Vernier Go Direct GDX-CL-BNC User manual

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Note: Do not completely submerge the sensor. The BNC connection is not
waterproof.
Preparing the Chloride ISE for Use
Soak the electrode in the High Standard solution (included with the ISE) for
approximately 30 minutes. The ISE should not rest on the bottom of the
container, and the small white reference contacts near the tip of the electrode
should be immersed. Make sure no air bubbles are trapped below the ISE.
Important: Do not leave the ISE soaking for more than 24 hours. Important: If
you plan to use the electrode outside the range of the standards provided, you
will need to prepare your own standards and use those for soaking.
Note: If the ISE needs to be transported to the field during the soaking process,
use the Short-Term ISE Soaking Bottle. Remove the cap from the bottle and fill
it 3/4 full with High Standard. Slide the bottle’s cap onto the ISE, insert it into
the bottle, and tighten.
For long term storage, greater than 24 hours, make sure the sensor is stored in its
storage bottle with the sponge slightly damp.
Collecting Data
1. Remove the storage bottle from the soaking solution (high standard).
Thoroughly rinse the lower section of the probe, especially around the tip,
using distilled or deionized water. Blot dry with a paper towel.
2. Insert the tip of the ISE into the aqueous sample to be tested. Important:
Make sure the ISE is not resting on the bottom of the container, the white
reference contacts near the tip of the electrode are immersed, and no air
bubbles are trapped below the ISE. Note: Do not completely submerge the
sensor. The handle is not waterproof.
3. Hold the ISE still until the reading stabilizes and record the displayed
reading. Note: With some aqueous samples, especially those at high
concentrations, it could take several minutes for the reading of the Chloride
ISE to stabilize. If you know the approximate concentrations of your
samples, it is best to analyze them from lowest concentration to highest.
Specifications
Range (mV) –1000 mV to +1000 mV
Range (concentration) 1 to 35,000 mg/L (or ppm)
Reproducibility (precision) ±30 mV
Interfering ions CN–, Br–, I–, OH–, S2–, NH3
pH range 2–12 (no pH compensation)
Temperature range 0–80°C (no temperature compensation)
Electrode slope –56 ±3 mV/decade at 25°C
Go Direct®Chloride
Ion-Selective Electrode BNC
(Order Code GDX-CL-BNC)
The Go Direct Chloride Ion-Selective Electrode BNC is used to measure the
concentration of chloride (Cl−) ions in aqueous samples. It is designed to be
used with the Vernier Go Direct Electrode Amplifier (order code GDX-EA).
Chloride ions are found in freshwater samples as a result of water flowing over
salt-containing minerals. These salts might include either sodium chloride
(NaCl) or potassium chloride (KCl). The EPA maximum contamination level for
chloride concentration in drinking water is 250 mg/L. The chloride ion
concentration in seawater is approximately 19,400 mg/L—well below the upper
limit of the Chloride ISE of 35,500 mg/L.
Note: Vernier products are designed for educational use. Our products are not
designed nor are they recommended for any industrial, medical, or commercial
process such as life support, patient diagnosis, control of a manufacturing
process, or industrial testing of any kind.
What's Included
lIon-Selective Electrode, packed in a storage bottle with a damp sponge
l30 mL bottle of High Standard solution with SDS (1000 mg/L Cl–)
l30 mL bottle of Low Standard solution with SDS (10 mg/L Cl–)
lShort-Term ISE Soaking Bottle
Using the Product
To prepare the electrode to make measurements, follow this procedure:
lConnect the Ion-Selective Electrode BNC to the Go Direct Ion-Selective
Electrode Amplifier. Push the BNC connector of the electrode onto the
connector on the amplifier, then turn the BNC connector about one-half turn
clockwise.
lConnect the amplifier to your computer, Chromebook™, LabQuest 2, or
mobile device and run the data-collection software. Change the sensor
channel to the appropriate ion or Potential, if necessary.
lYour ISE needs to be prepared before use. This includes a 30-minute soak in
the High Standard solution.
lIf you plan to use the electrode outside the range of the standards provided,
you will need to prepare your own standards and use those for soaking and
calibration.
lThe ISE should not rest on the bottom of the container.
lThe small white reference contacts near the tip of the electrode should be
immersed.
lMake sure no air bubbles are trapped below the ISE.
lDo not leave the ISE soaking for more than 24 hours.

