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SEMI F48-0600 © SEMI 2000 5 11 Sampling 11.1 Sam pling of Test Specimens 11.1.1 T est s pecimens shall be repres e n tat ive of the polymer m aterial being tested and shall be f ree of embedded partic les an d extraneous…
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10.1.2 Care must be taken in the handling and use of
the acids to avoid acid burns or contamination of the
acid. Acid should be neutralized before disposal.
10.1.3 Care must be taken when using the propane
torch to avoid burns. The torch should not be used near
flammable materials or solvents.
10.1.4 Care must be taken when using the muffle
furnace to avoid burns.
10.1.5 When ashing fluoropolymeric materials, the
ashing must be performed in a fume hood. When
heated, fluoropolymer materials outgas hydrofluoric
acid fumes and may also emit fluoropolymeric particles
which, if inhaled, can cause a condition known as
“polymer fume fever.” If hot fluoropolymer fumes are
inhaled, remove the individual to a well-ventilated area
and seek medical attention.
10.1.6 The outer layers of vessels used in the DCV
technique are frequently not as acid or reagent resistant
as the liner material. To retain the performance and
safety required these outer layers must be neither
chemically degraded nor physically damaged. Routine
examination of the vessel materials may be required to
ensure their safe use.
10.1.7 Only DCV containers with pressure relief or
control mechanisms or containers with suitably inert
polymeric or quartz liners and pressure relief
mechanisms are considered acceptable for use with this
process.
NOTE 4: Only microwave manufacturer’s approved vessels
for that device should be used.
10.1.8 Use of laboratory microwave systems is
required for this method. Users are advised not to use
domestic (kitchen) type microwave ovens or cookware.
Nor should inappropriately sealed containers without
pressure relief for microwave acid digestions be used.
See Section 16.3.1 for additional information on safety
issues concerning the use of laboratory microwave
systems.
10.1.9 Toxic nitrogen oxide(s), hydrogen fluoride, and
toxic chlorine (from the addition of hydrochloric acid)
fumes are usually produced during digestion.
Therefore, all steps involving open or the opening of
digestion vessels must be performed in a properly
operating fume ventilation system.
10.1.10 The analyst should wear appropriate
protective clothing, such as gloves and face protection,
and must not at any time permit a solution containing
hydrofluoric acid to come in contact with skin or lungs.
10.2 Technical Precautions – Digestion by Dry Ashing
(DDA)
10.2.1 Flaming and ashing temperatures must be
controlled so that they do not exceed 650°C to
minimize metal loss due to volatilization. If the
crucible becomes excessively hot for longer than about
one minute during flaming, it may have overheated.
When testing the method for recovery rates, it will
become apparent that the sample has been overheated
from the low recovery of metals.
10.2.2 One method of cleaning the crucibles and
covers is to flame them with a propane torch or other
appropriate heating source until they are sufficiently
hot, allow them to cool, rinse in dilute ultrapure nitric
acid, and then rinse in ultrapure water.
10.2.3 When ashing a sample, take care that all of the
ash residue remains in the crucible.
10.2.4 Several factors concerning selection of crucible
materials should be considered when performing the
DDA technique. For example, the crucible itself can
contribute elevated levels of its own composition into
samples at trace levels. Temperature restrictions are
another factor to consider in the selection of the
crucible material. Corrosion of the crucible during the
decomposition of the sample should also be considered.
For example, in the ashing of fluorinated materials,
platinum is preferred over quartz glass that could be
etched by the liberated hydrogen fluoride.
10.3 Technical Precautions – Digestion in Closed
Vessel (DCV)
10.3.1 Trace analysis requires a thorough cleaning.
One method of cleaning the vessels is to leach with hot
(1:1) hydrochloric acid (greater than 80 C, but less than
boiling) for a minimum of two hours followed with hot
(1:1) nitric acid (greater than 80 C, but less than
boiling) for a minimum of two hours and rinsed with
reagent water and dried in a clean environment.
10.4 Other Technical Precautions
10.4.1 When switching between high concentration
samples and low concentration samples, all crucibles or
digestion vessels should be cleaned according to the
corresponding and recommended cleaning procedure.
This cleaning procedure should also be used whenever
the prior use of the digestion vessels is unknown or
cross contamination from vessels is suspected.
