Page 30 - Solutions for Plastic Evaluation

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Product Evaluation
Hazardous Substances Hazardous Metals
AA

Evaluation of Plastic Materials Analysis of Cadmium in Plastics Using an AA Spectrophotometer
Atomic absorption (AA) spectrophotometers are able to analyze elements in solution with high sensitivity. Analysis of solid samples, such as
plastics, requires preparing a sample solution using pretreatment methods such as dry incineration or Kjeldahl digestion (wet digestion). In
this case, standard polyethylene samples BCR680 and 681 were prepared by dry incineration and Kjeldahl digestion and results were also
compared to those obtained by ICP emission spectrometry.
(1) Dry Incineration Method
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
Evaluation of Raw Materials 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
white SO3 smoke starts dissipating and then place it in an electric furnace and incinerate the contents to ash at 450°C. After incineration,
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
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
Product Evaluation 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)

Analytical Conditions and Results
Measurement Results
Measurement results were obtained using the flame atomization method. The cadmium (Cd) Analytical Conditions
Product Information obtained using different pretreatment and measurement methods (ICP emission spectrometry). Slit width:0.7 nm
Analytical wavelength: 228.8 nm
calibration curve used for measurements is shown in Fig. 1. Table 1 shows a comparison of data
Measurement mode: BGC-D2
These show that both methods gave results that were roughly consistent with certified values.
Acetylene gas flowrate:1.8 L/min
Given flame atomic absorption spectrophotometry is used and the sample is diluted by 100
Air flowrate:15 L/min
times before measuring, the lower quantitation limit in plastic is 0.5 mg/kg.

Fig. 1 Calibration Curve for Cd by Atomic Absorption Spectrophotometry

Table 1 Quantitation Results of Polyethylene
Dry incineration Wet digestion Certified value
AA ICP AA ICP (mg/kg)
BCR680 140 141 142 140 140.8
BCR681 20.0 21.0 22.0 21.4 21.7

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