ANALYSIS OF PHARMACEUTICAL EXCIPIENTS BY BROADBAND ACOUSTIC RESONANCE DISSOLUTION SPECTROSCOPY (1)
1. Name: Conor Moran Student No: 110366405
Page | - 1 -
Analysis of Silica, Freeze-Dried Powders, and
Pharmaceutical Excipients using Broadband Acoustic
Resonance Dissolution Spectroscopy (BARDS)
By
Conor Moran
110366405
Report submitted to the Department of Chemistry,
University College Cork as part of a CM4206 4th
year
Research project
March 2014
Under the supervision of Dr. Dara Fitzpatrick and Bastiaan
Vos
2. Name: Conor Moran Student No: 110366405
Page | - 2 -
Acknowledgements:
I would sincerely like to thank Dr. Dara Fitzpatrick, Bastiaan Vos, Rachel Evans-Hurson,
Sean McSweeney, Pierre Casaubieilh and and words of
encouragement throughout the duration of my research project. I would also like to thank
Victor Langsi for gathering the SEM images presented.
Declaration of Originality:
The work on this research project was carried out in the Department of Chemistry, University
College Cork, during the academic year 2013-2014. Unless otherwise stated, this is the
independent work of the author.
X
Conor Moran
3. Name: Conor Moran Student No: 110366405
Page | - 3 -
Abstract:
A new sonochemical technique has been developed in recent years, to analyse the
dissolution of compounds. It is known as Broadband Acoustic Resonance Dissolution
Spectroscopy (BARDS). The theory behind BARDS is based on an acoustic phenomenon
observed when a compound is added to a solvent. A compound generates a unique
acoustic profile, at a fixed solvent volume and solute concentration. The addition of
solute to solvent has an effect of slowing down the velocity of sound in the solvent. This
gives rise to a reproducible acoustic profile that can be applied to many areas of analysis
including, inter-batch variation and blend-uniformity analysis.
The aim of this project is to analyse a range of compounds using BARDS. The
compounds under analysis are freeze-dried powders (Coffee and hot chocolate), both
porous and non-porous silica and over-the-counter drug products (Panadol Soluble Max
and Panadol Max Strength). A concentration profile for the freeze-dried powders and the
over-the-counter products will be compiled, analysing their behaviour in solution. A
comparison between the dissolution of porous silica (varying pore size) and non-porous
silica will be given. An investigation into the effect of water on porous silica by analysing
at different drying intervals will be undertaken.
Freeze-dried products are increasingly used in the food industry to allow for the safe
packing and long lifetime of perishable foods. Porous and non-porous silica are both used
as packing material in chromatography columns along with other applications such as,
chemical polishers. Their size and morphology are key to their effective use in industry.
Over-the-counter drug products are one of the biggest generators of revenue for the
pharmaceutical industry today. Millions of dollars are invested annually in the quality
control of these products to satisfy regulatory purposes.
An introduction into the various principles and applications involved with BARDS will
be presented along with a background into the history of sonochemistry and its
applications. A description on the compounds under investigation will also be presented.
The physical and chemical mechanisms involved in the dissolution of all the compounds
involved will be discussed along with any future research due to be carried out.
4. Name: Conor Moran Student No: 110366405
Page | - 4 -
Table of Contents
Section 1: Introduction.......................................................................................................................- 6 -
1.1 Principles of Broadband Acoustic Resonance Dissolution Spectroscopy .....................................- 6 -
1.2. Sonochemistry and its applications .............................................................................................- 7 -
1.3 Fundamentals of Bubble Formation and Nucleation....................................................................- 9 -
1.4 Analysis of a BARDS Spectrum....................................................................................................- 10 -
1.5 Applications of BARDS and the competing analytical techniques used .....................................- 11 -
1.5.1 Blend Uniformity Analysis........................................................................................................- 11 -
1.5.2 Measurement of the thickness of the enteric coating in drug delivery spheres.....................- 12 -
1.5.3 Porosimetry..............................................................................................................................- 13 -
1.6 Information on compounds under investigation........................................................................- 13 -
1.6.1 Coffee and Hot Chocolate........................................................................................................- 14 -
1.6.2 Non-Porous Silica (Stöber particles) ........................................................................................- 14 -
1.6.3 Porous Silica.............................................................................................................................- 15 -
1.6.4 Panadol max strength (Hot Berry flavour)...............................................................................- 16 -
1.6.5 Panadol soluble max effervescent granules ............................................................................- 16 -
1.6.6 Aims and Objectives.................................................................................................................- 17 -
Section 2: Experimental ...................................................................................................................- 18 -
2.1 Materials .....................................................................................................................................- 18 -
2.2 Instrumentation..........................................................................................................................- 18 -
2.3 Sample Preparation ....................................................................................................................- 19 -
2.3.1 Hot-Chocolate..........................................................................................................................- 19 -
6. Name: Conor Moran Student No: 110366405
Page | - 6 -
Section 1: Introduction
1.1 Principles of Broadband Acoustic Resonance Dissolution
Spectroscopy
Broadband Acoustic Resonance Dissolution Spectroscopy is a novel spectroscopic and
sonochemical technique in analytical chemistry that is being developed by Dr. Dara
Fitzpatrick and his team of researchers in University College Cork. It works based on an
acoustic phenomenon w d v d y F nk S. C w d n 1980’s in a
, m n y “T H C E ”. Whereby when a solute is
introduced into a solvent there is the appearance of gas bubbles in the liquid. The
presence of these gas bubbles increases the compressibility of the solvent and reduces the
velocity of sound in the medium. Added to this, the presence of the solute has an effect of
reducing the gas solubility and therefore additional bubble generation occurs.1
In C w d’ , d v d qu n w d d
chocolate effect, simply because he discovered it while mixing a cup of Hot Chocolate.