10.4.2 Trace metallic levels of reagent blanks must be
significantly lower than those in the sample in order to
obtain accurate results for the analyte of interest.
10.4.3 Perform sample preparation in a clean
environment and under a fume hood to minimize
contamination.
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11 Sampling
11.1 Sampling of Test Specimens
11.1.1 Test specimens shall be representative of the
polymer material being tested and shall be free of
embedded particles and extraneous surface
contamination when visually inspected.
11.1.2 Two samples of each material shall be prepared
per SEMI F40. This test is performed in duplicate.
More samples may be analyzed if desired.
NOTE 5: The samples are cleaned and weighed according to
SEMI F40. The sample preparation described in this
document begins with either the ashing (DDA) or digestion
under pressure (DCV) of the polymer material.
11.2 Sample Preparation – Digestion by Dry Ashing
(DDA)
NOTE 6: Digestion by ashing using an oxygen plasma asher
differs considerably from the described procedures that refer
to ashing in open crucibles. Specific instructions are available
from the instrument manufacturers.
11.2.1 Clean the digestion container and cover using
appropriate methods for the vessel materials and
procedures being employed.
11.2.2 Place the sample into a cleaned crucible. For at
least two additional samples, add the recovery spike as
discussed in Section 12.
11.2.3 Use a propane torch or other appropriate heat-
ing source to carefully flame the outside of the crucible
until the polymer inside the crucible is completely
charred. Do not flame exceedingly, i.e., do not allow a
platinum crucible, for example, to become red hot, as
excessive heat will allow some metals to volatilize.
NOTE 7: This step must be carried out in a well-ventilated
fume hood.
11.2.4 Prepare at least three procedural blanks by
flaming three or more empty crucibles using the method
discussed in Section 11.2.3. The results from these
blanks will be used to determine the metallic
contribution from the crucibles themselves, from the
reagents and from the test procedure. These procedural
blanks should be treated like any other sample.
Crucibles should be rotated in and out of service so that
the same crucibles are not always used for blanks.
11.2.5 Place the charred sample crucibles and blank
crucibles in a muffle furnace, cover the crucibles with
the cleaned covers, and continue to char at 500 to
650°C until all the carbon is removed (usually over a
period of 6–18 hrs). The removal of all carbon is indi-
cated by the absence of black material in the sample.
NOTE 8: Some oxides (such as SnO
2
) are black and may
confound this determination. If a sample is still black after 18
hours, assume that it is an oxide and continue with the
procedure.
11.2.6 Allow the crucibles to cool.
11.2.7 Add the appropriate amount (1–2 mL) of
concentrated ultrapure hydrochloric acid to each
crucible.
11.2.8 Evaporate the hydrochloric acid to dryness in a
chemical hood at less than 100°C if necessary to permit
instrumental compatibility.
NOTE 9: The presence of chloride in the sample can result in
interferences for the determination of arsenic and vanadium
by ICP-MS.
11.2.9 Continue preparing the sample as described in
Section 11.4.
11.3 Sample Preparation – Digestion in Closed Vessel
(DCV)
11.3.1 Clean the digestion container and cover using
appropriate methods for the vessel materials and
procedures being employed.
11.3.2 Place the sample into a cleaned digestion
container. For at least two additional samples, add the
recovery spike as discussed in Section 12.
11.3.3 Add the reagents needed for the digestion.
11.3.4 Prepare at least three procedural blanks by
adding the same amount of all reagents, but no sample,
to three or more additional containers. The results from
these blanks will be used to determine the metallic
contribution from the containers themselves, from the
reagents and from the test procedure. These procedural
blanks should be treated like any other sample.
Containers should be rotated in and out of service so
that the same containers are not always used for blanks.
11.3.5 The analyst should be aware of the potential for
a vigorous reaction. If a vigorous reaction occurs upon
the initial addition of reagent or the sample is suspected
of containing easily oxidizable materials, allow the
sample to predigest in the uncapped digestion vessel.
Heat may be added in this step for safety considerations
(for example the rapid release of carbon dioxide from
easily oxidized polymeric material). Once the initial
reaction has ceased, the sample may continue through
the digestion procedure.
11.3.6 Seal the vessel according to the manufacturer’s
directions.
