The Determination of Trace Elements in Waters using the US EPA Method and the Thermo Scientific icap 6500 ICP-OES (Duo)

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1 Application Note: The Determination of Trace Elements in Waters using the US EPA Method and the Thermo Scientific icap 6500 ICP-OES (Duo) Matthew Cassap, Senior ICP Applications Specialist, Thermo Scientific, Cambridge, UK. Key Words ICP Water Environmental EPA Method Introduction In 1970, the United States government established the Environmental Protection Agency (EPA) in response to growing public demand for cleaner water, air and land. The Agency is responsible for researching and setting national standards for a variety of environmental programs and delegates the responsibility for issuing permits, and monitoring and enforcing compliance, to local government. Where national standards are not met, the EPA can issue sanctions and take other steps to assist local government in reaching the desired levels of environmental quality. The Development and Application of Method The Safe Drinking Water Act (SDWA) (last amended 1996) gave the US EPA power to set and regulate national standards for the quality of supplied drinking water and drinking water resources, such as ground waters. The EPA s Office of Ground Water and Drinking Water (OGWDW) administer control under the Federal Regulation 40 CFR part 141. This regulation states that all supplied waters must comply with the Maximum Contaminant Levels (MCLs) for the contaminants specified in the National Primary Drinking Water Regulations (NPDWRs). Further contaminants are given target maximum values in the National Secondary Drinking Water Regulations (NSDWRs) (40 CFR part 143). Tables 1 and 2 show the contaminants appropriate to ICP measurement and their MCLs. The approved ICP method for the determination of metallic contaminants for compliance measurements is the EPA Method 200.7, "Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry". Optical ICP is frequently employed for such measurements using method 200.7, although the required detection limit for some analytes is problematic with this technique, e.g. antimony, arsenic, mercury and thallium. Under the Arsenic Rule (part of 66 FR 6976, 2001) the EPA stated that as of January 2006 optical ICP methods were to be withdrawn from approval for the determination of arsenic since the typical detection limit of the technique was not generally thought to be routinely low enough to measure confidently at the MCL level of 10 µg/l. This leaves graphite furnace atomic absorption spectrophotometry (GF-AAS), hydride generation atomic absorption spectrophotometry (HG-AAS) and ICP- MS as the only available techniques for this analysis. Most of these problematic analytes have frequently been analyzed by GF-AAS. Mercury is often determined using cold vapor generation atomic absorption spectrophotometry (CV-AAS). This technique yields a lower detection limit than optical ICP, but has the disadvantage of allowing the determination of only one analyte at a time and of having a slower analysis time per sample. Contaminant MCL Antimony Arsenic 0.01 Barium 2 Beryllium Cadmium Chromium 0.1 Copper 1.3 Lead Mercury Selenium 0.05 Thallium Uranium 0.03 Contaminant Level Aluminum 0.05 to 0.2 Copper 1 Iron 0.3 Manganese 0.05 Silver 0.1 Sulfate 250 Zinc 5 Table 2: Metals Levels (mg/l) from Secondary Drinking Water Standard (40CFR143.3) Table 1: Metals MCLs (mg/l) from Primary Drinking Water Standard (40CFR141.51)

