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Fill volume as an indicator of surface           heterogeneity in glass vialsMatthew M. Hall, Associate Professor of Bioma...
The interior surface of a glass vial can be non-   uniform due to manufacturing processes                              Ima...
Standard tests for evaluating chemical stability arean average measure of the glass vial surface                          ...
Hypothesis: The heel region is a primary contributor tocorrosion processes with converted glass vialsExperiment:- Nine via...
8.5The pH of conditioned WFI is                                                          1dependent on fill volume        ...
Extractables results support                                                                    1.0hypothesis about heel r...
3.0Extractables results supporthypothesis about heel region(continued)                                                    ...
Conclusions  • Results of this study indicate that the heel region of vials made from converted    glass tubing can be mor...
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Fill volume as an indicator of surface heterogeneity in glass vials (expanded)

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This presentation summarizes a recent study conducted at Alfred University that examined the corrosion of glass vials using a modified version of the hydrolytic resistance test. Vials made from converted glass tubing were filled with increasing incremental volumes of WFI and then autoclaved. The recovered liquid was analyzed for shifts in pH and the extractables were measured using ICP-OES. The results support the hypothesis that the heel region is a primary contributor to corrosion of glass vials made from converted tubing.

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Fill volume as an indicator of surface heterogeneity in glass vials (expanded)

  1. 1. Fill volume as an indicator of surface heterogeneity in glass vialsMatthew M. Hall, Associate Professor of Biomaterials & Glass ScienceKazuo Inamori School of Engineering at Alfred UniversityE-mail: hallmm@alfred.edu
  2. 2. The interior surface of a glass vial can be non- uniform due to manufacturing processes Image taken from Stevanato Group web site Condensation Volatilization DiffusionIntense, localized heating during the conversion process can lead to modifications of the glass vialsurface through a combination of possible mechanisms, including mass transport driven by thermalgradients, evaporation of volatile species, and condensation of vapors on the interior surface.Glass vials produced from converted tubing experience the greatest heating in the heel and shoulder.The altered surface chemistry of these regions can potentially impact properties, including chemicalstability.
  3. 3. Standard tests for evaluating chemical stability arean average measure of the glass vial surface Test medium is in contact with the shoulder, body, and heel regions in standard hydrolytic resistance testsStandard hydrolytic resistance tests are quite useful for identifying drifts in a manufacturingprocess, but they may be of limited use for assessing the chemical stability of glass vialssince the primary regions of interest (heel and shoulder) represent a minority of the interiorsurface.In this study, we evaluated a simple modification to the standard hydrolytic resistance test.Vials were filled with incrementally increasing volumes of WFI to assess the possibleheterogeneity of the interior surface.
  4. 4. Hypothesis: The heel region is a primary contributor tocorrosion processes with converted glass vialsExperiment:- Nine vial types made from converted glass tubing were obtained from four different manufacturers- Vials were a mixture of 33 and 51 expansion Type I glass- None of the vials were subjected to a sulfate dealkalization treatment- One of the vial types (#6) was from a lot that failed the standard hydrolytic resistance test- One of the vial types is an amber glass- Each vial type was incrementally filled with WFI in volumes ranging from ~0.5 mL up to near maximum fill capacity using a semi-automated filling system (Watson-Marlowe, Flexicon FF15)- Five samples were prepared for each fill volume/vial type condition- Filled vials were autoclaved at 121 C for 1 h- Recovered liquid (called “conditioned WFI”) was measured for pH using a combination glass electrode and extractables using ICP-OES
  5. 5. 8.5The pH of conditioned WFI is 1dependent on fill volume 2 8.0 3Mean pH generally decreases 4with increasing fill volume 5 7.5 6Vial type that failed the hydrolytic 7resistance shows elevated pH 8 7.0over the entire range 9 Mean pHBehavior suggests that elevated 6.5pH at low fill volumes is due toenhanced sensitivity of the heelregion to corrosion 6.0Decrease in mean pH with 5.5increasing fill volume is due to adilution effect 5.0Interesting to note that some vialtypes may show evidence ofincreased corrosion near the 4.5shoulder region 0 2 4 6 8 10 Fill Volume (mL)
  6. 6. Extractables results support 1.0hypothesis about heel regionIn general, highest level of 0.9extractables observed for lowest fillvolumes; increasing fill mostly dilutes Correlation Coefficientthe contribution of the heel region 0.8Highest levels of extracted sodiumcorrelated with highest levels of 0.7 p=extracted silicon 0.00586Spearman rank correlation analysis 0.6demonstrates varying pattern ofdissolution behavior as a function offill volume p = 0.0141 Al-B Al-Na Al-Si 0.5- p value for all tested pairs <<0.001 except where noted p = 0.0791 B-Na B-Si Na-Si- Analysis performed on extractables data sampled from increasing fill 0.4 volume ranges ≤1 ≤2 ≤4 ≤ 10- Change in correlation coefficients for aluminum pairs implies that Fill Volume Range (mL) corrosion behavior is a function of fill volume
  7. 7. 3.0Extractables results supporthypothesis about heel region(continued) 2.5Ratio-based analysis of extractables B:Na Molar Ratio in Conditioned WFIresults also supports non-uniformcorrosion behavior 2.0For example, the figure to the rightplots the molar ratio of B:Na inconditioned WFI versus fill volume 1.5Horizontal line would be observed ifcorrosion behavior was independent 1.0of fill volumeNo clear pattern observed amongstthe various vial types, but non-linear 0.5 1 2 3behavior is clearly 4 5 6observed, particularly for fill volumes 7 8 9less than approximately 4 mL 0.0 0 2 4 6 8 10 Fill Volume (mL)
  8. 8. Conclusions • Results of this study indicate that the heel region of vials made from converted glass tubing can be more susceptible to corrosion • Mean pH of conditioned WFI generally decreases with increasing fill volume • Highest level of extractables generally observed for lowest fill volumes; increasing fill volumes dilute species extracted from the heel region • Correlation analysis and ratio-based analysis of extractables data shows that pattern of dissolution behavior varies depending on fill volume • Caveats: • Surface area-to-volume ratio changes as a function of fill volume • Geometry of vials can vary depending on vial type • Condensate formation on upper region of vial during autoclaving could be a potential contributor to corrosion • Results should not be taken as an indicator of relative performance of various vial typesMatthew M. Hall, Associate Professor of Biomaterials & Glass ScienceKazuo Inamori School of Engineering at Alfred UniversityE-mail: hallmm@alfred.edu

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