pH Amplifier

(Order Code PHA-DIN)

Our pH Amplifier is used with our pH electrode (7120B) as a general-purpose pH measurement system It can be used for any lab or demonstration that can be done with a traditional pH meter. This system offers the additional advantages of automated data collection, graphing, and data analysis. Typical activities using our pH system include studies of household acids and bases, acid-base titrations, monitoring pH change during chemical reactions or in an aquarium as a result of photosynthesis, investigations of acid rain and buffering, and investigations of water quality in streams and lakes.

This pH Amplifier is designed for use with the following interfaces available from Vemier Software:

• Multi Purpose Lab Interface (MPLI)

• Voltage Input Unit (VIU)

• Universal Lab Interface

• Serial Box Interface

• Texas Instruments Calculator-Based Laboratory (CBL) System

How the pH Amplifier Works

The pH Amplifier is a circuit which allows a standard combination pH electrode

(such as the Verriicr Software 7120B) to be monitored by a lab interface. The pH

electrode is connected to the BNC connector on one end of the box. The cable from the pH Amplifier ends in a 5-pin DIN plug for connection to a variety of lab

interfaces.

The pH Amplifier does three primary tasks:

• It steps up the voltage produced by the pH electrode to a range where it can be

monitored by the lab interface. A fairly common op-amp circuit is used.

• It offsets the voltage so it is always in the range of 0 to 3.5 volts. There is a

potentiometer inside the pH Amplifier which allows this offset to be adjusted.

• It provides the negative voltage required for the amplifier circuit. One of the Ics on the circuit board converts the +5 volt power supplied by the lab interface to -5

volts.

When a combination pH electrode is connected, the pH Amplifier will produce a

voltage of 1.75 volts in a pH 7 buffer. The voltage will increase by about 0.25 volts for every pH number decrease. The voltage will decrease by about 0.25 volts/pH number as the pH increases.

A complete schematic of the pH Amplifier is available. Contact Vernier Software.

The electrode and this amplifier are normally sold together as a Vernier pH System (Order code PH-DIN).

Calibration

In most cases you can simply load an experiment file which is designed for pH

measurement, and calibration of the pH system will be handled at the same time. For the best accuracy, you may want to calibrate your pH system. This allows for minor differences in pH electrodes and pH Amplifier circuits. To calibrate the system, you will need distilled water and two pH buffers of different pH. Buffer solutions and capsules are available from scientific supply houses. Vernier Software also sells capsules for making up buffers (order code PHB, $10). Calibration is done by first removing the electrode from its storage container and rinsing it in distilled water. Place it in one of the buffer solutions (e.g., 4.0 buffer). Follow the instructions on the screen and use this pH as one calibration point. Now rinse the electrode in distilled water again and move it to the second buffer solution (e.g., 7.0 buffer). Use this pH as the second calibration point. Save this calibration for later use.

Additional calibration information is included on the pH Electrode information sheets.

Using the pH Amplifier with your computer interface

1. Connect the lab interface (Serial Box Interface, ULI, MPLI, or VIU) to the

computer.

2. Connect the pH Amplifier to the lab interface.

3. Connect a combination pH electrode with a BNC connector to the pH Amplifier.

4. Start up your laboratory interface program. Make sure you select the correct probe with the program.

5. Load a pH calibration file using your data collection program. Calibration files for pH measurement are provided on all Vernier Software lab interface program

disks.

6. Try out the system measuring the pH of some known solutions or pH buffers.

7. For the best accuracy, you may want to calibrate your pH system. Follow the calibration instructions on the screen and in the lab interfacing program manual. Additional calibration tips are included on the pH electrode information sheets. Save the new calibration as a file on the disk so that it can be used at a later time.

Combination pH electrode Instructions

The pH electrode you have purchased is a hand crafted, precision analytical device. This electrode was fully tested prior to shipment.

The directions contained herein should be followed carefully to ensure optimum performance and maximum life.

Required Equipment and Solutions

• pH meter (A temperature componsator is recommended for increased pH measurement accuracy).

• pH Buffer 4.01

• pH Buffer 7.00

• Reference filling solution.

• Washbottle filled with distilled or deionized water.

• Laboratory magnetic stirrer and magnetic stir bars.

• Lab wipes.

• Clean beakers.

Electrode Preparation

Remove the Protective soaker bottle or cap from the electrode and thoroughly rinse the electrode with distilled water. Wipe carefully with a clean lab wipe

During shipment, air bubbles may have entered the electrode. Hold the electrode up to the light and inspect the internal chambers for air bubbles. If air is seen, carefully shake the electrode downward (like a thermometer) to dispel the air from the sensing elements inside the electrode.

Position the cover to expose the electrode reference chamber fill hole (for sealed, gel filled electrodes, disregard this operation).

For refillable electrode designs, fill the reference chamber with the appropriate pH reference filling solution. Use the appropriate reference filling solution. Use of the incorrect reference fining solution will damage the electrode and render it inoperable. Electrodes that have been filled with the incorrect filling solution are not covered under

warranty.

Electrode standardization

1- Carefully Connect the pH electrode to the input connector on the pH meter. Ensure that the electrode connection is secure.

2- Place the electrode into beaker containing pH 7.00 buffer and a stir bar. Stir at a moderato speed.

3- When the reading is stable, adjust the meter to read the value of the pH 7.00 buffer at the temperature in the laboratory (see the meter manufacturer’s instructions for details regarding temperature compensation.

4 Remove the electrode from the buffer. Rinse with distilled water and blot with a tab wipe.

5- Place the electrode in a beaker containing pH 4.01 buffer. Stir as before.

6- When the reading is stable, adjust the meter to read the value of the 4.01 buffer at the temperature in the laboratory.

