Analytical methods for additives in plastics

GC chromatographic retention times were recorded to facilitate identification by retention index data. Chromatographic methods were used to indicate the presence of any impurities in the commercial chemicals. Samples of the reference substances are available on request and the collection of spectra and other information will be made available in printed format and on-line through the Internet. Van Lierop and co-workers [5] give an overview of the work done to establish the reference collection and the spectral atlas, which together will assist enforcement laboratories in the characterisation of plastics and the selection of analytical methods for additives that may migrate. 

Most methods for the determination of additives in plastics come essentially under two headings, namely with or without sample preparation. The following eight analytical categories are thus distinguished ... 

Only with such modern analytical tools is it possible to give correct answers to the many problems occurring in interactions between plastics and food. Some of the results obtained with ill-suited analytical methods for high molecular additive mixtures can be re-evaluated in this manner. In addition, answers can be given about the mechanism of degradation and the nature of decomposition products (Chapter 3). Last but not least a much faster determination of low migrants concentrations is possible in many cases. This is an important assumption for quality assurance with low thresholds of concentrations for regulation. 

Selected testing and analytic techniques (Table 10.5) are briefly described in the following sections. An understanding of each method is necessary for the proper application and interpretation of results. Some of these techniques are specific to non-fluori-nated thermoplastics and may require modification when applied to fluoropolymers. Examples of the results of applying some of these techniques to fluoroplastic are presented to illustrate their use. The reader is referred to ASTM methods for additional details regarding the measurement of properties and characterization of the plastics. 

It has been known for a number of years that FD-MS is an effective analytical method for direct analysis of many rubber and plastic additives. Major components and impurities in commercial additives can be assessed quickly, and the FD-MS data can be used to help determine what (if any) additional analytical characterization is needed. Lattimer and Welch showed that FD-MS gives excellent molecular ion spectra for a number of polymer additives, including rubber accelerators (diWocarbamates, guanidines, benzothiazyl, and thiuram derivatives) antioxidants (hindered phenols, aromatic amines) p-phenylenediamine-based antiozonants, processing oils, and phthalate plasticizers. Zhu and Su characterized alkylphenol ethoxylate surfactants by FD-MS. Jackson et al. analyzed some plastic additives (hindered phenol antioxidants and a benzotriazole UV stabilizer) by FD-MS. ... 

Depth concentration measurement is an important application of surface analytical methods. Examples are depth distribution of additives in plastics, or interface analysis where polymers are in contact with metals or ceramics. All surface methods with a good depth resolution (XPS, AES, SIMS) are suitable for depth or profile measurements. Complete multilayer coating systems require analytical methods that are applicable to small sample sizes and low concentrations. Techniques for obtaining chemical composition and component distribution depth profiles for automotive coating systems, both in-plane (or slab) microtomy and cross-section microtomy, include /xETIR, /xRS, ToE-SIMS, optical microscopy, TEM, as well as solvent extraction followed by HPLC, as illustrated by Adamsons et al. [5]. Surface and interface/interphase analysis can now be done routinely on both simple monolayer coatings and complex multicomponent, multilayered... 

Analytical techniques for the quantitative determination of additives in polymers generally fall into two classes indirect (or destructive) and direct (or nondestructive). Destructive methods require an irreversible alteration to the sample so that the additive can be removed from the plastic material for subsequent detention. This chapter separates the additive wheat from the polymer chaff , and deals with sample preparation techniques for indirect analysis. 

In addition, as the PVC tubes contain a plasticizer and stabilizers of which producers do not give information this needs to be taken into account, particularly, when PVC additives may give problems in analytical methods. In this case, other materials may constitute a better choice. The supplier also informs the users that decaying organic material may influence N-NH4 analysis in auto-analyser systems. Another important consideration on polysulfone fibres application for soil solution sampling is the apparent retention of colloidal Fe at the fibre interface (Jones and Edwards, 1993b) which is not entirely clear and should not to be overlooked, because of the high retention of colloidal Fe and its role in the translocation of PTE in soil. 

Alternatively, the container may contain an opacifying agent, e.g., titanium dioxide. The use of multilayered bags was demonstrated to inhibit photochemical decomposition of vitamin E in TPN fat emulsions (Allwood and Martin, 2000). PVC films discolor on irradiative exposure due to photochemical degradation of the polymer (Hollande and Laurent, 1997). Plastic containers for parenteral use may contain several additives, e.g., antioxidants, stabilizers, plasticizers, lubricants, impact modifiers, and coloring matter when justified and authorized. In an appendix, the European Pharmacopoeia presents a list of plastic additives that may be used (European Pharmacopoeia, 2002). The additives should not be extracted by the contents in such quantities as to alter efficacy or stability of the product or to present any risk of toxicity (European Pharmacopoeia, 2002). However, organic additives extracted in concentrations below the detection limits of the analytical methods authorized by the European Pharmacopoeia may be sufficient to initiate photosensitized reactions in the formulation. 

The optical detection methods applied to microchip-based analysis are, for the most part, similar to those employed in capillary electrophoresis (CE). The main differences, however, are that UV absorbance is not as common and that the microchip format creates the possibility of incorporating additional functionality during the fabrication steps (especially in plastic devices). Each of the optical methods described here includes specific requirements, such as the nature of the analyte and the microchip substrate, and these must be taken into consideration when choosing and implementing a system. 

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