2 ICP method is also extensively used for regulatory analysis of wastewater samples for compliance with the permits issued within the National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act (CWA) (40 CFR part 136). Large numbers of water samples are analyzed using this method. These include supplied waters, natural waters and waste waters. Some states also require well waters within properties to be analyzed prior to purchase of real estate and the method is commonly used for this purpose. Method has also been used as the basis of water analysis methods by ICP across the world, especially in regions whose environmental monitoring industries developed later than that of the US. Method Summary Method describes a method for the determination of 32 elements in water samples. It suggests preferred wavelengths, calibration and quality control procedures as well as specifying procedures for determining method performance characteristics, such as detection limits and linear ranges. This section provides a brief overview of the procedures described. Method Detection Limit Method describes a protocol for determining the Method Detection Limit (MDL). The instrument hardware and method are set up as intended for the analysis. A reagent blank solution spiked at 2-3 times the estimated instrument detection limit is subjected to seven replicate analyses. The Standard Deviation (SD) of the measured concentrations is determined and multiplied by 3.14 (the Student s t value for a 99 % confidence interval for 6 degrees of freedom) to arrive at the MDL. It is important that contamination is kept under control, especially for environmentally abundant elements such as Al and Zn, since any contamination will degrade the MDL. Interference corrections also affect the MDL, since they employ the monitoring of additional lines and propagate the measurement errors accordingly. Linear Dynamic Range The upper linear range limit of a calibration is termed the Linear Dynamic Range (LDR). Method defines the upper LDR to be the concentration at which an observed signal deviates by less than 10 % from that extrapolated from lower standards. Sample dilution can facilitate the measurement of high concentrations, but with additional effort, cost and error and therefore a wide LDR is desirable. Quality Control Method specifies a variety of quality control standards. These are summarised in Table 3. Experimental 3.1 Equipment A Thermo Scientific icap 6500 ICP-OES (Duo) was used in conjunction with an ASX-520 autosampler. Internal standard (5ppm Y) was added on-line using a Y-connector. Typical instrument parameters are given in Table Instrumental Method Wavelengths were selected based on those suggested in method Additional wavelengths were measured in some cases. Plasma views were selected using the Thermo Scientific iteva Software automated view selection function. Axial and radial views were selected to provide optimum data quality by avoiding easily ionized element interferences in the axial view where necessary. Table 5 shows the elements, wavelengths and views used. Check Code Check Name Purpose Frequency Limits QCS Quality Control Checks the accuracy of the calibration Post calibration % recovery Standard with a second source standard SIC Spectral Interference Checks for the presence of spectral Periodically No specific Check Solution(s) interference and the effectiveness requirements of inter-element corrections IPC Instrument A continuing check of accuracy and drift Every 10 analyses % recovery Performance Check normally done by re-measuring a and at the end of the run immediately following standard as a sample calibration; % recovery thereafter BLANK Check Blank A continuing check of the blank level by Every 10 <IDL re-measuring the calibration blank as analyses and at a sample the end of the run LRB Laboratory Checks the laboratory reagents and sample 1 per batch of 20 or < 2.2 x MDL Reagent Blank preparation process for contamination fewer samples LFB Laboratory Checks the recovery of analytes by spiking 1 per batch of samples % recovery or Fortified Blank a known quantity into a blank within + 3 standard deviations of the mean recovery LFM Laboratory Checks recovery of analytes in a matrix 1 in 10 samples % recovery Fortified Matrix by spiking a known quantity into a real sample Table 3: Summary of method QC requirements

