Determining IEC on iCAP PRO Series
Issue
Interferences need to be accounted for
Environment
- iCAP PRO
Resolution
Optimize System / Method
1. Clean all glassware and sample introduction components. (Don’t forget the POP Window(s))
2. Ignite the plasma and allow the system to thermally stabilize for 15-20 minutes.
3. Optimize the Nebulizer Flow
Reference the Auto Tuning section of the Software manual for details on how to do so.
Note: select Signal to Background Ratio from the Optimzation dropdown menu.
4. Perform Fore Optics Alignment.
Reference the Auto Tuning section of the Software manual for details on how to do so
5. Perform an Auto Peak for wavelengths that have not been previously Auto Peaked.
Reference Auto Peak section of the Software manual for details on how to do so
Determine Analytical Range
6. Calibrate the system and calculate detection limits, ensure they are well below required reporting limits for each wavelength (3-5X at a minimum).
7. Create Limit check table titled “IEC” (Interfering Element Correction) in the Settings=>Limits section of the LabBook using the Limits (eQuant only) section of the Qtegra software manual as a guide to do so. A Limit table helps to identify interferences more easily in the Evaluation Results.
The High and Low Limits will oftentimes be a laboratory’s required reporting limit for an element. These limits are typically set by a regulatory agency program that your laboratory is adhering to or by your QA/QC department
Note: This document refers to Reporting Limit (RL) which is also known as LOQ (Limit of Quantification).
For example, in the Limit table below, the reporting limit for Pb which is +/- 0.010ppm has been entered into the table with a Low Limit of -0.010ppm and a High Limit of 0.010ppm. If a result is outside of this range, it will be highlighted in a red bold typeface.
8. Calibrate the system and perform a Linear Dynamic Range Study to determine the upper end of the analytical range for each element.
Perform IEC Experiment
9. Create contaminate free single element solutions at concentrations that are typically seen in real customer samples. This concentration should be within the linear range for the wavelength used for any given element and preferably not at the linear range value. The ICSA (Interfering Check Solution A) elements (Al, Mg, Fe, Ca) should be analyzed at the same levels that are in the ICSA and ICSAB (Interfering Check Solution AB).
Note: This document references the EPA methodology which is where the terms ICSA and ICSAB originate but in principle the guidelines listed in this document will apply to any application ran by ICP-OES.
10. For the single element solutions in the sample list, select the Limit check table “IEC” created in step 7 in the Limits Set cell for each single element solution.
11. Calibrate the system and run all single element solutions as Unknowns.
12. Overlay all single element solutions, calibration blanks, and calibration standards to view image data in the subarray.
13. Determine the appropriate position and number of Background Points to be used for each wavelength. Compromises will have to be made in some circumstances based upon which interfering element is more prevalent in customer samples.
· Avoid placing Background Points beneath interfering peaks
For example, in the subarray below, Fe at 500ppm is causing a direct interference on Cd 214.438. Therefore, the right background is not used.
· Avoid placing Background Points on last pixel column on either end of the subarray (far left or far right.)
· It may be necessary to widen some subarrays to find an appropriate Background Point location. If so, change the subarray width in the method, save the method, recalibrate the system, re-analyze the single element solutions, and position Background Points accordingly for that wavelength.
· Once the Background Point positions have been established, save the LabBook.
14. Analyze the results of the single element solution analysis to see if any of the analytes of interest are reporting a value which is outside of the range determined for that element in step 7 thus generating a failure action and requiring further investigation. This would potentially indicate that the element from which this single element solution was made has interfered with the analyte of interest.
15. View the image data for each failed result within each single element standard and make sure the failure was not caused by contamination. (If contamination is suspected do not calculate an IEC for that element. Better to re-make the standard cleanly and re-run)
Note: Also look for spectral contributions that do not fail the IEC Pass/Fail Criteria but may be border line within range. An IEC Calculation should be considered on an element by element basis.
16. Calculate the IEC factors by following steps 1-14 of the “To evaluate the results” subsection of the Inter Element Correction section of the software manual
17. Repeat this process for each interferent.
Sample Analysis
18. The sample introduction components should be cleaned (torch, center tube, nebulizer, POP window, and Radial viewing window) or replaced (pump tubing, capillary tubing, autosampler probe) on a regular basis as a preventative measure in order to maintain optimal performance. A record of this should be documented.
19. If your ICSA fails, re-run the ICSA single element solutions for the element that failed.
(Example: if Lead fails and the only IECs you have on Lead from the ICSA solution are Al and Fe then you only need to re-run the Al and Fe solutions.)
20. IECs can then be recalculated and inputted into LabBook (see step 16). Associated sample results will then be automatically updated with the new IEC factors.
21. If the location or number of Background Points or Center Pixels are modified for any wavelength which has an IEC factor applied to it, an IEC study will have to be performed again. This is because the IEC, Background Points, and Center Pixels all interact with one another. The accuracy of your IEC factor is dependent upon these variables remaining constant.