Alternative Solvents for Extractables and Leachables Evaluation - Pharmaceutical Technology

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Alternative Solvents for Extractables and Leachables Evaluation
The authors examine alternative solvents for evaluation of process components that provide extraction equivalence and do not interfere chromatographically.

Pharmaceutical Technology
Volume 37, Issue 8, pp. 51-53

Materials and methods
Polytetrafluoroethylene (PTFE)-lined polypropylene (PP) caps were extracted with 25 mL of each of the following surfactants: 1% nonionic, octylphenol ethoxylate surfactant (Triton X-100, Dow Chemical); 0.1% polysorbate 80 (PS 80); and 0.1% polysorbate 20 (PS 20). The same caps were also extracted with the following two alternative solvents: 60% IPA and 15% ethylene glycol monobutyl ether (EGMB). The caps were submerged in each solvent at 40 C at ambient relative humidity for seven days. The resulting extracts were tested by gradient HPLC using a time-of-flight (TOF) LC–MS (Agilent 6500 series) equipped with a multimode source (electrospray and atmospheric pressure chemical ionization) using positive ionization. Data were acquired using scan mode with a range of 80 to 1500 m/z and then by extracting ions that corresponded to the compounds of interest.

The PP caps were chosen for this experiment due to the presence of known additives that could be easily tracked during extractables screening. Compounds previously observed through extractables studies that were targeted in this experiment include a di-tert-butyl(phenyl)phosphite (Irgafos 168, BASF); a phosphate oxidative degradant of Irgafos 168; ethylene bis(heptadecanamide); pentaerythritol tetrakis 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1010, BASF); and erucamide. Determination of extraction efficiency equivalence was made by comparing the responses for each of the targeted extractables observed in each solvent.

Figure 1: Liquid chromatography–mass spectometry (LC–MS) time-of-flight (TOF) multimode positive total ion chromatograms (visual representation). (a): 60% isopropanol (IPA) and 15% ethylene glycol monobutyl ether (EGMB) (gray/red), 0.1% polysorbate (PS) 20 (green), 0.1% PS 80 (blue), and 1% octylphenol ethoxylate surfactant (Triton X-100, Dow Chemical) (purple). (b): 0.1% PS 80 (blue) and 60% IPA (gray). (ALL FIGURES ARE COURTESY OF THE AUTHORS)
Results and discussion
Figure 1a presents a visual representation overlay of LC–MS total ion chromatograms (TIC) of all the solvents used for the extraction study. The total ion chromatograms of the 60% IPA and 15% EGMB are similar; therefore, they cannot be distinguished in the figure but are shown as the gray/red line. Figure 1b presents a visual representation of just the overlay of 0.1% PS 80 and 60% IPA to show that any potential extractables would be masked by the PS 80 interference. Interferences are also observed with 0.1% PS 20 and 1% Triton X-100 as shown in Figure 1.

Figure 2: Results for the seven-day extraction study on polypropylene (PP) caps showing extractables of common PP additives using five different types of extraction solvents; IPA is isopropanol, EGMB is ethylene glycol monobutyl ether, Triton X-100 (Dow Chemical) is a nonionic octlyphenol ethoxylate surfactant, Irgafos 168 (BASF) is di-tert-butyl(phenyl) phosphite, Irganox 1010 (BASF) is 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.
Figure 2 presents the concentration results in g/mL of each extractable compound detected versus the type of solvent. Concentrations were estimated based upon the average of the responses of the reserpine system suitability standards. As Figure 2 indicates, not all of the compounds of interest were extracted in each of the solvents. Irgafos 168 and Irganox 1010 were extracted in both 60% IPA and 15% EGMB while ethylene bis(heptadecanamide) was only extracted in the 60% IPA solvent. Irgafos 168, Irganox 1010, and ethylene bis(heptadecanamide) were not extracted in the 0.1% PS 20, 0.1% PS 80, and 1% Triton X-100 solvents. Erucamide was extracted in all solvents. Irgafos 168 phosphate results were not presented because concentrations were similar to the blank concentrations.

Figure 3: Comparison of extractables of common polymer additives using 60% isopropanol (IPA) and 1% polysorbate 20 extraction solvents in two types of polymeric bioprocessing bags; DTBHP is bis(2,4-di-tert-butyl) hydrogen phosphate, Irgafos 168 phosphate is a common degradant of di-tert-butyl(phenyl) phosphite (Irgafos 168, BASF).
Based on the study results, 60% IPA was shown to be the worst-case model solvent for the extraction study because it extracted all of the compounds of interest except for Irgafos 168 phosphate. Not only did the 60% IPA extract the same compounds as the surfactants, it also extracted additional compounds that the surfactants did not extract. These results were comparable to findings from a related study (5) performed in 2011 in which two types of bioprocessing bag films were submerged for seven days at 40 C/ambient relative humidity in various types and strengths of solvents, as shown in Figure 3. Compounds that were targeted in the related study included bis(2,4-di-tert-butyl)hydrogen phosphate, erucamide, palmitamide, stearamide, and Irgafos 168 phosphate. The study also showed that 60% IPA had a greater extraction efficiency compared to the other solvents evaluated including 1% PS 20. Due to carryover issues associated with the 1% PS solutions, 0.1% PS solutions were used to perform the study using PP caps.

In addition to having greater extraction efficiency, as demonstrated in two separate studies using two different types of material, 60% IPA was also shown to eliminate interferences observed in the sample chromatography of surfactants. The use of extraction solvents that do not pose significant chromatographic interferences is critical so that potential extractable compounds are not missed during the extractables screening. In this case, erucamide was extracted in all of the solvents and was tracked using extracted ion analysis based upon the total ion chromatogram of the 60% IPA solvent. To perform extracted ion analysis, the ion of interest must be known. If only the total ion chromatograms of the surfactant solvents were used to screen for potential extractable compounds, and IPA was not used as one of the extraction solvents, erucamide would have been missed in the chromatograms of the surfactants. Erucamide elutes at approximately 7.7 minutes in Figure 1.


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