Decagon Devices AquaLab 4TE User manual

AquaLab
Water Activity Meter
Operator’s Manual
For Series 4TE, 4TEV, DUO
Version 7
Decagon Devices, Inc.

Decagon Devices, Inc
2365 NE Hopkins Court
Pullman WA 99163
[phone]
fax: [phone]
www.aqualab.com
[email protected]
[email protected]
Trademarks
AquaLab is a registered trademark of
Decagon Devices, Inc.
©2008-2012 Decagon Devices, Inc.

i
Contents
1. Introduction .................................1
About this Manual ....................................1
Customer Support .....................................1
Warranty ...................................................2
Seller’s Liability..........................................2
2. About AquaLab ...........................4
AquaLab Model and Options ....................4
AquaLab 4 Instrument Specications ........4
AquaLab 4 DUO Specications.................5
How AquaLab Works ................................6
AquaLab and Temperature ........................6
Chilled Mirror Dewpoint Limitations .......8
3. Water Activity eory...................9
Moisture Content ......................................9
Water Activity............................................9
Water Potential ........................................12
Sorption Isotherms ..................................13
4. Getting Started........................... 15
Components of your AquaLab................. 15
Choosing a Location ............................... 15
Preparing AquaLab for Operation............16
5. Menus ......................................... 18
Measurement Tab ....................................18

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Conguration Tab ...................................19
Admin Settings........................................25
Data Tab .................................................30
6. Cleaning and Maintenance........32
Cleaning the Block and Sensors ...............33
Cleaning a Series 4TEV: .......................34
Cleaning Procedure: ...............................34
Verication of Calibration .......................36
7. Ve r i cation and Calibration........37
Water Activity Verication.......................37
Verication of Calibration .......................39
8. Sample Preparation ....................46
Preparing the Sample...............................46
Samples Needing Special Preparation ......47
Slow Water-Emitting Samples..................48
Volatile Samples.......................................49
Low Water Activity..................................50
Samples Not at Room Temperature .........50
9. Taking a Reading .......................52
Measurement Steps..................................52
How AquaLab Takes Readings ................52
10. Duo Operation (Optional)....... 55
Obtaining Product Isotherm Models .......56
Loading and Organizing Product Models 56
Moisture Content Adjustment ...............60
Restore Original Moisture Content Model
Settings....................................................64

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How to Delete Models.............................66
11. Computer Interface...................68
AquaLink RG ..........................................68
Using Windows Hyperterminal .............68
12. Troubleshooting .......................70
13. Support and Repair ..................83
Repair Costs ............................................84
Loaner Service .........................................84
14. Further Reading ....................... 85
Water Activity eory & Measurement ...85
Food Safety and Microbiology.................89
Appendix A................................... 111
Preparing Salt Solution .......................... 111
Appendix B................................... 113
Temperature Correction ........................ 113
Appendix C................................... 114
AquaLab Verication Standards ............ 114
Declaration of Conformity ........... 119
Certicate of Traceability.............120

iv

AquaLab
1. Introduction
1
1. INTRODUCTION
Welcome to Decagon’s AquaLab Series 4, 4TE, 4TEV, and DUO,
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 researching or work-
ing on the production line, AquaLab will suit your needs. It is easy
to use and provides accurate and timely results.
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 in-
structions before operating 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 or feedback, there are several ways to contact us:
NOTE: If you purchased your AquaLab through a distributor, please
contact them for assistance.
E-mail
[email protected]
Please include your name, contact information, instrument 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.

AquaLab
1. Introduction
2
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 war-
ranty on parts and labor. Your warranty is automatically validated
upon receipt of the instrument. We will contact you within the rst
90 days of your purchase to see how the AquaLab is working for
you.
Seller’s Liability
Seller warrants new equipment of its own manufacture against de-
fective 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 corro-
sion from any cause are not to be considered a defect); but Seller’s
liability for defective parts shall in no event exceed the furnishing
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 prots), occasioned by or arising out of the installation,

AquaLab
1. Introduction
3
operation, use, misuse, nonuse, repair, or replacement of said ma-
terial and equipment, or out of the use of any method or process
for which the same may be employed. e use of this equipment
constitutes Buyer’s acceptance of the terms set forth in this warranty.
ere are no understandings, representations, or warranties of any
kind, express, implied, statutory or otherwise (including, but with-
out limitation, the implied warranties of merchantability and tness
for a particular purpose), not expressly set forth herein.