3 Parameter Pump Tubing Pump rate Nebulizer Nebulizer Argon Pressure Spray Chamber Centre tube Torch Orientation RF Forward Power Coolant flow Auxiliary flow Integration time Table 4: icap Parameters Setting Tygon Orange/White sample White/White drain 50 rpm Concentric 0.65 L/min / 26 MPa Cyclonic 2.0 mm Duo 1150 W 12 L/min 0.5 L/min 15 seconds (UV and VIS) 3.3 Solution Preparation Ultra pure water of resistivity >15MΩ cm (Milli-Q) was used, along with Fisher Scientific Primar grade hydrochloric acid and nitric acid. All analytical standard solutions were prepared from Fisher Scientific stock standards and reference samples (NIST, Gaithersburg, MD, USA and LGC Promochem, Teddington, UK) were analyzed along with various unknown water samples. All samples were preserved in a mixture of 2 % nitric acid and 2 % hydrochloric acid. 3.4 Calibration Solutions Table 6 gives the calibration solution concentrations. Calibration Conc. (mg/l) Analytes 0.25 Ag 1 As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, Ti, Tl, V, Zn 1.2 Hg 2 Al, Ba, Be, Li, Mg, Na 4 B 10 Ca, K, P, SO 4, SiO 2 Table 6: Calibration Concentrations Element Wavelength (nm) View Element Wavelength (nm) View Aluminum Radial Molybdenum , Axial (Al) (Mo) Antimony Axial Nickel , Axial (Sb) (Ni) Arsenic , Axial Phosphorus , Axial (As) (P) Barium Radial Potassium Radial (Ba) (K) Beryllium , Radial Selenium Axial (Be) (Se) Boron Radial Silica Radial (B) (SiO 2 ) Cadmium , Axial Silver Radial (Cd) (Ag) Calcium Radial Sodium Radial (Ca) (Na) Chromium Axial Strontium , Radial (Cr) (Sr) Cobalt Axial Sulfate Axial (Co) (SO 4 )* Copper Radial Thallium Axial (Cu) (Tl) Iron Radial Tin Axial (Fe) (Sn) Lead Axial Titanium , Radial (Pb) (Ti) Lithium Radial Vanadium Radial (Li) (V) Magnesium Radial Zinc Axial (Mg) (Zn) Manganese Radial Yttrium Axial (Mn) (Y) # Mercury , Axial Yttrium Radial (Hg) (Y) # * Not specified in method 200.7, but frequently of interest # Internal standard Table 5: Elements, wavelengths and views selected

4 3.5 Analytical Procedure A linear dynamic range (LDR) and method detection limit (MDL) study was performed as described in method The MDL study was performed with a reagent blank spiked with low concentrations of each element. An interference study was performed using single element SIC solutions as described in method To demonstrate the performance of the Thermo Scientific icap 6500 ICP-OES (Duo) for typical routine analysis of a variety of water samples with method 200.7, a sequence was set up as follows: Calibration QCS IPC Check Blank 10 samples IPC Check Blank The 10 samples analysed between each IPC and blank pair consisted of a variety of aqueous matrices. Table 7 gives details of these samples. The samples were analyzed multiple times throughout the analysis, replicating a run consisting of a total number of 240 samples (>300 samples, including QC and calibration solutions). Samples denoted unknown in Table 7 were also spiked for analysis as a laboratory fortified matrix (LFM). Spike recoveries for these are given in the following section. Reference Material/Sample Description NIST 1640 River water CRM BCR-610 Ground water CRM ERML-CA010A Hard drinking water CRM ERML-CA021A Soft drinking water CRM SPS-WW1 Waste water CRM SPS-WW2 Waste water CRM LGC6177 Landfill leachate CRM NIST 1641d Mercury in water CRM Unknown drinking water sample Hard tap water Unknown leachate sample Landfill leachate diluted 1:10 Unknown saline sample Estuarine water diluted 1:5 Unknown soil digest sample Aqua regia soil extract, 0.5 g/l Table 7: Reference materials and samples analyzed Cycle repeated 24 times in total with 1 re-calibration Results and Discussion Analyte and line (nm) SIC Solution Contribution (mg/l) Al nm 50 ppm V 0.8 Al nm 50 ppm Mo 0.4 Sb nm 50 ppm Cr 0.9 Zn nm 50 ppm Ni 0.2 Table 8: Major interferences and their contributions Analyte View* LDR Achievable Robust 3.14-s Drinking (mg/l) 3-s IDL MDL with Water Level with blank ** MDL solution of Interest Ag nm R >2 4 (0.7) Al nm R > (5) As nm A > As nm A > B nm R >50 6 (1) 10 - Ba nm R > Be nm R > (0.03) 1 4 Be nm R > (0.05) 4 4 Ca nm R >500 8 (1) 20 - Cd nm A > Cd nm A > Co nm A > Cr nm A > Cu nm R >50 3 (0.5) Fe nm R >300 2 (0.3) Hg nm A > Hg nm A > K nm R > (5) Li nm R >50 1 (0.1) 2 - Mg nm R > (0.008) Mn nm R > (0.08) Mo nm A > Mo nm A > Na nm R > (3) 70 - Ni nm A > Ni nm A > P nm A > P nm A > Pb nm A > S nm A > ,000 Sb nm A > Se nm A > Si nm R >50 8 (1) 20 - Sn nm A > Sr nm R > (0.01) Sr nm R > (0.02) Ti nm R >50 2 (0.3) 4 - Ti nm R >50 2 (0.3) 3 - Tl nm A > V nm R >50 3 (0.5) 6 - Zn nm A > *R = Radial, A = Axial ** Bracketed figures show axial view values for radially viewed elements Table 9: LDR, IDL and MDL results (µg/l, except where indicated)

