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Topic: Why is the ppm of stock solution different from ICP result?  (Read 6639 times)

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Offline Jcubed

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Hello all,

New member so here goes (hope I don't step on any toes)...

I made a stock solution of Re2O7 in DI water and adjusted the pH to 2 using sulfuric acid.  The addition of 1.3g of the rhenium (VII) oxide to the 1L of water should have given me a solution that is 1000ppm Re.

I then proceeded to run some timed reactions and analyzed samples from these reactions with an ICP.

I ran a stock solution sample and came up with only 100ppm as the Re concentration.  

What happened?  Could this be a problem with the pH level when running the sample in the ICP?  

I have checked the balances and they seem to be calibrated correctly and my math seems to be correct.  I'm off by a whole factor and need to figure out the stock solution problem before proceeding any further.  

Any advice or input would be greatly appreciated.  

Thanks in advance

Offline AWK

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #1 on: June 30, 2012, 04:12:00 PM »
Quote
I made a stock solution of Re2O7 in DI water and adjusted the pH to 2 using sulfuric acid.  The addition of 1.3g of the rhenium (VII) oxide to the 1L of water should have given me a solution that is 1000ppm Re.

With data given above all is OK
AWK

Offline Jcubed

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #2 on: June 30, 2012, 05:05:25 PM »
That's the thing...I know that the solution should be 1000ppm based on what I did etc.

But the ICP is giving me data that says my stock (1000 ppm) solution is really a 100 ppm solution...  therein lies the problem.  I must figure out the problem before proceeding. 

Offline AWK

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #3 on: June 30, 2012, 05:36:34 PM »
May be you intended to prepare 100 ccm solution and weighted 0.13 g then use 1 liter flask?
AWK

Offline Jcubed

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #4 on: June 30, 2012, 05:41:47 PM »
I thought that might be the case too.  I have recorded in my lab book that I measure out 1.3 g of the rhenium oxide.  I did check to make sure the balances were calibrated correctly. 

I just made another stock solution, prepared in the same way using a different balance that was checked for calibration.  I'm going to run a sample of this solution on Monday to check and see if the correct ppm's have been achieved. 

If it comes back as not being 1000ppm as expected, I guess I will go back to trying to figure out what happened. 

Offline Borek

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #5 on: June 30, 2012, 05:45:14 PM »
Assuming you prepared solution using numbers you listed (1.3 g and 1L), I would start checking possible problems related to the instrument/operator interface.
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Offline Jcubed

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #6 on: June 30, 2012, 06:25:26 PM »
Borek,

That is the reason I made the second solution...using the same numbers and being extremely careful.  I figure if I run the second solution and it reads 100ppm, then I know it is some sort of problem related to the icp and that my first solution is indeed 1000ppm as it should have been. 

Offline Arkcon

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #7 on: June 30, 2012, 07:40:45 PM »
It is a little bit "cute" you realize, that the result isn't 137.84 ppm for your 1000 ppm standard, but instead 100 ppm.  It just screams calculation setup failure -- a dropped zero entered somewhere.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Jcubed

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #8 on: June 30, 2012, 09:27:37 PM »
Arkon,

I understand that it is "cute."  The actual number is 98.874ppm so when discussing an order of magnitude, I assume it is ok to say that is an approximate 100ppm solution.  

My first thought was that I made a calculation error.  Hence why I went back and double checked the math...To show this quickly:

In rhenium (VII) oxide rhenium makes up approximately 77% of the wt. of the molecule

Thus.  To put 1g of rhenium into solution 1g=.77(x)  this give x as being approximately 1.3g of Re2O7

If I am mistaken on that math, I blame being sick haha.

The obvious answers to my problem (math calculation error, balance being wrong) are what I have checked and now I am seeking other ideas and help as to the cause of my problem. 

I thank you all for the responses. 

Offline discodermolide

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #9 on: July 01, 2012, 12:50:00 AM »
I think you need to look at the instrument calibration; may be something wrong with the injector? or the detector?
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Offline thohry

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #10 on: July 05, 2012, 03:22:30 AM »
May be your sample is too concentrated, it's out of range.

Offline Silppuri

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #11 on: July 15, 2012, 02:41:01 PM »
Checked that you have no dilution factors in the ICP application?
If you add 1,00 litres of ethanol to 1,00 litres of water, you get 1,92 litres of solution.

Offline 8bambi4

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Re: Why is the ppm of stock solution different from ICP result?
« Reply #12 on: September 14, 2012, 09:10:48 AM »
Hi there,

I'm still new working on an ICP machine, but I've also had the same problem, where my result should have been 1000ppm, and instead I got 100ppm.  After I re-calibrated the ICP, made up new calibration standard solutions, and getting the same results, it hit me.  The problem is quite simple, it's the ICP method settings under the calibration solution values.  This is especially a big problem as soon as you dilute the sample, and do a miss-calculation.  Just check your settings.

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