Suspended Metals Digestion Procedure

Transcription

1 Villanova University Date Oct 2011 Page 1 of 7 Villanova University Villanova Urban Stormwater Partnership Watersheds Laboratory Standard Operating Procedure VUSP E Suspended Metals Digestion Procedure Author: Water Resources Laboratory Technician Sonali Joshi Approved: VUSP Director Robert G. Traver SOP-E-1

2 Villanova University Date Oct 2011 Page 2 of 7 Distribution Sonali Joshi Laboratory Copy, maintained by Quality Assurance Officer Revision Date Responsible Person Description of Change 0 March 2008 Mary Ellen Dukart Initial 1 Oct 2011 Sonali Joshi Update 2 The following laboratory staff have read and been trained on this Manual. A copy of this page will be maintained in the Laboratory. Training is good for one year. Signature Name / Position Date Trainer Robert G. Traver Director Bridget Wadzuk PI John Komlos Quality Assurance Officer SOP-E-2

3 Villanova University Date Oct 2011 Page 3 of 7 TABLE OF CONTENTS 1.0 SCOPE AND APPLICATION METHOD SUMMARY DEFINITIONS HEALTH AND SAFETY WARNINGS SEE LAB SAFETY PLAN INTERFERENCES HANDLING AND PRESERVATION EQUIPMENT AND SUPPLIES QUALITY CONTROL PROCEDURES CALCULATIONS WASTE MANAGEMENT REFERENCES 6 SOP-E-3

4 Villanova University Date Oct 2011 Page 4 of Scope and Application 1.1 This standard operating procedure (SOP) delineates the total suspended metals digestion and preservation methods. 1.2 Membrane digestion for the determination of suspended metals is useful in quantifying the concentration of metals that do not pass through a 0.45-µm membrane filter. Following digestion, the total suspended metal concentration is measured via AA spectrophotometry (see SOP-VUSP-G, SOP-VUSP-F). 1.3 This method has been proven to be sensitive and reliable for preparing samples for the determination of trace level concentrations of Cadmium, Chromium, Copper, Lead, and Zinc metals suspended in stormwater run off Method Summary 2.1 Approximately 300 ml of all collected samples is passed through a pre-washed 0.45-µm membrane filter (see SOP D). The dried membrane containing the insoluble material is transferred to a 250-mL beaker, and digested using concentrated Nitric Acid (TM Grade). Digested filtrate is analyzed using AA spectroscopy Definitions 3.1 Suspended Metals: Those metals of an unacidified sample that are retained by a 0.45-µm membrane filter. 4.0 Health and Safety Warnings See Lab Safety Plan 4.1 Digestion must be performed in a regulation fume hood. 4.2 All concentrated acid waste must be placed in its appropriate waste disposal container. 4.5 Always add acid to water Interferences 5.1 Contamination from sampling device and possibly from filters. 5.2 Loss of metals from adsorption on and/or precipitation in sample container by failure to acidify the sample properly where required. SOP-E-4

