Pharma glass defects - 50. Water Spot

Welcome to part 50 of “Pharma glass defects”, a series devoted to visual defects that may be observed in pharma glass containers.  If you’ve been following the series, you know that I have been focusing on tubular glass vials since that is my main area of interest.   However, we’ve reached the end of the defect list for tubular vials, and so I’ll need to shift gears to a related topic to keep this series going. 

The subject of today’s post is the Water Spot defect.  A Water Spot is described as “white circular residue on the internal or external surface of the glass”.  As the name implies, the Water Spot defect may result from the drying of a droplet of residual water on the vial surface. 

So where is the white residue associated with a Water Spot coming from?  It depends on the source of the water droplet.  For example, the tubular converting process generally relies on natural gas burners to heat the glass, and water vapor is a significant by-product of the combustion process.  Water can potentially condense from the humid environment onto the converting equipment and drip onto vials.  I wouldn’t necessarily expect this to be high purity water, and so the residue of the resulting Water Spot might be crossing a line into a Contamination defect. 

Condensation of water droplets on glass vials being stored in a warehouse with large fluctuations in temperature and/or humidity is another potential source of Water Spots.  The atmospheric water condensing on the glass surface should be relatively pure in this case.  However, these same water droplets are capable of extracting inorganic elements from the glass surface that produce the residue of a Water Spot (see Footnote 1). 

One last example is residual water from the washing of vials. I would normally be thinking about ready to use vials in this context, although I recently came across another interesting case that I wanted to share.  Valentin Mayer-Eichberger from Isotronic GmbH sent me an image of a Water Spot defect they found while working with a customer on a new visual inspection system (see Figure 1).  This Water Spot is the result of washing freshly formed vials prior to the annealing process, presumably to remove low durability deposits on the interior surface created during the tubular conversion process.  We’re again dealing with high purity water in this case, and so the residue should principally be the result of inorganic extractables from the glass surface (see Footnote 2). 

A Water Spot is considered a Minor defect if it has a diameter greater than 0.8 mm – otherwise, it’s an Acceptable Imperfection.  However, I want to stress that some attention should ideally be given to confirming that the white residue you’re seeing is truly a Water Spot.  This can be evaluated using tools such as energy-dispersive X-ray spectroscopy and infrared/Raman spectroscopy.

Questions or comments? – please leave them below of feel free to directly contact me.

Footnotes

1.            The possibility of water condensing on the surfaces of glass vials being stored over extended periods of time has implications that go beyond just visual defects.  For example, refer to my prior posts on static fatigue and shelf life of pharma glass.

2.            As a side note, I would consider the persistent presence of Water Spot defects in RTU vials to be a potential issue for another reason beyond just cosmetics.  Glass vials containing excessive amounts of residual water before going into high temperature depyrogenation may have an increased risk for glass delamination.  See the below reference for more information: Ditter D, Mahler H-C, Gohlke L, Nieto A, Roehl H, Huwyler J, Wahl M, Allmendinger A (2018).  Impact of vial washing and depyrogenation on surface properties and delamination risk of glass vials.  Pharmaceutical Research, 35: 146.

About the Author

Matthew Hall is Technical Affairs Director for Corning Pharmaceutical Technologies , a manufacturer of primary glass packaging for parenteral drug products. Based in upstate New York, Dr. Hall serves as a technical expert supporting business operations, sales, and marketing and educating customers on pharmaceutical glass packaging. He is a member of the Parenteral Drug Association and the International Society of Pharmaceutical Engineering.