MP20 Flow Cell Cleaning, Storage & Calibration of the MP20 ph Probe

Transcription

1 FLW CELL Environmental Systems MP20 Flow Cell Cleaning, Storage & Calibration of the MP20 ph Probe P/N Environmental Systems P.. Box 3726 Ann Arbor, MI USA FAX (734)

2 Table of Contents Section Page 0.0 Introduction ph Sensing Bulb Cleaning Initial Cleaning of the ph Sensing Bulb More Vigorous Cleaning of the ph Sensing Bulb ph Probe Reference Junction Maintenance MP20 Storage Preparing the MP20 for Storage Storing the MP Use and Care of Standards Calibration of the ph Probe Pre-cleaning and Assessment of ph Probe Condition ph Probe Calibration Process 9 Table of Contents

3 0.0 Introduction After some period of use, your MP20 ph probe may show signs of slow response, difficulty in calibrating, inaccurate readings or large offsets from original performance. The reason for this is the measuring elements, ph Sensing Bulb and Reference Junction, may have become contaminated, coated or clogged. Removing these contaminants usually requires soaking or washing in some solution to remove the coating from the ph Sensing Bulb surface or replacement of the Reference Junction and/or Reference Electrolyte. MP20 ph Probe Measuring Elements Reference Tube (Contains Reference Electrolyte Solution) Reference Junction ph Sensing Bulb Reference Electrode (Located Inside Reference Tube) RP Electrode Examples of fouled, dirty or coated ph Sensing Bulbs are represented below. These conditions usually require maintenance to return the ph probe to proper working order. Page 1

4 1.0 ph Sensing Bulb Cleaning Based on a visual inspection of the ph Sensing Bulb, there are suggested cleaning procedures you can perform to restore performance. Examples of cleaning and reconditioning techniques are provided below. Please Note: Good Laboratory Practices should always be followed. Protective gloves and safety glasses should be worn while handling any chemicals. If you are unsure of the proper technique for handling a chemical or of its hazardous properties, it is best to send the MP20 to QED for service, eliminating the risk of danger. Please Note: Do not disassemble the Reference Junction and Reference Tube prior to Sensing Bulb cleaning, as outlined below. Be sure to leave the Reference Tube in place and filled with electrolyte solution. Please Note: Avoid the use of organic solvents such as Acetone, Methyl Ethyl Ketone (MEK), Tetrahydrofuran (THF), or Trichloroethane as these may damage the probe measuring elements. 1.1 Using the ph Reconditioning Kit to Clean the ph Sensing Bulb The ph Sensing Bulb cleaning procedures outlined below may be accomplished without removing the ph probe from the MP20 sonde (transmitter) by using the ph Recondition Kit, part number 40051, available from QED. The kit contains two sizes of plastic vials. The short version is for use with MP20 units containing a turbidity probe, and the long version is for use with MP20 units without a turbidity probe. These are used in the following manner MP20s with turbidity probes (figure 1.1) 1. Gently rotate the turbidity probe out of the way of the ph probe. Please Note: Do not rotate the turbidity probe more than 90 degrees or damage to the probe may occur. 2. Fill the short vial with enough cleaning solution so that the ph Sensing Bulb will be completely submerged. 3. With the probes pointing down, insert the vial up over the ph probe. 4. To support the MP20 sonde (transmitter) during cleaning, rotate the turbidity probe back to its original position and rest the vial on the top of the turbidity probe and gently rest the sonde on the turbidity probe. 5. Allow the ph probe to soak for the time outlined below and follow the remaining procedure. Page 2

5 Figure MP20s without turbidity probes (figure 1.2) Figure Fill the long vial with enough cleaning solution so that the ph Sensing Bulb will be completely submerged. 2. Place the filled vial into the storage cup. 3. To support the MP20 Sonde (transmitter) during cleaning, with probes pointing down, lower the sonde down into the storage cup so that the ph probe is submerged in the vial. 4. Allow the probe to soak for the time outlined below and follow the remaining procedure. Page 3