These equations form the basis form the basis for all BARDS responses.
( ) √ (1)
Equation (1) is the velocity of sound in a medium. W κ m y nd
nv u k m du u m d um nd ρ m d n y. T m g
bubbles that are generated in a liquid represent only a small fraction of the total liquid
volume and decrease the density in a negligible way with comparison to the large increase
in the compressibility. The net result is a large reduction of the sound velocity. Crawford
reported there to be a decrease of nearly three octaves as the supersaturated gas comes out
of solution and forms bubbles. This gave rise to the equation for the relationship between
fractional bubble volume and sound velocity in water2
.
√ (2)
In equation 2, and represent the velocity of sound in pure and bubble filled water
respectively. corresponds to the fractional volume occupied by gas bubbles. The factor
of was previously discovered by Albert Beaumont Wood in 19303
7. Name: Conor Moran Student No: 110366405
Page | - 7 -
When BARDS analysis is carried out it involves an induced acoustic response which
comes in the form of a magnetic stirrer bar striking the walls of the glass vessel. Analysis
of this response is focused on the lowest variable frequency time course (the fundamental
resonance mode of the liquid). The frequency of this mode is measured by the velocity of
sound in the liquid and the approximate height of the liquid column in the vessel; this
corresponds to one quarter of the frequency. This formulates the frequency response
equation,
√
(3)
and are the resonance frequencies of the fundamental resonance modes in
bubbled filled and pure water, respectively2
.
1.2. Sonochemistry and its applications
Sonochemistry is a relatively new area of chemistry in comparison to other fields. It is
d “ u n und w v n m v y”. On
major advantages of sonochemistry that sets it apart from other scientific developments is
that it does not require expensive instruments and a major degree of competence.
However given its ease of use and relative simplicity, it has a wide varying range of
applications in chemical technology.4
,5
Most of the applications of sonochemistry involve the phenomenon of cavitation. This is
the formation, growth and implosive collapse of bubbles in a liquid. Cavitation involves
high energy, short-lived localised collapse of bubbles. Experiments have been carried out
showing that temperatures during compression can reach up to 5000 K and pressures of
1000 atm. There are several parameters which govern the effects of cavitation including
frequency, temperature, solvent viscosity, solvent surface tension, and the applied
pressure. It is worth noting that there is no direct interaction between the ultrasonic wave
and the chemical species because the frequencies applied are too low to excite rotational
vibrations. Sonochemistry can be applied to a wide range of areas in chemistry. These
include, increasing the rates of reaction in organic synthesis, lowering the reaction
temperature and the ability to change a reaction pathway to yield different products to
name but a few. There are also a variety of uses for ultrasonic techniques in materials
chemistry and in life sciences and medicine4
,5
8. Name: Conor Moran Student No: 110366405
Page | - 8 -
Figure 1.1: A schematic of the cavitation process.
BARDS is a branch of sonochemistry that incorporates an induced sound frequency in the
form of the stirrer bar striking the walls of a vessel. There have however been analytical
techniques developed previously that involve a signal being transmitted through a sample.
Acoustic Resonance Spectrometry is an online process analytical technology that was
d v d n 1980’ . I n n-destructive approach that was developed to
characterise compounds, particularly drug tablets in the pharmaceutical industry.6
Figure 1.2: Schematic diagram of an Acoustic Resonance Spectrometer.6
ARS categorises compounds by sweeping it with an acoustic signal. The acoustic velocity
as it travels through the sample is measured and compounds are characterised
accordingly. It is a rapid and efficient way of characterising compound compared to PAT
methods that are already in place e.g. Near-IR Spectroscopy.6
9. Name: Conor Moran Student No: 110366405
Page | - 9 -
1.3 Fundamentals of Bubble Formation and Nucleation
Atmospheric gases such as nitrogen and oxygen can dissolve in water. The amount of gas
dissolved depends on the temperature of the water and the atmospheric pressure at the
air/water interface.
(4) H n y’ L w
(5) R u ’ L w
Colder water and higher pressure allow more gas to dissolve; conversely, warmer water
and lower pressure allow less gas to dissolve.
