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APPLICATION NOTE NO. 2D
Instructions for Care and Cleaning of Conductivity Cells
Revised October 2010 
 

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This application note presents new recommendations (as of October 2006), based on our recent research, for cleaning and storing conductivity sensors. In the past, Sea-Bird had recommended cleaning and storing conductivity sensors with a Triton X-100 solution, and cleaning conductivity sensors with an acid solution. Our latest research leads us to recommend adding the use of a dilute bleach solution to eliminate growth of bio-organisms, and eliminating the use of acid in most cases.

The application note is divided into three sections:

General Discussion

Since any conductivity sensor’s output reading is proportional to its cell dimensions, it is important to keep the cell clean of internal coatings. Also, cell electrodes contaminated with oil, biological growths, or other foreign material will cause low conductivity readings. A desire to provide better control of growth of bio-organisms in the conductivity cell led us to develop revised rinsing and cleaning recommendations.

Sea-Bird had previously recommended storing the conductivity cell filled with water to keep the cell wetted, unless the cell was in an environment where freezing is a possibility (the cell could break if the water freezes). However, no adverse affects have been observed as a result of dry storage, if the cell is rinsed with fresh, clean water before storage to remove any salt crystals. This leads to the following revised conductivity cell storage recommendations:

Note that the Tygon tubing looped around the ends of the conductivity cell, whether dry or filled with a bleach or Triton solution, has the added benefit of keeping air-borne contaminants (abundant on most ships) from entering the cell.

 

Rinsing, Cleaning, and Storage Procedures

Note: See Cleaning Materials below for discussion of appropriate sources / concentrations of water, Triton X-100, bleach, and tubing.

CAUTIONS:

Active Use (after each cast)

  1. Rinse: Remove the plumbing (Tygon tubing) from the exhaust end of the conductivity cell. Flush the cell with a 0.1% Triton X-100 solution. Rinse thoroughly with fresh, clean water and drain.
  1. Store: The intent of these storage recommendations is to keep contamination from aerosols and spray/wash on the ship deck from harming the sensor’s calibration.

Routine Cleaning (no visible deposits or marine growths on sensor)

  1. Agitate a 500 – 1000 ppm Bleach solution warmed to 40 °C through the cell in a washing action (this can be accomplished with Tygon tubing and a syringe kit -- see Application Note 34) for 2 minutes. Drain and flush with warm (not hot) fresh, clean water for 5 minutes.
  2. Agitate a 1%-2% Triton X-100 solution warmed to 40 °C through the cell many times in a washing action (this can be accomplished with Tygon tubing and a syringe kit). Fill the cell with the solution and let it soak for 1 hour. Drain and flush with warm (not hot) fresh, clean water for 5 minutes.

Cleaning Severely Fouled Sensors (visible deposits or marine growths on sensor)

Repeat the Routine Cleaning procedure up to 5 times.

Long-Term Storage (after field use)

  1. Rinse: Remove the plumbing (Tygon tubing) from the exhaust end of the conductivity cell. Flush the cell with a 0.1% Triton X-100 solution. Rinse thoroughly with fresh, clean water and drain. Remove larger droplets of water by blowing through the cell. Do not use compressed air, which typically contains oil vapor.
  2. Store: Attach a loop of Tygon tubing to each end of the conductivity cell to close the cell ends and prevent contaminants from entering the cell.
  1. When ready to deploy again: Fill the cell with a 0.1% Triton X-100 solution for 1 hour before deployment. Drain the Triton X-100 solution; there is no need to rinse the cell.

 

Cleaning Materials

Water

De-ionized (DI) water, commercially distilled water, or fresh, clean, tap water is recommended for rinsing, cleaning, and storing sensors.

Where fresh water is in extremely limited supply (for example, a remote location in the Arctic), you can substitute clean seawater for rinsing and cleaning sensors. If not immediately redeploying the instrument, follow up with a brief fresh water rinse to eliminate the possibility of salt crystal formation (salt crystal formation could cause small shifts in calibration).

Triton X-100

Triton X-100 is Octyl Phenol Ethoxylate, a mild, non-ionic surfactant (detergent). Triton X-100 is included with every CTD shipment and can be ordered from Sea-Bird, but may be available locally from a chemical supply or lab products company. It is manufactured by Mallinckrodt Baker (see http://www.mallbaker.com/changecountry.asp?back=/Default.asp for local distributors). Other liquid detergents can probably be used, but scientific grades (with no colors, perfumes, glycerins, lotions, etc.) are required because of their known composition. It is better to use a non-ionic detergent, since conductivity readings taken immediately after use are less likely to be affected by any residual detergent left in the cell.

