AquaLab Series 3 User manual

Water Activity Meter
Operator’s Manual
Version 6
for AquaLab Series 3
Decagon Devices, Inc.

Decagon Devices, Inc.
2365 NE Hopkins Court
Pullman WA 99163
[phone]
fax: [phone]
www.decagon.com
[e-mail]
Trademarks
AquaLab is a registered trademark of
Decagon Devices, Inc.
© 1990-2009 Decagon Devices, Inc.

AquaLab
Table of Contents
i
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . 1
About this Manual . . . . . . . . . . . . . . . . . . . . 1
Customer Support . . . . . . . . . . . . . . . . . . . . . 1
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . 3
2. About AquaLab . . . . . . . . . . . . . . . . . 4
AquaLab 3 Instrument Specifications . . . . 4
AquaLab and Water Activity . . . . . . . . . . . 5
How AquaLab works . . . . . . . . . . . . . . . . . . 5
AquaLab and Temperature . . . . . . . . . . . . . 6
Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Water Activity Theory . . . . . . . . . . . 9
Moisture content . . . . . . . . . . . . . . . . . . . . . . 9
Water activity . . . . . . . . . . . . . . . . . . . . . . . . 9
Temperature Effects . . . . . . . . . . . . . . . . . . . 11
Water Potential . . . . . . . . . . . . . . . . . . . . . . 12
Factors in Determining Water Potential . 13
Sorption Isotherms . . . . . . . . . . . . . . . . . . . 15
4. Getting Started . . . . . . . . . . . . . . . . 17
Components of your AquaLab . . . . . . . . . 17
Choosing a Location . . . . . . . . . . . . . . . . . . 17
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Preparing AquaLab for Operation . . . . . 19
5. The Menus . . . . . . . . . . . . . . . . . . . . 21
The Measurement Screen . . . . . . . . . . . . . 21

AquaLab
Table of Contents
ii
Changing Languages . . . . . . . . . . . . . . . . . . 21
Normal Sampling Mode . . . . . . . . . . . . . . .22
Continuous Mode . . . . . . . . . . . . . . . . . . . .23
Temperature Equilibration Screen . . . . . .23
System Configuration . . . . . . . . . . . . . . . . .24
6. Cleaning and Maintenance . . . . . . .27
Cleaning the Block and Sensors . . . . . . . .28
Cleaning Procedure: . . . . . . . . . . . . . . . . . .29
Checking Calibration . . . . . . . . . . . . . . . . .32
7. Verification and Calibration . . . . . .33
Water Activity Verification . . . . . . . . . . .33
Calibration Standards . . . . . . . . . . . . . . . .33
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . .35
8. Sample Preparation . . . . . . . . . . . . 41
Preparing the Sample . . . . . . . . . . . . . . . . . 41
Samples Needing Special Preparation . .43
Low Water Activity . . . . . . . . . . . . . . . . . .46
9. Taking a Reading . . . . . . . . . . . . . .48
Measurement Steps . . . . . . . . . . . . . . . . . .48
How AquaLab takes Readings . . . . . . . . .49
Cautions . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
10. Computer Interface . . . . . . . . . . . .52
AquaLink Software . . . . . . . . . . . . . . . . . . .52
Using Windows Hyperterminal . . . . . . . . .53
11. Troubleshooting . . . . . . . . . . . . . . .54
Component Performance Screen . . . . . . .62

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Table of Contents
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12. Support and Repair . . . . . . . . . . . 64
Shipping Directions: . . . . . . . . . . . . . . . . . .64
Repair Costs . . . . . . . . . . . . . . . . . . . . . . . . .66
Loaner Service . . . . . . . . . . . . . . . . . . . . . .66
13. Further Reading . . . . . . . . . . . . . . . 67
Water Activity Theory & Measurement 67
Food Quality and Safety . . . . . . . . . . . . . . 71
Water Activity and Microbiology . . . . . .73
Water Activity in Foods . . . . . . . . . . . . . .77
Pharmaceuticals/Cosmetics . . . . . . . . . . .86
Miscellaneous . . . . . . . . . . . . . . . . . . . . . . .88
Appendix A . . . . . . . . . . . . . . . . . . . . . 90
Preparing Salt Solution . . . . . . . . . . . . . . .90
Appendix B . . . . . . . . . . . . . . . . . . . . . 92
Declaration of Conformity . . . . . . . . . 93
Certificate of Traceability . . . . . . . . . 94

