AOAC ERP Fertilizers - December 2017

358 T hiex : J ournal of AOAC I nternational V ol . 99, N o . 2, 2016

manifold water. Start circulation to stabilize temperature in entire system 15 min before beginning Extraction 2. Do not circulate water more than 5 min prior to Extraction 2. Begin Extraction 2 exactly 1 h after Extraction 1 is complete. Add 475 mL extraction solution to flasks. Pump extraction solution and air from the flasks at 4 mL/min to the bottom of columns at predetermined time. Extract for exactly 2 h after solution first reaches samples. Swirl occasionally to mix extract solution during extraction. After 2 h, stop pump and reverse flow to top of columns, pumping solution back into flasks. Pump air for 1 min after all liquid is emptied to ensure maximum transfer of solution. Cool extract to 20°C, dilute to volume with solution, and mix. Using a clean, dry graduated cylinder, transfer exactly 250 mL extract to amber HDPE bottles, and add exactly 5.0 mL stabilizing solution I(d) . Extract is now ready for analysis. Keep all remaining 250 mL of solution in flasks to be used in next extraction. Add approximately 225 mL freshly prepared extraction solution to flasks, bringing total volume to approximately 475 mL. (c)  Extraction 3 .—Immediately after completion of Extraction 2, adjust bath to a temperature needed to maintain 55.0 ± 1.0°C in columns. Drain manifold(s) to preheat all manifold water. Start circulation to stabilize temperature in entire system 15 min before beginning Extraction 2. Do not circulate water more than 5 min prior to Extraction 3. Begin Extraction 3 exactly 1 h after Extraction 2 is complete. Remainder of Extraction 3 is identical to Extraction 2 except extraction time is exactly 20 h. (d)  Extraction 4 .—Immediately after completion of Extraction 3, adjust bath to a temperature needed to maintain 60.0 ± 1.0°C in columns. 1 h after completion of Extraction 3, begin Extraction 4. Remainder of Extraction 4 is identical to Extraction 2 except extraction time is exactly 50 h. (e)  Extraction 5 (if needed) .—1 h after completion of Extraction 4, begin Extraction 5. Extraction 5 is identical to Extraction 4 except extraction time is exactly 94 h. Following removal of the test portion, clean columns in place with a large brush. If there is buildup or precipitation in columns or tubing, flush by circulating 2% HCl through system for 5 min. Follow with two 5 min DI water washes. If there is no buildup, water washes are sufficient. Allow columns to dry before placing new packing and samples in column for next run. Determine nutrients of interest (e.g., N, P, and K) on each of the extracts obtained. (a)  Determine Total N using AOAC Method 993.13 (combustion) or AOAC Method 978.02 (modified comprehensive) or other equivalent applicable methods validated in your laboratory. Use an applicable method-matched reference material in each run. Use an internal reference standard appropriate for the range of the sample extracts; typically 10, 100, 1000, and 10000 mg N/L will cover the full range of N concentrations. (b)  Determine total phosphate (as P 2 O 5 ) using AOAC Method 962.02 or AOAC Method 978.01 or equivalent applicable methods validated in your laboratory. Use an L. Analytical Determinations

applicable method-matched reference material in each run. Use an internal reference standard appropriate for the range of the sample extracts; typically 10, 100, 1000, and 10000 mg P 2 O 5 /L will cover the full range of P 2 O 5 concentrations. (c)  Determine soluble potash (as K 2 O) using AOAC Method 958.02 (STPB) or AOAC Method 983.02 (flame photometry) or equivalent applicable methods validated in your laboratory. Use an applicable method-matched reference material in each run of samples. Use an internal reference standard appropriate for the range of the sample extracts; typically 10, 100, 1000, and 10000 mg K 2 O/L will cover the full range of K 2 O concentrations. Results for each extraction are presented as a cumulative percentage of total nutrient. Extraction 1 is water-soluble and not a slow-release fraction. However, slowly available water-soluble materials (low-MW urea formaldehydes and methylene ureas) may be present. These materials can be analyzed directly from Extraction 1 and expressed according to their definition. = % Total nutrient/analyte determined as in the Analytical Determinations section above, where A can be N, P, or K. AC (ex1) = Concentration (in mg/L) of nutrient/analyte in Extract 1, where A can be N, P, or K. %AR (ex1) = % Nutrient released during Extraction 1, where A can be N, P, or K. AC (ex2) = Concentration (in mg/L) of nutrient in Extract 2, where A can be N, P, or K. %AR (ex2) = % Nutrient released during Extraction 2, where A can be N, P, or K. AC (ex3) = Concentration (in mg/L) of nutrient in Extraction 3, where A can be N, P, or K. %AR (ex3) = % Nutrient released during Extraction 3, where A can be N, P, or K. AC (ex4) = Concentration (in mg/L) of nutrient in Extraction 4, where A can be N, P, or K. %AR (ex4) = % Nutrient released in Extraction 4, where A can be N, P, or K. A (tr) = % Total release of all extractions, where A can be N, P, or K. A (ne) =%Controlled release (nutrient not extracted, calculated below), where A can be N, P, or K. A (cr) = % Controlled release (nutrient released in Extractions 2–4), where A can be N, P, or K. W = Total unground test portion weight in g. %TAR = Total nutrient (analyte) released, where A can be N, P, or K. WIN = Water-insoluble N. 1.02 = Dilution factor (due to addition of the preservative) = 255 mL/250 mL. V = Total volume of respective extract in L. M. Expression of Results N. Calculations and Graphing the Release Plot Nomenclature for extraction calculations. —A (t)