WPI ISO-H2S-100 User manual

Instrumenting scientific ideas
WORLD
PRECISION
INSTRUMENTS
ISO-H2S-100
Microsensor for H2S measurement
Serial No._____________________
www.wpiinc.com
INSTRUCTION MANUAL
030316

ISO-H2S-100
World Precision Instruments i
Copyright © 2016 by World Precision Instruments, Inc. All rights reserved. No part of this publication
may be reproduced or translated into any language, in any form, without prior written permission of
World Precision Instruments, Inc.
CONTENTS
ABOUT THIS MANUAL ................................................................................................................... 1
INTRODUCTION .............................................................................................................................. 2
Notes and Warnings................................................................................................................. 3
Parts List...................................................................................................................................... 3
Unpacking................................................................................................................................... 3
OPERATING INSTRUCTIONS......................................................................................................... 4
Attaching the Sensor to the Microsensor Handle ............................................................ 4
Polarizing the Sensor ............................................................................................................... 4
Calibrating the Sensor ............................................................................................................. 5
Preparation of Na2S Stock Solution ................................................................................ 5
Calibration Procedure........................................................................................................ 5
MAINTENANCE ................................................................................................................................ 7
Storing the Sensor.................................................................................................................... 7
Cleaning the Sensor ................................................................................................................. 7
ACCESSORIES................................................................................................................................... 7
TROUBLESHOOTING ..................................................................................................................... 8
SPECIFICATIONS.............................................................................................................................. 9
WARRANTY .....................................................................................................................................11
Claims and Returns ................................................................................................................11
Repairs.......................................................................................................................................11

ii World Precision Instruments

ISO-H2S-100
World Precision Instruments 1
ABOUT THIS MANUAL
The following symbols are used in this guide:
This symbol indicates a CAUTION. Cautions warn against actions that can cause
damage to equipment. Please read these carefully.
This symbol indicates a WARNING. Warnings alert you to actions that can cause
personal injury or pose a physical threat. Please read these carefully.
NOTES and TIPS contain helpful information.
Fig. 1—The ISO-H2S-100 sensor is a platinum wire electrode that functions similar to
WPI’s ISO-H2S-2 sensor.

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INTRODUCTION
The ISO-H2S-100 is a hydrogen sulde sensor with a 100µm diameter tip. It is a dry
microsensors, however, it functions like a traditional ISO-H2S-2 sensor. The sensor
can be ordered in a variety of lengths from 2–5mm. It incorporates WPI’s proprietary
combination electrode technology in which the hydrogen sulde-sensing element and
separate reference electrode are encased within a single shielded sensor design.
The ISO-H2S-2 is WPI’s original 2mm H2S sensor, that incorporates a removable,
electrolyte-lled membrane sleeve. The new ISO-H2S-100 oers several advantages:
• It is much easier to use, because requires no sleeves or lling solutions.
• Because the ISO-H2S-100 is constructed with platinum wire, it is more
durable.
• It oers a bigger linear range than the ISO-H2S-2, and the range is based on
the length of the sensor tip.
Tip Length
Hydrophobic
gas permeable
coating
Stainless steel handle
Shielded cable
to the free radical
analyzer
Durable
sensor body
Diameter:
100µm
Fig. 2—The ISO-H2S-100 is used like the other microsensors.

ISO-H2S-100
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Notes and Warnings
The H2S microsensor is robust, but not indestructible. Exercise caution when handling
the sensor to avoid actions that could damage the tip. Do not bring the tip into
contact with hard surfaces like stir bars. See ”Unpacking” on page 3.
CAUTION: DO NOT EXPOSE SENSOR TO ORGANIC SOLVENTS.
Parts List
After unpacking, verify that there is no visible damage to the sensor. Verify that all
items are included:
(2) ISO-H2S-100 microsensors
(2) Sensor Performance Evaluations (each sensor is tested individually at WPI)
(1) Instruction Manual
Unpacking
Upon receipt of this instrument, make a thorough inspection of the contents and
check for possible damage. Missing cartons or obvious damage to cartons should be
noted on the delivery receipt before signing. Concealed damage should be reported
at once to the carrier and an inspection requested. Please read the section entitled
“Claims and Returns” on page 11 of this manual. Please contact WPI Customer
Service if any parts are missing at 941.371.1003 or [email protected].
Returns: Do not return any goods to WPI without obtaining prior approval (RMA
# required) and instructions from WPI’s Returns Department. Goods returned
(unauthorized) by collect freight may be refused. If a return shipment is necessary,
use the original container, if possible. If the original container is not available, use a
suitable substitute that is rigid and of adequate size. Wrap the instrument in paper or
plastic surrounded with at least 100mm (four inches) of shock absorbing material. For
further details, please read the section entitled “Claims and Returns” on page 11 of
this manual.

