• different gelling agents
• emulsifying agents
• active ingredients
• pH
• osmolarity

on the rheological behaviour of entire systems can be evaluated..

Zeta Potential Measurements
Zeta potential is a scientific term for electrokinetic potential in colloidal systems such as emulsions. It is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed droplet. The significance of zeta potential is that its value can be related to the stability of emulsions. According to this, the zeta potential is a crucial parameter for the development of stable emulsion systems. Within the development process of novel suspensions and emulsions most time consuming are storage stability studies of different formulations. Zeta potential measurements can accelerate this process, as unstable formulations can be identified much earlier because of an insufficient high zeta potential. Furthermore, the impact of parameters such as particle size, pH and viscosity on the stability of certain formulations can be determined within a few days. Consequently costs and time for storage stability studies can be substantially reduced.

Size Distribution Measurements of the Inner Phase of Emulsions
Size distribution measurements of the inner phase of dispersed systems such as creams and lotions are essential for the development of new cosmetic products. Green River Polymers performs such measurements routinely.

Freeze-Fracture Analyses
In order to characterize the inner structure and phase distribution of emulsion systems in detail Green River Polymers performs freeze-fracture SEM analyses. Based on results obtained we interpret these data and suggest formulation improvements based on them.

Active Ingredient Release Studies
The release rate of active ingredients from topically used formulations within a certain time period is an essential parameter for quality assessment of cosmetic products. As each formulation shows a specific release profile, in vitro active ingredient release studies provide valuable information about the properties of the cosmetic product. Green River Polymers performs such active ingredient release studies from liquid as well as semisolid formulations. The test system we use for such studies is the Franz diffusion cell depending on the type of formulation and the active ingredient to be evaluated, different synthetic or semi-synthetic membranes are used. After a lag-time the release rate is in most cases almost constant i.e. the amount of liberated active ingredient is proportional to the square root of time. Thereby obtained values are important for all further calculations and adjustments during product development..

Bioburden Testing according to Pharm. Eur.
Green River Polymers performs routinely microbial content and bioburden testing according to the method listed in the European Pharmacopoeia (Pharm. Eur.) for liquid, semisolid and solid formulations. As standardized test microorganism we use in particular:

• Staphylococcus aureus
• Candida albicans
• Pseudomonas aeruginosa

Storage Stability Studies
Green River Polymers designs and performs storage stability studies of new formulations with the final immediate packaging intended for marketing. Stability studies usually include long-term (12 months), intermediate (6 months) and accelerated (6 months) testing. Analyses include physical, chemical, biological, and microbiological tests. Green River Polymers is capable of testing all kinds of formulations according to ICH guidelines. Our climatic exposure test cabinets are frequently calibrated. An alarm system including SMS and e-mail alerts ensures that our climatic exposure test cabinets are permanently controlled. In case of any failure a back-up system including an emergency generator and additional climatic exposure test cabinets are available. Temperature and relative humidity (RH) are monitored continuously 365 days a year. Available test conditions are:

• -20°C
• 5°C
• 25°C/60% RH
• 30°C/60% RH
• 30°C/65% RH
• 40°C/75% RH
• photostability

Product analysis during storage stability studies include:

• chemical stability analyses of active ingredients via HPLC, LC-MS, FTIR and NMR analyses
• pH measurements
• rheological analyses
• microbial analyses

• Selection of appropriate and validated analytical methods
• chemical, physical and microbial aspects of stability studies
• Interpretation of test results
• Influence of formulation and packaging on stability
• Regulatory requirements