7- Rinse the electrode with distilled water and blot with a lab wipe. Place the electrode in a beaker containing the sample. Stir. Record the pH when the reading is stable.

Electrode storage

Between measurements, store the pH electrode in a beaker containing pH electrode storage solution.

When storing for longer periods, store the pH electrode in the storage bottle or refit the cap which came with the electrode. Ensure that there is adequate pH electrode storage solution in the storage bottle or cap.

When taking the electrode out of service for extended periods, rinse the electrode thoroughly, wipe with a lab wipe and refit the storage bottle or cap. Maintain the level of pH electrode storage solution in the storage bottle during storage.

If the pH electrode is equipped with a fill hole cover, slip the cover over the fill hole.

Electrode cleaning

Do not use strong solvents (acetone, carbon tetrachloride, etc.) to clean the pH electrode.

If the electrode has become coated with oil or grease, carefully wash the electrode under warm tap water using dish washing detergent. Rinse thoroughly with fresh tap water followed by a rinse with distilled water. Soak the electrode in pH electrode storage solution for 30 minutes after this cleaning procedure. Recalibrate before use.

If the electrode has been exposed to protein or similar materials. soak in acidic pepsin for 5 minutes. Rinse thoroughly with distilled water. Recalibrate before use.

If the previous cleaning procedures fail to restore response. soak the electrode in .1 N. HCl for 10 minutes. Rinse thoroughly with distilled water. Recalibrate before use.

If electrode response is not restored, replace the electrode.

Laboratory Products Warranty

Products designed and sold for use in laboratory applications are warranted to be free from defects in materials and workmanship for a period of twelve (12) months from the date of purchase, six (6) months for products manufactured with Epoxy bodies and three (3) months for products manufactured with PVC bodies, provided that the product is used in accordance with the instructions provided and that the product has not been subjected to accidental breakage, alteration, misuse, abuse used in an application not normally intended for the product.

In the event of a warranted failure within the warranty period, the electrode will be repaired or replaced.

If necessary, we will issue a RAN (return authorization number). Materials or goods resumed without an RAN will not be accepted. Return the product freight prepaid.

THE WARRANTY DESCRIBED ABOVE IS EXCLUSIVE AND IN LIEU OF ALL OTHER WARRANTIES WHETHER STATUTORY, EXPRESS OR IMPLIED INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AND ALL WARRANTIES ARISING FROM THE COURSE OF DEALING OR USAGE OF TRADE. THE BUYER'S SOLE AND EXCLUSIVE REMEDY IS FOR REPAIR OR REPLACEMENT OF THE NON-CONFORMING PRODUCT OR PART THEREOF, BUT IN NO EVENT SHALL ASI OR ITS DEALERS OR AGENTS OF ANY TIER BE LIABLE TO THE BUYER OR ANY PERSON FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES WHETHER THE CLAIMS ARE BASED IN CONTRACT IN TORT (INCLUDING NEGLIGENCE) OR OTHERWISE WITH RESPECT TO OR ARISING OUT OF THE PRODUCT FURNISHED HEREUNDER

No other representations of warranty made by any person shall be binding.

Flinn QuickStarts™

pH System

TC1121

The Connections:

1. Plug the pH Electrode into the pH Amplifier Interface Box.

2. Connect the pH Amplifier Interface Box to Port I of the Serial Box Interface.

3. Connect the Serial Box Interface to the COME or COM2 port of the computer using the cable provided. (Use the 9-pin to 25-pin adapter if necessary.)

4. Plug the Serial Box Interface into an electrical outlet using the AC adapter.

The Set-up/Customizing Data LoggerT":

1. Open the Data Logger program. For installation and start-up instructions, consult your Flinn QuickStart for Data Logger.

Note: If a message box reading "Warning! Cannot find the interface box" appears:

a) Check all connections,

b) Determine which port (COM1 or COM2) is accepting the cable from the

Serial Box Interface, and

c) Click on the appropriate button ("COM1" or "COM2").

A default graph called "Untitled-l" will appear.

The right mouse button is used only to access Data Logger menus. Use the left mouse button for all other operations.

2. Under the "File" menu, choose "Open...". A new window will appear, listing the various experiment files for Data Logger.

3. From the list, double-click on "PH.LXP" to open the file to measure pH. This will be the file used for the suggested introductory activity—see below. You may need to scroll the list by clicking the left mouse button and dragging the cursor down the list to find this file.

4. The program will ask "Do you want to load the calibration saved with this experiment ('PH.CLB')?" Click "Yes". While it is not necessary to recalibrate the pH electrode each time it is used, it is recommended that it be calibrated about once each hour.

5. You do not need to customize the axes for the introductory activity. However, if you would like to customize the axes:

a) Double-click anywhere on the graph. This causes the "Axes" dialog box to appear.

b) To change the y-axis pH range, simply double-click inside the lower and/or upper limit value box and enter the desired value.

c) The x-axis should already be in the appropriate units for the experiment. You may change the lower and/or upper limit value boxes in the same manner as you did for the y-axis above. d) Click "OK."

You are now ready to perform the introductory activity.

Introductory Activity:

1. Open the "PH.LXP" file and load the calibration file, as described above.

2. Under the "Windows" menu, drag the cursor to "Big Numbers" and release. This will create a window that will display data in large, easy-to-read numbers.

3. Remove the pH electrode from the storage solution bottle and rinse the bulb with distilled water.

4. Insert the electrode into a cup or beaker containing a soft drink.

5. Click on "Start" to read the pH of the soft drink.

6. Click "Stop" to discontinue data collection.

7. Remove the pH electrode from the soft drink, rinse with distilled water, and replace the electrode in the storage solution bottle.