Quicker Isn’t Always Better: Investigating Dissolution Dynamics of a Slow-Release Vitamin C Product

Slow release dietary supplement capsules got increasingly popular in the last decade due to their superior efficiency in nutrient uptake compared to their immediate-release counterparts. Understanding the dissolution dynamics plays an important role in designing and developing such products. In this application report, dissolution of a slow release vitamin C product was investigated using particle size analysis. By analyzing the particle size distribution in water over an extended time period, it was possible not only to determine the length of the main release phase, but also to visualize the disintegration of the particles and gather hints on structural features.


Slow-release and retard dietary supplement products have several advantages compared to the immediaterelease tablets. On one hand, as the nutrients are not released in the stomach they do not cause nausea, and therefore they don’t have to be taken with food. On the other hand, some nutrients are only absorbed by the body in small doses; therefore an extended release time leads to a higher efficiency in uptake.

One prime example is vitamin C (ascorbic acid). It is one of the most widely consumed dietary supplements around the globe due to its role in several essential biological functions such as wound healing and collagen synthesis. However, research found, that ascorbic acid taken in dietary excess is rapidly excreted in the urine[1].

In order to optimize the performance of these capsules it is of paramount importance to understand their dissolution process. Accordingly, there are several well established methods for determination of the amount of dissolved vitamin C, as well as for the measurement of undissolved particles.

Laser diffraction is a useful and easy-to-use tool for the study of dispersed particles. By setting up a series of repeated measurements in water, the change in particle size can be followed throughout an extended time period.

The method is not only an opportunity for further development of supplements, but also convenient for regular quality checks.


1. Urinary oxalate excretion after large intakes of ascorbic acid in man. Schmidt, Karl-Heinz, et al., et al. 3, s.l. : Oxford University Press, 1981, The American journal of clinical nutrition, Bd. 34, S. 305- 311.

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