Understanding Importance of Water Sorption...
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Understanding Importance of Water Sorption Isotherm Shape, Hysteresis, and Models on Pharmaceutical Materials Dr. Daniel J. Burnett Surface Measurement Systems, Ltd. [email protected] 27 September 2016
Transcript of Understanding Importance of Water Sorption...
Understanding Importance of Water Sorption Isotherm Shape, Hysteresis, and Models on Pharmaceutical Materials
Dr. Daniel J. Burnett
Surface Measurement Systems, Ltd.
27 September 2016
Overview
1. Vapor Sorption Techniques• Molecules as Probes • Sorption Mechanisms• Moisture Methods
2. Isotherms• Shape and Hysteresis• Isotherm Modeling• Hydrate Formation
3. Moisture-Induced Phase Changes• Glassy-Rubbery Transitions• Amorphous Content• Raman Spectroscopy
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Characterization of Solids
1. Energy as a Probe• Spectroscopy• Light, x-rays, lasers, etc. • Analytical and structural information
2. Heat as a Probe• Calorimetry• Thermodynamic information
3. Molecule as a Probe• Sorption techniques• Thermodynamic, chemical, and structural Information
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Characterization of Solids
Energy as a ProbeSpectroscopy
-Light, x-rays, lasers, etc. -Analytical and structural information
Heat as a Probe-Calorimetry
-Thermodynamic information
Molecules as a Probe-Sorption techniques
-Thermodynamic, chemical, and structural Information
Energy
Matter
Molecules as a Probe
Molecules Absorbed
Molecules Adsorbed
sam
ple
Vapour molecules
Molecules in Molecules out
Molecules as a ProbeWhere can Vapour Sorption occur?
• On the surface?
• In pores – micro/meso?
• Between the particles (condensation?)
• Sorbed into the bulk?
• Chemically reacted (hydrate formation)?
What can vapour sorption tell me?
• The stability of materials at different vapour concentrations.
• Vapour-solid interactions important for wide range of industries:
food, pharmaceutical, proteins, fuel cells, packaging, high energy materials (explosives), personal care
• Accurately determining water sorption isotherms is critical for proper development and storage of these materials
Quantifying Moisture Content
1. Karl Fischer Titration2. Loss On Drying3. Water Activity Meters4. Near IR5. Humidity Chambers/Desiccator Jars6. Dynamic Vapor Sorption Methods
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Karl Fischer Titration
CH3 OH + SO2 + RN → [RNH]SO3CH3
H2O + I2 + [RNH]SO3CH3 + 2 RN → [RNH]SO4 CH3 + 2 [RNH]I
(RN = Base)
• This reaction consumes water and iodine in a 1:1 ratio. • Coulometric
• Electrical current measured• Good for low moisture contents (<1%)
• Volumetric • amount of reagent to convert water• Sample dissolved into solvent• Moisture contents above 1%
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Loss on Drying
• Sample is weighed, then heated to remove moisture, then weighed again
• Also called moisture balance method• 0 to 100% moisture content range (~0.2% sensitivity)• Drying can be done under vacuum or over desiccant • US and European Pharmacopeia methods• Could use TGA instrumentation
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Water Activity Meters
• Sample is placed into a chamber with a dew point analyzer• Moisture will condense on chilled mirror at defined
temperature related to dew point• Moisture content in air surrounding sample is determined• Determines ‘free’ water, not ‘bound’ water• Automated instrumentation• Often related to microbial growth and product shelf-life• Commonly measured value in food industry
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Near-IR
• Utilize principle that water absorbs certain wave-lengths of light
• first overtone of OH stretching around 6800–7100cm−1
(1470–1408 nm) • Combination band of OH stretching and bending at around
5100–5300cm−1 (1960–11887 nm)
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Desiccator Jars
• Jar Method (Static gravimetric method)• Different jars/chambers at different %RH levels using
saturated salt solutions• Manual technique
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Dynamic Vapor Sorption Methods
• Automated method• Sensitive microbalance• Flow of humidified carrier gas• Constant weight measurement• Temperature control
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Overview
1. Vapor Sorption Techniques• Molecules as Probes • Sorption Mechanisms• Moisture Methods
2. Isotherms• Shape and Hysteresis• Isotherm Modeling• Hydrate Formation
3. Moisture-Induced Phase Changes• Glassy-Rubbery Transitions• Amorphous Content• Raman Spectroscopy
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Typical Water Sorption Data
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Moisture sorption/desorption kinetics (bottom and left axis) and isotherms(top and left axis) for proton exchange membrane (N-117) at 30°C.