AquaLab
1. Introduction
1
1. Introduction
Welcome to Decagon’s AquaLab Series 3, the industry
standard for measuring water activity (aw). AquaLab is the
quickest, most accurate, and most reliable instrument
available for measuring water activity. Whether you are
doing research or working on the production line,
AquaLab will suit your needs. It is easy to use and pro-
vides accurate and timely results. We hope you find this
manual informative and helpful in understanding how to
maximize the capabilities of your AquaLab.
About this Manual
Included in this manual are instructions for setting up
your AquaLab, verifying the calibration of the instrument,
preparing samples, and maintaining and caring for your
instrument. Please read these instructions before operat-
ing AquaLab to ensure that the instrument performs to its
full potential.
Customer Support
If you ever need assistance with your AquaLab, or if you
just have questions, there are several ways to contact us:
NOTE: If you purchased your AquaLab through a distributor,
please contact them for assistance.

AquaLab
1. Introduction
2
E-mail
[e-mail]
Please include your name, contact information, instru-
ment serial number(s), and a description of your problem
or question.
[email protected]
Please include your name, address, phone number, the
items you wish to order and a purchase order number.
Credit card numbers should always be called in.
Phone
1-800-755-2751 (USA and Canada Only)
1-509-332-2756 (International)
Our Customer Support and Sales Representatives are
available Monday thru Friday.
Fax
1-509-332-5158
Warranty
AquaLab has a 30-day satisfaction guarantee and a three-
year warranty on parts and labor. Your warranty is auto-
matically validated upon receipt of the instrument. We will
contact you within the first 90 days of your purchase to
see how the AquaLab is working for you.

AquaLab
1. Introduction
3
Seller’s Liability
Seller warrants new equipment of its own manufacture
against defective workmanship and materials for a period
of three years from date of receipt of equipment (the
results of ordinary wear and tear, neglect, misuse, accident
and excessive deterioration due to corrosion from any
cause are not to be considered a defect); but Seller’s liabil-
ity for defective parts shall in no event exceed the furnish-
ing of replacement parts Freight on Board the factory
where originally manufactured. Material and equipment
covered hereby which is not manufactured by Seller shall
be covered only by the warranty of its manufacturer. Seller
shall not be liable to Buyer for loss, damage or injuries to
persons (including death), or to property or things of
whatsoever kind (including, but not without limitation,
loss of anticipated profits), occasioned by or arising out of
the installation, operation, use, misuse, nonuse, repair, or
replacement of said material and equipment, or out of the
use of any method or process for which the same may be
employed. The use of this equipment constitutes Buyer’s
acceptance of the terms set forth in this warranty. There
are no understandings, representations, or warranties of
any kind, express, implied, statutory or otherwise (includ-
ing, but without limitation, the implied warranties of mer-
chantability and fitness for a particular purpose), not
expressly set forth herein.

AquaLab
2. About AquaLab
4
2. About AquaLab
AquaLab is the quickest and most accurate instrument
available for measuring water activity, giving readings in
five minutes or less. Its readings are the most reliable pro-
viding ±0.003awaccuracy. The instrument is easy to clean
and checking calibration is simple.
AquaLab 3 Instrument Specifications
Water Activity Range: 0.030 to 1.000
Water Activity Accuracy: ±0.003
Water Activity Resolution: ±0.001
Read time1: < 5 min.
Sample Temperature Range: 15 to 50°C
Sample Temperature accuracy2: ±0.2°C
Sample Temperature resolution: 0.1°C
Sample Dish Capacity: 7 ml recommended (15 ml full)
Operating Environment: 4 to 50°C;
0 to 90% Relative Humidity (non-condensing)
Case Dimensions: 24.1 x 22.9 x 8.9 cm
Weight: 3.2 Kg
Case Material: Powder Painted Aluminum
Display: 20 x 2 alphanumeric LCD with backlighting
Data Communication: RS232A compatible, 8-data bit
ASCII code, 9600 baud, no parity, 1 stop bit
Power: 110VAC to 220 VAC, 50/60 Hz
Warranty: 3 year parts and labor

