Dear Hassan,
Running this level of TDS on the ELAN should not cause a problem with the sample
introduction system at all, so it is not necessary to consider a high solids
nebulizer as someone suggested. I also do not think you have a problem with the
injector or spray chamber.
From your description and the data you presented from your ELAN (which shows a
mass dependance to the signal changes), it would appear that the ion lens needs
to be reoptimized. If you are using the AutoLens feature you will also need to
perform an AutoLens calibration, which should only take a few minutes. Please
refer to the ELAN manual or the on-line help on how to perform this operation,
if you are unfamiliar with it. If you prefer, you may contact me directly via
e-mail or phone and I can walk you through it.
Also please do not hesitate to contact me directly if you need further
assistance.
Best Regards,
Ruth E. Wolf, Ph.D.
ICP-MS Support
PerkinElmer
50 Danbury Road, MS 219
Norwalk, CT 06859
Phone: (203) 761-2902
Fax: (203) 761-2892
email: [log in to unmask]
"Hasan H. Al Muhanna" <[log in to unmask]> on 11/29/99 04:07:41 AM
Please respond to "Analytical Chemistry using ICP's, DCP's, MIP's."
<[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Ruth E Wolf/NOR/PKN)
Subject: Insensitive ELAN 6000 , any ideas ??...
We have been using the ELAN 6000 ICP/MS with satisfactory
results so far. Mainly we used it to analyze extracted
seawater (minimum original matrix present).
Lately ( last two weeks ) we started using the ELAN to
analyze marine sediment with very high calcium (about 30-40%
Ca). Two grams of the sediemnt were extracted using nitric
acid and volume made to 50 ml. From that solution , 0.5 ml
is taken and diluted to 25 ml (50 times dilution). This
diluted sample was analyzed by the ELAN.
The analysis revealed Cd and Mo readings of 0.1 ppb, and
higher ppb (under and around 10 ppb ) of most other
ĉenvironmental
Ĉ elements like Co, Ni, Pb .. etc., but
calcium was around 350-400 PPM (parts per MILLION).
In this attempt of analysis, we used four internal standards
in each standard and diluted sample. They are Be9, Rb85,
In115, and Bi209. Linearity and calibrations were
periodically checked by a quality control standard (The
calibartion std. had 200 ppb of each element and the QC
check had 100 ppb of each element). The result was also very
good.
The main problem here was SENSITIVITY. The more samples we
analyzed the more counts intensity decreased. That was
indicated by counts on the Daily Performance Test (DPT) and
the counts of the internal standards during analysis. First,
these are results of DPT for Nov. 23rd / 27th / and 29th
respectively:
Mg24 / 28494 / 14553 / 6034
Rh103 / 98821 / 32099 / 21216
Pb208 / 66440 / 16975 / 14012
Ba138 / 114940 / 35873 / 26786
Ba++69/ 0.009 / 0.017 / 0.031
Ce140 / 142478 / 45826 / 36203
CeO156/ 0.022 / 0.024 / 0.023
Bckgrnd /1.444 / 0.000 / 0.056
The last DPT (on Nov.29) was done after cleaning the cones.
But that did not help.
As an example of internal standard sensitivities in samples,
these are the count readings on Nov. 23rd / and Nov. 28th,
respectively:
Be9 / 49215 / 8741
Rb85 / 463188 / 58393
In115 / 747175 / 88187
Bi209 / 663324 / 100862
As you can see, they have decreased by 5-10 times. Although,
linnaearity and calibartion are still very good.
Can you please give us any hint of what should be done. We
have repeatedly run the instrument for 30 minutes on a blank
with 2% HNO3. This did not help.
Should we target the torch and/or the spray chamber and
clean them ?? If so, what is the best way to do that ??
Thank you very much.
p.s. by the way, we have reduced sample exposures to TWO
readings instead of three. We still got good calibration and
results. QC Check standards still read what they should be.
______
Hasan
KFUPM, Dhahran, Saudi Arabia
e-mail: [log in to unmask]
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