Clean Laboratory Techniques

Vanaja Sivakumar, Ph.D.

Vice President, Inorganic Manufacturing

Clean Laboratory Techniques

Housekeeping

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Introduction

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Modern analytical instrumentation has detection limits down to the PPB and PPT levels

– ICP

– ICP-MS

– GFAA

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Lower detection limits introduces increased importance of eliminating trace contaminations

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For accurate trace metals analysis at these low levels, eliminate trace impurities present in:

– Reference Materials

– Samples

– Reagents

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 1 drop vermouth / 500 barrels gin

1 drop vermouth / 500,000 barrels gin

Length 1 inch / 16,000 miles 1 inch / 16 million miles (6” step on trip to the sun)

Sources of Contamination

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Starting materials used in the

preparation of reference materials

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Sample digestion techniques

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Water

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Acids

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Glassware/ laboratoryware

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Storage containers

Starting Materials

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Starting materials have to be tested for trace impurities in addition to assaying for metal content

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Impurities present can give rise to overlap of spectra, resulting in

incorrect calibration curve and therefore inaccurate results

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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

Water

Specifications of Four Types of ASTM Water



The major component of an aqueous standard

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The overall quality and accuracy of analysis depends on the quality of water that is used

Requirement

ASTM Type

I II III IV

Specific Resist.

(megohm/cm) (max) 18 1 4 0.2

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) 3 µg/L 3 µg/L 500 µg/L high Total Organic Carbon

SPEX CertiPrep ASTM Type I

Water System

Acids

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Any part of analytical process must use high purity acids

– Dissolution of materials and samples

– Digestions

– Dilutions

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Contaminants present in acids can contribute to erroneous results

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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

Acid Purification Still

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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

Laboratory Glassware

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The most common sources of contamination in a

laboratory are the pipettes and other laboratory-ware

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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

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

Pipette Washer / Dryer

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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

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Pipette washer/dryer features:

–

Holds 23 pipettes

–

Accommodates 0.5mL to 200mL pipettes

–

Small footprint to fit most spaces

–

Dries pipettes using vacuum line

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

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

Storage Containers

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Bottles

– Bottles in which purchased standards were shipped

– Bottles laboratory stores its own dilutions

– Various sizes, shapes, and materials of construction

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Contaminants present in the materials of construction can leach into the solution

Ideal Storage Containers

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Best:

–

Fluoropolymers

–

Quartz – synthetic

–

Polyethylene

–

Quartz – natural



Worst:

–

Borosilicate glass

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* 24 19 Ca, Pb, Fe, Cu

Low Density PE-LDPE 18 23 Ca, Cl, K, Ti, Zn

Polycarbonate-PC 10 85 Cl, Br, Al

Polymethyl Pentene-PMP 14 178 Ca, Mg, Zn

FEP† 25 241 K, Ca, Mg

Borosilicate Glass 14 497 Si, B, Na

Polypropylene-PP 21 519 Cl, Mg, Ca

High Density PE-HDPE 22 654 Ca, Zn, Si

* TFE-Tetrafluoroethylene

Contamination from Bottling Pump

Tubing

Material: DI – H₂O 5% Nitric Element SILICON (leached) NEOPRENE (leached) PHARMED (leached) SILICON (leached) NEOPRENE (leached) PHARMED (leached) Al 1.0 1.0 1.0 10.0 5.0 5.0 Ba 0.02 0.04 0.03 0.15 0.09 0.10 Ca 0.0 0.0 0.0 0.0 0.0 0.0 Cu 0.05 0.01 0.03 0.35 0.20 0.20 Fe 0.0 0.0 0.0 27 5 5 K 2 2 2 2 2 5 Mg 7.0 0.5 0.4 8 2 3 Na 0.0 0.8 0.4 4 4 5 Ni 0.2 0.2 0.2 4 0.1 0.7 Pb 0.1 0.1 0.1 3 2 1 Si 0 0 0 500 0 0 Sn 0.01 0.01 0.18 1 1.9 3.3 Sr 0.04 0.05 0.04 1.1 0.8 0.2 Ti 0.1 0.1 0.1 0.2 0.2 0.2 Zn 1.0 55 25 4 50 27

Sample Preparation Method

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Traditional open vessel or microwave

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Sample to sample cross contamination

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Environment in which the samples are prepared

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Materials that come in contact with the sample

Is the Laboratory Clean?

Redistilled nitric acid concentrated in regular and clean labs.

