Documentation:Turbidimeter

From UBC Wiki

What is Turbidity?

Turbidity measures the relative transparency of a liquid, and when turbidity is measured in water it is an indication that there are impurities in the water. The higher the turbidity of a sample, the higher the intensity of scattered light. Turbidity is often measured in Nephelometric Turbidity Units (NTU). (Civilmint, 2024)

How Does the Turbidimeter Work?

A light beam is sent from the turbidimeter into the water being tested. The light will be scattered by any particles in the water and the light detector in the turbidimeter will detect the amount of light that is reflected back at it; hence, determining turbidity. (Aquaread, 2020)

HACH 2100P Standard Operating Procedure

The components of a turbidimeter.

Preparation of Standards:

For Infrequent Use of Standards (All standards except for StablCal <0.1 NTU standard):

  1. Shake the standard for 2-3 minutes.
  2. Let the standard sit undisturbed for 5 minutes
  3. Eliminate optical variances of the sample through 2 methods (oiling and marking the sample cell)
  4. Place the sample cell in the turbidimeter and record the value.

For Frequent (daily or weekly usage) Use of Standards

  1. Mix the StablCal standards by inverting 10 times
  2. Eliminate optical variances Eliminate optical variances of the sample through 2 methods (oiling and marking the sample cell)
  3. Let the sample sit undisturbed for 1-3 minutes
  4. Place the sample cell in the turbidimeter and record the value

For the Usage of StablCal<0.1NTU Standard: NEVER SHAKE OR INVERT THIS STANDARD (if the <0.1 NTU Standard has recently been mixed, let the standard sit for 10-15 minutes before using)

  1. Do not generate any bubbles in this solution and let the standard sit for 1-5 minutes before usage.
  2. Place the sample cell in the turbidimeter and record the value.

(Hach, 1998)


Preparation of Samples:

Ensure that cells are extremely clean and free of significant scratches. If there are minor imperfections, they can be masked by applying silicone oil (see section - Oiling the Sample Cells).

Clean the inside and outside of cells by washing with laboratory detergent and follow with multiple rinses of distilled or deionized water. Allow the cells to air dry. Handle cells by the top to minimize dirt and fingerprints on the glass. (TTT Environmental Supplies, 2008)


Calibration of the Turbidimeter: Primary Calibration:

  1. To restore default calibration, turn the instrument off. Next, press and hold DIAG, then press and release I/O. Release DIAG when the software version number disappears from the display. CAL? Will continue to appear until user-entered calibration has been successfully completed.
  2. Insert the StabCal <0.1 NTU standard into the cell compartment (located at the top of the instrument) aligning the black orientation mark on the cell with the mark on the front of the cell compartment. Close the lid
  3. Press I/O to turn on the machine.
  4. Choose signal average mode on or off. (Signal averaging compensates for reading fluctuations caused by drifting of sample particles through the path of light.)
  5. Press CAL (the CAL and S0 icons will be displayed and the 0 will flash)
  6. Press READ (the instrument will count from 60 to 0, or 67 to 0 if signal average is on)
  7. The display will show the S1 (with the 1 flashing) and 20 NTU.
    1. If the value is incorrect, edit the value by pressing the →  key until the number that needs editing flashes
    2. Use the ↑ key to scroll to the correct number (020.0 NTU)
  8. After edits to the number have been made, insert the 20 NTU StablCal Standard into the cell compartment by aligning the orientation mark on the cell with the mark on the front of the cell compartment. Close the lid.
  9. Press READ (the instrument will count from 60 to 0, or 67 to 0 if signal average is on)
  10. The display will automatically increment to the next standard and remove the standard from the cell compartment.
  11. Repeat steps 6-9 for the StablCal 100 NTU standard when the displays show S2 (with the 2 flashing) and 100 NTU.
  12. Repeat steps 6-9 for the StablCal  800 NTU standard when the displays show S3 (with the 3 flashing) and 800 NTU.
  13. Press CAL to accept the calibration and the instrument will return to measurement mode automatically.

