AOAC ERP Fertilizers - December 2017

OMAMAN-24 A /Single Laboratory Validation Expert Review Panel for Fertilizers September 2015

B ernius et al .: J ournal of AOAC I nternational V ol . 97, N o . 3, 2014  735

Table 4. Precision of the method

Abs SD

Sample Expected recovery S, % Average recovery, % Abs SL a

Day 1 b

Day 2

Day 3

HorRat

1 c

1.56 6.39

94.29 97.05 98.25

0.038 0.147

0.028 0.190 0.069 0.189 0.058 0.029 0.013 0.165 0.763 0.268 0.144

0.018 0.137 0.146 0.297 0.077 0.051 0.347 0.424 0.088 0.082 0.132

0.018 0.146 0.126 0.069 0.104 0.139

0.39 0.84 0.36 0.57 0.29 0.14 0.13 0.48 0.98 0.32 0.29

2 3 4 5 7 8 9

11.95 13.22

0.13

100.34 125.94 99.85 101.11 100.36

0.219 0.171 0.174 0.235 0.323 0.487 0.185 0.128

7.76

6 d

24 90

— — — — —

26.72

22 26 18

100.2 95.83 98.63

10 11

a  Abs SL defined as absolute SD among runs or within-laboratory precision. b  Abs SD defined as absolute SD within runs. c  Twelve replicates for Samples 1–5: four replicates run on 3 days. d  Eight replicates for Samples 6–11: four replicates run on 2 days.

according to AOAC Method 980.02  (2) within the experimental error.

Table 5. Ruggedness trial method deviations and squared differences Parameter Squared differences No blank measurement 0.08 WO 3 addition 8:1, 12:1 0.06 Wrong method oxygen dose 0.03 Wrong sample wrap, not tin 0.003 Combustion 1100 or 1170 ° C 0.002 Sample weight 20/60 mg 0.002 Broken oxygen dosing device 0.00001

Ruggedness

Ruggedness trial results showed no appreciable effect from the deviations of the method as noted, although caution should be taken to determine a blank measurement and use the proper 10:1 ratio of combustion aid to sample weight.

Precision

Within-run precision was calculated for all validationmaterials. In Table 4, SD values for within-run precision ranged from 0.013 to 0.424% abs. Samples that exhibited the widest spread between Day 1 and Day 2 were Sample 7 elemental S, Sample 8 cysteine, and Sample 9 sulpomag. Sample 4 lawn and garden blend with all sulfate varied the most of the Magruder samples. In Table 4, abs SL among-run precision ranged from 0.038 to 0.487. Sample 1 Magruder 2011-05 exhibited the tightest values. Sample 9 sulpomag, a mined natural fertilizer containing Langbenite, had the widest values possibly due to a high melting point. Arapidmethod for the determination of S and S/sulfate blended fertilizers using high temperature combustion with adsorption/ desorption columnswas validated as fit for the designated purpose. The method was shown to be accurate at 1% S concentration. The precision of the method was demonstrated to be acceptable. The method proved to be time- and resource-efficient, allowing analysis of as many as 50 samples/8 h day with a single calibration curve and much fewer hazardous reagents than the current procedure. Conclusions

Acknowledgments

We thank Bill Hall (Mosaic Fertilizer, Lakeland, FL) and Melton Bryant (retired, University of Kentucky, Lexington, KY) for guidance; April Holcomb (Agilent Technologies, Baltimore, MD) for analytical support; and Mark Larson (elementar Americas, Mt. Laurel, NJ) for editing support. AOAC Research Institute Expert Review Panel Use Only References

 (1) Camberato, J. (2012) Soil Fertility Update, Purdue University Department of Agronomy. http://www.king.corn.org/news/ timeless/SulfurDeficiency.pdf (accessed November 11, 2013)  (2)  Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 980.02  (3)  Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 993.13  (4)  Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 969.01  (5)  Official Methods of Analysis (2005) 18th Ed., AOAC INTERNATIONAL, Gaithersburg, MD, Method 929.01  (6)  AOAC Guidelines for Single-Laboratory Validation of Chemical Methods (2002) AOAC INTERNATIONAL, Gaithersburg, MD  (7) Youden, W.J. & Steiner, E.H., (1975) Statistical Manual of the AOAC , AOAC INTERNATIONAL, Gaithersburg, MD