Application of scanning electron microscopy and energy-dispersive X-ray analysis to the solution behaviour of Zn—insulin: precipitation phenomena

Abstract

Scanning electron microscopy (SEM) has been applied in combination with energy dispersive X-ray analysis (EDAX) to identify and analyse particles or particulate matter, occasionally present in clear neutral Zn—insulin solutions. SEM photographs revealed the existence of three different types of precipitate, consisting of particles with a crystalline, amorphous or gel-like nature, respectively. At present, it is not clear which conditions lead specifically to each of these three types of precipitate. The advantages of the EDAX method are shown. The technique enables semi-quantitative analysis to be performed on a single particle as small as 0.2 μm. It was demonstrated with the EDAX method that the particles occasionally found in clear Zn—insulin solutions contain insulin as well as Zn in roughly the same ratio as in the insulin starting material. It is concluded that the EDAX method has great potential in pharmaceutical technology, inter alia for the analysis of emulsion systems (in the frozen state), as well as suspensions and particulate matter in injection fluids. This technique is particularly useful in the latter case, due to its applicability to extremely small sample sizes.