When you pour a glass of cold water from your faucet and allow it to warm to room
temperature, nitrogen and oxygen slowly come out of solution, the solution is
supersaturated, with tiny bubbles forming and coalescing at sites of microscopic
imperfections on the glass (Nucleation site). If the atmospheric pressure happens to be
falling as the water warms, the equilibrium between gas molecules leaving and joining the
air/water interface becomes unbalanced and tips in favour of them leaving the water,
which causes even more gas to come out of solution. Hence bubbles form along the
insides of the glass.7
There are two types of nucleation that can occur, homogenous and heterogenous. The
m n y u u g n 100 m nd w n’ n d d n
this report. Heterogenous nucleation as mentioned above occurs when bubbles form
within pre-existing gas pockets located in surface cracks and imperfections of solids,
supersaturated gas diffuses into the gas pockets, causing bubble growth and eventual
detachment from the solid support. Unlike homogeneous nucleation, significantly less
dissolved gas supersaturation is required for heterogeneous bubble formation.7
10. Name: Conor Moran Student No: 110366405
Page | - 10 -
1.4 Analysis of a BARDS Spectrum
BARDS profiles are analysed by assigning specific features with designated terminology.
These terms are shown in Figure (1.3) below,
Figure 1.3: (A) BARDS profile of Na2CO3 in 100 mL H2O (B) Plan view of a prototype BARDS Spectrometer.2
In Figure (1.3A), the first thirty seconds of the profile shows several steady state
n n qu n v , “V um L n ” und m n esonance of
the glass due to the amount of solvent added and also the fabrication of the glass. Each
glass has a different resonance frequency; the importance of this will be explained in due
course.
After 30s, the solute is added and there is a decrease in the resonant frequencies of the
vessel. The “fundamental curve” or resonance line is selected as it is the most
interpretable and retrievable feature of the profile. The “frequency minimum ( )
represents a point in the analysis where the solution is in equilibrium between the rate of
m n g nd n g m u v n , ’
the point where the compressibility of the solution is at its greatest. The fundamental
curve can be found by following the fundamental resonance line along the time axis. The
time taken for the profile to go from to steady state is designated as
There are other resonance modes above the fundamental resonance curve that correspond
to overtones and ultrasonic frequencies of the vessel and air column above the solvent.
They do not have a direct correlation between bubble volume but occasionally give us an
insight into the origin of and other dissolution processes occurring2
.
The BARDS response is dependent on the compound under investigation and its chemical
make-up. Responses have been detected at concentrations as low as the micromolar level,
11. Name: Conor Moran Student No: 110366405
Page | - 11 -
however these reactions would need to be relatively vigorous with lots of gas evolution
involved, concentrations at the millimolar level are routinely observed however2
.
1.5 Applications of BARDS and the competing analytical techniques
used
The applications of BARDS are vast in the area of analytical chemistry, particularly in the
analysis of the dissolution of pharmaceutical compounds. There are also applications for
non-soluble or inorganic materials e.g. Silica, this shows that dissolution is not necessary
for BARDS to be effective simply that there is a necessity for a change in
compressibility. Some of the main areas of research focused on in the development of this
technique include:
Batch consistency analysis
Blend uniformity analysis
Distinguishing between Epimers e.g. Glucose and Mannose
Determination of crystalline materials
Resolving the moisture content in solvents
Porosimetry
Determination of particle size
Measurement of the thickness of enteric coating in drug delivery spheres
Analysis for the detection of counterfeit drug products
Research in these applications often requires sophisticated and expensive techniques.
BARDS is relatively inexpensive in comparison. For example, Pepsico Ltd have 640
bottling plants spread across the globe. For regulatory purposes they need a method of
proving that their 3 component mixture has come to completion. Up until now they had
been availing of Ion Chromatography to prove their results were correct. This costs
€150,000 per unit in conjunction with a lot of working hours. With preliminary trials
BARDS was able to prove their process had come to completion with better accuracy as
well as reducing the costs to €25,000 per unit.2
1.5.1 Blend Uniformity Analysis
In the pharmaceutical sector, Blend Uniformity Analysis (BUA) is highly regulated. This
is carried out by analysing individual components of a blend to find their mixture ratio. In
12. Name: Conor Moran Student No: 110366405
Page | - 12 -
2010, 54% of the shortages reported were associated with quality assurance. These
problems are associated with the averaging of test data for multiple batches to mask
results that were out-of-specification attributing to poor blend uniformity. It was found
that there was no readily available process analytical technology for blend uniformity
testing only that some companies were making use of Near-IR spectroscopy but this in
itself had major limitations, it is very sensitive to the presence of water in a sample and
other signals can often be overwhelmed if water is present. BARDS can be applied as a
fast and accurate method of analysing powder blends. In the pharmaceutical industry,
dissolution testing is normally done to replicate the conditions in the body e.g. a tablet
dissolving in the stomach. BARDS is limited here in that n’ d ng n
compressibility when tablets are tested so powdered blends must be used.8
1.5.2 Measurement of the thickness of the enteric coating in drug
delivery spheres
The profiling of the thickness of enteric coated sugar spheres for the controlled delivery
API’ n d ug du n n w v m un g n n n
the BARDS project. Enteric coatings are used to prevent the active pharmaceutical
ingredients from disintegrating in the acidic environment of the stomach. Their thickness
is important because it governs that rate of release in the small intestine. Enteric-coated
drug spheres have very unique acoustic profile when run in a BARDS spectrometer.
