WATERS Collaborative, Water Quality Study
SOLUTIONS AND SUPPLIES FOR CALIBRATING VERNIER SENSORS
Contact Information
Hach Company 1-800-227-4224, www.hach.com
Vernier Software and Technology 1-888-837-6437, www.vernier.com
Fisher Scientific: 1-800-766-7000
Flinn Scientific: 1-800 452-1261, www.flinnsci.com
Solutions and Supplies
Solution
For Sensor
Where to Order
When to Replace
pH 4.00 (storage)
pH
Expiration date on
bottle
pH 7.00
pH
Fisher Scientific:
SB107500 Buffer 500 ml
($4.95)
Fisher Scientific:
SB101500 Buffer 500 ml
($9.40)
pH 10.00
pH
Fisher Scientific:
SB115500 Buffer 500 ml
($9.40)
Expiration date on
bottle
100 NTU StablCal
Formazin Standard
turbidity
Vernier 1800-277-4224.
Turbidity Accessories Kit
(order code TRB-ACC)
includes one standard
and one empty cuvette
Replacement cuvettes turbidity
Hach Company: 6 empty
cuvettes (order code
24347-06)
2.0 M sodium sulfite
(Na2SO3) standard
solution
Flinn Scientific: sodium
sulfite standard solution,
2.0 M, 65 mL (order code
SO426); Vernier: 65 ml
bottle (order code DOCAL); or make (add 25.0
g solid anhydrous sodium
sulfite crystals to enough
Dissolved oxygen
Expiration date on
bottle
If the calibration
voltage displayed
during the first
calibration point is
higher than previous
calibrations
distilled water to yield
100 mL);
Flinn Scientific: order
code SO111 (for making
our own solution)
Sodium sulfite,
anhydrous solid, 500
g bottle
Dissolved oxygen
Electrode filling
solution
Dissolved oxygen
Vernier: Probe filling
solution (order code FS)
100 µS/cm
Conductivity
add 0.0474 g NaCl to 1
liter water
When used up
1000 µS/cm
Conductivity
add 0.491 g NaCl to 1
liter water
When used up
pH
•
Storage Solution: pH 4.00: storage solution. Add 2.0 mL of 0.1 M HCl to 1000 mL
of 0.1 M potassium hydrogen phthalate (provided)
•
pH-7 Solution: To make a pH 7.00 solution, add 582 mL of 0.1 M NaOH to 1000
mL of 0.1 M potassium dihydrogen phosphate
•
pH-10 Solution: To make a pH 10.00 solution, Add 214 mL of 0.1 M NaOH to
1000 ML of 0.05 M sodium bicarbonate
These can also be ordered from Vernier:
Low Range (150 μS/cm) CON-LST
Medium Range (1413 μS/cm) CON-MST
High Range (12880 μS/cm) CON-HST
•
100 NTU – (provided) Ask student to do this calibration in field
Turbidity
Dissolved Oxygen
•
2.0 M sodium sulfite (Na2SO3) solution: add 25.0 g of solid anhydrous sodium
sulfite crystals (Na2SO3) to enough distilled water to yield a final volume of 100
mL of solution.
The 2.0 M sodium sulfite (Na2SO3) solution can be prepared from solid sodium sulfite crystals.
The sodium sulfite crystals do not need to be reagent grade; laboratory grade will work fine.
Prepare the solution 24 hours in advance of doing the calibration to ensure that all oxygen has
been depleted. If solid sodium sulfite is not available, you may substitute either 2.0 M sodium
hydrogen sulfite solution, (sodium bisulfite, 20.8 g of NaHSO3 per 100 mL of solution) or 2.0 M
potassium nitrite (17.0 g of KNO2 per 100 mL of solution).
Having an oxygen-free solution to perform a zero-oxygen calibration point is essential for
accurate readings with your Dissolved Oxygen Probe. Suggestions for maintaining and replacing
this solution:
After your first use of the solution for calibration, the solution will no longer be brim full (some
overflow results when the probe is inserted into the solution). If you cap the solution with an
air space above the probe, oxygen gas in the space will dissolve in the sodium sulfite solution—
as a result, the solution may not be oxygen free. To prevent this from occurring, before putting
on the lid, gently squeeze the bottle so the level of the solution is at the very top of the bottle
neck; with the solution at this level, screw on the lid. The bottle will remain in this “collapsed”
position. Using this procedure, the 2.0 M Na2SO3 should remain oxygen free for a long period
of time. If the calibration voltage reading displayed during the first calibration point is higher
than in previous calibrations, it may be time to replace the solution, as described below.
Conductivity
Make the first two since we anticipate values in this range
•
100 µS/cm: add 0.0474 g NaCl to 1 liter water
•
1000 µS/cm: add 0.491 g NaCl to 1 liter water (provided)
•
2000 µS/cm: add 1.005 g NaCl to 1 liter water
•
10,000 µS/cm: add 5.566 g NaCl to 1 liter water
CALIBRATION OF VERNIER SENSORS
Probes to be Calibrated: pH, turbidity, dissolved oxygen and conductance probes all require
calibration
FIELD CALIBRATIONS
•
DO – to do the calibration, you need to know the barometric pressure and air
temperature of the site where the water is sampled. Barometric pressure is based on
elevation and is available for the Copeland Creek sites before going into the field. Air
temperature must be taken in the field. The calibration is probably best done by the
instructor or an assistant at the site.
