Method Development

Hello everyone

I'm trying to develop/ optimize my current method by implementing background corrections; I need some help  identifying which correction should best fit my conditions.

I run soil water and processed water analysis for Li, Na,K, Ca,Mg, Ba,Sr, Cr, Mn, Fe, Pb, Zn on a 5800 ICP-OES. I run a 3 point calibration with 10,50 and 100ppm standards. The standards are prepared from a 1000ppm multi-element calibration standard in 10% Nitric acid. 1000ppm Ag, Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, K, Li, Mg, Mn, Na, Ni, Pb, Sr, Tl, Zn. Needless to say I have many interferent elements for my wavelengths of interest. Our samples are high in Na (20k ppm- 50k ppm), Ca (1k-5k ppm) and I run 100x, 1000x dilutions for the sodium not to overrange and to avoid running that much salt through my instrument. I also run the 2 best wavelengths for each element of interest.

I'm thinking of adding analyte standards to my calibration setup, (Na and Ca) and using the IEC function to get more precise results, as well as doubling condition sets to axial and radial analysis.

Any help on how to develop my method will be greatly appreciated. Richard B.

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  • Hi Tina, Thank you very much for your help. 

    In response to your question, I'm not trying to run a regulated method like EPA. 200.7. I have a few questions about the internal standard and ionization buffer

    can the ionization buffer and the internal standard be the same?

    Will the internal standard will be mixed with the standard and samples at the nebulizer? if so, Does the pump rate/ sample flow need to be adjusted in anyway to get a specific amount of standard in the plasma?

    Is there any demo method I can look at, I'm having trouble putting it all together. Thanks again for your help

  • Richard, since you are making large dilutions, you may not need an ionization buffer. The ionization interference effects can be significantly minimized by viewing radially for those easily ionized elements like Na, K, Li, and Ca.  I would suggest you do a spike recovery on one of your samples to determine if there are any matrix or ionization effects affecting your accuracy. The internal standard alone may be enough, and it is definitely needed.  I would suggest a mixture of 5ppm Y and Sc. You do not have to enter the concentration of the internal standard in the software, it just has to be consistently added to the plasma. On the Elements tab of the software, add Y 371nm and Sc 361nm and with the drop-down, designate them as internal standards. Once you do that, you can then ratio the analyte element wavelengths to one of the IS wavelengths. After your data is collected, you can change the IS being ratioed from Y to Sc, and vice versa to see which one gives better accuracy for the analyte of interest. The data will be recalculated automatically. I would start out by ratioing everything to Y 371.  I suggest using white-white tubing for the sample, and orange-green tabbed tubing for the internal standard, as this will ensure a minimal dilution of the sample, in case some of your elements are very low in concentration.  Both pieces of tubing will connect onto the Y-piece, and then a small piece of tubing will connect the y-piece to the nebulizer. 

    I would suggest the following plasma parameters:  1.35kW for power, 1.1 L/min for Aux flow, 13L/min for plasma flow, and 0.7 L/min for neb flow. Pump rate 12 rpm.

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