5 Villanova University Date Oct 2011 Page 5 of Handling and Preservation All glassware and plastic ware used for collection, transportation, and laboratory analysis of the samples are acid-washed using 10% Nitric Acid Wash (TM Grade). The glassware and plastic ware is first cleaned with a laboratory detergent and rinsed with tap water. Next, the container is rinsed in 1:10 Nitric Acid Solution. The container is then rinsed with MilliQ water three times and allowed to air dry. The samples are digested immediately upon collection. In case these cannot be digested immediately, the filters that are oven dried at app. 105 degrees Celsius are stored in desiccators until digestion. Once digestion is done, the digested samples are analyzed promptly. However, in the event that the samples cannot be analyzed promptly, the samples are preserved in the refrigerator and analysis is done within six months Equipment and Supplies 7.1 Hot plate: A 20 x 17-in heating surface is adequate mL graduated beakers 7.3 TenSette Pipettes 7.4 Concentrated Nitric Acid (TM Grade) in. diameter watchglasses ml graduated cylinders ml plastic bottles with screw caps µm micro-fiber filters 7.9 Solution of 1:1 Nitric Acid (TM Grade) in MQ water 8.0. Quality Control 8.1 An unused, but pre-washed, filter will be digested with every filter batch/case to accommodate for any trace metals inherent in the membrane fibers. 9.0 Procedures Prior to starting the operations make sure that you wear gloves. All glassware, plastic ware and filters handled for these operations should be done only after wearing gloves. This is important as otherwise moisture from hands can cause a significant change in the weights. 9.1 Filter app. 300 ml sample through a pre-washed 0.45 µm micro-fiber filter, according to SOP-VUSP-D. 9.2 Dry and weigh the filter according to SOP-VUSP-D. 9.3 Place the dried filter in a 250 ml beaker. 9.4 Using a HACH Tensette pipette, add 3 ml concentrated nitric acid (TM Grade) to each sample filter/beaker. Swirl to cover the entire filter with the acid. 9.5 Place a pre-washed watch glass over the beaker and slowly heat under reflux ( ). SOP-E-5

6 Villanova University Date Oct 2011 Page 6 of After the filter dissolves, which takes around 4 to 6 minutes, remove the watch glass and increase the heat to app Allow the acid to evaporate until the beaker reaches near dryness. Do not bake! 9.8 Remove the beaker from the heat and add 3 ml more of the Nitric Acid (TM Grade). Heat under reflux until the solution is a bright yellow color. 9.9 Remove the cover and allow acid to evaporate. Do not boil! 9.10 Remove beaker from heat and add 0.5 ml of 1:1 HN O3. Warm the beaker gently. Swirl to be sure all residue is coated with the acid While heating, rinse the sides of the beaker with MQ water taken in the 50ml graduated cylinder. Remove beaker from heat Transfer the 50ml filtrate in pre-washed 50 ml container for analysis. Filter any samples that may still contain considerable particulates. 10 Data Analysis and Calculations The concentration of the metals calculated using AA spectroscopy is populated into the excel sheet Metals Testing in the WREE folder. Care is taken to include only those concentrations that lie between the lowest and highest calibrant. Concentrations below the lowest calibrant are given a designation ND (See SOPs F and G) Waste Management 11.1 All acid waste, including the 1:1 Nitric Acid solution, and all preserved sample waste, is directed into an enclosed, properly labeled container Concentrated Nitric Acid is placed in a tightly sealed, labeled glass bottle Unused filters are thrown in the trash References Standard Methods (1999). Standard Methods for the Examination for Water and Wastewater 20 th Edtion, American Public Health Association (APHA), American Water Works Association (AWWA), Water Environment Federation (WEF). U.S. Environmental Protection Agency (USEPA). Urban Stormwater BMP Performance Monitoring U.S. Environmental Protection Agency, 2002a. U.S. Environmental Protection Agency (USEPA). Methods for Chemical Analysis of Water and Wastes, U.S. Environmental Protection Agency, SOP-E-6

7 Villanova University Date Oct 2011 Page 7 of 7 Working Notes: 1) The lysimeter samples are assumed filtered and are directly tested for metals. We need to compare filtered vs. non Filtered lysimeter sample to see if it yields different metal concentrations. 2) There is a validity concern about the digestion of filters and the final extractant. As per the method, the output of digesting the filter with HNO3 isn t yielding 2% HNO3. But all the other samples and standards are made in 2% HNO3. Hence, it is advisable to check if 12% HNO3 matrix and the 2% matrix yield different results. 3) After digestion of filters, TIFFO2 sample still has some particulates. It was discussed that a second cycle of digestion can be performed to check if the particulates can dissolve. Even if they do not dissolve, it will be helpful to compare the one-time digested sample with a two-time digested sample and see if there is any difference in the metal concentration. SOP-E-7