11.3.7 Properly place the vessel in the digestion
system according to the manufacturer’s recommended
specifications and connect appropriate temperature and
pressure sensors to vessels according to manufacturer’s
specifications.
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11.3.8 Set the parameters of the digestion device to
manufacturer’s recommendations.
NOTE 10: If the pressure exceeds the pressure limits of the
vessel, the pressure will be reduced by the relief mechanism
of the vessel.
NOTE 11: Pressure control for a specific matrix is applicable
if instrument conditions are established using temperature
control. Because each matrix will have a different reaction
profile, performance using temperature control must be
developed for every specific matrix type prior to use of the
pressure control system.
11.3.9 At the end of the digestion program, allow the
vessels to cool for an appropriate period of time before
removing them from the system. When the vessels
have cooled to near room temperature, determine if the
microwave vessels have maintained a seal throughout
the digestion. Due to the wide variability of vessel
designs, a single procedure is not appropriate. The use
of a spiked control sample is appropriate to ensure that
analyte loss has not occurred due to vessel venting. For
vessels with burst disks, a careful visual inspection of
the disk may identify compromised sample digestions.
11.3.10 Complete the preparation of the sample by
carefully uncapping and venting each vessel in a fume
hood. Vent the vessels using the procedure
recommended by the vessel manufacturer. Transfer the
sample to an appropriate acid cleaned container.
11.3.11 If the digested sample contains particulates,
which may clog nebulizers or interfere with injection of
the sample into the instrument, the sample may be
centrifuged, allowed to settle, or filtered.
11.3.11.1 If necessary, centrifugation at 2,000–3,000
rpm for 10 minutes is usually sufficient to clear the
supernatant.
11.3.11.2 Settling –– If undissolved material remains
such as TiO, or other refractory oxides, allow the
sample to stand until the supernatant is clear. Allowing
a sample to stand overnight will usually accomplish
this.
11.3.11.3 Filtering –– If necessary, the filtering
apparatus must be thoroughly cleaned and pre-rinsed
with dilute (approximately 10% V/V) nitric acid. Filter
the sample through qualitative filter paper into a second
acid-cleaned container.
11.3.12 Continue preparing the sample as described in
Section 11.4.
11.4 Preparation of the Sample for Analysis
11.4.1 If the sample was obtained from the DDA
method, add 0.5 mL concentrated nitric acid to each
crucible.
11.4.2 For samples obtained from the DCV method,
transfer or decant the sample into volumetric ware.
11.4.3 Dilute either obtained sample to a required
volume with ultrapure water (usually 20 mL).
Alternatively, a gravimetric dilution of the samples is
also appropriate. The samples are now ready for
analysis. See Related Documents, Section 16 for
applicable trace inorganics test methods.
12 Recovery Preparation and Percentage
Recovery Rate Determination
12.1 Metal recovery percentage must be determined
for all instruments by the individual laboratory. This is
accomplished via spiking a crucible or digestion vessel
containing a polymer sample with a known
concentration of metals. Then, determining the
percentage of each metal recovered after the
decomposition process or acid digestion. The following
provides the recommended method for spiking:
12.1.1 Add a known volume of a standard to a crucible
or digestion container containing a polymer sample.
12.1.2 For DDA –– Gently evaporate the standard
solution to dryness.
12.1.3 Digest the dried standard and dried polymer
using the same procedure as for the samples. Typical
recovery rates are 70–110% for the alkali, alkaline
earths, and most transition metals.
13 Data Analysis
13.1 Calculations
13.1.1 The concentration of trace metals in the
solution must be calculated to determine the
concentration in µg/g (ppm) of the polymeric material
using the following equation:
polymer concentration (µg/g ) =
= solution concentration
(µg/L) × solution volume (L) / mass of the polymer(g)
13.1.2 Since the procedural blank does not contain a
weighed sample, the results must be transformed to
solid concentrations (in µg/g) by using the average
weight of the samples (see Section 11.1.2 and
corresponding NOTE).
14 Data Presentation
NOTE 12: Use the Report Form provided in Section 17 of this
document.
14.1 Sample Information
14.1.1 Provide the date(s) of the test, the person and/or
company requesting the analysis, the method in which
the sample was obtained (e.g., if it was separated from a