6 1.2 Initial Cleaning of the ph Sensing Bulb If, during examination of the ph Sensing Bulb, you suspect the bulb surface is coated or contaminated, you can first attempt using a liquid detergent solution. A detergent is most effective when removing grease and oils. Clean per the procedure outlined below. Please Note: Examples of suitable detergents would be non-phosphate laboratory cleaning solutions such as Liqui-Nox and Alconox. In the event these are not available other nonphosphate detergent solutions may be used such as Cascade or Dawn dishwashing detergents. 1. Using the ph reconditioning kit, soak for a minimum of 15 minutes in warm tap water containing approximately 1% liquid detergent. a. Soaking is to be accomplished by submerging the probe assembly in the detergent solution such that the ph Sensing Bulb is completely submerged. 2. Rinse the probe with deionized water. 3. Visually inspect the ph Sensing Bulb to assure that all contaminants were removed from the bulb s surface. a. You may repeat this process as needed to remove the contaminants and thoroughly clean the ph Sensing Bulb. b. You may use a small soft bristle toothbrush to remove stubborn contaminants following soaking. However, care must be taken when mechanically cleaning the ph Sensing Bulb or damage to the glass bulb may occur. 4. If all contaminants were removed from the ph Sensing Bulb surface, replace the reference electrolyte solution in the Junction Tube and then soak the probe in ph 4 buffer solution for approximately 15 minutes prior to attempting calibration. During soaking in the ph 4 buffer solution, assure that the ph Sensing Bulb is completely submerged in the solution. 1.3 More Vigorous Cleaning of the ph Sensing Bulb In the event the above procedure does not restore probe performance, more rigorous cleaning may be required to remove stubborn deposits such as metals, calcium, lime scale, organics or proteins on the ph Sensing Bulb s surface. 1. Using the ph reconditioning kit, soak the probe in 1.0 N hydrochloric acid (HCL) solution for one minute. a. Soaking is to be accomplished by submerging the probe assembly in the solution such that the ph Sensing Bulb is completely submerged. 2. Rinse the probe with deionized water Page 4

7 Please Note: If a 1.0 N concentration of hydrochloric acid (HCL) is not available, white vinegar or citric acid may be substituted; however, the soak times outlined above must be increased to approximately 30 minutes. Since white vinegar and citric acids are available from a wide range of manufacturers and sources, the concentrations may vary; therefore, your results may also vary. 3. Visually inspect to assure that all contaminants were removed from the ph Sensing Bulb surface. a. If contaminants were not completely removed, repeat the above process, soaking for up to 10 minutes, if necessary. 4. If all contaminants were removed from the ph Sensing Bulb surface, replace the reference electrolyte solution in the Junction Tube and then soak the probe in ph 4 buffer solution for approximately 15 minutes prior to attempting calibration. During soaking in the ph 4 buffer solution, assure that the ph Sensing Bulb is completely submerged in the solution. 2.0 ph Probe Reference Junction Maintenance The pores of the Reference Junction may become clogged such that surface cleaning will not restore proper function. If, after visual inspection of the Reference Junction, it is suspected to be clogged, contaminated, or if slow probe response time persists after cleaning the ph Sensing Bulb, then often the best practice is to replace the Reference Junction and Electrolyte Solution. Please Note: It is good practice to replace the Reference Junction at least every 6 months and the Electrolyte Solution every month to maintain probe performance. Please Note: During replacement of the Reference Junction, do not touch or attempt to clean the Reference Electrode located inside the Reference Tube, or damage to the Reference Electrode may occur. (The Reference Electrode is the long metal tube that resembles a matchstick.) 2.1 Replacing the Reference Junction can be accomplished by one of the following methods Recommended method for replacing the Reference Junction while leaving the Reference Tube installed on the Sonde (transmitter): 1. Remove the Reference Junction by unthreading it from the end of the Reference Tube. 2. Discard the Electrolyte Solution and any tablets present in the tube. 3. Rinse Reference Electrode and inside of Reference Tube with Electrolyte Solution and discard. Page 5