5 QCS (n=2) IPC (n=25) Analyte Mean Known Rec % Mean Known Rec % SD RSD % Ag nm Al nm As nm As nm B nm Ba nm Be nm Be nm Ca nm Cd nm Cd nm Co nm Cr nm Cu nm Fe nm Hg nm Hg nm K nm Li nm Mg nm Mn nm Mo nm Mo nm Na nm Ni nm Ni nm P nm P nm Pb nm S nm Sb nm Se nm Si nm Sn nm Sr nm Sr nm Ti nm Ti nm Tl nm V nm Zn nm Table 10: Results for QCS (post-calibration), and IPC (ongoing QC) measurements. All concentrations are expressed as mg/l.

6 NIST 1640 River Water CRM610 Ground Water Analyte Mean Known Rec % Mean Known Rec % Ag nm Al nm <MDL N/A As nm As nm B nm Ba nm Be nm N/A N/C N/A Be nm N/A N/C N/A Ca nm Cd nm Cd nm Co nm N/A N/C N/A Cr nm Cu nm N/A N/C N/A Fe nm K nm Li nm N/A N/C N/A Mg nm Mn nm Mo nm N/A N/C N/A Mo nm N/A N/C N/A Na nm Ni nm Ni nm Pb nm Sb nm Se nm Si nm N/A N/C N/A Sr nm N/A N/C N/A Sr nm N/A N/C N/A V nm N/A N/C N/A Zn nm Table 11: Results of analysis of river water and ground water CRMs (n=2). All concentrations are expressed as mg/l. CA010A Hard Tap Water CA021A Soft Water Analyte Mean Known Rec % Mean Known Rec % Ag nm N/A N/C N/A Al nm As nm As nm B nm N/A N/C N/A Ba nm Ca nm Cd nm N/A N/C N/A Cd nm N/A N/C N/A Cr nm Cu nm N/A N/C N/A Fe nm K nm Mg nm Mn nm Na nm Ni nm Ni nm Pb nm Sb nm Se nm Zn nm Table 12: Results of analysis of hard and soft drinking water CRMs (n=2). All concentrations are expressed as mg/l.

7 WW1 Waste Water WW2 Waste Water Analyte Mean Known Rec % Mean Known Rec % Al nm As nm As nm Cd nm Cd nm Co nm Cr nm Cu nm Fe nm Mn nm Ni nm Ni nm P nm P nm V nm Zn nm Table 13: Results of analysis of wastewater CRMs (n=2). All concentrations are expressed as mg/l. LGC6177 Landfill Leachate (1:10) NIST 1641D Mercury in Water Analyte Mean Known Rec % Mean Known Rec % B nm N/A N/C N/A Ca nm N/A N/C N/A Cr nm N/A N/C N/A Fe nm N/A N/C N/A Hg nm N/A N/C N/A Hg nm N/A N/C N/A K nm N/A N/C N/A Mg nm N/A N/C N/A Mn nm N/A N/C N/A Na nm N/A N/C N/A Ni nm N/A N/C N/A Ni nm N/A N/C N/A P nm N/A N/C N/A P nm N/A N/C N/A Zn nm N/A N/C N/A Table 14: Results of analysis of landfill leachate and mercury CRMs (n=2). All concentrations are expressed as mg/l.