DVS- Rice Starch IsothermsDVS Isotherm Plot
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0 10 20 30 40 50 60 70 80 90 100Target RH (%)
Cha
nge
In M
ass
(%) -
Dry
Cycle 1 Sorp Cycle 1 Desorp
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 07 Dec 2001 Time: 4:14 pm File: ricestarch071201_reduced.XLS Sample: rice starch
Temp: 24.8 °C Meth: duncan.sao M(0): 40.5303
Desorption
Sorption
Back to 0 reversible
Hysteresis
Point: from last 3-5 datapoints of each humidity step
Typical Water Sorption Isotherm
Isotherm Types (BDDT)
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• Type I: Lanmuir isotherm; chemisorption
• Type II: Monolayer formation, BET equation
• Type III: Strong sorbate-sorbateinteractions; water often has this behavior
• Type IV: Monolayer formation, BET equation, capillary condensation at high pressures
• Type V: Strong sorbate-sorbateinteracitons; capillary condensation at high pressures
• Type VI: only at liquid Kr temperatures
Adsorption Isotherm Models
Quartz-Surface Adsorption
• Isotherm shape (Type II) and low uptake indicate surface dominated sorption
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0
0.1
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1
0 10 20 30 40 50 60 70 80 90 100
Cha
nge
In M
ass
(%) -
Dry
Target RH (%)
DVS Isotherm Plot
Cycle 1 Sorp
© Surface Measurement Systems Ltd UK 1996-2001DVS - The Sorption Solution
Date: 05 Mar 2003Time: 3:47 pmFile: 03-05-03-quartz-gt-106.xlsSample: Quartz > 106 microns
Temp: 24.9 CMeth: BEToctane.SAOM(0): 5.9975
Lactose Isotherms
0.00
0.00
0.00
0.01
0.01
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0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
RH (%)
Cha
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in m
ass
(%)
WaterMethanolEthanolPropanolButanol
Effect of Sorbate Polarity
• Isotherm changes from Type II to Type III
Amorphous Carbon
• Hysteresis gap suggests mesoporosity (2 to 50 nm)• Capillary Condensation
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0
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0 10 20 30 40 50 60 70 80 90 100
Cha
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In M
ass
(%) -
Ref
Target % P/Po
DVS Isotherm Plot
Cycle 1 Sorp Cycle 1 Desorp
© Surface Measurement Systems Ltd UK 1996-2014DVS - The Sorption Solution
Date: 18 Jul 2016Time: 1:51 pmFile: Sample: Probe a
Water Sorption Isotherm for amorphous porcine lipase : fitted to D'Arcy–Watt adsorption model
BUT WHERE IS ALL THE SURFACE?POWDER IS 10um PARTICLES MUST BE ~2nm DIAMETER?
Surface vs Bulk Sorption
The water sorption isotherm of an amorphous protein such as BSA has three features (knee, plateau, upswing) and coincidentally resembles the shape of a BET type II physical adsorption isotherm
Water Sorption Isotherms-Model Amorphous Proteins
Amorphous proteins interact in a truly complex way with water that cannot be captured by adsorption models or simple solution approaches as the system is not even in equilibrium
Water Sorption Isotherms-Model Amorphous Proteins
Polymer-Solvent Isotherm Models
DVS Change In Mass (dry) Plot
-0.5
0
0.5
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0 200 400 600 800 1000 1200 1400
Time/mins
Cha
nge
In M
ass
(%) -
Dry
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Targ
et R
H (%
)
dm - dry Target RH
© Surface Measurement Systems Ltd UK 1996-2002DVS - The Sorption Solution
Date: 07 Jul 2004 Time: 10:51 am File: 07-07-04-MOX02.xls Sample: Labindia, MOX-2
Temp: 25.1 °C Meth: Labindia01.SAO M(0): 19.854
“Transformation” step
Reversible Hydrate