There is a double dissolution that takes place, firstly the dissolution of the enteric and
drug coating creates a lag time after which the dissolution of the sugar sphere occurs. By
mimicking the conditions that the drug experiences in the intestinal tract it is possible to
dissolve the drug spheres correctly. . By varying the concentration of base used it was
possible to manipulate the lag time (The time between the addition of spheres and the
dissolution of core sugar sphere). The length of the lag time then holds a direct
correlation to the thickness of the enteric coating. The technique ’ mm n y u d to
profile drug coatings is known as Laser Induced Breakdown Spectroscopy (LIBS). It is a
destructive technique that applies a high energy laser to a sample. The laser melts the
surface of the sample into a plasma and the excitation of the elements is measured. Not
only is this a destructive technique, it is highly costly and time consuming with respect to
BARDS. There are occasionally problems with the laser and its reproducibility,
something which BARDS is renowned for. 9
13. Name: Conor Moran Student No: 110366405
Page | - 13 -
Figure 1.4: Conceptual diagram of LIBS spectrometer.
1.5.3 Porosimetry
Porosimetry is also an area where much research has been done in the BARDS project.
Porosimetry is an analytical technique that is used to measure different aspects of a
porous material like silica, e.g. pore diameter, total pore volume, surface area, and bulk
and absolute densities. It is worth noting that BARDS cannot directly identify any of the
parameters mentioned above, previous profiles of known attributes, e.g. pore size need to
be obtained through different techniques like Scanning Electron Microscopy; the
reproducibility of future profiles is where these aspects are measured. The common
method of porosimetry is a technique known as Mercury Porosimetry. This involves
applying non-wetting mercury to a porous sample e.g. Silica at high pressures. Pore size
is measured by the amount of pressure needed to be applied to force the mercury into the
pore against the surface tension of mercury. The technique has some drawbacks compared
to BARDS however, there is the use of a toxic element such as mercury. There is also the
need for high pressures to operate the instrument, something w n’ n d d
BARDS.10
1.6 Information on compounds under investigation
As previously stated, the aim of the project is to investigate a variety of different
compounds including, Instant coffee, hot chocolate, porous and non-porous silica,
Panadol max strength (hot berry flavour) and Panadol soluble max effervescent capsules.
14. Name: Conor Moran Student No: 110366405
Page | - 14 -
1.6.1 Coffee and Hot Chocolate
Instant Coffee and hot chocolate are both freeze dried powders. Freeze drying, or
lyophilisation as it is known as in the pharmaceutical industry, is a dehydration technique
that allows products that have previously been frozen to be completely dried out under a
vacuum. This makes their handling and transport much easier as some may be
hygroscopic, harmful biological agents or perishable food goods as is the case with coffee
and hot chocolate.
Freeze drying involves many complicated steps which do not need to be covered,
however the main steps in the process are:
Freezing the product to -20 at atmospheric pressure
Sublimation of the frozen water at -20 and reduced pressure until the vapour
flows into a condenser unit
Vacuum release
Defrost
1.6.2 Non-Porous Silica (Stöber particles)
Non-porous silica or Stöber particles are mono-dispersed spheres of silica, ranging from
50-2000 nm depending on the synthesis used. Their importance is seen in many areas of
chemistry, including chromatography, catalysis, pigments and chemical polishers.
A common method for the synthesis of Stöber particles is the seed growth method, which
is derived from the Stöber process, the most common way of synthesising Stöber
particles. This involves adding small sub-micron seed particles that have been synthesised
through the Stöber process to a solution containing a low concentration of [NH3] and
[H2O] in isopropanol. Tetra-ethyl-orthosilicate (TEOS) is then introduced to the solution
to induce growth of the particles. The hydrolysed TEOS reacts to for larger particles
>1000 nm.11
15. Name: Conor Moran Student No: 110366405
Page | - 15 -
Figure 1.5: Cross-section of a monodispersed non-porous silica particle.
1.6.3 Porous Silica
Porous Silica comes in many different forms and sizes.. Porous silica is used as packing
material in HPLC Chromatography, greatly improving the diffusion paths of separations
carried out because of their even particle size,
Porous silica consists of a solid core shell and a superficial porous shell, the term
“P ” n n d n n y . T particles are firstly made via the
Stöber process mentioned above. The cores are then bonded to a urea/silane mixture and
urea/ formaldehyde polymers are grafted to their surface allowing for coacervation.
Coacervation involves adding the core shells to a mixture of sol particles, urea and
formaldehyde in an acidic environment. Urea and formaldehyde polymerises on the
surface and coacervated particles form on the surface with the sol particles. The polymers
are removed by calcination and the resulting superfacial silica particles are sintered at
high temperatures.12
Figure 1.6: Diagram of a poroshell particle.
16. Name: Conor Moran Student No: 110366405
Page | - 16 -
1.6.4 Panadol max strength (Hot Berry flavour)
Panadol max strength (hot berry flavour) is an analgesic, antipyretic drug made by
GlaxoSmithKline Ltd. It is a paracetamol-containing drug used to treat the effects of
influenza, fever, aches and pains. It comes in sachet form for oral use in solution. Along
with paracetamol, each sachet contains ascorbic acid, sucrose, aspartame, tartaric acid,
and flavourings.
Figure 1.7: Panadol Max Strength.
