Analysis of Food and Agricultural Samples Using the aurora M90 ICP-MS with Collision Reaction Interface (CRI)

IntroductionFoods and agricultural products contain various concentrations of nutrients, which can range from trace amounts to percentage levels. However, whilst most of their nutritional content is intended for maintaining good health, the benefits of the desired mineral content of such products can be compromised by concentrations of elements deemed to be toxic to humans and/or animals. The health effects of dietary exposure to different levels of minerals and metals have been widely investigated for humans. Accordingly, based upon the concentrations at which deficiencies and toxicities are observed, inorganic elements may be divided into four groups: Macrominerals–a regular intake of large quantities of these elements is needed to sustain life, that is, Ca, Mg, Na, K, P, S, Fe, Cu, and Zn. Required or essential trace minerals–a smaller quantity of each of these elements ensures good health, for example, Mn, Cr, Se, B, Br, Si, I, V, Li, Mo, Co, Ge, and others. Possibly required trace minerals–some studies propose the human body’s requirement for other elements, for example, F, As, Rb, Sn, Nb, Sr, Au, Ag, and Ni. Toxic metals–dietary intake of these deleterious elements should be minimized, for example, Be, Hg, Pb, Cd, Al, Sb, Bi, Ba, and U.Greater exposure to toxic metals in the modern diet has been postulated as a contributing factor in the apparent increased number of diagnoses of some of today’s medical conditions, such as, diabetes, hypothyroidism, and cancer.Similarly, looking upstream in our food supply chains and in particular to the agricultural industry, it is becoming increasingly clear that providing the correct balance of macrominerals and trace metals in their feed helps livestock to thrive and remain disease free. For example: magnesium intakes for ruminants have been established that prevent grass tetany; selenium is known to be a major factor in the fertility of cows; and cobalt supplements are often necessary for the well-being of sheep. Accurate measurement of elemental composition in food and agricultural products is essential in ensuring product safety Application Note # CA-270104Analysis of Food and Agricultural Samples Using the aurora M90 ICP-MS with Collision Reaction Interface (CRI)and maintaining adequate levels of nutritional content. With concentrations typically ranging from sub parts-per-billion to high parts-per-million in solution, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a vital tool, providing fast, reliable, and routine analysis of samples over a large concentration range. As such, this application note investigates the measurement of key elements in food and agricultural reference materials by ICP-MS, from trace to major levels within a single analysis.InstrumentationAn aurora M90 ICP-MS was used for the analysis and includes the patented 90 degree ion mirror [1] providing unsurpassed transmission of ions from the interface to the mass analyzer [2]. The aurora M90 ICP-MS is able to achieve unmatched sensitivity of more than 1000 million c/s per mg/L of analyte, while maintaining oxide ratios (CeO+/Ce+) below 3%. The aurora M90 ICP-MS is also equipped with the patented Collision Reaction Interface (CRI) interference management System [3], [4]. The CRI attenuates polyatomic ions formed in the plasma, which can interfere with the determination of elements, such as, As, Se, Cr, V, and Fe, thus