•
Turbidity – simple calibration done by students in the field
LAB CALIBRATIONS
•
pH
•
conductance
Note that after you store a calibration to a Sensor, this new calibration will be used
automatically, regardless of the interface to which the sensor is connected.
pH Sensor Calibration
Solutions Needed
•
pH 4.00 Storage Solution
•
pH-7 Solution
•
pH-10 Solution
1. Connect the pH Sensor to your LabQuest. The pH reading will be displayed.
2. Choose Calibrate  CH1: pH from the Sensors menu and tap Calibrate Now.
3. Remove the storage bottle from the pH Sensor by loosening the lid, then rinse the tip of
the sensor with distilled water.
4. First Calibration Point:
a. Immerse the sensor tip into the PH-7 buffer. Type 7 (the pH value of the buffer)
in the Value 1 field.
b. When the voltage reading stabilizes, tap Keep.
5. Second Calibration Point:
a. Rinse the pH sensor with distilled water and place it in the pH-10 buffer solution.
b. Type 10 (the pH value of the buffer) in the In the Value 2.
c. When the voltage reading stabilizes, tap Keep.
6. Store the Calibration Values
a. Tap Storage tab at the top of the screen.
b. On the Storage page, tap Save Calibration to Sensor. A message will appear:
“Saving this calibration to the sensor will result in it being the new Custom
Calibration 1”. Tap OK to proceed.
c. Tap OK to complete the calibration process. After you store a calibration to the
pH Sensor, this new calibration will be used automatically, regardless of the
interface to which the sensor is connected.
You can set the pH sensor back to its factory calibration by following these steps:
1. Choose Calibrate CH1: pH from the Sensors menu.
2. Tap the Storage tab.
3. Tap Restore Sensor Factory Defaults.
Turbidity Sensor Calibration
Solutions Needed:
•
100 NTU calibration solution
•
Distilled water
1. Find the Calibration Screen:
a. On the top left of the screen your will see:
FILE SENSORS
b. Click on SENSORS. A Menu will pop up. Click on “Calibrate ”, then click on CH1:
Turbidity, then choose “Calibrate Now.”
2. First Calibration Point (0 NTU standard):
a. Rinse the turbidity cuvette (small glass vial) with distilled water. Fill with distilled water
so the bottom of the meniscus is even with the top of the white line. Replace the lid. Dry
off the vial with tissue.
b. Check the cuvette for air bubbles. IF AIR BUBBLES ARE PRESENT, GENTLY TAP THE
BOTTOM OF THE CUVETTE TO DISLODGE THEM.
c. Hold the cuvette by the lid, place it in the Turbidity sensor. Align the mark on the
cuvette with the mark on the side of the Turbidity sensor opening. Close the lid.
d. Type 0 (the turbidity value of distilled water) in the Value 1 box.
e. When the displayed voltage reading stabilizes, click Keep
3. Second Calibration Point (100 NTU standard)
a. Take the cuvette with the Turbidity Standard (100 NTU) and gently invert it four time to
mix any particles that may have settled to the bottom. DO NOT SHAKE. SHAKING WILL
PRODUCE BUBBLES THAT WILL CAUSE ERRORS IN READINGS.
b. Tap cuvette to remove any air bubbles and wipe the outside of the vial with tissue.
c. Hold the cuvette by the lid, place it in the Turbidity sensor opening. Align the mark on
the cuvette with the mark on the side of the Turbidity sensor opening. Close the lid.
d. Type 100 (the NTU value of the standard) in the Value 2 box.
e. When the displayed voltage reading stabilizes, click Keep
DO Sensor Calibration
Solutions Needed:
•
2.0 M sodium sulfite (Na2SO3) solution
•
Distilled water
This must be done at the same elevation and temperature as the sampling location. Assign
assistant to do the calibration at the field site before the students use the sensors. Or assign
one team to do the calibration while students use the other sensors.
1. Prepare the Dissolved Oxygen Sensor
a. Remove the blue protective cap from the tip of the probe. This protective cap
can be discarded once the probe is unpacked.
b. Unscrew the membrane cap from the tip of the probe.
c. Use a pipet to fill the membrane cap with 1 mL of DO Electrode Filling Solution.
d. Carefully thread the membrane cap back onto the electrode.
e. Place the probe into a beaker filled with about 100 mL of distilled water.
2. Warm Up the Probe
a. Plug the Dissolved Oxygen Probe to Channel 3 of the LabQuest2 interface.
WARM PROBE FOR 10 MINUTES. To warm up the probe, leave is connected to
the LabQuest2 interface and turn interface on. The LabQuest2 will deliver power
to the sensor even if the screen goes to sleep. If the probe is disconnected for a
few minutes, start over.
b. DURING THIS TIME, KEEP THE PROBE TIP IN WATER.
