3. AOACRIFeedsFertilzerMethods-2018Awards

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( 6 )  600 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 30.0 mL of single element or combined 10000 mg/Lmultielement stock standard solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to acid-washed polypropylene bottle. ( 7 )  400 mg/kg Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 20.0 mL of single element or combined 10 000 mg/Lmultielement stock solution into a 1 L acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 8 )  300 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 15.0 mL of single element or combined 10000 mg/L multielement stock standard solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 9 )  200 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 10.0 mL of single element or combined 10000 mg/L multielement stock standard solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 10 )  100 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 10.0 mL of single element or combined 10000 mg/L multielement stock standard solution into a 1000 mL acid-washed volumetric flask. Add 90 mL trace metal grade HNO 3 and 30 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 11 )  80 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 4.0 mL of single element or combined 10000 mg/L multielement stock standard solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 12 )  50 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 5.0 mL of single element or combined 10000 mg/Lmultielement stock standard solution into a 1 L acid-washed volumetric flask. Add 90 mL trace metal grade HNO 3 and 30 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 13 )  30 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 3.0 mL of single element or combined 10000 mg/Lmultielement stock standard solution into a 1 L acid-washed volumetric flask. Add 90 mL trace metal grade HNO 3 and 30 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 14 )  0.0 mg/L all Ca, Cu, Fe, Mg, Mn, and Zn .—Add 45 mL trace metal grade HNO 3 and 30 mL trace metal grade HCl into a 500 mL volumetric flask, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( p )  Sampler wash solution, 9% HNO 3 :3% HCl .—Dilute 90 mL trace metal grade HNO 3 , G ( b ), and 30 mL trace metal grade HCl, G ( c ), to 1000 mL with H 2 O. H. Determination Analyze test solutions using an ICP-OES instrument calibrated with standard solutions. Insert a 10 mg/kg working standard or other suitable quality control solution every 10 test portions to monitor for instrument drift. For quality control, see section J .

I. Calculations , = �

, � ∗ � 100 . , � ∗ � 1 1000 � ∗ � 1000 1 � where 100 mL assumes the microwave digest is diluted to 100 mL. Some of the Group A and B elements are routinely reported as percent concentrations. To convert a mg/kg result to percent, divide the mg/kg result by 10000 and change the unit frommg/kg to percent. J. Quality Control Each run should contain adequate quality control to monitor the analytical system. The following are recommended to be included with each batch prepared for digestion: ( a )  Accuracy check .—One or more digested reference materials of known concentration (e.g., NIST 695, Magruder Check Samples, AFPC Check Samples, etc.). ( b )  Precision check .—One of the unknowns should be duplicated to ensure that the process can repeat a similar result. ( c )  Method blank .—A digestion tube containing all reagents with no test portion that is processed identically to all others within the batch is recommended to ensure that no contamination of reagents, glassware, etc. has occurred. ( d )  Matrix spike recovery (optional).— One of the unknowns or reference materials can be spiked with a known concentration of all elements to ensure that the matrix does not significantly reduce or enhance the recovery of the desired analyte. ( e )  Continuing calibration verification (CCV).— A calibration standard run at periodic intervals (every 10th test solution) to verify the instrument is maintaining calibration. ( f )  Internal calibration verification (ICV).— An undigested reference solution from a source different from the calibration standards is run after the calibration to check the accuracy of the calibration. ( g ) For each element not reaching predetermined QC criteria, the instrument must be recalibrated and the impacted samples must be reanalyzed. ( h ) Limits of quantitation and detection (LODs and LOQs) should be determined for each element by each laboratory using the method. The author’s LODs and LOQs should be used only as a guide, but due to different instruments and configurations, these will vary from user to user. ( i ) A typical analytical sequence is as follows: ( 1 ) Instrument calibration standards; ( 2 ) ICV; ( 3 ) a series of test solutions based on digestion batch size, including digested QC, spike blanks, and QC duplicates and spikes; ( 4 ) CCV; ( 5 ) another group of test solutions and periodic CCV until finished; ( 6 ) final CCV and QC. It is recommended that one or more QC samples be included after every 10 digests. References: J. AOAC Int . 97 , 700(2014) DOI: 10.5740/jaoacint.13-408 J. AOAC Int . (future issue) Posted: July 20, 2017

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03/10/2019