YSI Professional Plus User Manual

Page 29

CALIBRAtIoN - AMMoNIUM, NItRAtE, CHLoRIDE

the 6051030 ISE/conductivity cable has a specialized calibration container that

resembles a large test tube. this calibration chamber can be used to calibrate

the ISE sensors with the conductivity sensor. A ring-stand should be used to

support this chamber.

The ISE sensors can be calibrated at 1, 2, or 3-points.

A 2-point calibration without chilling a third calibration

solution is extremely accurate and is the preferred method.

Greatest accuracy is achieved if the actual samples to be

measured are within 10 ˚C of the calibration solutions.

CALIBRATION TIP: Exposure to the high ionic content of pH buffers can

cause a significant, but temporary, drift in the ammonium, nitrate, and chloride

ISE sensors. therefore, when calibrating the pH sensor, YSI recommends that

you use one of the following methods to minimize errors in the subsequent

readings:

When calibrating pH, remove ISE sensors from the cable bulkhead and

•

plug the ports. After pH calibration is complete, replace the ISE sensors and

proceed with their calibration with no stabilization delay.

Calibrate pH first, immersing all of the sensors in the pH buffers. After

•

calibrating pH, place the sensors in 100 mg/L nitrate or ammonium standard

or 1000 mg/L chloride standard depending on the sensor in use and monitor

the reading. Usually, the reading starts low and may take awhile to reach

a stable value. When it does, proceed with the calibration. this may take

several hours.

Preparing Chloride Standards

the following recipes are provided for preparation of 10 and 1000 mg/L chloride

reagents. Nitrate and Ammonium standards can be purchased from YSI or other

laboratory supply companies.

It is important to note that some of the chemicals required for these solutions

could be hazardous under some conditions. It is the responsibility of the user

to obtain and study the MSDS for each chemical and to follow the required

instructions with regard to handling and disposal of these chemicals.

You will need: Solid sodium chloride or a certified 1000 mg/L chloride solution

from a supplier, magnesium sulfate, high purity water, a good quality analytical

balance, 1000 mL volumetric flask, an accurate 10 mL measuring devices, and

1000 mL glass or plastic storage vessels.

1000 mg/L Standard: Accurately weigh 1.655 grams of anhydrous sodium

chloride and transfer into a 1000 mL volumetric flask. Add 0.5 grams of

anhydrous magnesium sulfate to the flask. Add 500 mL of water to the flask,

swirl to dissolve all of the reagents , and then dilute to the volumetric mark with

water. Mix well by repeated inversion and then transfer the 1000 mg/L standard

to a storage bottle. Rinse the flask extensively with water prior to its use in the

preparation of the 10 mg/L standard. Alternatively, simply add 0.5 grams of

magnesium sulfate to a liter of a 1000 mg/L chloride standard from a certified

supplier.

10 mg/L Standard: Accurately measure 10 mL of the above 1000 mg/L standard

solution into a 1000 mL volumetric flask. Add 0.5 grams of anhydrous magnesium

sulfate to the flask. Add 500 mL of water, swirl to dissolve the solid reagents, and

then dilute to the volumetric mark with water. Mix well by repeated inversion

and then transfer the 10 mg/L standard to a storage bottle.

AMMoNIUM (NH4+) , NItRAtE (No3-), AND CHLoRIDE CL-

2-PoINt

the calibration procedures for ammonium, nitrate, or chloride are similar to

pH. the only differences are the calibration solutions. Recommended values

for calibration solutions and the order of calibration are as follows:

Sensor

Point

Ammonium-nitrogen (NH4-N)

1 mg/L

100 mg/L

Nitrate-nitrogen (No3-N)

1 mg/L

100 mg/L

Chloride (Cl-)

10 mg/L

1000 mg/L

Place the proper amount of 1 mg/L standard for Ammonium or Nitrate (10

mg/l for Chloride) into a clean, dry or pre-rinsed calibration cup. Carefully

immerse the sensor into the solution. Allow at least 1 minute for temperature

equilibration before proceeding.

Press Cal

. Highlight Probe ID or User ID if you wish to add, select, edit,

or delete an ID. Probe ID must be enabled in the System GLP menu to appear

in the Calibrate menu. User ID will appear automatically. Select ‘None’ if you

do not want a User ID stored with the calibration. When enabled, these IDs are

stored with each calibration record in the GLP file.