1.6.5 Panadol soluble max effervescent granules
Panadol soluble max is an effervescent oral solution drug that has the same
pharmacological effects as Panadol max strength. However, some of the excipients are
varied. It contains sodium hydrogen carbonate, sucrose, povidone, saccharin sodium,
anhydrous citric acid, anhydrous sodium carbonate and flavourings.
Figure 1.8: Panadol Soluble Max.
17. Name: Conor Moran Student No: 110366405
Page | - 17 -
1.6.6 Aims and Objectives
The aims and objectives of this report were to analyse and compare different compounds
with the use of BARDS. The acoustic spectra of both hot chocolate and coffee will be
examined and a concentration profile will be compiled. A comparison of the acoustic
profiles of both non-porous and porous silica (varying pore size) will be analysed. An
investigation into the effects of water on the drying time of porous silica will be
undertaken. Different over-the-counter drug products (Panadol Soluble Max and Panadol
Max Strength) will also be analysed and concentration profiles for each gathered.
18. Name: Conor Moran Student No: 110366405
Page | - 18 -
Section 2: Experimental
2.1 Materials
The following materials were purchased from the local convenience store, pharmacy,
Thermo-Fischer and Glantreo Ltd. Cad u y’ d nk ng nd N g d
blend coffee were bought at the convenience store. Panadol soluble max effervescent
granules and Panadol max strength (hot berry flavour) were obtained from the
pharmacy. 2.5 m Porous silica was donated from Thermo-Fischer and 1.5 m non-
porous silica was received from Glantreo Ltd. Doubly-distilled water was used for
all experiments carried out.
2.2 Instrumentation
Throughout the course of the project, there was a migration from an open stirring
plate setup to a dedicated BARDS spectrometer. Firstly, the stirring plate setup
consists of a magnetic stirring plate with a glass tumbler placed slightly off centre.
The microphone is clipped onto a retort stand and placed slightly above the rim of
the glass.
Figure 2.1: Stirrer Plate setup.
The BARDS spectrometer consists of a specialised chamber with a glass tumbler, a
microphone, a 3D-printed base, a magnetic stirrer and a follower. There is a door at
the front for the glass to be placed in position and a sliding door on top to allow the
sample boat to be place on the tipper for dissolution. The microphone is situated
19. Name: Conor Moran Student No: 110366405
Page | - 19 -
inside the door directly above the glass vessel. The glass is placed on the 3D printed
base, above the stirring plate, to prevent it from ringing off the metal chamber and
disturbing the acoustic spectra. The motor for the stirrer is situated slightly off
centre so as to allow the stirrer bar to strike the walls of the glass. In the BARDS
spectrometer, the follower acts as the source of broadband acoustic excitation,
inducing the various acoustic resonance modes of the glass, liquid and the air
column above the liquid. These induced resonance modes are picked up by the
microphone and registered by the computer using a sound card and BARDS software
which has previously been developed. The resonances of the liquid vessel range
from 0-20 kHz in a typical BARDS experiment.
Figure 2.2: BARDS Spectrometer.
2.3 Sample Preparation
In the experiments carried out on coffee and both panadol products, the samples
were simply weighed out to 4 decimal places and placed in the spectrometer. There
was a need however to prepare hot chocolate and both porous and non-porous silica
before they could be analysed.
2.3.1 Hot-Chocolate
To ensure dissolution, the distilled H2O needed to be heated up in a water bath at
temperatures ranging from 45-60 .
20. Name: Conor Moran Student No: 110366405
Page | - 20 -
2.3.2 Porous silica
To analyse porous silica at drying intervals, 6 g was placed in a beaker of dH2O
and stirred for 20 minutes. The suspension was then allowed to settle and decanted.
The silica was then centrifuged for 20 minutes and placed in the oven at 160 so
that different drying times could subsequently be measured.
2.3.3 Non-Porous silica
When the non-porous silica was first received it was coagulated in nature. To
analyse it correctly it needed to be converted into a fine powder, however if a
spatula was used there was a risk that the spheres would be damaged and there
would be dangerous dust dispersed around the lab.
The silica was suspended in absolute ethanol and sonicated. It was then placed in the
fume hood to allow the ethanol to evaporate. This process was repeated a number of
times. The particles were then placed in the oven at 160 to fully dry the particles.
2.4 Experimental Procedure
At the start of each lab session, a bottle of distilled water is agitated between 30 s
and 1 minute and left to stand for 10 minutes to equilibrate the water and remove
any traces of gas oversaturation that may have built up while not in use. The inside
of the glass vessel is rubbed with NaHCO3 to ensure there is no grease or
fingerprints which could interfere with the acoustic profile by causing fouling. The
NaHCO3 is rinsed from the glass thoroughly. All other glassware and weighing boats
are rinsed. A test-run of 1.5 g of Na2CO3 in 100 mL of dH2O is carried out to ensure
’ n d .