AquaLab
2. About AquaLab
5
1on samples with no significant impedance to vapor loss
2AquaLab is calibrated to a NIST traceable temperature
standard.
AquaLab and Water Activity
Water activity (aw) is a measurement of the energy status
of the water in a system. It indicates how tightly water is
“bound”, structurally or chemically, within a substance.
Water activity is the relative humidity of air in equilibrium
with a sample in a sealed measurement chamber. The con-
cept of water activity is of particular importance in deter-
mining product quality and safety. Water activity
influences color, odor, flavor, texture and shelf-life of
many products. It predicts safety and stability with respect
to microbial growth, chemical and biochemical reaction
rates, and physical properties. For a more detailed descrip-
tion of water activity as it pertains to products, please refer
to Chpt. 3 of this manual, titled “Water Activity Theory”.
How AquaLab works
AquaLab uses the chilled-mirror dew point technique to
measure the water activity of a sample. In an instrument
that uses the dewpoint technique, the sample is equili-
brated with the headspace of a sealed chamber that con-
tains a mirror and a means of detecting condensation on
the mirror. At equilibrium, the relative humidity of the air
in the chamber is the same as the water activity of the
sample. In the AquaLab, the mirror temperature is pre-

AquaLab
2. About AquaLab
6
cisely controlled by a thermoelectric (Peltier) cooler.
Detection of the exact point at which condensation first
appears on the mirror is observed with a photoelectric
cell. A beam of light is directed onto the mirror and
reflected into a photodetector cell. The photodetector
senses the change in reflectance when condensation
occurs on the mirror. A thermocouple attached to the
mirror then records the temperature at which condensa-
tion occurs. AquaLab then signals you by flashing a green
LED and/or beeping. The final water activity and temper-
ature of the sample is then displayed.
In addition to the technique described above, AquaLab
uses an internal fan that circulates the air within the sam-
ple chamber to reduce equilibrium time. Since both dew-
point and sample surface temperatures are simultaneously
measured, the need for complete thermal equilibrium is
eliminated, which reduces measurement times to less than
five minutes.
AquaLab and Temperature
The AquaLab Series 3 does not control temperature, mak-
ing it ideal for the measurement of samples at room tem-
perature. However, samples that are not at room
temperature during the read cycle will equilibrate to the
temperature of AquaLab before the water activity is dis-
played. Large temperature differences will cause longer
reading times, since a complete and accurate reading will
not be made until the sample and the instrument are
within 2 degrees of each other. To better help you control

AquaLab
2. About AquaLab
7
the temperature difference between your sample and the
instrument, you can access a sample equilibration screen
at the main menu that can shows the difference in temper-
ature between the sample and chamber block (see chpt. 4).
If temperature control is desired, Decagon offers a tem-
perature-controlled model, the AquaLab 4TE. There are
several advantages in having a temperature-controlled
model. Here are a few major reasons:
1. Research purposes. To study the effects of tempera-
ture on the water activity of a sample, comparison of
the water activity of different samples independent of
temperature, accelerated shelf-life studies or other
water activity studies where temperature control is
critical. There are many shelf-life, packaging, and iso-
therm studies in which the added feature of tempera-
ture control would be very beneficial.
2. To comply with government or internal regula-
tions for specific products. Though the water activity
of most products varies by less than ± 0.002 per °C,
some regulations require measurement at a specific
temperature. The most common specification is 25°C,
though 20°C is sometimes indicated.
3. To minimize extreme ambient temperature fluc-
tuations. If the environment that the AquaLab oper-
ates in has temperatures that fluctuate by as much as ±

