Collaborative Efforts for Creating a Robust Trace Metals Analytical Procedure for Flue Gas Desulfurization Wastewaters by ICP-MS

Transcription

1 Collaborative Efforts for Creating a Robust Trace Metals Analytical Procedure for Flue Gas Desulfurization Wastewaters by ICP-MS Stan Smith and Ewa Pruszkowski, Ph.D., PerkinElmer, Inc. NEMC PerkinElmer

2 Background In 2009 US EPA completed study of wastewater discharges from the steam electric power generating industry Focus was on wastewater from flue gas desulfurization (FGD) systems as these comprised a significant portion of the plant pollutant discharges Rulemaking process was begun to address pollutants and waste streams not already covered in 40 CFR Part 423 (Steam Electric Power Guidelines) Proposed revisions to the effluent guidelines are expected May

3 Background Typical FGD treatment system using wet scrubber to remove SO 2 emissions from the flue gas 3 FDG Process

4 Background ICP-MS currently preferred technique for FGD due to sensitivity and wide availability (ICP-OES?) Current methods 200.8, 6020, and 1638 lack detailed treatment for interferences associated with FGD May 2010 EPA proposed draft testing procedure specific to FGD through a collaborative effort with a contract lab (instrument-specific) Draft procedure largely based on and 1638 with additional procedures on handling interferences Just what does FGD wastewater look like? 4 Analytical Techniques

5 Background Constituents of FGD wastewater come from the limestone used to make the slurry, the coal burned, and the water supply FGD wastewaters vary widely depending on above parameters as well as the efficiency of the FGD treatment system 5 Parameter Range (mg/l) Total Dissolved Solids ,000 Chloride ,000 Sulfate Calcium Magnesium Sodium Boron Total Organic Carbon Nearly 7% Polyatomic TDS Interferences e.g., 34 S 16 O 16 O on 66 Zn Also high ppm Al, Fe, and Mn FGD Wastewater

6 Collaborative Goals Merriam-Webster Definition of COLLABORATE 1. to work jointly with others or together especially in an intellectual endeavor 2. to cooperate with or willingly assist an enemy of one's country and especially an occupying force 3. to cooperate with an agency or instrumentality with which one is not immediately connected 6

7 Collaborative Goals Create alternate test procedure for different instrument and interference removal technology Along the way, opted to include significantly more detail; instrument hardware, interference removal techniques Digestion procedure (1638); evaluate open vessel digestion vs closed vessel digestion Minimal dilution needed for signal suppression for best DLs Dilution via traditional liquid dilution vs gas dilution 7

8 Speaking of Collaboration Collaborative process involves a process where ideas are exchanged, rarely does the first draft survive as the final 8 A non-inclusive list

9 Procedure Development Title: Standard Operation Procedure for Trace Element Analysis of Flue Gas Desulfurization Wastewaters Using ICP-MS Collision/Reaction Cell Procedure Introduction The ICP-MS spectrometer with the Universal Cell can operate in reaction, collision and standard modes The use of instrument configurations and/or accessories designed to accommodate samples with high dissolved solids levels is highly recommended This method was developed on a Perkin Elmer NexION 300D ICP/MS using an Environmental Scientific SC-DX FAST Automated Sample Introduction System. 1.3 analysis of 13 elements Al, As, Cd, Cr, Cu, Pb, Mn, Ni, Se, Ag, Tl, V, and Zn 9

10 Procedure Development, Hardware 2.4 A NexION 300D ICP-MS (Perkin Elmer, Shelton, CT) coupled to an SC DX FAST (ESI, Omaha, NE) automated sample delivery system is used for this procedure The FAST portion of the delivery system uses a 6-port switching valve containing a Teflon sample loop In this procedure, a 1.5 ml was adequate The baffled, cyclonic spray chamber used in the SC DX FAST introduction system is Peltier-cooled to 2 o C to ensure low oxides and greater stability of the instrument.

11 Procedure Development, Hardware The sample introduction system also includes a PFA ST concentric nebulizer, 2.0 mm quartz injector, and baffled cyclonic spray chamber with gas addition port (ESI, Omaha, NE) PVC peristaltic pump tubing, orange-white, is used to produce a sample flow rate of 270 ul/min A mixing tee is used to blend in the internal standards after the peristaltic pump and before the nebulizer The peristaltic pump tubing used for the internal standard solution is orange-whitered and when used in combination with orange-white pump tubing for the carrier solution or sample, creates a minimum dilution of approximately 8.1%.

