Page 31 - Solutions for Plastic Evaluation

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Hazardous Substances Hazardous Metals Product Evaluation

ICP-AES

Analysis of Hazardous Metals in Plastics Using an ICP-AES System
ICP emission spectrometers are able to analyze elements in sample solutions with high sensitivity. Solid samples, such as plastics,
require using dry incineration, wet digestion, microwave digestion, or other methods to pretreat samples to prepare a solution. Plastic Materials Evaluation of
However, that requires selecting the appropriate pretreatment method for the elements being analyzed. This example introduces
results from using respective pretreatment methods to prepare solutions of plastic samples (standard polyethylene samples
BCR680 and BCR681) and then analyze them for hazardous metals, such as lead (Pb) and cadmium (Cd), using a Shimadzu
multitype ICPE-9000 emission spectrometer.

Sample Pretreatment Methods

(1) Dry Incineration Method Raw Materials Evaluation of
Weigh 0.2 g of sample into a quartz crucible. Add enough sulfuric acid to immerse the sample. Heat the crucible on a hotplate until the
white SO3 smoke starts dissipating and then place it in an electric furnace and incinerate the contents to ash at 450°C. After incineration,
add 5 mL of hydrochloric acid (1 + 2) to the residue and evaporate it to dryness on a water bath. Add 10 mL of 1 mol/L nitric acid and
apply heat to dissolve the sample. After letting it cool, measure 20 mL of the digest solution. (Reference: Food Sanitation Inspection
Guidelines – Physics and Chemistry, 2005, supervised by the Japanese Ministry of Health, Labour, and Welfare)

(2) Wet Digestion Method Product Evaluation
Weigh 0.2 g of the sample in a Kjeldahl flask. Add sulfuric acid, nitric acid, and hydrogen peroxide to the flask and heat it on a heating
mantle (at about 300°C) to digest the sample. The contents will become black with carbon and white SO3 smoke is emitted. After the
solution turns black with carbon, add more nitric acid and hydrogen peroxide and continue heating (at about 350°C). Repeat this process
until the contents turn pale yellow. After letting the flask cool, measure 20 mL of the solution. (Reference: BS EN1122 Method A:2001)
(3) Microwave Digestion Method
Weigh 0.2 g of the sample in a digestion vessel. Add nitric acid and hydrogen peroxide and seal the vessel. Digest the sample in
microwave sample pretreatment unit. After letting the digestion vessel cool, measure 20 mL of the digest solution. Note: For samples Product Information
containing large amounts of coexisting components, such as additives, use a small amount of hydrofluoric acid.
(Reference: US EPA SW-846 Method 3052)

Analytical Conditions and Results

Analytical Results Analytical Conditions
Analytical results are shown in Table 1. Good results were obtained, with lead (Pb) and Instrument: ICPE-9000
cadmium (Cd) results from dry incineration, cadmium (Cd), total chromium (Cr), and High frequency output: 1.2 kW
mercury (Hg) results from wet digestion, and results for all elements from microwave Plasma gas flowrate: 10 L/min
digestion consistent with certified values.
Auxiliary gas flowrate: 0.6 L/min
Discussion Carrier gas flowrate: 0.7 L/min
The ICP emission spectrometer enabled measuring trace components with good precision. Sample introduction: Coaxial nebulizer
Nevertheless, Hg results were low for dry incineration, presumably due to scattering at high Spray chamber: Cyclone chamber
temperature and Pb results were low for wet digestion, presumably due to precipitation of lead Plasma torch: Mini torch
sulfate formed from reaction with the sulfuric acid used for digestion. Therefore, an appropriate Observation method: Axial
sample pretreatment method must be selected based on the elements being measured.
Table 1 Quantitation Results of Polyethylene Unit:mg/kg
sample BCR680 BCR681
Pretreatment Microwave Certified Microwave Certified
Dry incineration Wet digestion Dry incineration Wet digestion
Element digestion value digestion value
Cd 141 140 140 140.8 21.0 21.4 21.7 21.7
Pb 105 0.2 108 107.6 13.1 0.2 13.5 13.8
Cr 105 112 112 114.6 16.2 17.2 17.5 17.7
Hg 0.2 24.0 25.6 25.3 0.2 4.3 4.6 4.5
As 28 31 30 30.9 4 4 4 3.93

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