8 4. Refill the Reference Tube completely with Electrolyte Solution. 5. Drop in two potassium chloride (KCL) pellets, if desired (potassium chloride pellets are recommended to extend the life of the Electrolyte Solution). 6. Thread a new Reference Junction onto the end of the Reference Tube. The threading action will purge excess Electrolyte Solution and air from the tube. 7. If any bubbles are present on the surface of the Reference Electrode, gently shake the sonde (transmitter) to remove them Alternate method for replacing the Reference Junction after removing the Reference Tube from the Sonde (transmitter): 1. With the probes pointed toward the floor, remove the Reference Tube from the sonde (transmitter) by carefully pulling it loose. Please Note: Care needs to be taken to assure that removal of the Reference Tube does not damage the ph Sensing Bulb. 2. Discard the Electrolyte Solution and any tablets present in the Reference Tube. 3. Remove the Reference Junction by unthreading it from the end of the Reference Tube. 4. Rinse the Reference Electrode and the inside of the Reference Tube with Electrolyte Solution. 5. Thread on a new Reference Junction to the end of the Reference Tube. 6. Drop in two potassium chloride pellets, if desired (potassium chloride pellets are recommended to extend the life of the Electrolyte Solution). 7. Refill the Reference Tube completely with Electrolyte Solution. 8. Install the refreshed tube assembly onto the inverted sonde (transmitter) with the probes pointed toward the floor. a. nce the Reference Tube assembly has passed the o-ring, turn the sonde (transmitter) so that the probes point toward the ceiling, and push the Reference Tube down so the excess Electrolyte Solution and air are purged from the tube. 9. If any bubbles are present on the surface of the Reference Electrode, gently shake the sonde (transmitter) to remove them. Page 6

9 3.0 MP20 Storage Proper storage affects the life of the ph probe and how quickly it responds and stabilizes in different types of samples. When not in use, ph probes should be stored in ph 4 buffer solution. This insures that the ph Sensing bulb remains hydrated and ready to measure accurately and quickly. 3.1 Preparing the MP20 for Storage Prior to storing your MP20, the storage cup should be filled to the preset line, which is approximately 2.4 inches from the bottom of the storage cup, or filled with approximately 165ml of deionized or distilled water, and installed onto the MP20. Deionized or distilled water is preferred. However, tap water may be used if deionized or distilled water is not available. Shake the sonde (transmitter) to remove debris from the probes. Discard the water, and repeat this process at least two more times. Please Note: Do not leave the electrode in deionized or distilled water for more than minutes. The electrolyte or internal filling solution can become diluted and adversely affect the function of the probe. Storing ph electrodes for any length of time in distilled or deionized water is not recommended. 3.2 Storing the MP20 To store your MP20, fill the storage cup with approximately 165ml of ph 4 buffer solution, or to the preset line, which is approximately 2.4 inches from the bottom of the storage cup, and install it onto the MP20 sonde (Figure 3.1). The ph 4 buffer solution will not harm the sensors in your MP20 and is an effective solution for storage between uses and longer-term storage. Figure 3.1 ph 4 Buffer Storage Fill Level (Pri or to In s talling Cup) Storage Fill Level (P rior to Installing Cup) Storage Fill Level (P rior to Installing Cup) Page 7

10 Please Note: After long term storage, approximately one week or longer, replace the reference electrolyte solution prior to calibration. It may be necessary to replace the reference electrolyte after receiving the MP20 from QED. Please Note: Colored solution may cause the Teflon reference junction to become dyed to this color. This will not, in any way, negatively affect the function of the junction. 4.0 Use and care of Standards Buffers are only intended for single use and should be discarded immediately after use. Buffer solutions should always be poured directly into the calibration cup for calibration, and used buffers should never be poured back into the bottle. Please Note: ph 10 buffer solution is susceptible to rapid degradation after the bottle has been opened. pened ph 10 buffer solution has a more limited usable time frame than other buffer solutions and should be replaced with fresh solution after approximately 5 days. Please Note: During storage of an opened bottled of ph 10 buffer solution, be sure the bottle is tightly capped. Please Note: ph 4 buffer solution used for the calibration process may be saved and used as storage solution only. 5.0 Calibration of the ph Probe Calibration of the ph probe requires that the probe is clean and has been adequately maintained. If there are any doubts as to the condition of the probe, it should be serviced according to the previous sections. Even probes brought in from the field with an adequate service record should be cleaned thoroughly. 5.1 Pre-cleaning and Assessment of ph Probe Condition The storage cup should be filled to the preset line (approximately 2.4 inches from the bottom of the storage cup, or filled with approximately 165ml of solution) with deionized or distilled water. Deionized or distilled water is preferred; however, tap water may be used if deionized or distilled water is not available (Figure 5.1). Please Note: If you do not have a fill line on your storage cup, you can measure out approximately 165ml of water to adequately fill the cup. Page 8

