Clean Laboratory Techniques

Transcription

1 Clean Laboratory Techniques Thursday November 18 th, 2010 Vanaja Sivakumar, Ph.D. Vice President, Inorganic Manufacturing

2 Housekeeping Everyone in attendance will receive a copy of the slide deck The webinar is being recorded and will be available for everyone to view on demand The recording will be posted about one week after the event Questions will be answered at the end of the presentation Type any questions you may have in the question box and we will answer them during the Q & A portion Stay tuned after the Q&A session we re giving away two free gifts!

3 Introduction Modern analytical instrumentation has detection limits down to the PPB and PPT levels ICP ICP-MS GFAA Lower detection limits introduces increased importance of eliminating trace contaminations For accurate trace metals analysis at these low levels, eliminate trace impurities present in: Reference Materials Samples Reagents Environment

4 Trace Metal Analysis at PPB and PPT Concentrations Just how much is a part per billion or trillion? Unit 1 part per Billion 1 part per Trillion Time 1 second / 32 years 1 second / 320 centuries Money 1 cent / $10 million 1 cent / $10 billion Volume Length 1 drop vermouth / 500 barrels gin 1 inch / 16,000 miles 1 drop vermouth / 500,000 barrels gin 1 inch / 16 million miles (6 step on trip to the sun)

5 Sources of Contamination Starting materials used in the preparation of reference materials Sample digestion techniques Water Acids Glassware/ laboratoryware Storage containers Laboratory environment

6 Starting Materials Starting materials have to be tested for trace impurities in addition to assaying for metal content Impurities present can give rise to overlap of spectra, resulting in incorrect calibration curve and therefore inaccurate results Chloride, fluoride, oxalate, and sulfate contaminants have to be identified because presence of these ions can precipitate elements such as Ag, Pb, Ba, and the rare-earth elements

7 Water The major component of an aqueous standard The overall quality and accuracy of analysis depends on the quality of water that is used Specifications of Four Types of ASTM Water ASTM Type Requirement I II III IV Specific Resist. (megohm/cm) (max) ph N/A N/A N/A 5-8 Sodium (max) 1 µg/l 5 µg/l 10 µg/l 50 µg/l Total Silica (max) 3µg/L 3 µg/l 500 µg/l high Total Organic Carbon (max) 50 µg/l 50 µg/l 200 µg/l N/A

8 SPEX CertiPrep ASTM Type I Water System

9 Acids Any part of analytical process must use high purity acids Dissolution of materials and samples Digestions Dilutions Contaminants present in acids can contribute to erroneous results Example: An aliquot of 5 ml of acid containing 100 ppb of Ni as contaminant, used for diluting a sample to 100 ml can introduce 5 ppb of Ni into the sample High purity acid is very costly

10 Acid Purification Still PTFE Acid Still can produce sub-boiling high purity acids that can be used to prepare ultra pure acids right in the laboratory at a fraction of the cost of purchasing them The distillation method of surface evaporation without boiling is employed through the use of infrared heaters. Majority of the metals can be reduced below ppb levels in a single distillation

11 Laboratory Glassware The most common sources of contamination in a laboratory are the pipettes and other laboratory-ware Pipettes not only have to be calibrated frequently for accuracy but they have to be thoroughly cleaned to remove all the contaminants that are present even at the PPT levels

12 How Clean Are Your Pipettes? 2% nitric acid run through 5 ml pipettes that were cleaned manually and scanned on ICP-MS Element Conc. (PPB) Element Conc. (PPB) Ag 2.33 Mn 1.72 Al 6.43 Na 19.1 Be 2.62 Ni 0.96 Bi 1.07 Pb 5.4 Ca 18.8 Sn 0.55 Co 2.02 Th 0.24 Cr 0.91 Ti 0.56 Fe 1.62 Tl 1.53 Mg 2.56 Zn 9

13 Pipette Washer / Dryer Rows of conical shaped plastic pipette holders are connected to a water line. The water fills each pipette, shoots out of the pipette tip, and rains shower of water over the outside of pipette Pipette washer/dryer features: Holds 23 pipettes Accommodates 0.5mL to 200mL pipettes Small footprint to fit most spaces Dries pipettes using vacuum line Wash solutions & surfactants may be used

