Elan 9000 inconsistency problem

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kc85
kc85's picture
Elan 9000 inconsistency problem

  Hi,

I have posted the following in another subforum so apologies if rereading this. I'm just trying to reach out to as many peoples as possible.

I am relatvely new to the world of ICP-MS so forgive any potential ignorance. I have been analysing for around 6 months using an Elan 9000 now without any problems however over the past couple of weeks I have noticed our ICP-MS seems to be drifting (what I mean by this is after calibration the results of a known sample eg 160ug/L of Al will be close to 160 with the intensities of Al staying pretty good and remain at this for a while however if I analyse this same sample repeatedly, then after around 12 replicates I see that we are rising to around 172ug/L with an increase in our Al intensity). We use an In/Rh internal standard and the intensity of this remains consistant despite the drift so I think I can rule out bad tubing etc. 

Do to regulations a batch should procede without drifting so we check this by reanalysing our 2nd calibration at the end of the batch which should in theory be the same as what it was at the start but due to our drift issues this 'drift check' sample is higher than what it was during calibration in the same way as I described the sample above.

I have cleaned our cones and notice that we will usually run OK for one batch but then we notice the drift again after the second batch so I don't think the cones are the issue. We also were getting around 2 months use of our cones prior to this as we analyse drinking waters in a 1% HNO3 matrix so the samples are pretty clean to begin with.

This has only begun over the past few weeks as before this we could analyse the same sample at the beginning of a batch and then maybe 20 samples later and notice minimal difference. 

I looked at what has been changed in this time and we have replaced our RF coil and torch. Would it possibly be the alignment of either of these? Although I doubt this because our calibration usually looks pretty good with an R2 of 0.9999. 

Apart from this due to my lack of experience I am unsure at what else to look at. I am wondering if anybody has experienced this or could offer any advice on where to begin.

Thanks in advance,

KC