12 Procedure Development, Sample Preparation EPA Method 1638 was used as the reference for the digestion of the samples in which section 12.2 describes Aqueous Sample Preparation. Block digestion with vials sealed or open with watch glass covers? Sealed results in a dilution factor that must be accounted for Open has the potential for contamination No contamination was noted in digestion blanks 12

13 Procedure Development, Sample Preparation Transfer a 50mL (± 0.5 ml) aliquot from a well-mixed, acidpreserved sample to a 50mL block digestion tube Add 1.0mL of concentrated nitric acid and 0.25mL concentrated hydrochloric acid Place a ribbed disposable watch glass over the digestion tube Place the digestion tube into a block digester adjusted to achieve a temperature of approximately 85 C Heat for 2 hours after 85 C is obtained Remove the tubes from the block and allow to cool Add deionized water to digestates to bring them back to 50.0 ml. 13

14 Synthetic FGD Solution Mixed Interference Check Solution (Synthetic FGD Wastewater) The following solution is prepared in 1.6% HCl Calcium, 2,000 mg/l Magnesium, 1,000 mg/l Sulfate, 2,000 mg/l Sodium, 1,000 mg/l Butanol, 2000 mg/l 14 Simulates Typical FGD Samples

15 Synthetic FGD Solution Seemingly simple mixture Purchase custom solution from commercial supplier Prepare from neat reagents and stock elemental solutions Beware contamination in stock solutions In some cases it may not be possible to obtain interference check solutions that are completely free of contamination. In these cases, results up to 5X the reporting limit are acceptable if it is possible to demonstrate that the isotopic ratios correspond to natural abundances 15 To Purchase Or To Prepare?

16 Procedure Development, Interference Removal More detailed descriptions of interference removal techniques 2.0 Hardware Description 2.1 The NexION 300D allows the analyst to choose the most appropriate collision/reaction cell (CRC) conditions for each analyte in FGD wastewater Collision Mode: In this mode, the instrument offers conventional collision cell capability with kinetic energy discrimination (KED). By using a non-reactive gas, such as helium, the collision mode with KED removes many of the simple solvent- and argon-based polyatomic spectral interferences. This makes it ideal for elements such as Co, Ni, Cu and Zn which are prone to the larger crosssectional polyatomic interferences to be concerned about. It is also effective for other analytes, such as As and Se. 16

17 Procedure Development, Interference Removal Reaction Mode: A technique that offers the best available detection capability. This mode, known as DRC (Dynamic Reaction Cell ) technology, removes the majority of interferences with little or no loss of analyte sensitivity by using pure reaction gases like ammonia while not allowing any reaction byproducts to leave the cell which could cause further interferences. DRC technology features a scanning quadrupole with a bandpass that removes by-product reactions created in the Universal Cell. Therefore any reaction gas can be used and in its pure form This would be the mode of choice for the lowest possible detection limits for elements such as Cr, V and Mn. 17

18 Procedure Development, Interference Removal 18 Attachment 1: Suggested Mass Choices and Analysis Mode Mass Element of Interest Analysis Mode 27 Aluminum STD or He 75 Arsenic He 111, 114 Cadmium He 52, 53 Chromium NH3 or He 63, 65 Copper He 208, 207, 206 Lead STD 55 Manganese NH3 or STD 60, 62 Nickel He 78, 82 Selenium NH3 or He 107 Silver STD or He 205, 203 Thallium STD or He 51 Vanadium NH3 or He 66 Zinc He

19 Procedure Development, Detection Limits Important objective of analytical procedure; achieve detection limits to support FGD regulations Due to high TDS of typical FGD wastewaters, some dilution of samples is necessary to reduce signal suppression and to achieve minimum internal standard recovery of 60% What is minimum dilution needed for typical FGD? Traditional liquid dilution, approximately 1:10 needed Gas dilution, approximately 1:3 needed Automated sample dilution, liquid or gas, simplifies the dilution process and results in less matrix being deposited on the cones during analysis and minimizes the rinse times normally needed for difficult matrices 19

20 Procedure Development, Detection Limits Developing MDLs for EPA s Draft Collision Cell ICP/MS Procedure for Determination of Metals in FGD Effluent Samples Round Robin conducted by EPA and contractor with several participant labs Specific to subset of elements of particular interest to EPA; As, Cd, Cr, Pb, Se, and Tl MDLs in Synthetic FGD (KED/Collision Mode) Cr 52 (ug/l) As 75 (ug/l) Se 78 (ug/l) Cd 111 (ug/l) Tl 205 (ug/l) Pb 208 (ug/l)

21 Obtained Method Detection Limits Attachment 10: Typical Method Detection Limits 21 Mass/Element Int. Time (sec) Mode Internal Standard MDL (µg/l) 27 Al 0.5 STD Sc V 0.5 NH3 In Cr 0.5 NH3 In Mn 0.5 NH3 In Ni 0.5 He Ge Cu 0.5 He Ge Zn 0.5 He Ge As 1.5 He Ge Se 1.5 He Ge Ag 0.5 STD In Cd 0.5 He Ge Tl 0.5 STD In Pb 0.5 STD In 0.04 Determined in Synthetic FGD

22 The Final Product The SOP is available on the Steam Electric/FGD web page: 22

23 Procedure Highlights Specific to FGD wastewater Addresses physical matrix issues (robust) Addresses interference removal techniques (UCT) Specific hardware Enough detail to run the procedure 23

24 Thanks Thanks to the Collaboration Team U.S. Environmental Protection Agency Office of Science and Technology Engineering and Analysis Division (EAD) Washington, DC CSC Engineering and Mission Support Alexandria, VA Perkin Elmer, Inc. Shelton, CT 24

25 Questions 25