrite & molybdate in diesel coolant where you've used DCA-4, you must use the Fleetguard coolant strips otherwise you get a bad reading. Their strips have two separate pads, one for nitrite and one for molybdate. I have no idea what chemical is on the pad, and what reactions take place other than the pad turning a shade of purple or brown. Forget what the ppm are on the testing kit for the nitrite & moly. Fleetguard are the ones who make the DCA-4 and would be the ones to call.

 

[CoolantChemist]

quote:

---

Originally posted by Stinky Peterson:
Well I don't have access to my database at home so I can't tell you the Moly or nitrite level in DCA4 but when we test additives we do a 1:10 dilution before we do the titration. When we do the titration we use use 1 mL coolant or additive into 9 ml water and use 2 drops of indicator.

---

I do the same titration pretty much. Doesn't work for me though.

 

[Stinky Peterson]

CC is your ceric sulfate fresh? It does have a shelf life but I can't remember how long. We don't encounter moly levels any higher than about 900 ppm. You should be below that with a 50 to 1 dilution. What are observing?

 

[Stinky Peterson]

CC I don't think you are using enough ferroin. We use 2 drops for 10 mL of water/coolant. If you have 50 mL then I would try maybe 10 drops or else take 10 mL of the diluted and titrate it using 2 drops. When the ferroin is in the solution it should be an deep red/orange color and change to blue when oxidized. We do this with 900 ppm MoO4 solutions all the time and have no problem.

Good luck

 

[CoolantChemist]

quote:

---

Originally posted by Stinky Peterson:
CC is your ceric sulfate fresh? It does have a shelf life but I can't remember how long. We don't encounter moly levels any higher than about 900 ppm. You should be below that with a 50 to 1 dilution. What are observing?

---

Ceric should be fine. All that happens with the titration is that it turns from the color of the solution into the color of the ceric sulfate.