AquaLab
2. About AquaLab
4
2. About AquaLab
AquaLab is the fastest and most accurate instrument for measuring
water activity, giving readings in ve minutes or less. Its readings
are reliable, providing ±0.003 awaccuracy. e instrument is easy
to clean and checking calibration is simple.
AquaLab Model and Options
Series 4: Uses chilled-mirror dewpoint sensor, but lacks tempera-
ture control features of premium models.
Series 4TE: User-selectable internal temperature control model,
uses thermoelectric (Peltier) components to maintain internal tem-
perature.
Series 4TEV: Uses both a chilled-mirror dewpoint sensor and a ca-
pacitance sensor for measuring non-volatile and volatile substances,
respectively. Either sensor is easily selected using the instrument’s
menu system.
Series 4TE DUO: Uses chilled-mirror dewpoint and programmed
models obtained from isotherm data to give the user both water ac-
tivity and moisture content simultaneously in ve minutes or less.
AquaLab 4 Instrument Specications
Water Activity Range: 0.050 to 1.000 aw
Water Activity Accuracy: ±0.003 (4TE Dew Point Mode)
Water Activity Accuracy: ±0.015 (4TEV Capacitance Mode)
Water Activity Resolution: 0.0001

AquaLab
2. About AquaLab
5
Read Time1:≤5 min.
Sample Temperature Range: 15 to 50° C
Sample Temperature Accuracy: ±0.2° C
Sample Temperature Resolution: 0.01° C
Sample Dish Capacity: 15ml Full
Operating Environment: 5 to 50° C 20 to 80% Humidity
Case Dimensions: 26.7 x 17.8 x 12.7cm
Weight: 3.1 Kg
Case Material: Lustran 433 (ABS) with re retardant
Display: 64 x 128 Graphical
Data Communications: RS232A Serial, 9600 to 115200 baud
Power: 110 to 220 VAC, 50/60Hz
Warranty: 3 year parts and labor
1 On samples with no signicant impedance to vapor loss
AquaLab 4 DUO Specications
Moisture Content Repeatability: 0.02%
Accuracy to Moisture Content Ref.: 0.1% to 0.5%
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 hu-
midity of air in equilibrium with a sample in a sealed measurement
chamber. e concept of water activity is of particular importance
in determining product quality and safety. Water activity inuences
color, odor, avor, 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 de-
tailed description of water activity as it pertains to products, please
refer to Chapter 3 of this manual, titled “ Water Activity eory”.

AquaLab
2. About AquaLab
6
How AquaLab Works
AquaLab uses the chilled-mirror dewpoint technique to measure the
water activity of a sample. In an instrument that uses the dewpoint
technique, the sample is equilibrated with the head-space of a sealed
chamber that contains a mirror and a means of detecting condensa-
tion 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 precisely controlled by a
thermoelectric (Peltier) cooler. Detection of the exact point at which
condensation rst appears on the mirror is observed with a photo-
electric cell. A beam of light is directed onto the mirror and reected
into a photo detector cell. e photo detector senses the change
in reectance when condensation occurs on the mirror. A thermo-
couple attached to the mirror then records the temperature at which
condensation occurs. AquaLab then signals you by beeping and dis-
plays the nal water activity and temperature.
In addition to the technique described above, AquaLab uses an in-
ternal fan that circulates the air within the sample chamber to reduce
equilibrium time. Since both dewpoint and sample surface tempera-
tures are simultaneously measured, the need for complete thermal
equilibrium is eliminated, which reduces measurement times to less
than ve minutes.
AquaLab and Temperature
Samples not read at room temperature during the read cycle will
equilibrate with the AquaLab’s temperature before the water activity
is displayed. Large temperature dierences will cause longer reading
times, since a complete and accurate reading will not be made until
the sample and the instrument are within 2°C of each other.