14 Pipettes Cleaned With Washer 2% nitric acid run through 5mL pipettes and scanned on ICP-MS Element Conc. PPB Element Conc. PPB Ag <0.01 Mn <0.01 Al <0.01 Na <0.01 Be <0.01 Ni <0.01 Bi <0.01 Pb <0.01 Ca <0.20 Sn <0.01 Co <0.01 Th <0.01 Cr <0.04 Ti <0.02 Fe <0.20 Tl <0.02 Mg <0.01 Zn <0.01

15 Manual Cleaning Vs. Pipette Washer Comparison Chart Element Manual (ppb) Washer (ppb) Al 6.43 <0.01 Ca 18.8 <0.20 Fe 1.62 <0.20 Mg 2.56 <0.01 Na 19.1 <0.01 Zn 9 <0.01

16 Storage Containers Bottles Bottles in which purchased standards were shipped Bottles laboratory stores its own dilutions Various sizes, shapes, and materials of construction Contaminants present in the materials of construction can leach into the solution

17 Ideal Storage Containers Best: Fluoropolymers Quartz synthetic Polyethylene Quartz natural Worst: Borosilicate glass

18 Summary of Average Element Content in Storage Containers Material Total No. of Elements Total PPM Major Impurities Polystyrene-PS 8 4 Na, Ti, Al TFE* Ca, Pb, Fe, Cu Low Density PE-LDPE Ca, Cl, K, Ti, Zn Polycarbonate-PC Cl, Br, Al Polymethyl Pentene-PMP Ca, Mg, Zn FEP K, Ca, Mg Borosilicate Glass Si, B, Na Polypropylene-PP Cl, Mg, Ca High Density PE-HDPE Ca, Zn, Si * TFE-Tetrafluoroethylene FEP-Fluorinated ethylene propylene

19 Contamination from Bottling Pump Tubing Material: DI H 2 O 5% Nitric Element SILICON (leached) NEOPRENE (leached) PHARMED (leached) SILICON (leached) NEOPRENE (leached) PHARMED (leached) Al Ba Ca Cu Fe K Mg Na Ni Pb Si Sn Sr Ti Zn Zr (Units in ppb)

20 Sample Preparation Method Traditional open vessel or microwave Sample to sample cross contamination Environment in which the samples are prepared Materials that come in contact with the sample

21 Is the Laboratory Clean? Redistilled nitric acid concentrated in regular and clean labs. Element Regular Lab Clean Lab Element Regular Lab Clean Lab Ag Mn Al Mo As 0.17 <0.02 Na TOO HIGH 25 Ba Nd Ca Pb Cd Rb 0.03 <0.001 Ce Sb Co Sm Cr Sr Cu Th Fe 50 9 Ti Ge 0.02 <0.01 V 0.35 <0.3 Mg 10 4 Zn (Units in ppb)

22 Clean Laboratory What is a clean room? Filtered Air Transports particulate contaminants away from sensitive samples Maintains a clean environment with low particle concentrations Applicable Standards: ISO US Federal Standard 209E

23 Clean Laboratory Environment of class 100 No more than 100 particles, >0.5µm in diameter, per cubic foot Walls, ceilings, and floors are sealed and dust free HEPA filters mounted in the ceiling No exposed metal parts

24 Common Contaminating Sources Ceiling tiles, paints, cements, and dry walls Dust and rusts on shelves, equipment, and furniture Temperature control systems

25 Prep Lab for Trace Analysis

26 Packaging Comparison Comparison of a solution made in clean room environment and packaged in regular lab and clean lab Elem Regular Lab Clean Lab Elem Regular Lab Clean Lab Al 5 ppb 0.1 ppb Na As 0.05 <0.01 Ni 0.1 <0.01 Co 0.2 <0.01 Sb 1.0 <0.01 Fe 7.0 <0.7 Sn 2.0 <0.01 Mn 0.08 <0.01 Zn 8.0 <1.0 Mo 0.02 <0.01 Zr 0.1 <0.01

27 Impurities Increase With Time There was a considerable increase in concentration of impurity for elements such as Al, Ca, Fe, Mg, Na, Si, and Zn Several probable reasons: Dust from the lab environment can contribute to Ca, Na, K, Mg, and Si Ti and Zn from LDPE bottles Al and Fe from the materials of various fixtures in the laboratory