improving their detection limits. Another innovative feature of the aurora M90 ICP-MS is the fully digitized, discrete dynode electron multiplier (DDEM) detection system. This system provides nine orders (109) of linear dynamic range in ‘pulse-counting’ mode only, allowing routine measurement of elements from ultra trace to percentage levels within a single analysis. The linearity of a fully digitized DDEM provides an advantage over dual-mode detection systems that must also operate in an analog mode to achieve an equivalent dynamic range. Dual-mode detectors typically have a dynamic range of only six orders (106) in pulse-counting mode. When the ion signal is too strong – as can occur when measuring major element concentrations – the detector must switch to an analog measurement mode that extends the range by a further three orders. Accordingly, if required to operate across the same concentration range, a dual-mode detector system must employ a complex and inaccurate cross-calibration to bridge the discontinuity in linearity that occurs in switching between its disparate modes. These cross-calibrations need to be performed regularly, posing an inconvenience for laboratories routinely analyzing food and agricultural samples. By using the latest in ICP-MS detector technology, the DDEM detector system eliminates the need for analog measurements, while maintaining maximum dynamic range. When exposed to strong ion signals, the DDEM detector attenuates the resulting electron beam within the detector itself, quickly and accurately. Three attenuation modes are available: none, medium, and high, with the necessary attenuation being set automatically for each element during the sample analysis. This allows isotope ratios and element concentrations from sub parts-per-trillion to high parts-per-million to be accurately measured in pulse-counting mode only. ConditionsOperating parameters are summarized in Table 1. The method parameters were optimized using the ICP-MS software’s Automax routine, which automates setting of all CRI and plasma gas flow rates and ion optic voltages.Sample PreparationAll samples were prepared by accurately weighing approximately 0.5 g into a microwave vessel, into which 10 mL of HNO3 and 1 mL HCl was then added. The vessel was then heated for 25 min. and held at 200 °C for a further 30 min. Samples were left to cool to ambient temperature and made up to 20.00 mL using ultra-pure water (>18 M?•cm).Sample AnalysisPrior to analysis, samples were diluted ten-fold with ultra-pure water (>18 M?•cm). An internal standard solution was prepared containing 20 µg/L of 45Sc, 89Y, 103Rh, 159Tb, and 175Lu, which was added online to the sample line via a ‘Y piece’. Isotopes were run in normal sensitivity and CRI mode in one continuous method. When operating in CRI mode, hydrogen or helium gas was added to the CRI skimmer cone to attenuate all polyatomic interferences. Hydrogen was used for elements Ca, Fe, and Se, and helium for V, Cr, Cu, Ni, and As. Non CRI mode was used for the remaining elements.CalibrationCalibration standards were created from high-purity, multi-element solutions and the acid matrix matched to the samples.Results and DiscussionA variety of food and agricultural reference materials, including tea leaves [5], coffee, milk powder [6], bread, kidney, and loam [7], and ‘intra-laboratory’ samples of Table 1: aurora M90 ICP-MS instrument operating parametersInstrument ParametersSettingsGas Flow Parameters(L/min)Plasma flow 