Before each experiment, the volume, temperature, atmospheric pressure and
humidity are recorded using the BARDS software. The weighing boat containing the
sample is loaded onto the tipper and the experiment is started. There is a 5 second
countdown to allow the magnetic follower to speed up and form a stable volume
line. For the first thirty seconds, the steady state resonances of the system are
measured. Upon addition of the solute, the resonance modes of the liquid decrease
significantly until they reach upon which the pitch starts to increase and the
solution returns to steady state over a period of a few minutes. All experiments in
21. Name: Conor Moran Student No: 110366405
Page | - 21 -
this report were carried out over a period of 400-800 seconds depending on the rate
of return to steady state. All experiments were run in triplicate and the average was
calculated with standard error. Graphs were created using the Sigma-Plot software.
2.5 Variables involved in a BARDS spectrum
The principle and efficiency of BARDS is based on the reproducibility of the spectra
that are obtained. To obtain this reproducibility certain experimental parameters or
variables need to be kept constant. There has been a great amount of research carried
out on the effects of controlling variables such as temperature, volume,
concentration, density and solvent.
Firstly, the effect of temperature is very noticeable in a BARDS spectrum. At higher
temperatures the dissolution process is stimulated faster and thus the return to steady
state is faster. At lower temperatures there is a delayed and also a delayed .
With acoustic profiles of increasing concentration, there is the anticipated increasing
deflection to and a deferred return to steady state because with increasing
concentration of solute there are more entrained gases being introduced into solution
and a resulting increase in compressibility.
Solvent effects are also decisive in the formation and reproducibility of a BARDS
response. There is a requirement for an equilibrated solvent to be used because of
gas oversaturation. If a solvent, e.g. Distilled H2O, is used without agitation there
will be dissolved gases from the solvent contributing to the compressibility of the
dissolution process, and thus interfering with the acoustic profile.
With regards to the mechanical variables, it is imperative that the same glass is used
to analyse a certain compound. This is because every glass has a particular resonant
frequency and using a different glass after each acoustic profile is obtained would
interfere with the reproducibility of the spectra.
It is also important to use the same stirrer bar when trying to obtain reproducible
spectra. The width is negligible however the length of stirrer bar and stirring rate is
essential particularly when a compound is at its solubility limit. If there variables in
a BARDS profile are kept constant then it is possible to rule out problems with the
instrument when analysing differences in acoustic profiles.
22. Name: Conor Moran Student No: 110366405
Page | - 22 -
Section 3: Results and Discussion
3.1 Training Compounds
Figure 3.1: Graph of Training Compounds, KBr, Na2CO3 and NaCl. All salts are at 1.37 M concentration in
100 mL dH2O (NaCl: Lot#BCBF6074V, Na2CO3: Lot# SZBA2090, KBr Lot# 83520)
The training compounds of KBr, Na2CO3 and NaCl are used to instruct analysts in
how to operate a BARDS spectrometer. For KBr, there is an initial decrease in
resonant frequency of 10 kHz after addition of solute. A U-shaped response is
observed which is indicative of gas oversaturation in the solution. In the spectrum of
NaCl gas oversaturation is also observed to a larger extent that that of KBr, showing
that NaCl has a greater increase on the compressibility of water given the increased
mass of solute added. For the profile of Na2CO3, an initial decrease to of 12
kHz is observed. There is a sigmoidal to exponential return to the frequency of the
solution prior to addition after has been reached. The frequency of the
fundamental curves of both KBr and NaCl decrease at 120 s and 180 s respectively.
This is the result of a process known as fouling. It is caused to the formation of gas
bubbles forming on the inside of the glass and preventing the resonant frequencies
from stabilizing. There is more of an effect in the spectrum of NaCl due to more
solute being added.
23. Name: Conor Moran Student No: 110366405
Page | - 23 -
3.2 Hot-Chocolate
Figure 3.2: Annotated Spectrum of 0.9998 of Hot Chocolate (B/N OCI0432911) in 100 mL dH2O using a
stirring plate.
Figure 3.2 shows the acoustic profile of 0.9997 g of hot chocolate. It can be seen
from the acoustic profile that hot chocolate shows a very weak BARDS response
with no definitive fundamental curve. There was a decrease in the resonant
frequency after addition of ~ 1.5 kHz, which is relatively small for such a high
concentration of solute. This was a result of the water that was used not being at the
correct temperature to allow sufficient dissolution at a specific time. After addition,
the hot chocolate would float on top of the surface of the liquid, only to break the
surface tension periodically and at different times in each test carried out. In an
attempt to eradicate this problem, the stirring rate was increased, however this
caused a large vortex to form in the glass which disrupted the acoustic profile. The
u g m u w n’ v u d u k d m g ng
glass. It was also difficult to heat the water to a consistent temperature so as to
collect accurate and precise data.
Fouling could have occurred inside the vessel after addition which may have been a
cause for the acoustic profile disappearing near . Hot chocolate contains fats
which may have deposited on the walls of the glass allowing for the nucleation of
bubbles.
24. Name: Conor Moran Student No: 110366405
Page | - 24 -
3.3 Coffee
Figure 3.3: Concentration profile of 0.125 g, 0.25 g, and 0.5 g of coffee in 100 mL dH2O (B/N 32801080BB)
Figure 3.3 shows the concentration profile of coffee. At 0.125 g, there is a V-shaped
acoustic profile indicating the instantaneous release of entrained gases into solution
before gradually returning to steady state at 800 s. The concentration profile shows
an increase in acoustic response with increasing concentrations of coffee. This
results from the increased compressibility of the solution, caused by the solute being
introduced into the solvent. With increasing concentration comes a slower return to
steady state, this is due to more bubble nucleation centres forming on particles. The
presence of large error bars at 0.5 g is due to the granulated nature of the coffee
w n k n m j , n’ n v n z d u n nd u
readings may be inaccurate.
