When we talk about glass quality, we mostly talk about first hydrolytic class borosilicate glass with different expansion coefficients, which range from 70 type basic glass to 51 type, up to 33 type. What does that mean? Expansion coefficient actually describes the activity of the surface of the glass wall, which relates to the amount of free silanol groups present that can react with analytes and bind them to the glass surface.
70 type glass can be seen as having a surface with about 70% free silanol groups. Additionally, as the following pictures show, the glass surface is not even. Coupled with large number of free silanol groups, these surface imperfections (irregular surface structure as well as scratches and holes) lead to higher surface activity. Higher surface activity increases the amount that a susceptible analyte will stick to, or be adsorbed, on the surface. This problem is further compounded because the degree of adsorption varies over time, particularly when complex matrices are present (for example in the presence of serum). When analysing low concentration of susceptible analytes the percentage of analyte adsorbed is relatively greater and the scale of the problem is compounded. This results in less free analyte available for analysis on the chromatographic system and potentially incorrect results.
Click here for more information.