Method validation Polymer/additive analysis

Compton et al. [18] have worded some (fairly obvious) conditions for the feasibility of a quantitative method (Table 6.4). In developing quantitative methods for polymer/additive analysis Murphy s Law always applies, as also apparent from some of the following Case Studies. Quantitative determinations of new additives should be validated, e.g. by calibration on the basis of more than one mother liquor, repeatability/reproducibility experiments or the use of SPC charts. The analyst must constantly be aware of unwanted interferences. For example, the presence of certain additives, particularly fillers and pigments, may cause serious interferences with the measurement of other additives present [23]. More trivially, contaminations of Chi-massorb 944 residues accumulated in a rotavapour may interfere with subsequent analyses. Care should... 

Whereas the components of (known) test mixtures can be attributed on the basis of APCI+/, spectra, it is quite doubtful that this is equally feasible for unknown (real-life) extracts. Data acquisition conditions of LC-APCI-MS need to be optimised for existing universal LC separation protocols. User-specific databases of reference spectra need to be generated, and knowledge about the fragmentation rules of APCI-MS needs to be developed for the identification of unknown additives in polymers. Method development requires validation by comparison with established analytical tools. Extension to a quantitative method appears feasible. Despite the current wide spread of LC-API-MS equipment, relatively few industrial users, such as ICI, Sumitomo, Ford, GE, Solvay and DSM, appear to be somehow committed to this technique for (routine) polymer/additive analysis. 

Table 8.14. Selection of typical validated company standard in-polymer additive analysis methods...

In the field of polymer/additive analysis various validated procedures (after interlaboratory tests) do exist. Various such procedures have been given in the present text (cfr also Chp. 8.3 for CRM development). Here we just mention the ASTM Standard Method of Test for Carbon-Black in Polyethylene Plastics (E 1603) and the ASTM Test Method for Compositional Analysis by Thermogravimetry (ASTM Standard Method E 1131) [89], which outlines a general technique for analysis of... 

RATIONAL STEP-BY-STEP METHOD DEVELOPMENT AND VALIDATION FOR POLYMER/ADDITIVE ANALYSIS... 

As yet, there are no generally accepted formats for the overall method development of in-polymer additive analysis. However, one may take a lead from the work of Swartz et al. [6], and various other sources [20,80,87,128], who have presented a rationale for the process of successful development of (HPLC-based) analytical methods, their optimisation, and eventually validation. A sequence of steps is necessary in the development of a fully validated method for the analysis of additives in polymeric matrices, in which the user has specified validation parameters and limits, as follows ... 

A comprehensive overview of preconcentration techniques for uranium (VI) and thorium (IV) prior to analysis was published (Prasada Rao et al. 2006). The multitude of off-line techniques that were reviewed includes liquid-liquid extraction, liquid membranes, ion exchange, extraction chromatography, flotation, absorptive electrochemical accumulation, solid-phase extraction (SPE), and ion imprinting polymers. In addition, online preconcentration methods for uranium, thorium, and mixtures of the two are also briefly surveyed. This overview includes over 100 references and is a good source for finding a suitable preconcentration technique with regard to the enrichment factor, retention and sorption capacity, method validation, and types of real samples. The review article focused on samples in which the uranium was already in solution so that digestion procedures for solid samples were not discussed (Prasada Rao et al. 2006). 

In order to obtain quantitative results by HS-GC, the system must be calibrated. Absolute quantitation is not possible. Quantification can be done by the conventional external calibration method with liquids containing the analytes concerned in known concentrations or by means of standard addition. Pausch et al. [958] have developed an internal standard method for solid headspace analysis of residuals in polymers in order to overcome the limitations of external standardisation cfr. Chp. 4.2.2 of ref. [213a]). Use of an internal standard works quite well, as shown in case of the determination of residual hydrocarbon solvent in poly(acrylic acid) using the solid HS-GC-FID approach [959]. In the comparison made by Lattimer et al. [959] the concentrations determined by solid HS-GC exceeded those from either solution GC or extraction UV methods. Solid HS-GC-FID allows sub-ppm detection. For quantitative analysis, both in equilibrium and non-equilibrium conditions, cfr. ref. [960]. Multiple headspace extraction (MHE) has the advantage that by extracting the whole amount of the analyte, any effect of the sample matrix is eliminated the technique is normally used only for method development and validation. 

In the analysis of in-polymer additives, the entire procedure from extraction to quantitation must be validated, as safeguarding against analytical complications. The current methods for detecting and controlling additives still present some serious problems to the industrial analytical community. A first step to be validated is the (analytical) extraction in order to ensure that the additive is extracted quantitatively from the polymer. In practice, 90% or more is usually acceptable. Of course, it is important that whatever the extraction procedure used a known, constant, percentage is extracted without transformation. This requires checking samples of the polymer with known amounts of additive present. Chapters 6.2.3 and 6.2.4 give sufficient evidence that considerable improvement is required in this area. 

We have intended to demonstrate that a flaw spectrum analysis presents a plausible and useful approach to the problem of multiple flaw failure phenomena in solid polymers. Effects of orientation and stress state may be explained by such an approach, but much additional theory and experiments are required to establish the validity of the method. Several obvious shortcomings of the theory can be overcome, in principle, by a more rigorous analysis. The more serious assumptions or limitations which we intend to either remove or justify in future work are as follows. 

Research the type of additives and normal concentrations. Learn about their properties. Do they have a unique element or chemical tag that can be used for quantitative measurements Is an analysis method available from the supplier or in the literature Many sources are available scientific journals, trade journals, technical application sheets from instrument manufacturers and standards compendia. Any method selected must be validated in your own laboratory. Learn as much as possible about the polymer matrix. Thermoplastics can be hot pressed into thin films. Many polymers are solvent resistant, so extraction techniques can be used to isolate the additives. 

Helmroth and co-workers [63] have described a method based on microtoming and GC analysis for studying transport processes of additives in polymers. As a test case, they used a combination of the polymer antioxidant Irganox 1076, LDPE, and the contacting solvent, ethanol [25,46,47,64]. Validation of the method was performed in two steps ... 

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