Tag Archives: DVS

Blog

A Survey of Material Science and Physical Characterization Techniques and Equipment for Small Molecules – Part I 

Material science and physical characterization are crucial to ensure drug products’ or drug substances’ identities with measurements and analysis. There are many types of techniques and equipment to do this, each with its own features and qualities. In this blog, the first part of a series, we will review the advantages of a range of techniques and equipment. 

We’ll begin with X-Ray Powder Diffraction (XRPD) or XRD analysis. It is a powerful, non-destructive, and rapid technique for analyzing a wide range of materials (1 µm to 100 mm), including metals, polymers, catalysts, plastics, pharmaceuticals, and other materials. It is used for identification, crystal form characterization, and crystalline content in amorphous products.  

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is useful for the detection of elemental content and elemental impurities. ICP-MS is also 

efficient as it is a multi-element technique. Ions are directly detected by an MS detector rather than by emission of light, as in the case of ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy). The ions are separated by a Quadrupole based on the mass-to-charge ratio. The best detection limits are available for most of the elements in ICP-MS as the number of ions produced is high, and although some spectral interference is seen, these are defined and limited.   

Dynamic Vapor Sorption (DVS) is a gravimetric technique used to measure the change in

 mass of a material in response to changes to surrounding conditions such as temperature or humidity. DVS is primarily used with water vapor but can be applied to other organic solvents as well for the physicochemical characterization of solids.  Some of the most common uses of DVS include:  

  • To determine the sorption isotherm;   
  • To evaluate the hygroscopicity of an API powder;   
  • To compare the hygroscopicity of different solid-state forms: solvates, polymorphs, salts, amorphicity, and cocrystals;  
  • To determine the deliquescence point of a material;  
  • To quantify and qualify the amorphous content in drug substance or excipient, and 
  • To evaluate the efficacy of packaging materials. 

We will wrap up with Differential Scanning Calorimetry (DSC). It is one of the most used thermoanalytical techniques for determining freezing and melting points and phase transitions. Specifically, it measures the heat flow produced by a sample when it is either heated, cooled, or held isothermally at an unchanging temperature. Crystallization behavior and chemical reactions are some other characteristics that can be measured by this technique. 

Our next entry will conclude with a look at Thermogravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), and, of course, the definitive analytical technique, Mass Spectroscopy (both GCMS and LCMS). 

Resources 

Blog

Dynamic Vapor Sorption

Dynamic Vapor Sorption (DVS) is a gravimetric technique used to measure the change in mass of a material in response to changes to surrounding conditions such as temperature or humidity. DVS is primarily used with water vapor but can be applied to other organic solvents as well for the physicochemical characterization of solids. 

DVS was developed by Daryl Williams, the founder of Surface Measurement Systems Ltd., in 1991. The company then delivered the first working DVS instrument to Pfizer in 1992.1 Since then, many other equipment manufacturers have entered the field. 

Figure 1: A DVS isotherm plot indicating sorption and desorption rates and hysteresis. The isotherm shows a typical hysteresis curve where the adsorption phase is almost identical to the desorption phase (i.e. reversible). Note that at 80 %RH, there is net sorption of 0.9% between adsorption and desorption traces. The material appears to be slightly hygroscopic according to the definition in Ph. Eur.2 

Sorption, Desorption, Absorption, and Adsorption
There are five main physical processes that occur during the DVS experiment. The first, sorption, is when a material takes on moisture due to increased humidity. Conversely, desorption is the process that occurs when the material loses moisture due to decreasing humidity. Sorption can be classified as one of two types. Adsorption is moisture that is observed on a surface of a material, while absorption is moisture that has penetrated the surface of a material. The fifth term and the term that relates sorption and desorption is called hysteresis. The overall chart that includes and tracks the sorption and desorption rates and hysteresis is called the isotherm. These curves are crucial for understanding the physicochemical characteristics of a solid, such as porosity, polymorphic change, or liquefying of a sample.2 

Applications 

There are numerous reasons to utilize DVS, and some of the most common within the active pharmaceutical ingredient (API) industry are: 

  • To determine the sorption isotherm;  
  • To evaluate the hygroscopicity of an API powder;  
  • To compare the hygroscopicity of different solid-state forms: solvates, polymorphs, salts, amorphicity, and cocrystals; 
  • To determine the deliquescence point of a material; 
  • To quantify and qualify the amorphous content in drug substance or excipient,3 and 
  • To evaluate packaging materials. 

Of course, there are a variety of other applications in other industries, including for building materials, food science, cosmetics, coatings, and sealants. 

DVS Analysis of APIs
For pharmaceutical development, DVS is used for a variety of applications, including screening early drug and excipient candidates, establishing processing parameters, and identifying packaging and storage requirements (Figure 2).4,5  

 

Figure 2: A DVS isotherm of an API showing that the material started to gain significant mass after exposure to relative humidity values of more than 60 %RH. The change here was irreversible, as demonstrated by the desorption curve. DVS could be a useful tool to suggest storage conditions in terms of humidity contents in the surrounding environment. 

However, due “to the typically slow establishment of an equilibrium, DVS experiments are rather time-consuming.”4 Nevertheless, “water content of solid active pharmaceutical ingredients and excipients, individually and when formulated in pharmaceutical dosage forms, is a parameter that should be monitored throughout the drug lifecycle.”5  

As an analytical technique for APIs, DVS has become a necessary step within drug development and production, reducing issues that can arise during manufacturing, packaging, transportation, solubility, dissolution rate, stability, or storage. AMPAC Analytical’s sister company, SK biotek Ireland Analytical Services, has the experience, technology (including a Surface Measurement System’s DVS Resolution Dual Vapor Gravimetric Sorption Analyser), and support, to assist with this vital testing. Both companies are part of SK pharmteco and can easily transfer your project from either business unit to ensure the most optimal solution and logistical support are provided to meet your product timeline. We invite you to contact our team members and discuss how we can assist with your sorption testing requirements.  

Figure 3: A SMS DVS instrument like the one located at SK biotek Ireland. 

References  

  1. https://surfacemeasurementsystems.com/our-story/ 
  1. Ph. Eur., 2023, 11.2 Edition, Chapter 2.9.39  
  1. https://www.sciencedirect.com/science/article/abs/pii/S0022354915303348 
  1. https://www.sciencedirect.com/science/article/abs/pii/S0022354918302193 
  1. https://www.sciencedirect.com/science/article/abs/pii/S0022354916325230 
  •