18Auxiliary flow 1.8Sheath gas 0.15Nebulizer flow 1.0RF Setting RF power (kW) 1.45Sample IntroductionSampling depth (mm) 6.5Pump rate (rpm) 4Stabilization time (s) 30QuadrupoleScanScan mode Peak HoppingDwell time (ms) 30Acquisition Points per peak 1Scans/Replicated 10Replicates/Sample 5Detector Settings Attenuation mode Automatic: Mn, Co, Cu, Fe, Zn, and PbHigh: Na, K, Ca, Mg, and PNebulizer Quartz MicroMist-con-centric (0.4 mL/min)Spray- chamberPeltier-cooled (3 oC), double-pass Scott typePump TubingSample and internal standard linesBlack/Black(0.030 in. ID)Spraychamber waste lineBlue/Blue(0.065 in. ID)CRI Skimmer gas type No gas H2 HeSkimmer flow (mL/min) 0 80 120Ion Optics (volts)First extraction lens -1 -35 -25Second extraction lens -150 -150 -150Third extraction lens -200 -240 -240Corner lens -210 -230 -230Mirror lens left 38 28 28Mirror lens right 26 16 16Mirror lens bottom 32 26 26Entrance lens 1 1 1Fringe bias -2.9 -2.9 -2.9Entrance plate -40 -40 -40Pole bias 0 0 0lime, hay, and animal feed were analyzed. The results are presented in Tables 2–10. Tables 2–6 summarize the results obtained for five different food samples. Measured concentrations for each of the samples were typically within the certified range or ±10% of the certified value, demonstrating the validity of the method. Element Units Measured Certified27Al mg/kg 2145 229055Mn mg/kg 1540 157056Fe mg/kg 423 43223Na mg/kg 24.0 24.765Cu mg/kg 20.4 20.466Zn mg/kg 34.6 34.751V mg/kg 1.84 1.9752Cr mg/kg 1.84 1.9159Co mg/kg 0.350 0.38760Ni mg/kg 6.04 6.1275As mg/kg 0.104 0.10678Se mg/kg 0.062 0.076109Tl mg/kg 0.064 0.063114Cd mg/kg 0.027 0.03121Sb mg/kg 0.046 0.050206-8Pb mg/kg 1.56 1.78238U mg/kg 0.100 0.099Table 2: Results for tea leaf reference material INCT-TL-1Table 3: Results for skim milk powder reference material BCR-150Table 4: Results for pig kidney reference material BCR-186Element Units Measured Certified†56Fe mg/kg 12.3 11.8 ± 0.665Cu mg/kg 2.17 2.23 ± 0.0855Mn mg/kg 0.224 (0.236)66Zn mg/kg 47.7 (49)78Se mg/kg 0.130 (0.127)206-8Pb mg/kg 1.005 1.000 ± 0.04059Co µg/kg 6.2 (6.4)60Ni µg/kg 58.0 (61.5)109Tl µg/kg 1.0 (1.0)114Cd µg/kg 20.7 21.8 ± 1.4Element Units Measured Certified†56Fe mg/kg 291 299 ± 1065Cu mg/kg 31.9 31.9 ± 0.466Zn mg/kg 126 128 ± 352Cr mg/kg 0.063 (0.058–0.142)‡ 55Mn mg/kg 8.3 8.5 ± 0.360Ni mg/kg 0.436 (0.420)75As mg/kg 0.068 0.063 ± 0.00978Se mg/kg 9.9 10.3 ± 0.5114Cd mg/kg 2.703 2.710 ± 0.150206-8Pb mg/kg 0.296 0.306 ± 0.011Element Units Measured Certified†24Mg mg/kg 513 50039K mg/kg 3128 310044Ca mg/kg 422 41055Mn mg/kg 19.9 20.3 ± 0.756Fe mg/kg 39.0 40.7 ± 2.365Cu mg/kg 2.6 2.6 ± 0.166Zn mg/kg 19.0 19.5 ± 0.552Cr mg/kg 0.077 (0.068–0.360)‡ 60Ni mg/kg 0.46 (0.44)75As mg/kg 0.024 (0.023)78Se mg/kg 0.026 (0.025)114Cd mg/kg 0.0270 0.0284 ± 0.0014202Hg mg/kg 0.003 (0.002)206-8Pb mg/kg 0.182 0.187 ± 0.014Table 5: Results for brown bread reference material BCR-191Table 6: Results for coffee powder reference material T0759 (FAPAS)Table 7: Results for Silty Clay Loam reference material CRI7003 (aqua regia soluble)Element Units Measured Certified75As mg/kg 0.52 0.27–0.57‡114Cd mg/kg 0.23 0.12–0.28‡65Cu mg/kg 1.89 1.06–1.98‡206-8Pb mg/kg 0.24 0.20–0.45‡Tables 7–10 summarize the results obtained for four different agricultural samples. All measured concentrations for each of the samples were within ±10% of the certified value, demonstrating the validity of the method. In fact, the majority of results easily fell within ±5% of the certified value.Element Units Measured Certified52Cr mg/kg 41.4 42.455Mn mg/kg 517 52959Co mg/kg 10.1 10.360Ni mg/kg 28.4 28.865Cu mg/kg 24.8 25.466Zn mg/kg 68.8 69.475As mg/kg 11.3 11.6114Cd mg/kg 0.31 0.32202Hg mg/kg 0.091 0.093206-8Pb mg/kg 24.6 25.2†Values in brackets are not certified.