8 Spike Hard Tap Water Leachate (1:10) Analyte Value Unspiked Spiked Rec % Unspiked Spiked Rec % Ag nm 0.08 <MDL <MDL Al nm 0.45 <MDL <MDL As nm 0.5 <MDL As nm 0.5 <MDL B nm Ba nm Be nm 0.45 <MDL <MDL Be nm 0.45 <MDL <MDL Ca nm Cd nm 0.45 <MDL <MDL Cd nm 0.45 <MDL <MDL Co nm 0.45 <MDL Cr nm 0.5 <MDL Cu nm Fe nm Hg nm 0.1 <MDL <MDL Hg nm 0.1 <MDL <MDL K nm Li nm Mg nm Mn nm 0.45 <MDL Mo nm 0.5 <MDL <MDL Mo nm 0.5 <MDL <MDL Na nm Ni nm Ni nm P nm P nm Pb nm 0.45 <MDL <MDL S nm Sb nm 0.5 <MDL <MDL Se nm 0.5 <MDL <MDL Si nm Sn nm 0.5 <MDL Sr nm Sr nm Ti nm 0.5 <MDL Ti nm Tl nm 0.45 <MDL <MDL V nm 0.45 <MDL Zn nm Table 15: Results of analysis of unfortified and fortified tap water and leachate matrices with spike recoveries (n=16). All concentrations are expressed as mg/l.

9 Spike Saline Water (1:10) Soil Digest (1:10) Analyte Value Unspiked Spiked Rec % Unspiked Spiked Rec % Ag nm 0.08 <MDL Al nm As nm 0.5 <MDL As nm 0.5 <MDL B nm <MDL Ba nm Be nm 0.45 <MDL Be nm 0.45 <MDL <MDL Ca nm Cd nm 0.45 <MDL Cd nm Co nm Cr nm 0.5 <MDL Cu nm Fe nm N/A Hg nm 0.1 <MDL Hg nm 0.1 <MDL K nm Li nm Mg nm Mn nm Mo nm 0.5 <MDL Mo nm 0.5 <MDL <MDL Na nm Ni nm 0.45 <MDL Ni nm 0.45 <MDL P nm P nm Pb nm 0.45 <MDL S nm N/A Sb nm 0.5 <MDL Se nm 0.5 <MDL <MDL Si nm Sn nm 0.5 <MDL Sr nm Sr nm Ti nm Ti nm Tl nm 0.45 <MDL V nm 0.45 <MDL <MDL Zn nm Table 16: Results of analysis of unfortified and fortified saline water and soil digest matrices with spike recoveries (n=16). All concentrations in mg/l.

