Quantifying the cleanliness of glass capillaries |
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Authors: | Charles L Bowman |
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Institution: | (1) Dept. of Biophysical Sciences, School of Medicine, State University of New York at Buffalo, 14214-3005 Buffalo, NY;(2) Veterans Administration Medical Center, Buffalo, NY |
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Abstract: | I used capillary rise methods to investigate the lumenal surface properties of quartz (fused silica, Amersil T-08), borosilicate
(Corning 7800), and high-lead glass (Corning 0010) capillaries commonly used to make patch pipets. I calculated the capillary
rise and contact angle for water and methanol from weight measurements. The capillary rise was compared with the theoretical
maximum value calculated by assuming each fluid perfectly wetted the lumenal surface of the glass (i.e., zero contact angle,
which reflects the absence of surface contamination). For borosilicate, high-lead, and quartz capillaries, the rise for water
was substantially less than the theoretical maximum rise. Exposure of the borosilicate, lead, and quartz capillaries to several
cleaning methods resulted in substantially better—but not perfect—agreement between the theoretical maximum rise and calculated
capillary rise. By contrast, the capillary rise for methanol was almost identical in untreated and cleaned capillaries, but
less than its theoretical maximum rise. The residual discrepancy between the observed and theoretical rise for water could
not be improved on by trying a variety of cleaning procedures, but some cleaning methods were superior to others. The water
solubility of the surface contaminants, deduced from the effectiveness of repeated rinsing, was different for each of the
three types of capillaries examined: Corning 7800>quartz>Corning 0010. A surface film was also detected in quartz tubing with
an internal filament. I conclude that these borosilicate, quartz, and high-lead glass capillaries have a film on the lumenal
surface, which can be removed using appropriate cleaning methods. The surface contaminants may be unique to each type of capillary
and may also be hydrophobic. Two simple methods are presented to quantitate the cleanliness of glass capillary tubing commonly
used to make pipets for studies of biological membranes. It is not known if the surface film is of importance in electrophysiological
studies of biological membranes. |
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Keywords: | Patch clamp electrophysiology surface tension micropipets ion channels capillary rise |
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