AOACRIFeedsFertilzerMethods-2017Awards

T hiex : J ournal of aoaC i nTernaTional V ol . 99, n o . 4, 2016 917

Table 2015.18B. ICP calibration standards from commercial custom blend stock standard solutions Standard ID Volume, mL Citrate, mL Stock 1, mL a Stock 2, mL b P concn, μg/mL P 2 O 5 , μg/mL P 2 O 5 solution, % P 2 O 5 fertilizer, % K concn, μg/mL K 2 O, μg/mL K 2 O solution, % K 2 O fertilizer, % Blank 100 40 0 0 0 0 0 0 0 0 0 0 1 100 38 5 of Std 6 c 12 12 27.5 0.00275 1.4 360 434 0.04336 21.7 2 100 36 10 of Std 6 c 10 24 55 0.00550 2.7 300 361 0.03614 18.1 3 100 36 10 of Std 9 c 8 50 115 0.01146 5.7 240 289 0.02891 14.5 4 100 40 5 6 100 229 0.02291 11.5 180 217 0.02168 10.8 5 100 40 8 4 160 367 0.03666 18.3 120 144 0.01441 7.2 6 100 38 12 5 of Std 6 c 240 550 0.05499 27.5 63 76 0.00759 3.8 7 100 40 15 NA d 300 687 0.06874 34.4 NA NA NA NA 8 100 38 20 5 of Std 6 c 400 917 0.09165 45.8 36 43 0.00434 2.2 9 100 38 25 5 of Std 6 c 500 1146 0.11457 57.3 18 22 0.00217 1.1 10 100 40 NA 15 NA NA NA NA 450 542 0.05421 27.1 11 100 40 NA 20 NA NA NA NA 600 723 0.07227 36.1 12 100 40 NA 25 NA NA NA NA 750 903 0.09034 45.2 13 100 40 NA 30 NA NA NA NA 900 1084 0.10841 54.2 14 100 40 NA 35 NA NA NA NA 1050 1265 0.12648 63.2 a  Stock 1 = 2000 μg/mL P as PO 4 custom stock standard [ see Alternative A, section C(p) ].

b  Stock 2 = 3000 μg/mL K from KCl custom stock standard [ see Alternative A , section C(q) ]. c  Serial dilution from another standard (e.g., 5 of Std 6 = add 5 mL from Standard 6). d  NA = Not applicable.

only for calibration within the batch of test solutions with which they were extracted. These standard extract solutions have the same shelf life (i.e., approximately 16 h) as the other fertilizer extracts and must be prepared fresh with each run. Calculations for converting the percentage P 2 O 5 in these materials to milligrams per liter P are provided in the Calculations section ( see Alternative A , section H ). Fertilizer materials below 40% P 2 O 5 (approximately 350 μg/mL P) typically do not experience this suppression issue, so standards below this concentration can be obtained using those listed in Tables 2015.18A and 2015.18B . Empirical calibration is not the preferred option and should be used as a last resort. The test solution and internal standard/ionic buffer solution [ see Alternative A , section C(o) ] are blended using aY-connector

(Part No. 30703-90; Cole-Parmer, Bunker, CT) or T-connector (Part No. 116-0522-01; Bran+Luebbe, Mequon, WI) just before the nebulizer, using the conditions described in Table 2015.18D .

E. Sample Preparation

Collect a primary field sample using one of the recommended AOAC sampling procedures (i.e., Method 929.01 , 969.01 , or 992.33 ) or other recognized protocol. Prepare solid fertilizer materials by riffling [ see Alternative A , section B(g) ] the entire laboratory sample to select an approximate 100 g subsample. Grind the entire 100 g subsample [ see Alternative A , section B(h) ] to pass through a 0.50 mm mesh screen. Place the ground analytical sample into a one-quart (0.946 L) glass jar

Table 2015.18C. Calibration criteria for direct-available P and soluble K by ICP-OES Element ID Wavelength, nm a Calibration range, μg/mL Standards used b

Curve fit

Spectral deconvolution

P P P P P P P P K K K K

177.434 ( 1 ) 177.434 ( 2 ) 178.222 ( 1 ) 178.222 ( 2 ) 213.618 ( 1 ) 213.618 ( 2 ) 214.914 ( 1 ) 214.914 ( 2 ) 766.485 ( 1 ) 766.485 ( 2 )

0–100

Blank, 1, 2, 3, 4 4, 5, 6, 7, 8, 9 Blank, 1, 2, 3, 4 4, 5, 6, 7, 8, 9 Blank, 1, 2, 3, 4 4, 5, 6, 7, 8, 9 Blank, 1, 2, 3, 4 4, 5, 6, 7, 8, 9 Blank, 1, 2, 3, 4

Linear Linear Linear Linear Linear Linear Linear Linear

None None None None

100–500

0–100

100–500

0–100

Cu 213.598 Cu 213.598 Cu 214.898 Cu 214.898

100–500

0–100

100–500

0–126

Quadratic Quadratic Quadratic Quadratic

None None

50–379 126–505 505–1046

3, 4, 5, 6, 7 4, 5, 6, 7, 8

769.897 404.721

Possible LiNO 3

8, 9, 10, 11, 12 None a  The designators ( 1 ) and ( 2 ) are used to distinguish between the same wavelength selected twice to cover two separate concentration ranges. b  The standards correspond to those listed in Table 2015.18A .