High Pt background on ICP-MS

[joelyue]

I am getting very high counts of Pt in the background in my Agilent 4500 ICP-MS. Is it because that i am using Pt cones?

Interesting thing that it happens only when i inject blanks with nitric acid ~1%. This does not occur with pure water or dilute HF ~ 1%

[jerole]

Hi,

If you just get high blanks using nitric acid I don't think that the problem are the Pt cones. If it were the cones you would get high blanks always. In that case you'd have to check the cooling of the cones, degradation of the cones is a sympton of insufficient cooling.

This sounds more like a contamination problem, either your nitric acid or the tubing. I'd try using a new bottle of nitric acid and replacing the tubing.

Do you have a set of usual Ni cones? If you have you can try with those and see if you still get high blanks, just to be sure it's not the Pt cones.

[joelyue]

i have tried using a different bottle and batch of nitric and the same occurs. As for tubings, i have replaced and cleaned the inlet system.

As for insufficient cooling of the cones, how do i check that?FYI, i am using the Agilent ICPMS 4500 with shieldtorch system.

i dont have Ni cones, so i couldnt try out with them.

[Biocheckup]

Hello,

did you check different Pt isotopes for this high background effect?

[joelyue]

Hi,

yes i check the isotope ratios and it gives me the correct ratio so that rules out interference.

i have tried injecting aqua regia with no effect.

does anyone know other than the shield plate and the cones, which other part of the icpms of made of platinum?

[joelyue]

now i suspect the high pt counts are from the platinum injector. has anyone tried successfully in cleaning the injector, especially its interior?

[jerole]

Can you give us some more information?

At what RF Power do you work?
What kind of samples (what matrix) do you nebulise?
How many CPS do you have as Pt background?
What happens if you nebulise 1%HCl?

[joelyue]

RF power 1350
sample matrix 1% HNO3
Pt background 5000cps
6000cps with 1ppb standard

havent tried with 1% HCl

[jerole]

I still suspect that it may be the cooling of the cones. If the temperature is too high the nitric acid will attack the cones and I suppose that HF passivates the cones, that's why you don't have a background.

[joelyue]

I finally found the root of the problem. The Pt injection rod was inserted too near the plasma. I moved the Pt rod backwards about 2mm and the Pt counts dropped to near zero.