25. Name: Conor Moran Student No: 110366405
Page | - 25 -
3.4 Non-Porous Silica
Figure 3.4: (A) SEM image of 1.5µm Non-Porous Silica particles (B) Graph comparing Non-Porous Silica with
Porous Silica of varying pore size. All runs were 1.5 g in mass in 100 mL dH2O (4 nm Pore - Lot# 1114, 9 nm Pore -
Lot# 1092) (C.Moran/B.Vos)
Figure (3.4A) demonstrates the even particle size distribution achieved in the synthesis of
Stöber particles. In figure (3.4B), the acoustic profiles of non-porous and porous silica are
compared. From the graph, an initial deflection to of 6 kHz is observed for non-
porous silica with a V-shaped response returning to steady state after 100 s. The acoustic
A
B
26. Name: Conor Moran Student No: 110366405
Page | - 26 -
profiles of porous silica are different however, both in there deflection to and the
time taken to return to steady state. The acoustic profile of 4 nm pore silica contains a
deflection to of 6.5 kHz and returns to steady state at approximately 700 seconds.
In the 9 nm acoustic profile of porous silica, a deflection to of 4 kHz is seen along
with a return to steady state at 700 s. The compressibility of the solution undergoes a
larger increase for 4 nm silica than the 9 nm particulates. This demonstrates that there is
less surface area for bubble nucleation centres to form with smaller pore size. The slope
of for 9 nm also reiterates this point, a lower slope constitutes to more nucleation sites
being formed. It is also worth noting the reason for the uneven nature of the return to
steady state for both samples of porous silica. When the analysis was carried out, both
samples were pristine and difficult to handle in addition. After addition, some of the
sample would float on the surface of the liquid, only to break the surface tension when
sucked down by the vortex after a number of seconds. This process was not even over the
course of each run, resulting in inaccurate results. This was not the case for non-porous
silica however, with the entire mass of the sample entering the suspension upon addition.
27. Name: Conor Moran Student No: 110366405
Page | - 27 -
3.5 Porous Silica
Figure 3.5: (A) SEM image of 5 m Porous Silica Particles (B) Graph showing the acoustic profiles of 1.5
g Porous Silica that has been analysed at different drying intervals in 100 mL dH2O
The effect of water on silica revealed interesting results, evident from the graph of
drying intervals. There was an initial decrease in the resonant frequency post-
addition of ~5-6 kHz in each case. All tests showed a V-shaped response indicating
n n n d g . B u d n’ d v n w re is no
A
B
28. Name: Conor Moran Student No: 110366405
Page | - 28 -
evidence of gas oversaturation, simply an initial decrease in the compressibility of
the vessel. There is an exponential return to steady state in each case, this would
indicate that no bubble nucleation centres have formed in the pores of the
particulates, which was unexpected. There is a noticeable decrease in the frequency
of after each drying interval, this shows that the compressibility of the
particulates as they enter solution is decreasing. One reason for this could be that
traces of water located within the pores of the particles are being evaporated with
the longer drying time. The presence of small error bars demonstrates the even
particle size distribution of the spheres.
3.6 Panadol Soluble Max Effervescent Granules
Figure 3.6: Concentration profile of Panadol Soluble Max in 100 mL dH2O
Figure 3.6 shows the concentration profile of the effervescent Panadol Soluble Max.
There is a decrease in the resonant frequency of between 6-6.5 kHz in each case.
One would presume that there would be a larger decrease in with increasing
concentration, however, when there is such a large increase in compressibility and
total bubble volume that it is more difficult for the frequency to decrease any
further. Each concentration shows a dual dissolution occurring, firstly an initial
large increase in compressibility lowering the resonant frequency and a short time
later CO2 evolution from the effervescent granules reduces the frequency further
29. Name: Conor Moran Student No: 110366405
Page | - 29 -
before gradually returning to steady state. The characteristic S-shape of the acoustic
profile becomes more pronounced with increasing concentration. There is a
noticeable decrease in the steady state frequencies after dissolution with increasing
concentration. This is a result of the increased amount of bubbles created by the
effervescence of the granules increasing the compressibility of the solution.
3.7 Panadol Max Strength (Hot Berry flavour)
Figure 3.7: Concentration profile of Panadol Max Strength in 25 mL dH2O
The concentration profile for Panadol Max Strength demonstrates a feature known as
a transition concentration range. This is when the shape of an acoustic profile shifts
from a V-shaped to U-shaped response over varying concentrations. In the 1 g
profile of Panadol Max Strength, an initial decrease in the resonant frequency
followed by a quasi-exponential return to the pre-addition frequency. With
increasing concentration the frequency becomes non-linearly dependent on the
equation for the relationship between fractional bubble volume and sound velocity in
water.2
The profiles for 2 g and 3 g respectively reinforce the evidence of a
transition concentration range. In the 2g spectrum, an intermediate mass of solute
was added and the appearance of a shoulder is seen. This is indicative of the
transition concentration range from the V-shaped to the U-shape and demonstrating
30. Name: Conor Moran Student No: 110366405
Page | - 30 -
the change between entrained gases causing a response to gas oversaturation. In the
3 g acoustic profile, a U-shaped response is observed, demonstrating the decrease in
gas solubility with increasing solute mass leading to bubble formation and growth.
