Determination of Trivalent and Hexavalent Chromium in Mineral and Spring Water Using HPLC Coupled to ICP-MS


The extensive use of chromium in various industrial processes, and the erosion of chromium from natural sources have resulted in the widespread occurrence of this chemical in the environment. Monitoring chromium in environmental compartments as well as food and water sources is key to assessing the potential risk from exposure. The US Environmental Protection Agency (EPA) and the European Union (EU) have specified maximum admissible concentrations of 0.1 and 0.05 mg/L in water for total chromium under their respective drinking water regulations.


) and hexavalent (CrVI valence states of chromium. CrIII


However, due to significant differences in toxicity, reactivity and bioavailability, it is also vital to distinguish between the trivalent (CrIII


) is


essential to human life as it plays a vital role for glucose, protein and fat metabolism with a daily intake of 50 to 200 µg recommended for adults. Acute animal tests have shown CrIII


toxicity from oral exposure. CrVI


to have moderate , on


its strong oxidizing properties. There is evidence to suggest that CrVI


the other hand is highly toxic if orally ingested or inhaled due to is


capable of causing skin, nose, eye and throat irritations in cases of limited exposure, and damage to liver, kidney circulatory, nerve tissues and cancer of the respiratory tract in more extreme cases. For these reasons, the World Health Organization (WHO) recommends maximum allowable concentrations of 0.05 mg/L for CrVI The use of CrVI


in drinking water. is also restricted by the European Restriction of Hazardous


Substances Directive 2002/95/EC. To assess human health risks from environmental exposure to chromium and chromium species, an accurate analytical method comprising highly sensitive and specific detection is needed. The combination of High Performance Liquid Chromatography (HPLC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) provides a viable solution for rapid, accurate and sensitive determination of CrIII and CrVI


species in mineral and spring water.


Experimental A fully inert Thermo Scientific SpectraSYSTEM™ HPLC pump (Thermo Fisher Scientific) equipped with an AS3500 autosampler (Thermo Fisher Scientific) was coupled to the XSERIES 2 ICP-MS (Thermo Fisher Scientific) using an HPLC-ICP-MS Coupling Pack and HPLC Wiring Harness (Thermo Fisher Scientific). The ICP-MS was operated under standard hot plasma conditions using a one-piece quartz torch with a 1.5 mm ID injector. The spray chamber was peltier cooled to 2ºC. Integral HPLC and ICP-MS software packages were used in conjunction with an external trigger card to enable automated HPLC accessory control using bi-directional communications and intelligent peak integration facilities. The associated HPLC parameters and analytical conditions for the HPLC-ICP-MS applications are shown in Table 1. The reversed phase HPLC methodology employed comp- lexation of CrIII


with EDTA to improve


separation. Due to the carbon containing mobile phase, optional collision cell technology (CCTED


) was


optimized for the prevention of the polyatomic interference on chromium. The CCT additionally suppresses interference from matrix in the water samples. The analytical methodology was validated using a CRM (BCR CRM-544, lyophilized solution) and method limits of detection (LOD) were deter-mined from three times the standard deviation of species concentrations found in the blank (n = 5).


Sample Preparation Daily working standards were prepared by diluting the appropriate quantity of the commercially available stock solutions (1000 µg/mL) of each chromium standard in the HPLC mobile phase. The stock


Table 1 October/November 2008 AET Figure 1


External calibration curves were generated in the PlasmaLab ICP-MS software using a blank and CrIII


and CrVI 0.5, 1, 2, 5 and 10 µg/L. Quantification of CrIII


calibration standards of 0.1, 0.2, and CrVI


species was


achieved in several samples using the external calibration curves presented in Figure 2 and fully quantitative data processing was achieved using the software’s automated peak integration tools. The mineral water samples were selected from a local supermarket and were analyzed in triplicate. Their mineral content and the quantitative data for CrIII


and CrVI are presented in Table 2. The


chromatograms for samples D and E are presented in Figure 1 (b.) and (c.) respectively. All the samples contained CrVI


as the major species


with concentrations varying between 0.054 and 0.409 µg/L. Three of the five water samples contained CrIII


at levels above the limit of detection


but only just above or below the quantification limit. Due to the low levels of chromium species in these samples, the detection and quantification limits of the methodology were improved with a 200 µL sample loop, rather than a 50 or 100 µL sample loop. Figures of merit are presented in Table 3.


solutions were kept at 4°C in the dark. The lyophilized solution was extracted according to the method outlined in the certification report supplied with the CRM. The sample was reconstituted with 20 mL HCO-3


/H2 CO3 buffer at pH 6.4.


Aliquots of the reconstituted CRM were diluted 1:1 in 20mM EDTA, 2.5 mM TBAP. Mineral and spring water samples were diluted 9:1 in 20 mM EDTA, 2.5 mM TBAP. Spikes of CrIII


and CrVI were added to the


reconstituted CRM and the mineral water samples prior to dilution with the EDTA solution. Both the standards and samples were placed in a heated water bath at 70°C for one hour to accelerate complexation of the CrIII


with EDTA. Results and Discussion


Following the analysis, the chromatographic data was displayed automatically in the Thermo Scientific PlasmaLab ICP-MS software. An example of the chromatographic separation of chromium-containing standards at a concentration of 1µg/L is shown in Figure 1 (a.). The HPLC methodology using EDTA as complexation agent allowed the baseline separation of CrIII respectively.


and CrVI with retention times of 215 and 260 seconds


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