SPSFAM Heavy Metals ERP Book

7. FINAL ACTION REQUIREMENTS

Has the method author addressed Final Action requirements as noted by the ERP Report, if any?

Yes.

8. RECOMMENDED CHANGES (If any)

Are there any recommended changes to the AOAC First Action method as written?

I have several recommendations: 1. Section B. EQUIPMENT (a) INSTRUMENTATION - Remove "free-running 40 MHz RF generator". Some other manufacturers use 27 MHz RF generators. 2. Section B. EQUIPMENT (a) AUTOSAMPLER CUPS - This sections instructs the chemist to check the volume mark on the cup by determining the mass of 20 mL and 50 mL of DI water in 10 cups per case of cups. I suggest removing sections (f) (1) to (3) and instead require a gravimetric determination of the final mass of dilution. Gravimetric dilutions are much accurate and reproducible and faster. Section F. SAMPLE PREPARATION paragraph (f) would also have to be changed to instruct the dilution to be done gravimetrically. 3. Section C. REAGENTS and STANDARDS (e) INTERNAL STANDARD SOLUTION - The method specifies the internal standard solution to be 40 ppb. I suggest changing to 40 ppb of other appropriate concentration that will result in 100,000 to 500,000 cps signal. 4. TABLE 2015.01A CALIBRATION STANDARDS - I suggest making the 5 ppb HG standard optional. Instruments with a Scott type spray chamber can have memory and wash out problems when Hg standards are > 2 ppb. 5. Section C. REAGENTS and STANDARDS (e) INTERNAL STANDARD SOLUTION - 20% acetic acid is specified for the internal standard solution. Instead, the concentration of the acetic acid after mixing with the sample and presented to the spray chamber should be specified. Instruments brands will vary the ratio of peristatic pump tube internal diameter between the internal standard and the sample. Chemists will also vary this ratio based on personal preference. Therefore if the acetic acid concentration presented to the torch is specified, the chemist can choose the concentration in the internal standard solution based on the mixing ratio of their instrument. 6. TABLE 2015.01B - The recommended isotopes for Hg are 200 and 202. Both of these isotopes can suffer from tungsten oxide interference. Therefore either 201Hg should be specified. If 200Hg or 202Hg are to be used then there must be instructions to monitor for the lack of tungsten in the sample. 7. Section D. CONTAMINATION AND INTERFERENCES (f) Resolution of Interferences - Add a section that describes He collision cell use and kinetic energy discrimination (KED) for reduction of interferences. 8. Section G. PROCEDURE (c) INTERNAL STANDARDIZATION and CALIBRATION part (4) - Add "IRT must be used for Cd unless monitoring for Mo shows that Mo is not present at a concentration that will interfere. 9. Section H. QUALITY CONTROL (a) - List what type of weighting is recommended. Software from manufacturers offer several types of calibration weighting. I also suggest adding a statement allowing a blank offset algorithm be offered as a choice instead of weighting. 10. Section H. QUALITY CONTROL - Add a section that addresses linearity. Samples with solution concentrations above the highest calibration standard must be diluted such that the analyte concentration is at or below the highest calibration standard. 11. Section C. REAGENTS and STANDARDS part (j) SPIKING SOLUTION - I suggest adding a statement, " The Lu solution concentration can be adjusted down in order to maintain the detector in pulse mode." 12. Section I. METHOD PERFORMANCE (a) - To be scientifically and statistically rigorous, the method cannot set the LOQ as 3 X