These bubbles serve as nucleation centres for further bubble growth thus lengthening
the time taken to return to steady state. The concentration profile shown in Figure
3.7 is in significant agreement with BARDS spectra previously undertaken,
demonstrating the efficiency of the technique with regards to reproducibility.
31. Name: Conor Moran Student No: 110366405
Page | - 31 -
Section 4: Conclusions and Future Work
In this research project, it has been demonstrated how different compounds have
unique acoustic spectra when analysed using BARDS. These acoustic spectra
demonstrate the capability that BARDS possesses with regards to obtaining
reproducible spectra
Given more research time, a more effective method development for obtaining an
acoustic profile of hot chocolate would have been established. The acoustic spectra
for coffee indicated that at low concentrations the presence of entrained gases alter
the compressibility, to generate an acoustic response. At high concentrations, the
reduction in gas solubility results in bubble growth which accounts for a longer
return to steady state.
The spectra of both porous and non-porous silica demonstrated a number of
properties about BARDS. Primarily, that dissolution is not necessary for a BARDS
response to be obtained. Secondly, in the comparison of porous and non-porous
silica, we can see that a difference in pore size of a few nanometres can have a
profound effect on the acoustic response.
The spectra of Panadol Soluble Max and Panadol Max Strength revealed that
analysis of over-the-counter products is highly compatible with BARDS. Panadol
Soluble Max demonstrated that effervescence causes an additional gas
oversaturation, heightening the effect of the increased mass of solute. The
concentration profile of Panadol Max Strength revealed the characteristic transition
concentration range, where there is a migration from a V-shaped to a U-shaped
response via an S-shaped response at intermediate concentrations.
The potential future work associated with the research undertaken in this project
includes; quality control of powder blends in freeze-dried powders, analysis of
porous and non-porous packing material used in chromatography to infer the
distribution of particle size and analysis of powdered oral drug solutions for inter-
batch variation and blend uniformity.
32. Name: Conor Moran Student No: 110366405
Page | - 32 -
Section 5: References
(1) Crawford, F. S. Am. J. Physics 1982, 50, 398.
(2) Fitzpatrick, D.; Kruse, J.; Vos, B.; Foley, O.; Gleeson, D.; O'Gorman, E.; O'Keefe, R.
Analytical chemistry 2012, 84, 2202.
(3) Wood, A. B. A textbook of Sound; 1st edn ed.: New York, 1930.
(4) Mason, T. J. Practical sonochemistry : user's guide to applications in chemistry and
chemical engineering, 1991.
(5) Mason, T. J. Sonochemistry: the uses of ultrasound in chemistry, 1990.
(6) Medendorp, J., Lodder, Robert. A AAPS PharmSciTech 2006, 7.
(7) Scardina, P., Edwards, Marc, The fundamentals of BubbleFormation in Water
Treatment, 2000.
(8) Fitzpatrick, D.; Scanlon, E.; Krüse, J.; Vos, B.; Evans-Hurson, R.; Fitzpatrick, E.;
McSweeney, S. International Journal of Pharmaceutics 2012, 438, 134.
(9) Fitzpatrick, D.; Evans-Hurson, R.; Fu, Y.; Burke, T.; Kruse, J.; Vos, B.; McSweeney, S.
G.; Casaubieilh, P.; Keating, J. J. The Analyst 2014, 139, 1000.
(10) Zgrablich, G., Mendioroz, S et al Langmuir 1991, 7, 779.
(11) Wang, X. D.; Shen, Z. X.; Sang, T.; Cheng, X. B.; Li, M. F.; Chen, L. Y.; Wang, Z. S.
Journal of colloid and interface science 2010, 341, 23.
(12) (a) Chen, W., Ta-Chen Wei, Long, William In Agilent Technologies Inc, 2013; Vol.
2014(b) Kirkland, J. J. Anal. Chem 1992, 64, 1239.
Figure 1.1: http://eswt.net/wp-content/uploads/2011/10/cavitation.gif
Figure 1.4: http://www.isibrno.cz/omitec/images/libs/plasma_formation.png
Figure 1.5:
http://www.worldscientific.com/na101/home/literatum/publisher/wspc/journals/conte
nt/nano/2013/nano.08.issue-
04/s1793292013500367/20130717/images/small/s1793292013500367.gif
Figure 1.6:
http://www.crawfordscientific.com/images/Bev/Agilent/HPLC/Poroshell120-
Particle.jpg
Figure 1.7: http://ballymoreshoponline.stormwebhost.com/prodimages/Panadol%20-
%20Soluble%20Max.JPG
Figure 1.8: https://www.panadol.ie/PageFiles/5427/blue_hotberry5sachets.png
Figure 2.2: http://bards.ie/products/instrument/