100% Triton X-100 is supplied by Sea-Bird; dilute the Triton as directed in Rinsing, Cleaning, and Storage Procedures.

Bleach

Bleach is a common household product used to whiten and disinfect laundry. Commercially available bleach is typically 4 % - 7% (40,000 – 70,000 ppm) sodium hypochlorite (Na-O-Cl) solution that includes stabilizers. Some common commercial product names are Clorox (U.S.) and eau de Javel (French).
Dilute to 500 – 1000 ppm. For example, if starting with 5% (50,000 ppm) sodium hypochlorite, diluting 50 to 1 (50 parts water to 1 part bleach) yields a 1000 ppm (50,000 pm / 50 = 1000 ppm) solution.

Tygon Tubing

Sea-Bird recommends use of Tygon tubing, because it remains flexible over a wide temperature range and with age. Tygon is manufactured by Saint-Gobain (see www.tygon.com). It is supplied by Sea-Bird, but may be available locally from a chemical supply or lab products company.

Keep the Tygon in a clean place (so that it does not pick up contaminants) while the instrument is in use.

Acid

In rare instances, acid cleaning is required for mineral contamination of the conductivity cell. Sea-Bird recommends that you return the equipment to the factory for this cleaning. Information below is provided if you cannot return the equipment to Sea-Bird.

CAUTIONS:

WARNING! Observe all precautions for working with strong acid. Avoid breathing acid fumes. Work in a well-ventilated area.

The acid cleaning procedure for the conductivity cell uses approximately 50 - 100 cc of acid. Sea-Bird recommends using a 20% concentration of HCl. However, acid in the range of 10% to full strength (38%) is acceptable.

If starting with a strong concentration of HCl that you want to dilute:

For each 100 cc of concentrated acid, to get a 20% solution, mix with this amount of water --

Water = [(conc% / 20%) – 1 ] * [100 + 10 (conc% / 20% )] cc

Always add acid to water; never add water to acid.

Example -- concentrated solution 31.5% that you want to dilute to 20%:

[(31.5% / 20%) – 1 ] * [100 + 10 (31.5% / 20% )] = 66.6 cc of water.

So, adding 100 cc of 31.5% HCl to 66.6 cc of water provides 166.6 cc of the desired concentration.

For 100 cc of solution:

100 cc * (100 / 166.6) = 60 cc of 31.5% HCl

66.6 cc * (100 / 166.6) = 40 cc of water

For acid disposal, dilute the acid heavily or neutralize with bicarbonate of soda (baking soda).

  1. Prepare for cleaning:
  1. Place a 0.6 m (2 ft) length of Tygon tubing over the end of the cell.
  2. Clamp the instrument so that the cell is vertical, with the Tygon tubing at the bottom end.
  3. Loop the Tygon tubing into a U shape, and tape the open end of the tubing in place at the same height as the top of the glass cell.
  1. Clean the cell:
  1. Pour 10% to 38% HCl solution into the open end of the tubing until the cell is nearly filled. Let it soak for 1 minute only.
  2. Drain the acid from the cell and flush for 5 minutes with warm (not hot), clean, de-ionized water.
  3. Rinse the exterior of the instrument to remove any spilled acid from the surface.
  4. Fill the cell with a 1% Triton X-100 solution and let it stand for 5 minutes.
  5. Drain and flush with warm, clean, de-ionized water for 1 minute.
  6. Carefully remove the 0.6 m (2 ft) length of Tygon tubing.
  1. Prepare for deployment, or follow recommendations above for storage.

 


Application Note Revision History
Date Description
January 1998 Initial release.
October 2002 Remove reference to part number for small anti-foul cylinders (which have been eliminated) in Tygon tubing.
January 2005 Change in recommendations.: Clean with bleach solution as well as Triton. Acid cleaning is not recommended in general, but some information on acid is still provided for the few cases where it is necessary. A section on Materials added, defining water, Triton, etc. in more detail.
July 2005 Include information on common names of commercially available bleach.
October 2006 Update manufacturer name and website link for Triton.
September 2008 Add SBE 52-MP to list of instruments with integral, internal pump that should not have acid cleaning.
October 2010 - Add reference to IDO MicroCATs, with caution to following cleaning and storage procedures in Application Note 64 instead of in this application note.
- Update address.

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Last modified: 14-Oct-2010

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