7 Replies Latest reply on Jan 2, 2019 9:57 AM by tmcsweeney

    ICP-OES Method Development Strategy Advice

    agricult

      Hi,

      I am working with an Agilent ICP-OES 5100 / 5110 instrument and involved in analytical method development. We plan on analysing biological samples (undigested blood serum) for a combination of macro, meso and trace elements, i.e. Na, P, K, Ca, Mg, Fe, Zn ideally through a dilute and shoot method without digesting the serum previously or matrix matching the calibration standards used for creating the external calibration curve if we can avoid it. We plan to start with preparing pure standard solutions of the mentioned elements singly, to identify the best wavelengths, instrument conditions and interference impact / influence.

       

      My experience in ICP-OES is quite basic at present but I'm in the process of updating my knowledge on both the instrument and analytical method development process. Out of this I've 2 questions:

       

      1.Would anyone be able to offer advice or suggest / share information or even outline the main standard steps for OES method development?

       

      2. Does anyone have information on interrupting sample spectrum, i.e. peak shifting,background, etc.

       

      I'd really appreciate people's experience and advice as I find the instrumentation and process fascinating so hope to learn.

        • Re: ICP-OES Method Development Strategy Advice
          tmcsweeney

          I would recommend that you use an internal standard since you cannot matrix match your standards to your samples. You can use an element like Yttrium or Scandium and add it on-line via the peristaltic pump.

            • Re: ICP-OES Method Development Strategy Advice
              agricult

              Thank you for that input, yes we plan on using an appropriate internal standard to compensate between differences between the standards and serum samples.

               

              At the moment we are at an earlier stage of the MD process of identifying the best interference free wavelengths for each element singly and identifying the optimum instrument conditions through using Time scan & Read features. Therefore I just wish to know if we are beginning on the right track in the OES MD process?

            • Re: ICP-OES Method Development Strategy Advice
              tmcsweeney

              Method development encompasses several steps. I typically begin with "IntelliQuant" to get an idea of the elements present in the samples and their semi-quantitative concentration ranges. Based on the element concentrations, I then go to the "Elements" tab and select wavelengths. The wavelengths are listed in order of sensitivity and freedom from interference. Therefore, if the element concentration is low, I add the top 2 wavelengths from the list, as they are going to yield the best sensitivities. It's always best to add more than one wavelength, as this gives added confirmation in your results. If the element concentration is high, I add a couple of wavelengths from lower down the list. If you add the top 2 wavelengths, and the concentration is high, you may experience an over-range in signal and experience non-linearity. The relative intensities for the wavelengths in the list are relative to 1ppm.

              After line selection, you want to optimize your conditions using the "Conditions" tab and the "Read" function. Right-mouse click to overlay spectra and optimize using both a standard and a sample. Power and nebulizer flow are the 2 most important parameters to optimize with your sample. Look for the optimum signal-to-background ratio, not raw signal.

              Using a multi-element standard and a sample, check for spectral interferences by going to "Analysis" and running them as samples. Be sure to perform a wavelength calibration on the "Instrument" tab prior to doing this. Then you know that any wavelength outside the "H" bar is an interferent.  Fitted background correction is usually sufficient to separate the analyte from the interferent, but sometimes you may need "FACT". Look up "FACT" in the software HELP to find out how to do this.

              Finally, perform spikes of your samples with a known amount and look for your spike recoveries to be between 90-110%. If the spike recoveries are poor, then you have a matrix effect that needs to be corrected by either diluting the samples, using an internal standard, adding an ionization buffer if viewing axially (or view radially and optimize the viewing height), or by using the method of standard additions.

              I hope this helps.

                • Re: ICP-OES Method Development Strategy Advice
                  agricult

                  Thank you very much for sharing your general MD approach, it is quite similar to approaches I've previously read so its good to know that there is a general format to OES MD work. I'll definitely take all of that on board in my current MD work.

                   

                  Regarding use of the "Read" function, would you be aware of any material available which may aid in my understanding in interrupting the spectrum displays? I would like to better understand what an ideal element spectrum peak and an interferent peak should look like. Also to understand more about background interference, i.e. what causes high backgrounds occuring and how low the background intensitiy should be vs element intensity, in order to be reliable.

                   

                  I understand that knowledge of spectrum interpretation also comes with experience so any advice you could offer would be valuable and only deepen my understanding.

                   

                  Happy New Year.