AquaLab
2. About AquaLab
8
5°C daily, water activity readings will vary by ± 0.01aw .
Such variations in ambient temperatures are uncom-
mon. As stated above, this much uncertainty in sample
water activity is sometimes acceptable, so there may be
no need for temperature control. However, if your lab
temperature varies to this degree and you require bet-
ter than 0.01awprecision, you may want a tempera-
ture-controlled model.
If your application meets any of the criteria listed above,
you may want to use the AquaLab 4TE.
Limitations
AquaLab’s only major limitation is its ability to accurately
measure samples with high concentrations of certain vola-
tiles such as ethanol or propylene glycol, which can co-
condense on the surface of the chilled mirror. Not all vol-
atiles react this way, but it is important to note that some
volatiles can affect the performance of your instrument.
The extent of the effect is both concentration- and matrix-
dependent; thus, just because a product contains some
ethanol or proplylene glycol does not necessarily mean the
readings will be erroneous. Therefore, if your sample con-
tains propylene glycol or a high concentration of other
volatiles, it is still possible to make accurate readings. Refer
to the section titled “Volatile Samples” in Chapter 8 or
contact Decagon for more details.

AquaLab
3. Water Activity Theory
9
3. Water Activity Theory
Water is a major component of foods, pharmaceuticals,
and cosmetics. Water influences the texture, appearance,
taste and spoilage of these products. There are two basic
types of water analysis: water content and water activity.
Moisture content
The meaning of the term moisture content is familiar to
most people. It implies a quantitative analysis to determine
the total amount of water present in a sample. Primary
methods for determining moisture content are loss on
drying and Karlf Fisher titration, but secondary methods
such as infrared and NMR are also used. Moisture content
determination is essential in meeting product nutritional
labeling regulations, specifying recipes and monitoring
processes. However, moisture content alone is not a
reliable indicator for predicting microbial responses and
chemical reactions in materials. The limitations of
moisture content measurement are attributed to
differences in the intensity with which water associates
with other components.
Water activity
Water activity is a measure of the energy status of the

AquaLab
3. Water Activity Theory
10
water in a system, and thus is a far better indicator of per-
ishability than water content. Figure 1 shows how the rela-
tive activity of microorganisms, lipids and enzymes relate
to water activity. While other factors, such as nutrient
availability and temperature, can affect the relationships,
water activity is the best single measure of how water
affects these processes.
Fig. 1: Water Activity Diagram—adapted from Labuza
Water activity of a system is measured by equilibrating the
liquid phase water in the sample with the vapor phase
water in the headspace and measuring the relative humid-
ity of the headspace. In the AquaLab, a sample is placed in
a sample cup which is sealed against a sensor block. Inside
the sensor block is a fan, a dew point sensor, a tempera-
ture sensor, and an infrared thermometer. The dew point
sensor measures the dew point temperature of the air, and

AquaLab
3. Water Activity Theory
11
the infrared thermometer measures the sample tempera-
ture. From these measurements the relative humidity of
the headspace is computed as the ratio of dew point tem-
perature saturation vapor pressure to saturation vapor
pressure at the sample temperature. When the water activ-
ity of the sample and the relative humidity of the air are in
equilibrium, the measurement of the headspace humidity
gives the water activity of the sample. The purpose of the
fan is to speed equilibrium and to control the boundary
layer conductance of the dew point sensor.
In addition to equilibrium between the liquid phase water
in the sample and the vapor phase, the internal equilib-
rium of the sample is important. If a system is not at inter-
nal equilibrium, one might measure a steady vapor
pressure (over the period of measurement) which is not
the true water activity of the system. An example of this
might be a baked good or a multi-component food. Ini-
tially out of the oven, a baked good is not at internal equi-
librium; the outer surface is at a lower water activity than
the center of the baked good. One must wait a period of
time in order for the water to migrate and the system to
come to internal equilibrium.
It is important to remember
the restriction of the definition of water activity to equilibrium.
Temperature Effects
Temperature plays a critical role in water activity determi-
nations. Most critical is the measurement of the difference
between sample and dew point temperature. If this tem-

