Detection of Uranium in a Very Hard Water Matrix Using Ultrasonic Nebulization with ICP-AES Detection December 3, 2015 Introduction Uranium is a regulated element in drinking water per the USEPA guideline of an MCL (maximum contaminant level) of 30 micrograms per liter. Human health risks from long-term exposure to elevated uranium levels in drinking water can include impaired kidney function and cancer. Uranium in groundwater can occur from natural leaching of mineral deposits; subsequent very hard water matrices are present in areas such as southeastern United Kingdom and southern Germany. This presentation will examine the utility of coupling an ultrasonic nebulizer (USN) with an ICP-AES instrument for improved detection of uranium in a simulated very hard water matrix. Uranium Human Health Concerns Heavy Metal Impaired kidney function (nephritis) Radionuclide Alpha emitter 238 U 234 Th + = 4 He 2 Uranium Sources in the Environment Mineral deposits Mining Burning of coal Emissions from nuclear power plants Munitions Phosphate fertilizers Hard Water Dissolved solids content of groundwater can vary upon exposure to mineral deposits such as calcium and magnesium carbonate. Hard water designation describes water that is hard to use with soap (less formation of soap lather) Units used to describe the extent of water hardness include: Degrees of General Hardness (dGH) Grains per Gallon German Degrees (dH) English Degrees or Clark French Degrees (fH) Parts per million (mg/L as CaCO 3 ) Note: 1 grain = 64.8 mg CaCO 3 Hard Water Definition of Units United States Geological Survey (USGS) Soft 0 to 60 mg/L (ppm) Moderately Hard 61 to 120 mg/L (ppm) Hard 121 to 180 mg/L (ppm) Very Hard > 181 mg/L (ppm) Web Link:Hardness as mg/L CaCO 3. United Kingdom Map Hard Water UK Map Source: Wikipedia Harder water is generally observed to the right of the blue line. Newcastle Exeter Detailed UK Hard Water Map: United Kingdom Map Uranium in Water UK Map Source: Wikipedia Detailed UK Uranium in Water Map: B.Smith, P.L.Smedley, C. Abesser, D. Lapworth, Uranium Occurrence And Behavior in British Groundwater, British Geological Survey Commissioned Report, CR/06/050N Central Lowlands West Midlands Region Germany Map Hard Water Germany Map Source: FreeVectorMaps Hard water areas include NW Germany and southern Germany. Mecklenburg Vorpommern Baden- Wurttemburg Bayern Detailed Hard Water Map of Germany: Germany Map Uranium in Water Germany Map Source: FreeVectorMaps Detailed Information for Uranium in Waters in Germany: Uranium in German Tap and Groundwater Occurrence and Origins in The New Uranium Mining Boom, Merkel B. and M.Schipek, Eds., Springer. Berlin, Thuringen Sachsen United States of America Map Hard Water Omaha USA Map Source: FreeVectorMaps States marked have more areas of hard or very hard waterDetailed hard water map of USA: TX OK CO WY UT KS AZ NM CA NE United States of America Map Uranium in Water USA Map Source: FreeVectorMaps High Plains Aquifer: SD, NE, WY, CO, KS, OK, NM, TX Central Valley Aquifer: CA Detailed Uranium in Groundwater Map: J. Dolan, K.A. Weber, Natural Uranium Contamination in Major U.S. Aquifers Linked to Nitrate, Environ.Sci.Technol.Lett., 2, , CA NE KS CO OK TX SD WY NM Selected Drinking Water Standards for Uranium Entity or Country Uranium Limit ( g/L) WHO30 Australia20 Canada20 Germany10 USEPA30 Notes: WHO limit based on consumption of 2 Liters of water per day and a human weight of 60 kg. There is a provisional WHO limit of 15 g/L U. An additional German standard is 2 g/L for water used for preparation of baby food. Equipment ICP-AES Instrument PerkinElmer 5300DV ICP-MS Instrument ThermoFisher iCAP Q Ultrasonic Nebulizer Teledyne CETAC U5000AT + Instrument Detection Limits: Uranium ICP-AES 1 to 10 g/L Possible need for pre-concentration of U by chelation ICP-MS 0.1 ng/L R.Thomas, Practical Guide to ICP-MS 3 rd Ed., CRC Press, New York, 2013. Emission Wavelengths Uranium nm nm nm nm nm Decreasing Intensity Ultrasonic Nebulizer Front View Ultrasonic Nebulizer Principle of Operation In place of a regulated gas flow for generation of a liquid sample aerosol (pneumatic nebulization), liquid sample is pumped across an oscillating (piezoelectric) crystal. The oscillations will cause formation of a sample aerosol. Ultrasonic nebulization is typically 10-15% efficient for conversion of liquid sample into a useable aerosol. An in-line desolvation system is used to prevent plasma overloading with water vapor and maintain ICP stability. Note that the host ICP-AES / ICP-MS nebulizer