(TTT Environmental Supplies, 2008)


Secondary Calibration:

  1. Complete the Primary Calibration
  2. Select the automatic range mode using the RANGE key.
  3. Thoroughly clean and apply a thin layer of silicone oil to the Gelex vials.
  4. Place the 0-10 NTU Gelex standard in the cell compartment so the white diamond on the vial aligns with the orientation mark on the instrument. Close sample compartment lid.
  5. Press READ and record the displayed value on top of the sample.
  6. Repeat Steps 4-5 for the other Gelex standards.

(TTT Environmental Supplies, 2008)


Oiling the Sample Cells:

  1. Thoroughly clean the sample cell with water and laboratory detergent.
  2. Apply a small bead of silicone oil from the top to the bottom of the cell (there should be enough to coat the cell with a thin layer of oil)
  3. Using the provided soft and lint-free spread the oil uniformly and wipe off the excess. (The cell should appear nearly dry with no visible oil)

(TTT Environmental Supplies, 2008)


Orienting the Samples: Orienting the samples is important to ensure that samples are placed into the instrument oriented the same direction every time a reading is taken.

For the following steps of both cases, use the continuous reading mode. This is achieved by pressing and holding READ (continuous reading mode cannot be used if Signal Average is on).


Orienting a Single Cell:

  1. Fill a sample with high quality water (<0.5 NTU) just below being completely filled. Cap and wipe the sample with a lint-free cloth. Apply silicone oil - see Oiling the sample cell. Wipe and apply silicone oil to samples as well.
  2. Press I/O
  3. Insert the sample into the sample compartment and close the cover.
  4. Press READ and record the cell position in the cell compartment relative to the raised mark on the instrument. Also record displayed reading
  5. Remove the cell and rotate it slightly and reinsert into the cell compartment. Close the cover and press READ.
  6. Record the position and the displayed reading
  7. Repeat Step 6 until the lowest reading is displayed. Place an orientation mark on the cell’s marking band near the top of the cell. When using this particular sample cell, place it into the instrument so that the orientation mark aligns with the raised mark on the instrument.


Orienting Multiple Sample Cells:

Steps 1-3 are the same for orientation of both single and multiple cells.

  1. Fill a sample with high quality water (<0.5 NTU) just below being completely filled. Cap and wipe the sample with a lint-free cloth. Apply silicone oil - see Oiling the sample cells. Wipe and apply silicone oil to samples as well.
  2. Press I/O
  3. Insert the first sample cell into the sample compartment and close the cover.
  4. Press READ and record the cell’s position and displayed reading. Place an orientation mark on the cell’s marking band.
  5. Insert the second sample cell into the compartment and close the cover.
  6. Press READ and record the cell’s position and displayed reading.
  7. Remove the cell, rotate it slightly and reinsert into the cell compartment. Press READ and record the position and reading again.
  8. Repeat Step 7 until the second cell is within 0.01 NTU of the first cell. Place a marking on the marking band of the second cell to ensure that the cell is being placed into the cell compartment with the same orientation every time.

(TTT Environmental Supplies, 2008)


Cleaning:

Keep the turbidimeter and the accessories as clean as possible and in the carrying case when not in use. Avoid prolonged exposure to sunlight or ultraviolet light. Wipe spills up as soon as possible. Avoid scratching the cells and wipe all moisture and fingerprints off cells before inserting them into the instrument. (TTT Environmental Supplies, 2008)

References

Aquaread (2020). Turbidity | Aquaread Turbidity Sensor. Retrieved from: https://www.aquaread.com/sensors/turbidity#:~:text=A%20turbidimeter%20works%20by%20sending,is%20reflected%20back%20at%20it.

Civilmint (2024).Turbidity Test of Water | How to Measure Turbidity of Water | Determination of Turbidity of Water. Retrieved from: https://civilmint.com/turbidity-test-of-water/

Hach (1998). STABLCAL Stabilized Formazin Standards For Use On Any Model Turbidimeter. Hach Company

TTT Environmental Supplies (2008). Portable Turbidimeter Model 2100P Instrument and Procedure Manual. Hach Company

Retrieved from "https://wiki.ubc.ca/index.php?title=Documentation:Turbidimeter&oldid=838859"