28 Controlling Contamination Minimize exposure: The apparatus that will contact samples, blanks or standards should be opened in clean room, clean bench, or glove box When not in use, the apparatus should be covered well in plastic bag or box Clean work surfaces: Before processing samples, all work surfaces in the hood, clean bench, or glove box should be cleaned with a wipe soaked with reagent water

29 Controlling Contamination cont. Wear gloves: Sampling personnel must wear clean gloves when handling equipment, samples, blanks and standards Sweat contains K, Pb, Ca, Mg, SO 4, PO 4, and NH 4 ions, in addition to Na and Cl Use metal free containers: Volumetric flasks, beakers made out of FEP, polycarbonate, and polypropylene should be used

30 Controlling Contamination cont. If clean room is not available, all sample preparation should be performed in a class 100 clean bench or glove box with a flow of air or preferably nitrogen Use adhesive mats at entry points to control dust and dirt from shoes Change shoes and / or wear shoe coverings to reduce bringing in dirt from the outside

31 Controlling Contamination cont. Humidity: Keep lab humidity around 45% to minimize electrostatic charge Surface charges can be eliminated: By use of commercial static eliminators By wetting a lint free cloth with high purity ethanol or high purity water and letting it evaporate

32 Controlling Contamination cont. Separate labware into low level & high level : Low level labware is used only for solutions that have metals at below 1 ppm concentration High level labware for solutions with above 1 ppm concentration of metals Reason: Labware tends to exhibit memory effects from previous solutions

33 Controlling Contamination cont. Segregate labware for specific metals Metals such as Pb and Cr are highly absorbed by glass but not by plastics For B and Si analysis, avoid borosilicate glass. Use plastic, TFE or quartz labware Samples containing low levels of Hg (PPB levels) should be stored in glass, polypropylene, or fluoropolymer because Hg vapors diffuse through polyethylene bottles Avoid lint-producing paper products

34 Controlling Contamination cont. Use membrane filters instead of ashless filter paper Ashless filter paper contains 20 trace elements at >1 ppm level Use NOCHROMIX instead of Chromic Acid to clean labware No jewelry, cosmetics, or lotions Cosmetics and lotions can introduce the contaminants Al, Be, Ca, Cu, Cr, K, Fe, Mn, Ni, Ti, and Zn into the samples Some hair dyes contain lead acetate Calamine lotion used for skin irritations contains ZnO Se is an active ingredient in some anti-dandruff shampoos Wash lab coats regularly

35 Controlling Contamination cont. No powder gloves Powder in the gloves contains high conc. of Zn Replace gloves and shoe covers regularly Use ultra clean sample introduction system How do you determine if you have a clean lab? By running blanks! THINK BLANK Blanks have to be clean to avoid false positive and false negative results Carry blanks through all steps of an analytical procedure Anything that touches the sample must be absolutely clean!

36 Helpful Hints Test personnel, equipment, and methods with QC samples Observe clean lab procedures and techniques Use reference materials that have not expired Make up and use only freshly prepared calibration standards Rerun samples using a different dilution factor Spike appropriate QC samples with expected levels of analytes or use standard additions

37 Helpful Hints cont. Prepare the dilution in plastic or FEP (as much as possible) Rinse volumetric flasks with 1% nitric acid and keep in nitric acid until used Do dissolutions in metal free clean hood Use high pure reagents and acids: Ammonium hydroxide and nitric acid are relatively clean HCl has high impurities Rinse pump tubing with high pure acids (about 2%) used in the matrix

38 Helpful Hints cont. New Product: OdorEroder Effectively neutralizes offensive odors and fumes in the lab Absorbs & chemically transforms chemical odors into harmless compounds that remain trapped within the product Highly effective at neutralizing volatile compounds Non-toxic and environmentally safe Non contaminating

39 References Guidance in Establishing Trace Metal Clean Rooms in Existing Facilities: USEPA 821-B Accuracy in Trace Analysis: NBS Special Edition 422 Guide to Environment Analytical Methods: Roy-Keith Smith Clean Manufacturing: A2C2, April 2003 Water Environment Laboratory Solutions: April/May 2003 Sampling of sea and fresh water for the analysis of trace Metals: E. Helmers 1997 New Solutions for Trace Metals Analysis, Agilent Technologies, 2005 Nalgene Labware Technical Data

40 Thank You! Patric Blackett Born 18 November, 1897 Nobel Prize winner 1948

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