AquaLab
2. About AquaLab
7
ere are several advantages in having a temperature-controlled wa-
ter activity meter. A few major reasons are:
1. Research purposes. Temperature control can be used to study
the eects of temperature on the water activity of a sample, make a
comparison of the water activity of dierent samples independent
of temperature, and conduct accelerated shelf-life studies or other
water activity studies where temperature control is critical. ere are
many shelf-life, packaging, and isotherm studies in which tempera-
ture control would be very benecial.
2. To comply with government or internal regulations for specic
products. ough the water activity of most products varies by less
than ± 0.002 per °C, some regulations require measurement at a spe-
cic temperature. e most common specication is 25°C, though
20°C is sometimes indicated.
3. To minimize extreme ambient temperature uctuations. If the
environmental and AquaLab temperatures uctuate by as much as ±
5°C daily, water activity readings will vary by ± 0.01 aw. Temperature
control eliminates variations due to changes in ambient conditions.
Series 4TE/4TEV/4TE-DUO
e AquaLab Series 4TE models have thermoelectric components
installed to allow the instrument to maintain a set chamber tem-
perature. e temperature is set using the conguration menu of any
of the Series 4 models.

AquaLab
2. About AquaLab
8
Chilled Mirror Dewpoint Limitations
AquaLab’s limitation is its ability to accurately measure samples with
high concentrations (typically >1%) of certain volatiles such as etha-
nol or propylene glycol, which can condense on the surface of the
chilled mirror. e extent of the eect is determined by how readily
the material volatilizes, which is both concentration- and matrix-
dependent. erefore, even if your sample contains materials that
could volatilize, it may still be possible to make accurate readings
using the chilled mirror dewpoint sensor.
AquaLab Series 4TEV which incorporates both a chilled mirror sen-
sor and a capacitance sensor for measuring volatile substances is
Decagon’s solution for products containing volatile materials. If you
are unsure if you need the TEV model, please call and discuss your
product with a Decagon Representative. Refer to Chapter 8’s section
titled ”Volatile Samples” or call Decagon for more details.

AquaLab
3. Water Activity eory
9
3. Water Activity eory
Water is a major component of foods, pharmaceuticals, and cosmet-
ics. Water inuences the texture, appearance, taste and spoilage of these
products. ere are two basic types of water analysis: moisture content
and water activity.
Moisture Content
e meaning of the term moisture content is familiar to most peo-
ple. 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 Karl Fisher titration, but
secondary methods such as infrared and NMR are also used. Mois-
ture content determination is essential in meeting product nutri-
tional labeling regulations, specifying recipes and monitoring pro-
cesses. However, moisture content alone is not a reliable indicator
for predicting microbial responses and chemical reactions in materi-
als. e limitations of moisture content measurement are attributed
to dierences in the intensity with which water associates with other
components.
Water Activity
Water activity is a measure of the energy status of the water in a
system, and thus is a far better indicator of perishability than water
content. Figure 1 shows how the relative activity of microorganisms,
lipids and enzymes relate to water activity. While other factors, such
as nutrient availability and temperature, can aect the relationships,
water activity is the best single measure of how water aects these
processes.

AquaLab
3. Water Activity eory
10
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 head-
space and measuring the relative humidity of the head-space. In
the AquaLab, a sample is placed in a sample cup which is sealed
inside a sample chamber. Inside the sample chamber is a fan, a dew
point sensor, a temperature sensor, and an infrared thermometer.
e dewpoint sensor measures the dewpoint temperature of the air
in the chamber, and the infrared thermometer measures the sample
temperature. From these measurements, the relative humidity of
the head-space is computed as the ratio of dewpoint temperature
saturation vapor pressure to saturation vapor pressure at the sample
temperature. When the water activity of the sample and the rela-
tive humidity of the air are in equilibrium, the measurement of the
head-space humidity gives the water activity of the sample. e pur-
pose of the fan is to speed equilibrium and to control the boundary
layer conductance of the dewpoint sensor.

