Baltimore PM supersite
April 20, 2003
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GFAAS-Z
RP – DRAFT -
ELEMENTAL ANALYSIS OF AMBIENT AIR PARTICUALATE SAMPLES COLLECTED FROM SEAS USING GFAAS-Z
Identification code: RP GFAAS-Z / APPROVALSRP Working RP pages
Issue Date: 01/04/2001 / Local PI:01/22/2001
Revision No:1
Revision date:06/10/2002
Revision description:
End cap GF tubes and 5% H2 for group 2 elements. Improved detection limits for As, Se, Pb and Ni / Local PI:
Revision No:3
Revision date:5/1/03
Revision description:
Inclusion of NIST’s interim PM2.5 RM results for method validation. / Local PI:
Revision No:
Revision date: / .
Revision description: / Local PI:
Distributed to: Name of recipient: / Original date / Rev. 1. date / Rev. 2. date / Rev. 3. date
Dr Phil Hopke / 1/4/01 / 1/9/01
Dr John Ondov
ELEMENTAL ANALYSIS OF AMBIENT AIR PARTICUALATE SAMPLES COLLECTED FROM SEAS USING GFAAS-Z
1. PURPOSE AND APPLICABILITY
This research protocol (RP) contains protocol for performing multi elemental analysis of aqueous slurry samples using Perkin-Elmer SIMAA 6000. This is an evaluation version of an anticipated standard operating procedure (SOP), which will result from experiences with this RP. Due to this fact, this RP is subject to change. The SIMAA6000 is capable of determining upto six elements simultaneously. Samples are analyzed for multiple multielement suites to achieve analyses for all of the elements desired. Note that the number and choice of elements to be determined in each analytical suite are being reoptimized, and both are subject to change.
2. REFERENCES
The Perkin Elmer SIMAA 6000 Instrument Manual, ‘Installation, Maintenance, and System Description’ (Part Number 0993-5218).
The Perkin Elmer SIMAA 6000 Instrument Manual, ‘Setting Up and Performing Analyses’ (Part Number 0993-5219).
The Perkin Elmer SIMAA 6000 Instrument Manual, ‘AA WinLab for SIMAA 6000, Software Guide’ (Part Number 0993-5216).
Kidwell, C. B., Ondov, J. M. (Submitted), ‘Elemental Analysis of Sub-Hourly Ambient Aerosol Collections’, Aerosol Sci. Technol., Jan 2001.
Caulcutt, R., Boddy, R., ‘Statistics for Analytical Chemists’, Chapman and Hall, New York, 1983.
Miller, J.C., Miller, J.N, ‘Statistics for Analytical Chemistry’, 3rd edition, Ellis Horwood PTR Prentice Hall, 1993.
3. TERMINOLOGY
GFAAS-Z: Graphite Furnace Atomic Absorption Spectrometer with Zeeman background correction.
SIMAA: Simultaneous Multielemental Atomic Absorption
NIST: National Institute of Standards and Technology, Gaithersburg, USA
SEAS: Semicontinuous Environmental Aerosol Sampler
RSD: Relative Standard Deviation
RP: Research Protocol
Analyte: The component of a sample that is under investigation whose concentration is sought.
Accuracy: The degree to which the results obtained agrees with the actual concentration.
Precision: Nearness of the measurements made on the same sample with same measurement system.
SRM : RM certified by a certifying body such as National Institute of Standards and Technology (NIST), National Institute of Environmental Studies, Japan (NIES) or Japan Society for Standards (JSS), whose constituent concentrations are certified by a procedure which establishes its traceability and is accompanied by an uncertainty statement at a stated level of confidence.
Characteristic mass: Mass of the analyte that gives one percent absorption.
4. EQUIPMENT
4.1 Perkin Elmer SIMAA 6000:
This instrument operates under Stabilized Temperature Platform Furnace Technology (STPF) that uses a transversely heated graphite atomizer with an integrated L’vov platform. Suspended solids up to about 1% can be accommodated, but analytical results will suffer somewhat. Multielemental analyses are accomplished using a tetrahedral echelle polychromator (TEP) optical arrangement. The detector is a monolithic solid-state type with 61 high performance photodiodes which allow for simultaneous determination of up to six elements. Background correction is achieved by a longitudinal Zeeman system. SIMAA6000 is also equipped with 40 and 80-position autosampler trays.