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How the Sensor Works
Combination Ion-Selective Electrodes consist of an ion-specific (sensing) half-
cell and a reference half-cell. The ion-specific half-cell produces a potential that
is measured against the reference half-cell depending on the activity of the
target ion in the measured sample. The ion activity and the potential reading
change as the target ion concentration of the sample changes. The relationship
between the potential measured with the ISE and the ion activity, and thereby
the ion concentration in the sample, is described by the Nernst equation:
E= measured potential (mV) between the ion-selective and the reference
electrode
Eo= standard potential (mV) between the ion-selective and reference electrodes
R = universal gas constant (R = 8.314 J mol-1 K-1)
T= temperature in K (Kelvin), with T (K) = 273.15 + t °C where tis the
temperature of the measured solution in °C.
F = Faraday constant (96485 C mol-1)
n= valence of the ion
C= concentration of ion to be measured
Co= detection limit
Since R and F are constant, they will not change. The electrical charge of the
ion (valence) to be measured is also known. Therefore, this equation can be
simplified as:
E = Eo–S •log(C + Co)
where is the ideal slope of the ISE.
The following table describes ideal behavior:
Ion Examples n (valence of
ion)
S (at 25 °C),
mV/decade
Calcium (Ca2+) +2 +29.58
Potassium (K+), Ammonium (NH4+) +1 +59.16
Nitrate (NO3-), Chloride (Cl-) –1 –59.16
Assuming C0is near zero, the equation can be rewritten as:
C= 10˄[(E – Eo) / S]
allowing for the calculation of the ion concentration.
It is very important to note that this table reflects ideal behavior. Ion-selective
electrodes have slopes that are typically lower than ideal. It is generally
Electrode resistance 1 to 5 MΩ
Minimum sample size Must be submerged 2.8 cm (1.1 in)
Care and Maintenance
Short-term wet storage (less than 24 hours): Fill the Short-Term ISE Soaking
bottle 3/4 full with High Standard. Loosen the cap, insert the electrode into the
bottle, and tighten.
Long-term storage of the ISE (longer than 24 hours): Moisten the sponge in
the bottom of the long-term storage bottle with distilled water. When you finish
using the ISE, rinse it off with distilled water and blot it dry with a paper towel.
Loosen the lid of the long-term storage bottle and insert the ISE. Note: The tip
of the ISE should NOT touch the sponge. Also, make sure the white reference
mark is inside the bottle. Tighten the lid. This will keep the electrode in a
humid environment, which prevents the reference junctions from completely
drying out.
Maintaining and Replacing the ISE Standard Calibration Solutions
Having accurate standard solutions is essential for performing good calibrations.
The two standard solutions that were included with your ISE can last a long
time if you take care not to contaminate them. At some point, you will need to
replenish your supply of standard solutions. Vernier sells replacement standards
in 500 mL volumes. Order codes are:
lCL-LST: Chloride Low Standard, 10 mg/L
lCL-HST: Chloride High Standard, 1000 mg/L
To prepare your own standard solutions, use the information in the following
table. Note: Use glassware designed for accurate volume measurements, such as
volumetric flasks or graduated cylinders. All glassware must be very clean.
Standard
Solution
Concentration
(mg/L or ppm)
Preparation Method Using High Qual-
ity Distilled Water
Chloride
High
Standard
1000 mg/L as
Cl–
1.648 g NaCl / 1 L solution
Chloride
Low
Standard
10 mg/L as Cl– Dilute the High Standard by a factor of
100 (from 1000 mg/L to 10 mg/L).*
*Perform two serial dilutions as described below.
a. Combine 100 mL of the High Standard with 900 mL of distilled water. Mix
well.
b. Combine 100 mL of the solution made in the previous step with 900 mL of
distilled water. Mix well.

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for one calibration point (or 1.806 parts per thousand, or ppt). For the second
calibration point, prepare a standard that is 20,000 mg/L Cl–by adding 32.96 g
of solid NaCl to enough distilled water to prepare 1 L of solution:
If you are calibrating in ppt, call this solution 36.13 ppt.