‡Range of results observed.References[1] I. Kalinitchenko, Ion Optical System for a Mass Spectrometer, US Patent 6614021 B1, 2 December, 2003[2] Elliott, S., Knowles, M. and Kalinitchenko, I. 2004. A New Direction in ICP-MS. Spectroscopy, 19 (1): 30 [3] I. Kalinitchenko, Mass spectrometry apparatus and method, US Patent 7,329,863 B2, 12 February 2008[4] X. Wang and I. Kalinitchenko, Principles and performance of the Collision Reaction Interface for the aurora M90 ICP-MS, Bruker Technical Note # CA-270111[5] Dybczynski R., Danko B., Kulisa K., Maleszewska E., Polkowska- Motrenko H., Samczynski Z. and Szopa Z. 2004. Preparation and preliminary certification of two new Polish CRMs for inorganic trace analysis. Journal of Radioanalytical and Nuclear Chemistry, 259 (3): 409 [6] Certified Reference Materials 2004, Institute for Reference Materials and Measurements[7] LGC Standards, Analytical Reference Materials Catalog 2008/2009. Bruker Daltonics is continually improving its products and reserves the right to change specifications without notice. © Bruker Daltonics 02-2011, CA- 270104Author: René ChemnitzerFor research use only. Not for use in diagnostic procedures. Table 8: Results for Lime intra-laboratory reference material Table 10: Results for Hay intra-laboratory reference materialTable 9: Results for Feedstuff intra-laboratory reference materialElement Units Measured Certified†24Mg % 0.94 (0.97)31P % 1.46 (1.51)44Ca % 28.5 (29.5)52Cr mg/kg 5.5 (5.7)60Ni mg/kg 2.50 (2.58)75As mg/kg 1.25 (1.29)114Cd mg/kg 0.48 (0.49)202Hg mg/kg 0.03 (0.03)206-8Pb mg/kg 7.7 (7.9)Element Units Measured Certified†23Na % 8.67 (8.87)24Mg % 2.77 (2.83)31P % 2.07 (2.12)39K % 0.34 (0.35)44Ca % 17.7 (18.1)56Fe % 0.33 (0.33)66Zn % 0.54 (0.56)55Mn mg/kg 2.44 (2.50)59Co mg/kg 15.2 (15.5)65Cu mg/kg 568 (581)75As mg/kg 1.61 (1.65)114Cd mg/kg 0.084 (0.086)202Hg mg/kg 0.002 (0.002)206-8Pb mg/kg 1.14 (1.17) Element Units Measured Certified†23Na % 0.33 (0.34)24Mg % 0.19 (0.21)31P % 0.37 (0.39)39K % 0.34 (0.35)44Ca % 0.54 (0.57)55Mn mg/kg 79.1 (81.9)52Cr mg/kg 1.8 (1.9)56Fe mg/kg 498 (531)59Co mg/kg 0.18 (0.19)60Ni mg/kg 1.53 (1.61)65Cu mg/kg 7.5 (7.8)66Zn mg/kg 33.0 (34.9)75As mg/kg 0.27 (0.28)78Se mg/kg 0.047 (0.049)114Cd mg/kg 0.079 (0.083)202Hg mg/kg 0.014 (0.015)206-8Pb mg/kg 1.14 (1.19)ConclusionThis work has successfully demonstrated that the aurora M90 ICP-MS with CRI technology provides a simple and effective solution for the direct determination of elements from trace to percentage levels in food and agricultural samples within a single, routine, and reliable analysis. This has been achieved through technological innovations in interference management through the Collision Reaction Interference, high efficiency ion mirror for superior sensiti-vity, and an all-digital detector allowing fast, accurate, and precise measurement from sub parts-per-trillion to high parts-per-million element concentrations.KeywordsFood and AgricultureAll-digital detectionICP-MSInstrumentation aurora M90 ICP-MSBruker Daltonik GmbH Bremen · GermanyPhone +49 (0)421-2205-0 Fax +49 (0)421-2205-103 sales@bdal.deBruker Daltonics Inc. Billerica, MA · USAPhone +1 (978) 663-3660 Fax +1 (978) 667-5993 ms-sales@bdal.comwww.bruker.com/chemicalanalysis