gas now acts as a carrier gas, moving the generated aerosol to the plasma. Ultrasonic Nebulizer Schematic Transducer Assembly Transducer Close-Up View Piezoelectric Disk Quartz Faceplate Ultrasonic Nebulizer Top View Heated J-Tube Condenser Ultrasonic Nebulizer with ICP-AES Operating Conditions - I ICP-AES: PE Optima 5300DV ICP RF Power: 1350 W Plasma Gas: 15 L/min Auxiliary Gas:0.2 L/min Nebulizer Gas:0.62 L/min Viewing:Axial Torch Injector:Alumina, 2.0 mm i.d. Torch Position:-2 Nebulizer: Glass concentric Spray Chamber: Glass cyclonic Resolution:Normal Points/peak:3 Integration time: 20s, 3 replicates Operating Conditions - II Nebulizer System:CETAC U5000AT + Heater Temp: 140C Cooler Temp: 3C Torch position: -4 Nebulizer Gas:0.52 L/min Solution Uptake: 2.0 mL/min (pumped) U5000AT + Setup Front View Nebulizer Gas Line Sample Out Line With Torch Adapter U5000AT + Setup Back View Nebulizer Gas Line Sample Out Line Drain Pump Very Hard Water Matrix* Calcium: 500 mg/L Magnesium: 200 mg/L Sodium: 200 mg/L Potassium: 200 mg/L Iron: 200 mg/L *Made from single-element 10,000 mg/L ICP grade standards. Tapwater Matrix ElementWavelength (nm)Concentration (mg/L) Na / K / Ca / Mg / Uncertainty is 2 Municipal water source, Omaha, NE Conversion of the mg/L Ca to mg/L CaCO 3 gives ~123 mg/L CaCO 3 classifying this tapwater sample as hard water. An approximate uranium concentration of 4.2 g/L measured by ICP-MS using a 1-pt standard addition. Evaporated Water Samples Deionized Water Omaha, NE Tapwater Estuarine Water (St.Lawrence Seaway) V. Hard Water Matrix Experiment Details 1. A matrix blank and four calibration standards (matrix-matched) were prepared using the 10,000 mg/L single element standards, preserved in 1% high-purity nitric acid. 2. Four calibration standards were prepared: 20, 50, 100 and 200 g/L. No internal standard was used. 3. The matrix blank and matrix-matched standards were introduced to the standard concentric nebulizer and the U5000AT + using the on-board peristaltic pump of the host ICP-AES. 4. Instrument detection limits (IDLs) are 3x the standard deviation of the matrix blank concentration; limits of quantitation (LOQs) are 10x the standard deviation of the matrix blank concentration. 5. The 100 g/L standard was reintroduced to measure % recoveries. Maximum Contaminant Levels (MCLs) for USEPA Regulated Elements Element MCL in g/L As10 Ba2000 Be4 Cd5 Cr100 Cu1300 Pb15 Sb6 Se50 Tl2 U30 Uranium nm Ca and Fe Interference 200 ppb U 200 ppm Fe, 500 ppm Ca U5000AT + USN Uranium nm Iron Interference 200 ppm Fe 200 ppb U U5000AT + USN Uranium Detection w. ICP-AES Very Hard Water Matrix Mixed results in generating interelement correction factors (IECs) for the nm and nm U emission lines Attempt to use one or more of the less sensitive U emission lines Enhance signal with ultrasonic nebulization Uranium nm Probable Ca Interference ( nm) U5000AT + USN Saturated Uranium nm Calibration Standards in Very Hard Water 20, 50, 100, 200 ppb U In very hard water U5000AT + USN Uranium nm Calibration Standards in Very Hard Water 20, 50, 100, 200 ppb U In very hard water U5000AT + USN ICP-AES Intensity Comparison Very Hard Water Matrix, 100 g/L ElementWavelength (nm) Std NebulizerU5000AT+Factor As , Ba ,2414,756, Be ,5372,217, Cd ,43357, Cr ,82880, Cu ,529135, Pb ,5887, Sb , Se , Tl , U ,45013, U ,25810,6748.4 Uranium nm Calibration in Very Hard Water U5000AT + USN 20, 50, 100, 200 ppb U Uranium nm Calibration in Very Hard Water U5000AT + USN 20, 50, 100, 200 ppb U Standard Concentric Nebulizer Very Hard Water Matrix ElementWavelength (nm) IDL ( g/L)LOQ ( g/L) %Recovery As Ba Be Cd Cr Cu Pb Sb Se Tl U U5000AT + Ultrasonic Nebulizer Very Hard Water Matrix ElementWavelength (nm) IDL ( g/L)LOQ ( g/L) %Recovery As Ba Be Cd Cr Cu Pb Sb Se Tl U U ICP-AES LOQ Comparison Very Hard Water Matrix ElementWavelength (nm) Std Nebulizer ( g/L) U5000AT+ ( g/L) Factor As Ba Be Cd Cr Cu Pb Sb Se Tl U Uranium nm Calibration in Very Hard Water U5000AT + USN 10, 20, 50, 100 ppb U Uranium nm Calibration in Very Hard Water U5000AT + USN 10, 20, 50, 100 ppb U Uranium Detection Limits Very Hard Water Matrix ElementWavelength (nm) IDL ( g/L)LOQ ( g/L) % Recovery U U U5000AT + USN % Recovery of 10 g/L standard Use 10, 20, 50, 100 ppb U standard spikes Summary ICP-AES with ultrasonic nebulization can detect 10 g/L U in a very hard water matrix Uranium emission wavelengths are chosen to avoid interferences from Ca and Fe, with ultrasonic nebulization providing sufficient sensitivity for less intense U emission lines