Element Regular Lab Clean Lab Element Regular Lab Clean Lab

Ag 0.006 0.01 Mn 1.1 0.1 Al 60 15 Mo 0.8 0.03 As 0.17 <0.02 Na TOO HIGH 25 Ba 1.95 0.25 Nd 0.14 0.025 Ca 150 100 Pb 0.5 0.4 Cd 0.3 0.003 Rb 0.03 <0.001 Ce 1.5 0.06 Sb 0.04 0.013 Co 0.6 0.008 Sm 0.015 0.003 Cr 2.5 0.4 Sr 0.6 0.3 Cu 1.7 0.23 Th 0.017 0.001 Fe 50 9 Ti 1 0.77 Ge 0.02 <0.01 V 0.35 <0.3 Mg 10 4 Zn 5.5 0.7

Clean Laboratory

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What is a clean room?

– Filtered Air

– Transports particulate contaminants away from sensitive samples

– Maintains a clean environment with low particle concentrations

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Applicable Standards:

– ISO 14644

Clean Laboratory

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Environment of class 100

– No more than 100 particles, >0.5µm in diameter, per cubic foot

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Walls, ceilings, and floors are sealed and dust free

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HEPA filters mounted in the ceiling

Common Contaminating Sources

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Ceiling tiles, paints, cements, and dry walls

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Dust and rusts on

shelves, equipment, and furniture

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Temperature control systems

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 6.0 0.1 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

Impurities Increase With Time

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There was a considerable increase in

concentration of impurity for elements such as Al, Ca, Fe, Mg, Na, Si, and Zn

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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

Controlling Contamination

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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

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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

Controlling Contamination – cont.

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Wear gloves:

– Sampling personnel must wear clean gloves when handling equipment, samples, blanks and standards

– Sweat contains K, Pb, Ca, Mg, SO₄, PO₄, and NH₄ ions, in addition to Na and Cl



Use metal free containers:

– Volumetric flasks, beakers made out of FEP, polycarbonate, and polypropylene should be used

Controlling Contamination – cont.

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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

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Use adhesive mats at entry points to control dust and dirt from shoes

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Change shoes and / or wear shoe coverings to reduce bringing in dirt from the outside

Controlling Contamination – cont.

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Humidity:

–

Keep lab humidity around 45% to minimize electrostatic charge

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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

Controlling Contamination – cont.

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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

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Reason:

– Labware tends to exhibit “memory effects” from previous solutions

Controlling Contamination – cont.

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Segregate labware for specific metals

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Metals such as Pb and Cr are highly absorbed by glass but not by plastics

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For B and Si analysis, avoid borosilicate glass. Use plastic, TFE or quartz labware

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Samples containing low levels of Hg (PPB levels) should be stored in glass, polypropylene, or fluoropolymer because Hg vapors diffuse through polyethylene bottles

Controlling Contamination – cont.

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Use membrane filters instead of ashless filter paper

– Ashless filter paper contains 20 trace elements at >1 ppm level

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Use “NOCHROMIX” instead of Chromic Acid to clean labware

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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

Controlling Contamination – cont.

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No powder gloves

– Powder in the gloves contains high conc. of Zn

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Replace gloves and shoe covers regularly

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Use ultra clean sample introduction system

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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

Helpful Hints

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Test personnel, equipment, and methods with QC samples

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Observe clean lab procedures and techniques

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Use reference materials that have not expired

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Make up and use only freshly prepared calibration standards

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Rerun samples using a different dilution factor

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Spike appropriate QC samples with expected levels of analytes or use standard additions

Helpful Hints – cont.

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Prepare the dilution in plastic or FEP (as much as possible)

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Rinse volumetric flasks with 1% nitric acid and keep in nitric acid until used

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Do dissolutions in metal free clean hood

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Use high pure reagents and acids:

–

Ammonium hydroxide and nitric acid are relatively clean

–

HCl has high impurities

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Rinse pump tubing with high pure acids (about 2%) used in the matrix

Helpful Hints – cont.

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New Product: OdorEroder

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Effectively neutralizes offensive odors and fumes in the lab

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Absorbs & chemically transforms chemical odors into harmless compounds that remain trapped within the product

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Highly effective at neutralizing volatile compounds

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Non-toxic and environmentally safe

References

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Guidance in Establishing Trace Metal Clean Rooms in Existing Facilities: USEPA 821-B-95-001

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Accuracy in Trace Analysis: NBS Special Edition 422

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Guide to Environment Analytical Methods: Roy-Keith Smith

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Clean Manufacturing: A2C2, April 2003

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Water Environment Laboratory Solutions: April/May 2003

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Sampling of sea and fresh water for the analysis of trace Metals: E. Helmers 1997

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“New Solutions for Trace Metals Analysis,” Agilent Technologies, 2005

Thank You!



Patric Blackett



Born 18 November, 1897



Nobel Prize winner 1948

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