Method Development

Hi Richard, in addition to considering background correction strategies, you need to also consider physical and ionization interferences. I would suggest adding both an internal standard and an ionization buffer. You can mix them in the same container and add them on-line via an extra channel on the peri-pump. This will improve your accuracy, especially for the easily ionized elements such as Na and Ca. Regarding background corrections, are you following a regulated method such as EPA 200.7? If so, you will want to implement IECs. If you are not adhering to a regulated method, you could use fitted and FACT which is much easier than setting up IECs. Which model ICP-OES do you have? 

Sorry, I see you are using a 5800 ICP-OES. 

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.

Thank you Tina I will give it a try.