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OPERATING INSTRUCTIONS
Attaching the Sensor to the Microsensor Handle
Once removed from the package, plug the microsensor into a microsensor cable
(WPI #91580) connected to the free radical analyzer (Fig. 3).* Be very careful that
the sensor tip does not come into contact with anything that could damage
it. The sensor should plug in easily. If you encounter resistance, it is probably due to
misalignment of the sensor plug with the socket connector inside the microsensor
cable. Simply realign the sensor by gently rotating it until it snaps into place.
*NOTE: Current WPI free radical analyzers include the TBR4100 and TBR1025.
Previous analyzers manufactured by WPI (like Apollo1000, Apollo4000) may also be
used.
Insert sensor connector into microsensor cable
Microsensor Cable (91580)
Microsensor Cable (91580)
connector
Fig. 3—Microsensors may be changed or replaced quickly and easily
Polarizing the Sensor
When a non-polarized microsensor is initially connected to a free radical analyzer,
it will display a high (sometimes o-scale) background current. It takes time for the
background current to drop down to a stabilized baseline value. Set the poise voltage
to 0.15V. (For the TBR4100/1025, set the Probe Select dial to H2S. ) The amount of
time required to reach a stable baseline current varies for each sensor. New sensors
typically take longer, on the order of four hours.
The Performance Evaluation included with your sensor shows the baseline current
and the sensitivity of your sensor when it was quality tested at WPI. (In addition,
it shows the polarization time of your sensor in the WPI labs.) The baseline value
attainable in your lab may be slightly higher or lower, depending on the temperature*
and composition of the test media. For initial performance verication of an
ISO-H2S-100 in your lab, WPI recommends using the Na2S calibration method
described below. Once a stable baseline current is achieved (usually between 100–
2,000pA), the microsensor is ready for use.

ISO-H2S-100
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It is possible for the background current to be negative after the polarizing. This does
not aect the functionality of the sensor.
*NOTE: The background current of the sensor will usually increase with increasing
temperature of the experiment. Although the sensitivity of the sensor does not
change signicantly within the range 20-37°C, it is recommended that the calibration
procedure be performed at the same temperature and salinity as the experiment.
Calibrating the Sensor
Once the sensor is polarized, it can be calibrated. The following example briey
describes the fundamental concepts behind a standard calibration protocol. Known
concentrations of H2S are generated in buer solution by adding a known volume of
the prepared Na2S stock solution.
NOTE: To avoid thermal artifacts during the calibration procedure, both the
calibration media and Na2S stock solution should be maintained at the same
temperature.
NOTE: For additional information, refer to the free radical analyzer manual. Most WPI
manuals can be downloaded directly from www.wpiinc.com. This information can also
be e-mailed when you contact the WPI Technical Support team at 941.371.1003 or
[email protected].
Preparation of Na2S Stock Solution
1. Dissolve 5mg EDTA in 100mL distilled water (18mΩ) in 100mL volumetric ask.
2. Purge the solution vigorously with argon gas for 15 minutes.
3. Weigh 48.0mg sodium sulde (Na2S .9 H2O–reagent plus, 99.99+% – Sigma
#431648) and dissolve it in the solution under argon atmospheres.
4. Seal the ask with a rubber stopper. The solution is 2.0mM Na2S. Keep the
solution refrigerated (2-8 °C) and away from light.
Calibration Procedure
The polarized sensor should already be immersed in solution and plugged into the
free radical analyzer. Set the range to 10nA and the poise voltage to +150mV.
The H2S sensor is sensitive to salinity and temperature, and H2S solubility is sensitive
to temperature. Calibration and subsequent measurements should be performed in a
solution with the same temperature and salinity.
1. Place 20mL PBS buer solution (pH 7.2, 0.05M) in a 20mL vial, drop a small
stirring bar into the PBS solution and place the vial on a magnetic stirring plate.
2. Immerse the tip of the H2S sensor in the solution and secure it in an electrode
holder such as WPI’s Pro-Guide (WPI #47510, 47520, 47530, 47540) or a
micromanipulator. The sensor tip should be immersed about 10–15mm into the
solution. It should not contact the stir bar, which could damage the tip.

6 World Precision Instruments
3. Wait until the current on the display stabilizes again before continuing and
record the value. This may take several minutes if the sensor has undergone a
large temperature change.
4. To the vial containing 20mL of PBS solution, sequentially inject four aliquots of the
Na2S solution (5µL, 10µL, 20µL and 40µL) into the glass vial. Typically, each aliquot
is twice the volume of the previous one. The current output jumps rapidly after
each addition and then plateaus. As soon as it reaches a plateau, inject the next
aliquot.
The reaction produces H2S gas. When H2S gas passes through the gas permeable
coating, it generates an output current that is measurable, and the results can
then be graphed using a third party spreadsheet with graphing capability like
Microsoft®Excel.
NOTE: The volume of injected calibration aliquots may be adjusted to
accommodate the anticipated concentration range for the experiment.
5. Construct a calibration curve by plotting the signal output (pA) against the
concentration (nM) of H2S. Using a third party spreadsheet with graphing
capability like Microsoft®Excel, it is possible to generate a linear regression
analysis that will display the equation and the R2 coecient. To do this in Excel,
enter the data and generate a “scatter plot” graph. Then, select the line and right
click. Choose Add Trendline. The Add Trendline dialog box appears. On the
Type tab, select Linear, and on the Options tab, select the Display equation
on chart and Display R-value on chart.
***The H2S sensor measures the dissolved H2S gas, which is only one component
of the total sulde equilibrium system. The total sulde concentration [S2] = [H2S] +
[HS-] + [S2-], so the H2S concentration can be calculated by: [H2S] = [Na2S]/{ 1+ K1/[H+]
+ K1K2/[H+]}
For K1and K2, ( pK1= 6.89, pK2=19) see
Frank J. Millero, Tinka Plese, Marino Fernandez(1988)
Limnology and Oceanography, 33(2): 269
Giggenbach, W. (1971). Inorg. Chem. 10:1333.
Meyer, B.; Ward, K.; Koshlap, K.; & Peter, L. (1983). Inorganic Chemistry 22:2345.
Myers, R. J. (1986). Journal of Chemical Education 63:687.