The Development and Characterisation of the in-house Quality Control Material “Soil of Jamaica”

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The Development and Characterisation of the in-house Quality Control Material “Soil of Jamaica”

Introduction

picture2.pngJamaican soils are known to be enriched in many elements including arsenic, cadmium and uranium. Suitable reference materials such as NIST 698 Bauxite (Jamaican) do not include reference or information values for measurands of interest such as As, Cd or U. Elevated CRMs such as NIST 2710 introduced effects specific to Instrumental Neutron Activation Analysis such as self-shielding. ICENS therefore decided to develop a natural matrix in-house reference material. The parish of Manchester in Jamaica is known for bauxite mining as well as its naturally elevated levels of several trace elements. It was thought that this would be a suitable area to source the material for the “Soil of Jamaica” quality control material.

Table 1: Comparison of ranges and means for Jamaican and world soils for selected elements 


Natural Matrix Source Area & Control Material Preparation

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  • Sample preparation procedure the same as test soil samples.
  • Storage in similar containers housed in reference material cabinet

Analytical Technique

Instrumental Neutron Activation Analysis (INAA) performed using the SLOWPOKE-2 research reactor at ICENS to irradiate sub-samples.

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Figure 3: SLOWPOKE-2 Research Reactor    Figure 4: Irradiation Regime Flowchart for “Soil of Jamaica

 Quality control material was also irradiated with a suitable certified reference material.


Results

“Soil of Jamaica” was analysed for twenty-four    elements of interest and Shewhart charts generated for all the measurands of interest to determine whether the system was under statistical control. 

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Figure 5:  Control Charts for Br, Eu, La and U in in-house reference material “Soil of Jamaica”

Westgard rules were applied to make the charts more sensitive to smaller shifts and to reduce false alarms.

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Figure 6: Cs Control Chart for the in-house Reference Material “Soil of Jamaica”

With two observations that surpass the upper warning limit in four runs there was clearly an effect that warranted the attention of the analyst and quality assurance manager for the Cs control chart.


Discussion

picture11.pngThe QCM “Soil of Jamaica” was analyzed under routine analytical conditions for geological samples to characterize the expected measurement variation and range of values. The mean and standard deviation were calculated from these initial analyses. Descriptive statistics were performed on the elemental   results, including skewness, kurtosis and normalcy plots to determine whether the data was normally distributed. It was important in the analysis of the control charts to   determine whether observations that violated control criteria were the results of analyst performance, performance of instrumentation, improper standardization or some other deviation from standard operating procedure. Figure 7 suggests a systematic error with two instances of rule 9X violations for Zn (illustrated by the red lines and points). Figure 7: Zn Control Chart for the in-house Reference Material “Soil of Jamaica”


Conclusion

The in-house reference material “Soil of Jamaica” appears to be a stable, natural matrix. Of the 24 elements analysed 14 were accepted as recommended values with the remainder regarded as information values. It has proven useful to analysts at ICENS for assessing various analytical methods, assigning values to elements in Jamaican soils and in general supplementing the quality assurance and control mechanisms in place at the Centre. Bode, P., van Dijk, C.P.,(1997). Operational management of results


Acknowledgements

The authors would like to thank Professor Gerald Lalor for his instruction in this work and the numerous analysts, past and present, who through their efforts at ICENS contributed to this work.


References

In INAA utilizing a versatile system of control charts. Journal of     Radioanalytical and Nuclear Chemistry, 215, 87-94.

Chilian, C., St-Pierre, J., Kennedy, G., (2006). Dependence of    thermal and epithermal neutron self-shielding on sample size and       irradiation site. Nuclear Instruments and Methods in Physics       Research Section A, 564 (2), 629 – 635. 

Grant, C.N., Lalor, G.C., Vutchkov, M.K.(1998). Neutron Activation Analysis of Cadmium in Jamaican Soils. Journal of Radioanalytical and Nuclear Chemistry, 237 (1-2), 109-112.

Grant, C.N., Lalor, G.C., Vutchkov, M.K. (2005). Comparison of bauxites from Jamaica, the Dominican Republic and Suriname. Journal of Radioanalytical and Nuclear Chemistry, 266 (3) 385-388.

IAEA, 2003. Development and use of reference materials and     quality control materials. IAEA-TEC-DOC 1350. International Atomic Energy Agency.

Lalor, G.C. (1995). A Geochemical Atlas of Jamaica.Kingston,       Jamaica: Canoe Press

 

 

 

 

 

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