4.2 ACCESSORIES
1. HEPA filter
2. Exhaust hood
3. Hollow Cathode Lamps (HCL) Pb, Bi, Cd, Al, Ag, Ti, Ca, V, Cr, Mn, Fe, Ni, Cu and Zn
4. Electrodeless Discharge Lamps (EDL) As, Se
5. Pyrollytically coated graphite tubes
6. Autosampler vials
7. Auto sampler pipettes
4.3 OTHER MATERIALS
1. Elemental standard solutions
2. Volumetric flasks(class A)
3. Autopipettes and tips
4. Ultrapure Conc nitric acid
5. Milli-Q water(18.2 MW cm-1)
6. Ultrahigh pure grade Argon gas
7. Computer
8. Laboratory notebook
9. Data entry forms
5. PROCEDURES
5.1 Cleaning of sample vials, volumetric flask, reagent bottles and autosampler cups
1. Rinse material with distilled water.
2. Soak overnight in (10+1) reagent grade nitric acid.
3. Rinse 3 TIMES with Milli-Q water.
4. Soak overnight in Milli-Q water.
5. Dry overnight in clean hood.
6. Wear disposable powder-free gloves for all handling of the materials after step 4. Cleaning may be done in bulk quantities
Note: The word ‘Clean’ in this RP implies that the ones, which had been treated as said above.
5.2 Preparation of working standards from stock solution
1. The following procedures must be performed in a laminar flow workbench (or in class 100 clean room).
2. Shake the stock solutions well before use.
3. Use only calibrated flasks (Class A), and auto pipettes having precision £ 0.25 for dilutions.
4. Never attempt dilutions more than 100 times at a single step
5. Always use 0.5% (v/v) ultrapure nitric acid for dilutions. Working standards can have 0.1% nitric acid. Remember to prepare fresh working standards every week as hydrolysis could change metal concentrations at low acid strength.
6. Give sufficient time (~30 min) for the solution to attain equilibrium after every step of dilution.
7. Transfer the appropriately diluted standard solution into a clean polyethylene bottle. It should have a label stating the element name, concentration, and date prepared.
6. GFAAS-Z OPERATIONS
6.1 To power up
- Make sure the computer is securely connected to the instrument and switched on.
- Check the autosampler rinse and waste containers. Fill the rinse container with ultrapure 5% (v/v) nitric acid and 0.001% triton x-100 solution mixture.
- Set the supply valve on the argon tank to 50 psi.
- Turn on exhaust fan and HEPA filter.
- Make sure that the water level is at maximum in the cooling tank
- Turn on the SIMAA 6000 from the green button on the lower left front.
- Wait approximately 1 minute for the autosampler to warm up.
- Start AA Winlab on the computer. After about 1 minute, the startup screen will appear.
- Click the Default button. Follow the on-screen message.
6.2 To shut down:
- Exit AA Winlab.
- Turn off the SIMAA 6000 from the green button on the lower left front.
- Close the supply valve on the argon tank.
- Turn off the exhaust fan and HEPA filter.
6.3 To analyze samples:
- Elements of interest are grouped into three suites. [Suite 1 (Al, Cr, Mn, Cu, Fe), Suit 2 (Se, As, Ni, Pb), and Suite 3 (Zn, Cd)]. Select the customized methods by calling the method name. Refer to Chapter 1 of “AA WinLab for SIMAA 6000” manual for details.
- Install the appropriate (each suite has a separate lamp holder with lamps installed already) lamp assembly.
- From the Lamps window, turn on the desired lamps and align them to get the maximum signal intensity. Allow 45 minutes for lamps to warm up before beginning analysis.
- Enter sample data into the Sample Information File and fill the autosampler tray with sample vials. Sample vials should only be filled about 75% of the capacity of vials (1 ml). Adding more solution will cause droplets to adhere to the autosampler tip that will lead to pipetting errors.
- To reduce evaporation of water from the sample vials, place about 20 ml of Milli-Q water in the bottom of the autosampler tray, i.e., enough to cover the bottom but without touching the sample vials.
- From the Automated Analysis Control window, click the Setup tab and select locations for samples to be analyzed. Specify the Sample Information File (SIF) to be used and the Results file to store data.
- Click the ‘Analyze All’ button to analyze all specified samples in SIF.
6.4 Furnace Tubes:
Graphite furnace tubes should be good for 500 - 600 firings. Samples with high concentrations of acid and/or high atomization temperatures will cause faster degradation.
Graphite tube replacement:
- In the Furnace Control window (Chapter 4), click the Open/Close button.
- Unscrew the autosampler assembly, using the knob below the autosampler, and swing aside.
- Swing the furnace support lever aside and tilt the furnace contact down.
- Use the clothespin to remove and inspect the graphite tube. Never handle graphite tubes with bare hands.
- Clean the furnace contacts with a cotton swab to remove any carbon buildup.
- Insert the graphite tube into the rear contact. The higher side of the platform within the furnace tube should be located to the rear of the furnace.
- Carefully tilt the furnace contact up and replace the support lever.
- Replace the autosampler assembly.
- Click the Open/Close button.
- Check the autosampler tip alignment using the Tip Align button.
If a new tube is inserted, click the Condition Tube button. Also go to Diagnostics in the Tools menu, click the Furnace tab, and click Reset for the number of tube cycles.