AquaLab
3. Water Activity eory
11
In addition to equilibrium between the liquid phase water in the
sample and the vapor phase, the internal equilibrium of the sample
is important. If a system is not at internal 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. Initially out
of the oven, a baked good is not at internal equilibrium; 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 denition of water activity to equi-
librium.
Temperature Eects
Temperature plays a critical role in water activity determination.
Most critical is the measurement of the dierence between sample
and dewpoint temperature. If this temperature dierence were in er-
ror by 1°C, an error of up to 0.06 awcould result. In order for water
activity measurements to be accurate to 0.001, temperature dier-
ence measurements need to be accurate to 0.017°C. AquaLab’s in-
frared thermometer measures the dierence in temperature between
the sample and the block. It is carefully calibrated to minimize tem-
perature errors, but achieving 0.017°C accuracy is dicult when
temperature dierences are large. Best accuracy is therefore obtained
when the sample is near chamber temperature.
Another eect of temperature on water activity occurs when sam-
ples are near saturation. A sample that is close to 1.0 awand is only
slightly warmer than the sensor block will condense water within the
block. is will cause errors in the measurement, and in subsequent
measurements until the condensation disappears. A sample at 0.75 aw
needs to be approximately 4°C above the chamber temperature to

AquaLab
3. Water Activity eory
12
cause condensation. e AquaLab warns the user if a sample is more
than 4°C above the chamber temperature, but for high water activity
samples the operator 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 understanding what
water activity is and why it is such a useful measure of moisture
status in products. Water activity is closely related to a thermody-
namic property called the water potential, or chemical potential (μ)
of water, which is the change in Gibbs free energy (∆G) when water
concentration changes. Equilibrium occurs in a system when (µ) is
the same everywhere in the system. Equilibrium between the liquid
and the vapor phases implies that () is the same in both phases. It
is this fact that allows us to measure the water potential of the vapor
phase and use that to determine the water potential of the liquid
phase. Gradients in (µ) are driving forces for moisture movement.
us, in an isothermal system, water tends to move from regions of
high water potential (high aw) to regions of low water potential (low
aw). Water content is not a driving force for water movement, and
therefore can not be used to predict the direction of water move-
ment, except in homogeneous materials.
Factors In Determining Water Activity
e water activity of the water in a system is inuenced by factors
that eect the binding of water. ey include osmotic, matric, and
pressure eects. Typically water activity is measured at atmospheric
pressure, so only the osmotic and matric eects are important.
Osmotic Eects
Osmotic eects are well known from biology and physical chemis-
try. Water is diluted when a solute is added. If this diluted water is

AquaLab
3. Water Activity eory
13
separated from pure water by a semi-permeable membrane, water
tends to move from the pure water side through the membrane to
the side with the added solute. If sucient pressure is applied to the
solute-water mixture to just stop the ow, this pressure is a measure
of the osmotic potential of the solution. Addition of one mole of an
ideal solute to a kilogram of water produces an osmotic pressure of
22.4 atm. is lowers the water activity of the solution from 1.0 to
0.98 aw. 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 con-
centrations of solute surrounded by semi-permeable membranes,
the osmotic eect on the free energy of the water is important for
determining microbial water relations and therefore their activity.
Matric Eects
e sample matrix aects 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. is
reduction in energy status of the water is not osmotic, because the cellu-
lose or protein concentrations are far too low to produce any signicant
dilution of water. e reduction in energy is the result of direct physical
binding of water to the cellulose or protein matrix by hydrogen bonding
and van der Waal forces. At higher 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 aect both the osmotic and matric bind-
ing of water in a product. us a relationship exists between the
water activity and water content of a product. is relationship is

AquaLab
3. Water Activity eory
14
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. ese fac-
tors 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 into water content specications 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 content. is is particularly attrac-
tive because water activity is much more quickly measured than wa-
ter content. is 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. Decagon
sells an Isotherm Generator called the AquaSorp IG or you can also
have Decagon run the isotherm for a fee.
For example, if one were using the AquaLab to monitor the water
content of dried potato akes, one would measure the water activity
and water content of potato akes dried to varying degrees using the
standard drying process for those akes. An isotherm would be con-
structed using those data, and the water content would be inferred
using the measured water activity of samples and that isotherm. We
have an upgrade available to Series 4TE users that would allow you
to determine moisture content and water activity simultaneously.
is instrument is called the Series 4TE DUO.
e importance of the concept of water activity of foods, pharma-
ceuticals, and cosmetics cannot be over emphasized. Water activity is
a measure of the energy status of the water in a system. More impor-
tantly, the usefulness of water activity in relation to microbial growth,
chemical reactivity, and stability over water content has been shown.