3. Calibrate the Sensor:
a. Find the Calibration Screen:
i. On the top left of the screen your will see:
FILE SENSORS
ii. Click on SENSORS. A Menu will pop up. Click on “Calibrate ”, then click
on CH: Dissolved Oxygen, then choose “Calibrate Now.”
b. First Calibration Point (Zero-Oxygen):
i. Remove the probe from the water and place the sensor tip into the
Sodium Sulfite Calibration Solution.
ii. When the displayed voltage reading stabilizes (be patient), enter 0 (the
known dissolved oxygen value in mg/L) in the Value 1 box and click
Keep
iii. The voltage should be somewhere between 0.2 V and 0.5 V. If it is not,
make sure there is not an air bubble at the tip of the electrode.
iv. To prevent the Sodium Sulfite Calibration Solution from taking on oxygen
(this is your zero-oxygen calibration), make sure there is no air in the
bottle when you close it: before putting on the lid, gently squeeze the
bottle so the level of the solution is at the very top of the bottle neck;
with the solution at this level, screw on the lid. The bottle will remain in
this “collapsed” position.
c. Second Calibration Point (Saturated DO)
i. Rinse the probe with distilled water and gently blot dry.
ii. Unscrew the lid of the calibration bottle provided with the probe. Slide
the lid and the grommet about ½ inch onto the probe body. (This may
already be on the probe)
iii. Add distilled water to the bottle to a depth of about ¼ inch and screw the
bottle into the cap, as shown. DO NOT TOUCH THE MEMBRANE OR GET
IT WET DURING THIS STEP.
d. Keep the probe in this position for about a minute. When the displayed voltage
reading stabilizes (be patient), enter the correct saturated dissolved oxygen
value (in mg/L) from Table 1 using the current barometric pressure and air
temperature values at the sampling site. The barometric pressure for the
WATERS sampling sites on Copeland Creek are:
Copeland Creek Site
Elevation
Commerce
Santa Alicia Stream
Gauge
SSU Outfall
SSU Bridge
Pressley Rd
Lichau Rd Bridge
Osborn Preserve
93 ft
Barometric
Pressure
757
100 ft
757
129 ft
163 ft
280 ft
467 ft
1606 ft
756
755
752
747
721
i. Click Keep
ii. At the saturate oxygen point, the voltage should be above 2.0V. If not,
make sure the electrode is not touching the water in the bottle. Rinse
with distilled water, blot dry. DON’T TOUCH MEMBRANE.
4. Store the Calibration Values
a. Tap Storage tab at the top of the screen.
b. On the Storage page, tap Save Calibration to Sensor. A message will appear:
“Saving this calibration to the sensor will result in it being the new Custom
Calibration 1”. Tap OK to proceed.
c. Tap OK to complete the calibration process. After you store a calibration to the
pH Sensor, this new calibration will be used automatically, regardless of the
interface to which the sensor is connected.
5. Ready the Sensor for the Field:
a. Plug the dissolved oxygen sensor into the Channel 3.
b. To keep the probe tip submerged in the water until students can take samples,
fill the DO Calibration bottle with water. Then fit the probe down into the lid and
tighten the lid onto the bottle.
TDS Calibration
Solutions Needed
•
100 µS/cm
•
1000 µS/cm
For the WATERS project, we measure the conductivity and then ask students to multiply
conductivity by 0.7 to obtain the TDS estimate. We calibrate the conductivity sensor, but do not
do a TDS calibration which allows the interface to transform conductance into TDS values.
For best results, it is recommended that the two-point calibration be performed using two
standard solutions that bracket the expected range of conductivity or concentration values you
will be testing. For example, if you expect to measure conductivity in the range of 600 mg/L to
1000 mg/L (TDS), you may want to use a standard solution that is 500 mg/L for one calibration
point and another standard that is 1000 mg/L for the second calibration point. Make sure the
correct switch setting is used for the middle range of conductivity.
To Calibrate:
1. Select the medium conductivity range setting on the probe box: medium = 0 to 2000 μS.
Previous conductivity values on Copeland Creek range from 100-600 μS (which roughly
corresponds to TDS of 70-420 mg/L).
a. Find the Calibration Screen:
i. On the top left of the screen your will see:
FILE SENSORS
ii. Click on SENSORS. A Menu will pop up. Click on “Calibrate ”, then click
on CH: Conductivity 2000MICS, then choose “Calibrate Now.”
b. First Calibration Point
i. Perform the first calibration point with the probe in the 100 μS solution.
ii. Enter 100 in the Value 1 box and click Keep
c. Second Calibration Point
i. Place the Conductivity Probe into the 1000 mg/L TDS standard solution.
The hole near the top of the probe should be completely covered.
ii. Enter 1000 in the Value 2 box. Click
Keep
, then click
Done
2. Store the Calibration Values
d. Tap Storage tab at the top of the screen.
e. On the Storage page, tap Save Calibration to Sensor. A message will appear:
“Saving this calibration to the sensor will result in it being the new Custom
Calibration 1”. Tap OK to proceed.
f. Tap OK to complete the calibration process. After you store a calibration to the
pH Sensor, this new calibration will be used automatically, regardless of the
interface to which the sensor is connected.