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发表于 2009-2-21 23:35:00
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SAMPLE PREPARATION METHODS
Either of two methods outlined below have been found by LSC staff to be suitable for
preparation of metal samples within the scope of this document for subsequent elemental
analysis.
A. Hot Block Method
1. If the item is coated with paint or a similar surface coating, the coating should be
removed and analyzed separately from the base metal for lead content, as described in
the CPSC Standard Operating Procedure for Determining Lead (Pb) in Paint
(http://www.cpsc.gov/businfo/leadsop.pdf). Care should be taken to remove as little of
the substrate metal as possible.
2. Weigh out a 30-100mg aliquot of a component part in a labeled 50ml digestion vessel.
Component parts of children’s products including metal jewelry items generally weigh
1
Determination of Total Lead in Metallic Consumer Products
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Microwave Assisted Acid Digestion of Sediments, Sludges, Soils, and Oils -4-
several grams or more, and an aliquot (with no paint or similar surface coating, but
including any electroplated coating which is considered to be part of the substrate) will
have to be obtained. Samples should be cut or ground into many small pieces to
increase the dissolution rate. If a grinding apparatus (such as a rotary grinding tool with
disposable grinding bits) is used, then any contaminated parts must be thoroughly
cleaned or disposed of between uses to prevent cross-contamination. Record the actual
weight of the aliquot of the ground up component part to the nearest 0.1mg.
3. In a chemical fume hood, add 8ml of concentrated nitric acid to each beaker and
evaporate to approximately 3ml on a hot block digester at 105±3°C.
4. After cooling to below 50°C, add 2ml of concentrated hydrochloric acid and stir.
5. Dilute with distilled water, washing the side of the beaker, to 20ml.
6. Warm up the solution to at least 60°C without boiling and gently agitate on an orbital
shaker or with a stirrer or shaker bath for a minimum of 4 hours.
7. Transfer quantitatively into a 50ml volumetric flask or disposable volumetric digestion
cups and dilute to 50ml with distilled water.
8. Dilute samples so that Pb results are within the calibration range of the instrument.
Generally a 1:50 dilution is sufficient.
B. Microwave Method
1. If the item is coated with paint or a similar surface coating, the coating should be
removed and analyzed separately from the base metal for lead content, as described in
the CPSC Standard Operating Procedure for Determining Lead (Pb) in Paint
(http://www.cpsc.gov/businfo/leadsop.pdf). Care should be taken to remove as little of
the substrate metal as possible.
2. Weigh out a 30-100mg piece of metal item into an appropriate microwave vessel
equipped with a controlled pressure relief mechanism. Component parts of children’s
products including metal jewelry items generally weigh several grams or more, and an
aliquot (with no paint or similar surface coating, but including any electroplated coating
which is considered to be part of the substrate) will have to be obtained. Samples should
be cut or ground into many small pieces to increase the dissolution rate. If a grinding
apparatus (such as a rotary grinding tool with disposable grinding bits) is used, then any
contaminated parts must be thoroughly cleaned or disposed of between uses to prevent
cross-contamination. Record the actual weight of the aliquot of ground up component
part to the nearest 0.1mg.
3. In a chemical fume hood, add 4.5ml of concentrated nitric acid and 1.5ml of
concentrated hydrochloric acid to each vessel. Wait for the initial reaction of acid and
sample at room temperature to be complete (to the point of no obvious fuming or
bubbling) before sealing vessels. Seal vessels in accordance with the microwave
digester manufacturer’s directions.
4. The microwave method should involve increasing the temperature of each sample to
175±5°C in approximately 5.5 minutes, and holding at 175±5°C for 4.5 minutes.
5. Allow the samples to cool for a minimum of 5 minutes before removal of the vessels
from the microwave. Vent the microwave vessels in fume hood before uncapping.
6. Quantitatively transfer the sample to a 50ml volumetric flask or disposable volumetric
digestion cups. Dilute to 50ml with deionized water.
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II. Total Pb in Metals - Analysis of Sample Using ICP Method
Analyze diluted samples for Pb concentration using an ICP spectrometer (or Atomic
Absorption spectrometer). Analysis procedures for ICP-OES and FLAA and GFAA are
based on the methodology in ASTM E1613-043
. ICP-MS may also be employed with
appropriate procedures, such as EPA 6020A4
. Calculate total lead concentration in the
component part from that of the diluted sample, accounting for all dilution and reported as
percent by weight of the component part itself.
ICP Operating Procedures and Quality Control Measures
Analysis
1. Ignite plasma. Perform wavelength calibration or torch alignments per instrument
manufacturer’s recommendations.
2. Allow the instrument to become thermally stable before beginning.
3. Ensure the following element and wavelength are selected in analytical method:
a. Pb 220.353
b. One other Pb line, such as Pb 217.00, to ensure spectral interferences are not
occurring during analysis.
4. An internal standard such as 2 µg/ml yttrium is used.
5. Perform calibration using Calibration Blank and at least 3 standards appropriate to the
concentration of the analyte and instrument, such as 0.25, 0.5, 1.0 and 5.0 µg/ml.
Calibration shall be performed a minimum of once a day when used for analysis, or each
time the instrument is set up. Results for each standard shall be within 5% of the true
value. If the values do not fall within this range, recalibration is necessary.
6. Analyze the QCS immediately after the calibration. The analyzed value of Pb should be
within ±10% of the expected value. If the Pb value is outside the ±10% limit,
recalibration is required.
a. At least one LRB must be analyzed with each sample set. If the Pb value exceeds
3 times the MDL, then laboratory or reagent contamination should be expected.
The source of the contamination should be identified and resolved before
continuing analyses. The LRBs should be the same acid concentrations as added
to the sample, and should be taken through the same digestion procedure but
without added sample.
7. At least one certified reference material (CRM) should be analyzed with each batch of
samples. The CRM should be similar material as the test specimen with a known amount
of Pb. Analyte recoveries should be within ±15% of expected values. If recoveries are
outside this limit, the source of the problem should be identified and resolved before
continuing analyses.
8. Dilute any samples that have Pb values exceeding 1.5 times the high calibration
standard, and reanalyze.
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Standard Test Method for Determination of Lead by Inductively Coupled Plasma Atomic Emission Spectrometry
(ICP-AES), Flame Atomic Absorption Spectrometry (FAAS), or Graphite Furnace Atomic Absorption Spectrometry
(GFAAS) Techniques
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Inductively Coupled Plasma-Mass Spectrometry -6-
Calculations and Results Reported
Results for the Pb test methods are calculated and reported as follows:
Total Percentage Pb: % Pb (wt./wt.) = [(C x D) / (W x 1000 µg/mg)] x 100% where:
C = concentration of Pb detected (in units of µg/ml)
D = dilution factor (in ml units)
W = weight of aliquot digested (in mg units)
Example:
A 50 mg aliquot of a component part was digested and diluted to 1000 ml in order to analyze
by ICP. The ICP analysis found 20 µg/ml of lead in the solution, which showed that the
original component part contained 40% Pb by weight. |
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