10 The results in Tables show that the icap consistently produced accurate and precise data in all of the reference material matrices. The vast majority of results were within 10 % of the certified concentration, the few exceptions tending to be when the measured value was close to the method detection limit. The accurate results for the LFM samples (see Tables 15 and 16) show that quantitative recovery can be achieved in a variety of real environmental matrices. All spike recoveries were well within the allowable range of %. Graph 1: The stability of successive IPC measurements during the 240 sample analysis. Control limits are shown with dashed red lines. Interference Study Very few significant interferences were found during the analysis of the SIC solutions, showing that the instrument is relatively free of interferences. Those that were observed can easily be corrected by using inter-element corrections when necessary. LDR The high standards analyzed for the linear dynamic range check showed little deviation from their expected values, indicating linearity up to at least the levels indicated in Table 9. These levels are normally more than sufficient for the analysis of typical water samples. MDL The method detection limits calculated from analysis of the MDL solution are generally in the low ppb range for the majority of elements. All MDLs are sufficiently below the typical levels of interest for drinking water analysis, with the exception of antimony, mercury, thallium, and aluminium. The MDLs for these elements are of the same magnitude as the level of interest. For this reason ICP-MS may be a more appropriate alternative for regulatory drinking water measurements for these elements. The use of the axial view can, however, significantly improve the detection limit of some elements measured using the radial view in this study. MDLs for some elements, such as aluminium may be compromized by spot contamination in the sample tubes. Accuracy, Precision and Stability The icap 6500 ICP-OES (Duo) produced consistently accurate results with minimal intensity drift, as shown by the results for the QCS and IPC solutions (see Table 10). The ongoing IPC results were consistently within the allowed range of % of the known value, as shown in Graph 1. The precision of the 25 IPC measurements across the 240 sample run are also shown to be very good. Table 10 indicates that the relative standard deviation (RSD) of these measurements is well within 5 % across the duration of the run (16 hours). Conclusions The Thermo Scientific icap 6500 ICP-OES (Duo) demonstrated compliance with the requirements of EPA Method for a wide range of water sample types and showed that it easily coped with the stringent AQC requirements of the method. A combination of specifically designed hardware and software tools enable and simplify compliant analysis as outlined below. Wavelength verification is quick and easy with the autopeak function and method and instrument optimization are automatically performed with the built-in optimization procedures. Along with the high transmission optical design and sensitive CID 86 detector, this helps to produce the optimum performance, as indicated by the excellent method detection limits obtained. The lack of physical and spectral interference in environmental samples, demonstrated in the interference study, makes the icap 6500 ICP-OES (Duo) ideal for analyzing waters and other environmental materials. This yields accurate results for all environmental sample types. Careful attention was paid to the thermal conductivity of the instrument components during the design phase. This has produced an extremely stable system that continues to give good accuracy over long periods of time without frequent re-calibration and also produces good precision over extended runs. This is demonstrated by the consistent IPC results. The Thermo Scientific iteva Software has a QC checking feature that is designed to meet the requirements of EPA methods. The software also includes monitored uptake / washout features which reduces the amount of non-productive time and maximizes useful analytical time. The productivity tools in iteva Software, combined with the speed of the icap 6500 ICP-OES (Duo) and the lowvolume sample introduction system result in rapid analysis times. Samples in this study were being processed at a speed of 1 sample every 3 minutes and 30 seconds (17 samples per hour). This level of productivity makes the Thermo Scientific icap 6500 ICP-OES (Duo) the ideal, cost effective and powerful elemental analzyer.

11 Plasma Capabilities from Thermo Fisher Scientific The use of an Inductively Coupled Plasma source (ICP) is the accepted and most powerful technique for the analysis and quantification of trace elements in both solid and liquid samples. Its applications range from routine environmental analyses to the materials industry, geological applications to clinical research and from the food industry to the semiconductor industry. We are the only instrument manufacturer to offer the full range of Inductively Coupled Plasma Spectrometers (ICP, Quadrupole and Sector ICP-MS) to satisfy every aspect of plasma spectrometry from routine to highly demanding research applications. Thermo Scientific icap ICP-OES Thermo Scientific ELEMENT2 HR-ICP-MS Develop your lab from the easy-to-use icap ICP-OES to the high performance XSERIES 2 Quadrupole ICP-MS and up to the ultra-sophisticated ELEMENT2 and NEPTUNE Sector ICP-MS instruments. Each instrument combines leading-edge technology, fit for purpose and affordability with a tradition of quality, longevity, accuracy and ease of use. Thermo Scientific XSERIES 2 ICP-MS Thermo Scientific NEPTUNE Multi-collector ICP-MS In addition to these offices, Thermo Fisher Scientific maintains a network of represen - tative organizations throughout the world. Africa-Other Australia Austria Belgium Canada China Denmark Europe-Other Finland / Norway/ Sweden France Germany India Italy Japan Latin America Middle East Netherlands New Zealand South Africa Spain Switzerland UK USA Thermo Fisher Scientific Inc. All rights reserved. Milli-Q is a registered trademark of Millipore Corporation. ASX-520 is a trademark of CETAC Corporation. All other trademarks are the property of Thermo Fisher Scientific Inc. and its subsidiaries. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details. Thermo Electron Manufacturing Ltd (Cambridge) is ISO Certified. AN40853_E 08/10C Part of Thermo Fisher Scientific