Streamlined Heavy Metal Detection Using Automated ICP-MS Technology

Multi-element analysis of surface and waste waters using triple quadrupole ICP-MS with prepFAST autodilution Authors: Simon Lofthouse1 , Claudia Charko2 , Kristof Tirez3 and Johan Annys4 ; 1 Thermo Fisher Scientific, Hemel Hempstead, UK; 2 Thermo Fisher Scientific Breda, NL; 3 Vito NV, MOL, BE; 4 Flanders Environment Agency (VMM), Aalst, BE Keywords: Multi-element analysis, PrepFAST, surface water, triple quadrupole ICP-MS, waste water Goal To demonstrate routine automated multi-element analysis of environmental samples using triple quadrupole ICP-MS. Introduction The adverse effects of increased concentrations of heavy metals in the environment and their potential impact on human, animal and plant health are of key concern. Consequently, monitoring of the content of these elements in a variety of environmental matrices (ground and surface waters, drinking water, waste waters, soils and sediments) is one of the most frequently performed analyses in the context of environmental legislation. Some of the most common guidelines for different regions are summarized in Table 1. Elemental analysis of environmental waters usually requires a number of different analyses to cover the different elements depending on element chemistry, interferences and linear range. Ideally, a single technique that could measure all environmentally relevant elements from a single sample, based on an easy sample preparation procedure (e.g. dilution or digestion), and with potential for automated and unattended analysis is desirable. 2 Parameter Value Nebulizer PFA-ST nebulizer pumped at 40 rpm Spraychamber Quartz cyclonic spraychamber cooled at 2.7 ˚C Injector 2.5 mm i.d., Quartz Interface High Matrix (3.5 mm) insert, Ni cones RF power 1,550 W Nebulizer gas flow 1.00 L·min-1 Interface High Matrix QCell settings SQ-NA SQ-KED TQ-O2 Gas flow N/A 4.7 mL·min-1 0.42 mL·min-1 CR bias -2.0 V -21 V -7.2 V Q3 bias -1.0 V -18 V -12 V Regulation Region Applicable for Comment EPA method 200.8 USA Drinking waters and waste waters Use of collision cell is only approved for waste waters EPA method 6020 B USA Solid waste Use of collision cell technology approved CEN/TS 17200:2018 Europe Digests and eluates of construction products Aqua regia and nitric acid digests FprEN 16171:2015 Europe Sludge, treated biowaste and soil Use of collision cell or high resolution technology approved EN ISO 17294 Europe Drinking waters, surface waters, ground waters, waste waters GB3838-2002 China Surface waters GB5749-2006 Drinking waters IS 10500:2012 India Drinking waters Mentions ICP-OES primarily, methods for bottled drinking water require ICP-MS for analysis Table 1. Overview of applicable regulatory guidelines for the analysis of drinking waters and waste waters globally Following the introduction of triple quadrupole ICP-MS, the routine removal of all types of spectral interferences is now possible (including doubly charged ions interfering for example on arsenic and selenium). Used in combination with an online dilution system, this kind of instrumentation can offer the possibility of sensitive and robust, quantitative analysis for all relevant matrix and trace elements in a wide variety of environmental sample matrices. Triple quadrupole ICP-MS systems such as the Thermo Scientific™ iCAP™ TQ ICP-MS, allow the use of reactive gases following a mass filtration step in a quadrupole mass filter situated axially in front of the collision/reaction cell (CRC). Therefore, more confidence in the results for a number of critical elements (for example cadmium, mercury, arsenic, selenium, sulphur or silicon) can be achieved compared to the single quadrupole ICP-MS instruments present in most environmental laboratories. In combination with the use of an automated inline dilution system, such as the Elemental Scientific prepFAST, the iCAP TQ ICP-MS offers the potential to determine all relevant matrix and trace elements in a single analysis. A feasibility study was carried out in collaboration with the Flemish reference laboratory for environmental monitoring (Vito), and Flanders Environment Agency (VMM) on 25 waste waters and 25 surface waters. The aim of this study was to evaluate the performance of the iCAP TQ ICP-MS for the quantitative multi-element determination of 68 elements in aqueous environmental samples, in accordance with the performance requirements included in the compendium for sampling, measurement and analysis of water (Compendium voor analyse van water, commonly abbreviated as WAC)1 . The results obtained were verified using a combination of quality control standards and certified reference materials. Instrumentation All measurements were performed using an iCAP TQ ICP-MS. The instrument was operated using the Thermo Scientific™ Qtegra™ Intelligent Scientific Data Solution™ (ISDS) Software and was initially optimized using the supplied tune solution to optimize the interface parameters for maximum sensitivity. Modes using reactive gases were also tuned using the supplied autotune procedures to determine optimum gas flows and potentials for the CRC and the analysing quadrupole. Typical operating conditions are summarized in Table 2. Table 2. Typical instrumental parameters 3 The calibration of the system was carried out daily using a mixed multi-elemental standard solution. The concentration levels for the individual calibration standards were as shown in Table 3. Element Standard concentrations Na 5, 25, 50 mg·L-1 Mg 1, 5, 10 mg·L-1 Si 0.5, 2.5, 5 mg·L-1 P 0.2, 1, 2 mg·L-1 S 2.5, 12.5, 25 mg·L-1 K 0.1, 5, 10 mg·L-1 All other elements 0, 10, 50, 100 µg·L-1 Ca 2, 10, 20 mg·L-1 Table 3. Concentration levels for calibration standards The digested samples were automatically diluted 5 times by the prepFAST syringe-driven inline dilution system, by defining a prescriptive dilution factor 5 in the sample list. The internal standard (Rh 20 µg·L-1 in 1%HNO3/5% butanol) was added on-line, again utilizing the prepFAST system. In order to select the appropriate instrument settings (e.g. choice of reaction gas and the mass to be transmitted in each quadrupole (Q1 and Q3)), the Reaction Finder method development assistant was used. Reaction Finder allows analytical methods to be set up without prior detailed knowledge of potential reaction pathways caused by other components in the sample. It also determines the applied resolution setting for Q1 automatically (intelligent Mass Selection (iMS) vs. ≤1 amu). Further optimization of the method parameters, such as for example the use of different reactive gases for some analytes (e.g. NH3 for the analysis of Ti and platinum group elements), can also be accomplished. For this work, different measurement modes were selected outside the default Reaction Finder settings and were automatically applied to scan all elements in each sample using a single aspiration. • O2 was used for the analysis of 28Si, 31P, 32S, 75As, 80Se, 111Cd and 202Hg in TQ mode • Single quadrupole no gas mode was selected for 7 Li, 9Be and 11B • All other isotopes measured in single quadrupole KED mode The performance characteristics included in this note are indicative and additional optimization of the multi-element method is necessary, including the use of multiple internal standards in addition to Rh (e.g. 6Li, Sc, Ge, Ir). Sample preparation All 50 samples (25 waste waters and 25 surface waters collected at different sites in the Flanders region of Belgium) were digested in accordance with NBN-EN-ISO 15587-1. In brief, 6 mL of HCl + 2 mL of HNO3 were added to a 25 mL aliquot of each sample, and digested at 105 ˚C for 2 hours using a hot block digestion system. After cooling, the samples were diluted to a final volume of 50 mL with ultra-pure water. The list of elements to be determined is summarized in Table 4, which contains the following three subcategories: • NBN EN ISO 17294: 2016 “Water – Application of mass spectrometry with inductively coupled plasma – Part 2: Determination of selected elements including uranium isotopes”: 63 elements are included in this standard method • Monitoring: 33 elements that are currently being monitored in the context o