11 Figure 5.1 de-ionized water, distilled water, or tap water Storage F ill Level (Pri or to In stalling Cup) Storage Fill Level (P rior to Installing Cup) Storage Fill Level (P rior to Installing Cup) Attach the storage cup to the sonde (transmitter). Shake the sonde to remove debris from the probes. Discard the water, and repeat this process at least two more times, (Figure 5.2). Carefully examine the ph probe. If there are signs of accumulated debris, salts or heavy staining of the bulb or reference tube, follow the cleaning instructions in the previous sections. nce you are satisfied that the probe is clean, calibration may begin. Figure 5.2 Shake Storage Fill Level (Pri or to Installing Cu p) Discard water Repeat 2 times 5.2 ph Probe Calibration Process 1. Calibration may be carried out using the storage cup or the calibration cup. a. If using the storage cup, fill with enough ph 7 buffer solution to assure that the ph probe Sensing Bulb is completely immersed in the buffer solution. Page 9

12 Figure 5.3 b. If using the calibration cup, invert the MP20 sonde and clamp it firmly in the vertical position, with the probes pointing up. Place the calibration cup on the sonde and secure it. This method is shown in Figure 5.3. Fill the cup with enough ph 7 buffer solution to assure that the solution completely covers all of the probes. A ph 7 Buffer 2. Switch the MP20 meter (display) unit on. 3. Verify that the ph reading is between ph 6.5 and 7.5 and then wait until the reading is stable; that is, when the change in ph reading does not exceed 0.02 ph units per 5 seconds. a. Stabilization of the reading may take approximately 60 seconds. 4. Use the up/down and left/right keys to select calibrate and press the enter key (Figure 5.4). 5. Using the up/down and left/right keys, select the ph symbol on the screen, this will flash to indicate it has been selected, and press the enter key. The ph symbol will stop flashing and the ph reading will be displayed, flashing on the screen (Figure 5.4). 6. Using the up or down keys, adjust the reading to the standard being used. a. The value entered will depend on the temperature. Consult the side of the bottle for the temperature corrected value, enter this value and press enter. This will fix the zero point for the instrument when measuring ph (Figure 5.4). Page 10

13 Esc Esc Esc U Figure 5.4 Temp C Temp SpC MS/cm SpC D Mg/L D PH Units PH PH Units Calib Review Screen Store Setup Calib Calib ENTER BUTTN ESCAPE/CIRCULATR BUTTN LEFT, UP BUTTN DWN, RIGHT BUTTN PWER BUTTN Temp, C ph Select Calib Press Enter Select ph Press Enter Enter adjusted ph Press Enter 7. Press the escape key, this will return you to the main screen. a. The ph reading should be ph 7 +/ It will most likely read within a few hundredths of ph Discard the ph 7 buffer (Figure 5.5). 9. Rinse out the calibration or storage cup and the sonde with deionized or distilled water. Discard and shake out excess water (Figure 5.5 below). Deionized or distilled water is preferred; however, tap water may be used if deionized or distilled water is not available. Figure 5.5 de-ionized water, distilled water, or tap water Discard ph 7 Buffer Discard water 10. Pour a small amount of ph 4 buffer solution, enough to fill the cup up to approximately ¾ of an inch, into the calibration or storage cup, depending on which you are using. Shake for 5-10 seconds and discard the solution (Figure 5.6). Page 11

