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    Minerals in Grass

    Application Note EDXRF1552

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    Scope

    The analysis of important mineral elements in grass is demonstrated.

    Background

    The mineral content of animal feeds is carefully blended and monitored to ensure optimal animal health and product quality. Grass-fed dairy cattle require the optimum balance of the major minerals calcium, potassium, magnesium, and phosphorus and the trace minerals copper, manganese, and zinc. Proper mineral balance ensures optimum milk quality and production. To meet the industry's need of monitoring the mineral content, Rigaku offers the NEX QC+ EDXRF analyzer for fast and simple measurement of grass and other animal feeds.

    NEX QC+ high-resolution EDXRF analyzerModel: NEX QC+

    Calibration

    A set of twelve assayed grass samples were submitted by an industry user for demonstration. Empirical regressions calibrations were built to provide optimum accuracy.

    Element Units Concentration range
    K % 1.8 – 3.2 %
    Ca % 0.4 – 0.8 %
    Mg % 0.14 – 0.22 %
    P % 0.22 – 0.32 %
    S % 0.13 – 0.30 %
    Mn ppm 45 – 105 ppm
    Cu ppm 5 – 12 ppm
    Zn ppm 20 – 50 ppm

    Note: 1 ppm = 1 mg/kg

    Precision

    Representative calibration standards were measured ten consecutive times each in a static position to demonstrate effective recovery and analytical precision.

    Sample I.D.: Standard #73
    Element ICP value NEX QC+ average value Std. dev
    K 2.713 % 2.738 % 0.054
    Ca 0.536 % 0.540 % 0.006
    Mg 0.180 % 0.163 % 0.009
    P 0.254 % 0.249 % 0.002
    S 0.300 % 0.288 % 0.0005
    Mn 105.6 ppm 106.1 ppm 1.5
    Cu 11.9 ppm 12.4 ppm 0.7
    Zn 47.0 ppm 45.9 ppm 0.9
    Sample I.D.: Standard #77
    Element ICP value NEX QC+ average value Std. dev
    K 1.912 % 1.947% 0.026
    Ca 0.836 % 0.828 % 0.007
    Mg 0.222 % 0.197 % 0.002
    P 0.341 % 0.334 % 0.001
    S 0.125 % 0.119 % 0.0002
    Mn 84.8 ppm 85.6 ppm 2.8
    Cu 6.9 ppm 7.3 ppm 0.2
    Zn 48.8 ppm 49.5 ppm 0.1
    Sample I.D.: Standard #79
    Element ICP value NEX QC+ Average value Std. dev
    K 3.241 % 3.199 % 0.024
    Ca 0.543 % 0.533 % 0.008
    Mg 0.143 % 0.131 % 0.008
    P 0.308 % 0.302 % 0.001
    S 0.201 % 0.195 % 0.0011
    Mn 31.0 ppm 30.4 ppm 1.5
    Cu 10.9 ppm 8.6 ppm 0.5
    Zn 21.2 ppm 20.7 ppm 0.5
    Sample I.D.: Standard #87
    Element ICP value NEX QC+ average value Std. dev
    K 1.379 % 1.440 % 0.010
    Ca 0.424 % 0.431 % 0.002
    Mg 0.168 % 0.142 % 0.002
    P 0.252 % 0.244 % 0.001
    S 0.127 % 0.124 % 0.0004
    Mn 73.4 ppm 73.6 ppm 0.8
    Cu 5.7 ppm 5.9 ppm 0.2
    Zn 23.1 ppm 22.6 ppm 0.3

    Analysis of unknown samples

    Unknown samples with ICP values were submitted by the user for measurement against the calibrations built. Results are shown here.

    Sample I.D.: Sample #76
    Element ICP value NEX QC+ average value Std. dev
    K 2.508 % 2.474 % 0.026
    Ca 0.652 % 0.666 % 0.002
    Mg 0.169 % 0.171 % 0.001
    P 0.288 % 0.290 % 0.0002
    S 0.198 % 0.197 % 0.0005
    Mn 36.7 37.5 2.1
    Cu 7.8 8.5 0.2
    Zn 30.5 30.6 0.4
    Sample I.D.: Sample #84
    Element ICP value NEX QC+ average value Std. dev
    K 2.619 % 2.580 % 0.003
    Ca 0.455 % 0.477 % 0.002
    Mg 0.168 % 0.175 % 0.0048
    P 0.315 % 0.289 % 0.001
    S 0.259 % 0.246 % 0.0011
    Mn 77.9 ppm 75.2 ppm 0.7
    Cu 6.9 ppm 7.0 ppm 0.2
    Zn 30.8 ppm 31.7 ppm 0.2

    Conclusion

    The NEX QC+ offers analysts a simple yet powerful and versatile system for quantifying elemental composition using the empirical approach. The results of this study indicate that given stable samples, proper sample handling, and proper calibration technique, the Rigaku NEX QC+ EDXRF can achieve excellent results for measuring the key mineral elements in grass and other animal feeds.

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