Determining Salinity of Saltwater or Brackish Water
Salinity is the total of all salts dissolved in water, expressed either as mg/L
(equal to parts per million, ppm) or in parts per thousand (ppt). Seawater
contains a fairly constant quantity of chloride ions. From your measurement of
chloride ion concentration (in the previous section), salinity can be calculated
using the following formula:
Salinity (mg/L or ppm) = 1.8066 × [Cl–concentration, mg/L]
Using this formula, the salinity of saltwater is calculated to be:
Salinity (mg/L or ppm) = 1.8066 × (19400 mg/L) = 35,000 mg/L
The level of salinity of seawater in parts per thousand, or ppt, would be:
Salinity (ppt) = 35000 / 1000 = 35 ppt
Using Ionic Strength Adjuster Solutions to Improve Accuracy
For optimal results at low concentrations of chloride ions, a standard method for
taking measurements with the Chloride Ion-Selective Electrode (ISE) is to add
ionic strength adjuster (ISA) solutions to each of your standard solutions and
samples.
Adding an ISA ensures that the total ion activity in each solution being
measured is nearly equal, regardless of the specific ion concentration. This is
especially important when measuring very low concentrations of specific ions.
The ISA contains no ions common to the Chloride ISE itself. Note: The
additions of ISA to samples or standards described below do not need to have a
high level of accuracy—combining the ISA solution and sample solution
counting drops using a disposable Beral pipet works fine.
Use an ISA with the Chloride ISE by adding 5.0 M NaNO3ISA solution (42.50
g NaNO3/ 100 mL solution) to the Cl–standard or to the solution being
measured, in a ratio of 1 part of ISA (by volume) to 50 parts of the total solution
(e.g., 1 mL of ISA to 50 mL of total solution, or 2 drops of ISA to 5 mL of total
solution).
When the response of the Chloride ISE begins to slow, the membrane may need
polishing. Cut a small piece (about 1 inch square) from a polishing strip. Wet
the end of the electrode and the dull side of the polishing strip thoroughly with
distilled water. Using only moderate pressure, polish the end of the electrode by
gently rubbing it in a circular motion. This will remove the inactive layer of the
membrane which impedes measurement. Rinse thoroughly with distilled water
and recalibrate in the usual manner.
accepted that an ISE slope from 88–101% of ideal is allowable. The slope (S) is
an indicator of ISE performance. If the slope changes significantly over time, it
may indicate that it is necessary to replace the ISE sensor tip.
Convert Potential to Concentration (Optional)
To measure the mV readings from an aqueous sample, calibration is not
required. To convert mV readings to concentration (mg/L or ppm), you will use
a modified version of the Nernst Equation:
C= 10˄[(E – Eo) / Sm]
C= concentration of ion to be measured (mg/L or ppm)
E= measured potential of sample (mV)
Eo= measured potential (mV) at a C = 1 mg/L Cl−concentration
Sm= measured electrode slope in mV/decade
The value of Sm, the measured electrode slope, is determined by measuring the
potential of two standard solutions, and solving the equation below:
Sm= – [(Low Standard – High Standard) / # of decades*]
*A decade is defined as the factor of the difference between the two standard
solutions. For example, the difference between a 1mg/L standard and a
100mg/L standard is 2 decades (a factor of 100 difference, or 1 × 102).
Example Calculation, converting mV to mg/L
For this example, the measured quantities are shown in the chart below:
Solution Measured Potential
1 mg/L Cl– standard 288 mV
10 mg/L Cl– standard 230 mV
1000 mg/L Cl–standard 114 mV
unknown sample 188 mV
C= 10^[(188 mV – 288 mV)/ –58 mV/decade] = 53 mg/L Cl–
Troubleshooting
Sampling Freshwater Samples for Chloride Concentration
For best results, calibrate the Chloride ISE using the 10 mg/L and 1000 mg/L
standards.
Measuring Chloride Concentration of Saltwater or Brackish Water
When measuring chloride concentration in seawater or brackish water, calibrate
the Chloride ISE using the 1000 mg/L standard included with your Chloride ISE

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See general tips for using Ion Selective Electrodes at www.vernier.com/til/665
Repair Information
If you have followed the troubleshooting steps and are still having trouble with
your Go Direct Chloride Ion-Selective Electrode BNC, contact Vernier
Technical Support at [e-mail] or call 888-837-6437. Support
specialists will work with you to determine if the unit needs to be sent in for
repair. At that time, a Return Merchandise Authorization (RMA) number will be
issued and instructions will be communicated on how to return the unit for
repair.
Accessories/Replacements
Item Order Code
Standard High Cl ISE Solution CL-HST
Standard Low Cl ISE Solution CL-LST
Storage Solution Bottles, pkg of 5 BTL
Warranty
Vernier warrants this product to be free from defects in materials and
workmanship for a period of five years from the date of shipment to the
customer. This warranty does not cover damage to the product caused by abuse
or improper use.
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Rev. 04/02/18
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