14 Figure 5.6 A ph 4 Buffer Discard 4 Buffer 11. Pour ph 4 buffer solution into the cup. Figure 5.7 a. If using the storage cup fill with enough ph 4 buffer solution to assure that the ph probe Sensing Bulb is completely immersed in the buffer solution. b. If using the calibration cup, invert the MP20 sonde and clamp it firmly in the vertical position, with the probes pointing up. Place the calibration cup on the sonde and secure it. This method is shown in Figure 5.7. Fill the cup with enough ph 4 buffer solution to assure that the solution completely covers all of the probes. A ph 4 Buffer 12. Verify that the ph reading is between ph 3.5 and 4.5 and then wait until the reading is stable; that is, when the change in ph reading does not exceed 0.02 ph units per 5 seconds. a. Stabilization of the reading may take approximately 60 seconds. 13. Use the up/down and left/right keys to select calibrate, and press the enter key (Figure 5.8). Page 12

15 Esc Esc Esc U 14. Using the up/down and left/right keys, select the ph symbol on the screen (this will flash to indicate it has been selected) and press the enter key. The ph symbol will stop flashing and the ph will be displayed, flashing on the screen (Figure 5.8). 15. Using the up or down keys, adjust the reading to the standard being used. Figure 5.8 a. The value entered will depend on the temperature; consult the side of the bottle for the temperature corrected value. Enter this value and press enter. This will fix the span for the instrument when measuring ph (Figure 5.8). Temp C Temp SpC MS/cm SpC D Mg/L D PH Units PH PH Units Calib Review Screen Store Setup Calib Calib ENTER BUTTN ESCAPE/CIRCULATR BUTTN LEFT, UP BUTTN DWN, RIGHT BUTTN PWER BUTTN Temp, C ph Select Calib Press Enter Select ph Press Enter Enter adjusted ph Press Enter 16. Press the escape key. This will return you to the main screen. a. The ph reading should be ph 4 +/ It will most likely read within a few hundredths of ph You may discard the ph 4 buffer solution or save it in a clean container to use as storage solution when the calibration process is complete (Figure 5.9). Please Note: If you are not saving the ph 4 buffer solution to use for storage, the solution should be discarded, and not reused for any further calibrations. 18. Rinse out the calibration or storage cup with deionized or distilled water. Discard and shake out excess water (Figure 5.9). Deionized or distilled water is preferred; however, tap water may be used if deionized or distilled water is not available Page 13

16 Figure 5.9 de-ionized water, distilled water, or tap water Discard ph 4 Buffer Discard water 19. To verify that the probe has been properly calibrated, pour a small amount of ph 10 buffer solution, enough to fill the cup up to approximately ¾ of an inch, into the calibration or storage cup, depending on which you are using. Shake for 5-10 seconds and discard the solution (Figure 5.10). Figure 5.10 A ph 10 Buffer Discard 10 Buffer 20. Pour ph 10 buffer solution into the cup. a. If using the storage cup, fill with enough ph 10 buffer solution to assure that the ph ] probe Sensing Bulb is completely immersed in the buffer solution. b. If using the calibration cup, invert the MP20 sonde and clamp it firmly in the vertical position, with the probes pointing up. Place the calibration cup on the sonde and secure it. This method is shown in Figure Fill the cup with enough ph 10 buffer solution to assure that the solution completely covers all of the probes. Page 14

17 Figure 5.11 A ph 10 Buffer 21. Note the ph indicated on the display, once the reading has stabilized. The reading should be between ph 9.8 and a. Stabilization of the reading may take approximately 60 seconds. 22. The MP20 is now calibrated. 23. Rinse out the calibration or storage cup with deionized or distilled water. Discard and shake out excess water (Figure 5.12 below). Deionized or distilled water is preferred; however, tap water may be used if deionized or distilled water is not available. 24. The MP20 can now be used to measure ph accurately. Figure 5.12 de-ionized water, distilled water, or tap water Discard ph 10 Buffer Discard water Page 15