AquaLab
3. Water Activity Theory
12
perature difference were in error by 1°C, an error of up to
0.06awcould result. In order for water activity measure-
ments to be accurate to 0.001, temperature difference
measurements need to be accurate to 0.017°C. AquaLab’s
infrared thermometer measures the difference in tempera-
ture between the sample and the block. It is carefully cali-
brated to minimize temperature errors, but achieving
0.017°C accuracy is difficult when temperature differences
are large. Best accuracy is therefore obtained when the
sample is near chamber temperature.
Another effect of temperature on water activity occurs
with samples are near saturation. A sample that is close to
1.0awand is only slightly warmer than the sensor block
will condense water within the block. This will cause
errors in the measurement, and in subsequent measure-
ments until the condensation disappears. A sample at
0.75awneeds to be approximately 4°C above the chamber
temperature to cause condensation. The AquaLab warns
the user if a sample is more than 4°C above the chamber
temperature, but for high water activity samples the opera-
tor needs to be aware that condensation can occur if a
sample that is warmer than the block is put in the
AquaLab.
Water Potential
Some additional information may be useful for under-
standing what water activity is and why it is such a useful
measure of moisture status in products. Water activity is

AquaLab
3. Water Activity Theory
13
closely related to a thermodynamic property called the wa-
ter potential, or chemical potential (m) of water, which is
the change in Gibbs free energy (G) hen water concentra-
tion changes. Equilibrium occurs in a system when m is the
same everywhere in the system. Equilibrium between the
liquid and the vapor phases implies that m is the same in
both phases. It is this fact that allows us to measure the wa-
ter potential of the vapor phase and use that to determine
the water potential of the liquid phase. Gradients in m are
driving forces for moisture movement. Thus, in an isother-
mal system, water tends to move from regions of high wa-
ter potential (high water activity) to regions of low water
potential (low water activity). Water content is not a driving
force for water movement, and therefore can not be used
to predict the direction of water movement, except in ho-
mogeneous materials.
Factors in Determining Water Potential
The water potential of the water in a system is influenced
by factors that effect the binding of water. They include
osmotic, matric, and pressure effects. Typically water activ-
ity is measured at atmospheric pressure, so only the
osmotic and matric effects are important.
Osmotic Effects
Osmotic effects are well known from biology and physical
chemistry. Water is diluted when a solute is added. If this
diluted water is separated from pure water by a semi-per-

AquaLab
3. Water Activity Theory
14
meable membrane, water tends to move from the pure
water side through the membrane to the side with the
added solute. If sufficient pressure is applied to the solute-
water mixture to just stop the flow, this pressure is a mea-
sure of the osmotic potential of the solution. Addition of
one mole of an ideal solute to a kilogram of water pro-
duces an osmotic pressure of 22.4 atm. This lowers the
water activity of the solution from 1.0 to 0.98aw . For a
given amount of solute, increasing the water content of
the systems dilutes the solute, decreasing the osmotic
pressure, and increasing the water activity. Since microbial
cells are high concentrations of solute surrounded by
semi-permeable membranes, the osmotic effect on the
free energy of the water is important for determining
microbial water relations and therefore their activity.
Matric Effects
The sample matrix affects water activity by physically
binding water within its structure through adhesive and
cohesive forces that hold water in pores and capillaries,
and to particle surfaces. If cellulose or protein were added
to water, the energy status of the water would be reduced.
Work would need to be done to extract the water from
this matrix. This reduction in energy status of the water is
not osmotic, because the cellulose or protein concentra-
tions are far too low to produce any significant dilution of
water. The reduction in energy is the result of direct phys-
ical binding of water to the cellulose or protein matrix by
hydrogen bonding and van der Waal forces. At higher

AquaLab
3. Water Activity Theory
15
water activity levels, capillary forces and surface tension
can also play a role.
Sorption Isotherms
Relating Water Activity to Water Content
Changes in water content affect both the osmotic and
matric binding of water in a product. Thus a relationship
exists between the water activity and water content of a
product. This relationship is called the sorption isotherm,
and is unique for each product. Besides being unique to
each product, the isotherm changes depending on
whether it was obtained by drying or wetting the sample.
These factors need to be kept in mind if one tries to use
water content to infer the stability or safety of a product.
Typically, large safety margins are built in to water content
specifications to allow for these uncertainties.
While the sorption isotherm is often used to infer water
activity from water content, one could easily go the other
direction and use the water activity to infer the water con-
tent. This is particularly attractive because water activity is
much more quickly measured than water content. This
method gives particularly good precision in the center of
the isotherm. In order to infer water content from water
activity, one needs an isotherm for the particular product;
produced, ideally, using the process that brings the prod-
uct to its final water content.