Elsevier

Analytica Chimica Acta

Volume 769, 26 March 2013, Pages 22-29
Analytica Chimica Acta

Accurate measurement of bromine contents in plastic samples by instrumental neutron activation analysis

https://doi.org/10.1016/j.aca.2013.01.037Get rights and content

Abstract

Accurate measurements of bromine contents in plastic samples were made by the direct comparator instrumental neutron activation analysis (INAA). Individual factors affecting the measurements were comprehensively evaluated and compensated, including the volatility loss of bromine from standard comparators, the background bromine level in the filter papers used for preparation of the standard comparators, nuclear interference, γ-ray spectral interference and the variance among replicates of the samples. Uncertainty contributions from those factors were thoroughly evaluated and included in the uncertainty budgeting of the INAA measurement. 81Br was chosen as the target isotope, and the INAA measurements for bromine were experimentally confirmed to exhibit good linearity within a bromine content range of 10–170 μg. The established method has been applied to the analysis of eight plastic samples: four commercially available certified reference materials (CRMs) of polyethylene and polystyrene and four acrylonitrile butadiene styrene (ABS) samples prepared as the candidate reference materials (KRISS CRM 113-01-012, -013, -014 and -015). The bromine contents of the samples were calculated at three different γ-ray energies and compared, showing good agreement. The results of the four CRMs also showed good consistency with their certified values within the stated uncertainties. Finally, the bromine contents of the ABS samples were determined with expanded uncertainties (at a 95% level of confidence) between 2.5% and 5% in a bromine content range of 25–900 mg kg−1.

Highlights

► Volatility loss of bromine from solution pipetted onto filter paper was ignorable. ► Good linearity of INAA was confirmed within a bromine content range of 10–170 μg. ► Variation of measured concentrations among samples was major source of uncertainty.

Introduction

Bromine is typically contained in various plastics in the form of brominated flame retardants (BFRs). However, reports of the hazards of BFRs have been steadily issued [1], [2], [3], and their use has recently been restricted by such regulations as the restriction of hazardous substances (RoHS) directive [4]. The RoHS directive is a representative piece of environmental regulation that restricts the use of two specific families of BFRs, polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs), in electrical and electronic equipment to less than 0.1% by weight. In response to such regulation, measurement techniques for PBBs and PBDEs in plastic materials are in increasing demand. Along the same lines, the measurement of total bromine is emerging as a simple and useful screening tool for brominated compounds. There are some analytical techniques fit for this purpose: XRF [5], pyrohydrolytic ion chromatography [6], [7], [8], and flow-injection coupled inductively coupled plasma-mass spectrometry [9]. The first feature required for these techniques is quick screening, but the validation and/or verification of those methods by using certified reference materials are still important. In 2009, the pyrohydrolytic ion chromatography was proposed as a new protocol for the screening of total bromine in polymers and electronic products, and some inter-laboratory studies were performed for the validation of the method [8], [10]. At the right moment, we prepared some candidate certified reference materials for the analysis of hazardous elements in acrylonitrile butadiene styrene (ABS) polymers. This study was carried out to certify bromine contents in those reference materials and to provide materials for the inter-laboratory studies.

Instrumental neutron activation analysis (INAA) is one of the most reliable methods for measuring the total bromine, regardless of chemical form. It does not require complicated sample digestion steps, which minimizes the possibility of analyte loss and contamination. It is less strongly affected by the matrix of the sample because of the high penetration power of neutrons and γ-rays and is not affected by the chemical and physical states of the analyte elements [11]. The processes involved in the measurement are physically well understood. Thus, INAA is considered a primary method for elemental analysis by the Consultative Committee for Amount of Substance (CCQM) in the Bureau International des Poids et Mesures (BIPM) [11]. INAA has been successfully applied to bromine measurement in not only plastic samples but also biological and food samples [12], [13], [14]. It also has been used as a reference method to validate newly devised sample preparation or measurement methods [15], [16]. R.R. Greenberg presented an excellent set of guidelines on the individual factors affecting INAA and the uncertainty in general [14], [17]; but the detailed considerations specific to bromine measurements were limited.

In this study, the factors affecting bromine measurement by INAA were exhaustively accounted for, evaluated and considered in the uncertainty budget. The direct comparator INAA method [11] applied provided the highest degree of accuracy by irradiating and counting the samples and the calibration standards under the same conditions. The established method was applied to the measurement of total bromine in the ABS samples.

Section snippets

Apparatus

A digital analytical balance (MX5, Mettler Toledo, Greifensee, Switzerland) was used to weigh the samples. The specification of the balance was as follows: maximum load of 5.1 g and readability, repeatability and linearity of 1 μg, 0.9 μg and 2 μg, respectively. The height of the draft shield of the balance was not sufficient to load a syringe on the balance pan to weigh the mass of the bromine standard solution. Therefore, the draft shield was extended by replacing the original cap with an

On the preliminary irradiation

As mentioned in experimental Section 2.3.1 volatile loss of acidified bromine compounds was checked. Decay corrected specific count rates of the sample filter papers with and without the NH4OH treatment were compared. The mean decay corrected specific count rates at 776.5 keV for the NH4OH treated and un-treated sample filter papers were (285.8 ± 2.0) mg−1 s−1 and (287.6 ± 1.9) mg−1 s−1, respectively. The values following “±” are standard deviations of the means. Both the results were not different in

Conclusion

The performance of INAA method for the determination of total bromine in ABS plastics has been assessed. Factors affecting bromine measurement in the INAA were thoroughly investigated theoretically or experimentally. The possibility of volatility loss of bromine due to the acidification was investigated and found to be negligible under the experimental conditions described in this paper. The background bromine level was determined and corrected for the standard comparators used for calibration.

Acknowledgements

This work was supported by the Korea Research Institute of Standards and Science (KRISS) under the project “Establishing Measurement Standards for Food and Environmental Analysis”, grant 12011026, and National Research Foundation of Korea (NRF) grant 20090078333 funded by Korean Government (MEST).

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