ANALYSIS OF PHARMACEUTICAL EXCIPIENTS BY BROADBAND ACOUSTIC RESONANCE DISSOLUTION SPECTROSCOPY (1)

Name: Conor Moran Student No: 110366405

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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


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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


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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.


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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 -


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2.3.2 Porous silica ............................................................................................................................. - 20 -

2.3.3 Non-Porous silica ..................................................................................................................... - 20 -

2.4 Experimental Procedure ............................................................................................................. - 20 -

2.5 Variables involved in a BARDS spectrum .................................................................................... - 21 -

Section 3: Results and Discussion .................................................................................................... - 22 -

3.1 Training Compounds ................................................................................................................... - 22 -

3.2 Hot-Chocolate ............................................................................................................................. - 23 -

3.3 Coffee .......................................................................................................................................... - 24 -

3.4 Non-Porous Silica ........................................................................................................................ - 25 -

3.5 Porous Silica ................................................................................................................................ - 27 -

3.6 Panadol Soluble Max Effervescent Granules .............................................................................. - 28 -

3.7 Panadol Max Strength (Hot Berry flavour) ................................................................................. - 29 -

Section 4: Conclusions and Future Work ......................................................................................... - 31 -

Section 5: References ....................................................................................................................... - 32 -


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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


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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 rotat ional

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


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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


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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


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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,


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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


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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


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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.


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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


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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.


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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.


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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.


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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 gl ass 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


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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 .


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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 experiment s in


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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.


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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.


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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.


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 dH 2O (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.


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


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.


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


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 dH 2O

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


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 dH 2O

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


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.


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.


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.

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Figure 1.5:

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Figure 1.6:

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Particle.jpg

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%20Soluble%20Max.JPG

Figure 1.8: https://www.panadol.ie/PageFiles/5427/blue_hotberry5sachets.png

Figure 2.2: http://bards.ie/products/instrument/

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ANALYSIS OF PHARMACEUTICAL EXCIPIENTS BY BROADBAND ACOUSTIC RESONANCE DISSOLUTION SPECTROSCOPY (1)

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