6.5 Instrumental operating conditions
The GFAAS-Z operating conditions are summarized below.
Suite 1 / Suite 2 / Suite 3Elements / Al, Cr, Mn, Cu, Fe / Se, As, Ni, Pb / Cd, Zn
Sample Volume / 20 µL / 20+20 µL / 10 µL
Dry Stage 1 / 25 s, 110°C / 25 s, 110°C / 20 s, 110°C
Dry Stage 2 / 25 s, 130°C / 20 s, 130°C / 20 s, 130°C
Char / 25 s, 1250°C / 20 s, 1000°C / 15 s, 500°C
Purge pas / 5% H2/Ar mix / 5% H2/Ar mix / Ar gas
Atomize / 5 s, 2400°C / 5 s, 2300°C / 5 s, 1900°C
Cleanout / 3 s, 2450°C / 3 s, 2400°C / 3 s, 2450°C
6.6 INSTRUMENT MAINTENANCE/CHECK
Everyday check/maintenance.
1. Check water level in the cooling tank.
2. Check Ar gas pressure
3. Inspect graphite tube for surface contamination and perform furnace cleaning through software.
4. Fill the rinse bottle with Triton X-100 and nitric acid solution.
5. Lamp intensity (there shouldn’t be much fluctuation).
6. Autosampler tip alignment in graphite tube.
Monthly maintenance
1. Change the fume extraction unit filter.
2. Calibrate auto sampler pipette by weighing the dispensed volume.
7. DETERMINATION
Calibration:
Quantitative measurements in atomic absorption are based on the Beer-Lambert law, which states that the concentration of an analyte is proportional to its absorbance:
C = KA = K log I0 / I
In this expression C is the concentration, A is the integrated absorbance, I0 and I are the incident and transmitted source intensities, and K is a proportionality constant. It is well known that for most elements, the observed relationship between concentration and absorbance is not linear over an extended concentration range. For this reason, generally a suitable non-linear curve equation is used to construct calibration plot.
Blanks and samples:
The calibration standards, reagent blank, SEAS system blank, and SEAS samples have the following composition when their solution is placed in the graphite furnace for the analysis of elemental concentration.
Reagent blank / Calibration standards / SEAS System blank / SEAS sampleMatrix modifier +
0.2 % HNO3 in milliQ water. / Matrix modifier +
0.2 % HNO3 in milliQ water +
Appropriate metal ions / Matrix modifier +
0.2 % HNO3 in
milliQ water +
Atmospheric air particles from uncontrollable sources/ temporary contamination from SEAS instrument / Matrix modifier +
0.2 % HNO3 in milliQ water +
atmospheric air particles
As the volume of the sample injection, and the nature and amount of matrix modifiers remains same for the entire suite of elements, the elemental impurities associated with reagent blank are determined first and stored in the temporary memory of the method data-file of the instrument software. The software automatically subtracts this value for all subsequent measurements performed using this method file. Finally, as is evident from the above table, the actual elemental concentrations (in calibration units) in the atmospheric air particles are obtained by subtracting SEAS system blank values from SEAS sample values.
Atmospheric concentration of elements:
Assuming the density of the sample slurry produced by SEAS is 1.0 g/ml, elemental mass in the SEAS sample is obtained by multiplying the concentration of the element (in the calibration units, i.e. ng/ml) by the sample slurry mass (in g). The volume of air sampled is obtained by multiplying the duration of sample collection (in min) by the airflow rate (in m3/min). The atmospheric concentration (in units of ng/m3) of the element is obtained by dividing the elemental mass by the volume of air sampled.
Propagation of measurement uncertainties
As shown above, the atmospheric concentration of an element is calculated from a combination of experimental quantities such as concentration of the element in the SEAS sample solution, weight of the SEAS sample solution, duration of collection, and air flow rate. If the precision of each quantity is known, then simple mathematical rules can be used to estimate the precision (random error) of the overall result. These rules are summarized as follows:
1) Linear combination
If the final value, y, is calculated from a linear combination of measured qunatities a, b, c, etc.. by:
Y = k + kaa + kbb + kcc +…
Where k, ka, kb, kc, ..are constants,
Then, the standard deviation of y, ys, is given by
ys = Ö(ka sa)2 + (kb sb)2 + (kc sc)2 + ..
Illustration:
Weight of the sample is obtained by:
wsample = w(sample+bottle) – w(bottle
Therefore,
sw = Ö(ssample+bottle)2 + (sbottle)2 ------(2)
Since the precision of the balance at both the measurement places are expected to be the same, we may rewrite the equation-(2) as: sw = sÖ2
2) Multiplicative expressions:
If y is calculated from an expression of the type
Y = K ab/cd
Where K is a constant and a, b, c and d are independently measured quantities, then
sy is given by
3) If y is calculated from an expression