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PLASMACHEM-L  June 2018

PLASMACHEM-L June 2018

Subject:

Re: Negative Data- ICP-MS

From:

Azam Noori <[log in to unmask]>

Reply-To:

Azam Noori <[log in to unmask]>

Date:

Fri, 1 Jun 2018 20:52:10 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (109 lines)

 Steven,
Thank you very much for the great comments. I see I need to learn a lot. 
You are right, the internal standard has declined. It should not happen. I will check the neutralizer and change the tubes.
A quick question about the digestion method. In this case I will have HNO3, H2O2  and HCl in tubes. Should I make the rinse solution with the same concentration of HNO3 and HCl or it does not matter. At this point I have 2% HNO3.
I appreciate your time and help.
Regards,
Azam Noori, Ph.D.

Assistant Professor
Department of Biology
Merrimack College
315 Turnpike Street
North Andover, MA 01845
Mailstop: N8
978-837-5744
    On Friday, June 1, 2018, 4:03:19 PM EDT, Pappas, Richard Steve (CDC/ONDIEH/NCEH) <[log in to unmask]> wrote:  
 
 Azam, one more thing. Rob Franks's trifocals are better than mine for looking at data expressed in 16x6 matrices.
He noticed that your Indium internal standard concentrations(?) went negative after the first couple of samples.
It is possible that the undigested plant material clogged the nebulizer or similar blockage. You should check to see if the nebulizer is indeed partially or completely blocked.
It may be that you do not understand the purpose of an internal standard. An internal standard is usually not quantitated by calibration. Its concentration is not increased with higher concentration standards. It is designated as internal standard in the software. Then as signal fluctuations occur as caused by plasma fluctuations, signal drift, etc.; the change in the constant concentration internal standard corrects the calibration standard-calibrated analyte measurements for these fluctuations.
If I understood the matrix correctly (and I was a math minor and took linear algebra), In concentration should not increase from 5 to 10, 25, 50, 75, 100 units, whatever the units are.

R. Steven Pappas, Ph.D.
Team Lead, Tobacco Inorganics Group
Centers for Disease Control & Prevention
4770 Buford Highway, NE
M.S. F44, Building 110
Atlanta, GA 30341-3717, USA

-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Azam Noori
Sent: Friday, June 1, 2018 2:17 PM
To: [log in to unmask]
Subject: Re: Negative Data- ICP-MS

 Hello All,
Thank you very much for the comments and suggestions. In response to your questions: Bill, I digested plant tissues in 2% HNO3 using hot block. Samples were filtered using Whatman #1. The final volume for all samples were brought to 50ml. I used "In" as an internal standard for Ag with the concentration of 2ppb. Internal standard was added to all samples, blank, and standards. I analyzed Ag 107 as well. The result is similar to Ag 109. The 10ppb standard showed 661ppb for Ag 107. It is not just about Ag, most elements are showing similar data.
Steve, thank you for the article. I agree that it could be related to Ag. I will follow your suggestion to clean the instrument. Laurel, I checked the internal standards. It shows the concentration of internal standards as percentage.  I copy-pasted some of the data here (I am not sure if you can see them). 

|  | Mo 98
 (ug/L) | Ag 107
 (ug/L) | Ag 109
 (ug/L) | Cd 111
 (ug/L) | In 115 (IS) |
| Std1 5 ppb | 5.064 | 5.000 | 5.000 | 5.000 | 98.7% |
| Std2 10 ppb | 9.705 | 9.884 | 9.888 | 9.897 | 99.9% |
| Std3 25 ppb | 25.549 | 25.586 | 25.580 | 25.262 | 90.0% |
| Std4 50 ppb | 49.744 | 49.520 | 49.410 | 49.944 | 92.7% |
| Std5 75 ppb | 75.283 | 77.423 | 77.270 | 75.369 | 89.4% |
| Std6 100 ppb  | 100.216 | 101.912 | 102.669 | 101.297 | 89.1% |
| Ag30-1 S  | 1.257 | 41.048 | 39.526 | 1.134 | 80.9% |
| Ag30-2 S  | 25.396 | 45.313 | 51.452 | 29.933 | 9.3E-5% |
| Ag30-3 S  | 29.705 | 107.315 | 115.015 | 37.079 | 4.8E-5% |
| Ag30-4 S  | 20.048 | 44.295 | 35.463 | 34.051 | 1.0E-4% |
| Ag30-5 S  | 13.070 | 330.094 | 348.927 | 41.944 | 7.5E-5% |
| 10 ppb | 29.326 | 661.546 | 623.595 | 26.292 | 7.9E-5% | Cal Blank |   
| |   |   |   | 100.0% |
| NO10-1 S | -0.544 | -58.368 | -43.304 | 32.019 | 61.7% |
| NO10-2 S |   | -189.509 | -177.342 | 16.160 | 74.4% |
| NO10-3 S | -13.904 | -229.558 | -213.942 | -15.295 | 449.8% |
| NO10-4 S | -14.204 | -220.707 | -207.380 | -17.115 | 531.1% |
| NO10-1 S | -16.075 | -221.138 | -207.707 | -16.105 | 486.6% |
| 5 ppb | -16.204 | -219.315 | -204.345 | -15.270 | 484.8% |


Regards,
Azam Noori, Ph.D.
Assistant Professor
Department of Biology
Merrimack College
315 Turnpike Street
North Andover, MA 01845
Mailstop: N8
978-837-5744
    On Friday, June 1, 2018, 11:18:52 AM EDT, Mc Ellistrem, Laurel J. <[log in to unmask]> wrote:  
 
 Hi-
In case you haven't checked this, can you check the concentrations of the internal standard entered in the file?  Open the file to see the number, rather than trusting the file name.  I had a similar problem that occurred because I had entered the concentrations for the internal standard but apparently hadn't hit "enter" but saved it.  When searching for the problem in the known sample analysis, the numbers for the internal standard were listed as the 1.0000ppb, the default starting value when you open a new standard file.  Good luck, Laurel

Laurel McEllistrem, Ph.D.
715-836-2723
[log in to unmask]
University of Wisconsin-Eau Claire
Materials Science and Engineering Center Eau Claire, WI 54701

-----Original Message-----
From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). <[log in to unmask]> On Behalf Of Azam Noori
Sent: Friday, June 1, 2018 9:12 AM
To: [log in to unmask]
Subject: Negative Data- ICP-MS

Good morning,

My name is Azam Noori. I am an assistant professor at Merrimack College. We have purchased an ICP-MS lately. It is NEXION 350X (Perkin Elmer). I am working with plants. I analyzed some samples yesterday. The calibration curve for most elements was good (Correlation factor: 0.998-0.999).
The concentration of elements in the first 5 samples was reasonable. Then I used the standard 10ppb as a sample to make sure the instrument is reporting the correct concentration. The concentration of most elements was much higher than 10 ppb in this sample. For example for silver (109), it was 623 ppb while when same sample was used as a standard the concentration was 9.88 ppb. I analyzed some samples after this, and the concentration of most elements (Ag, Mo, Cd, Sn, As, Ni, Fe, Cr, Pb, and V) in all samples were negative. It is not what I expected. Do you have any suggestions for troubleshooting?

Regards,

Azam Noori, Ph.D.
Assistant Professor
Department of Biology
Merrimack College
315 Turnpike Street
North Andover, MA 01845
Mailstop: N8
978-837-5744  
  

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