Panel description of the automatic potentiometric titrator

The principle of the potential method is: Selecting an appropriate indicator electrode and a reference electrode to form a working battery with the solution to be tested. With the addition of the titrant, the concentration of the measured ions constantly changes due to the chemical reaction, thus indicating the potential of the electrode. It changes accordingly. Near the end of the titration, the measured ion concentration is abrupt, causing a sudden jump in the electrode potential. Therefore, the titration end point can be determined based on the jump of the electrode potential.

The instrument is divided into two parts: the electronic meter and the titration system. The electric meter uses an electronic amplification control circuit to compare the potential between the indicator electrode and the reference electrode with a preset end point potential. The difference between the two signals is amplified and controlled to titrate. The drip rate of the system. After reaching the preset potential at the end point, the titration stops automatically. The instrument controls the amount of dripping for the microcomputer, and its structure is divided into two parts: the electric meter and the titration system.

Panel description

1) Power indicator. Turn on the power, this indicator should be on;

2) Titration indicator. This indicator flashes when the titration is started;

3) End point indicator. Used to indicate if the titration is over. Turn on the power, this indicator lights up, and the indicator goes off after the titration is started. This indicator lights up after the titration is complete.

4) Slope compensation adjustment knob. The pH is used regularly.

5) Temperature compensation adjustment knob. Used for pH calibration and measurement.

6) Position the adjustment knob. The pH is used regularly.

7) "Settings" selector switch. When the switch is set to "end point", the end point mV value or pH value setting (pH/mV switch "pH" can be set to set the pH end point; set "mV" to set the mV end point). When this switch is set to â€œMeasureâ€, mV or pH measurement is performed (mV or pH measurement is also dependent on the position of the pH/mV switch). When the switch is placed at the pre-control point, the pH or mV pre-control point setting can be performed. For example, if the pre-control point is set to 100mV, the instrument will automatically switch from fast drop to slow drop at 100mV from the end point.

8) "pH/mV" selector switch. When this switch is placed at "pH", pH measurement or pH endpoint setting or pH pre-control point setting can be performed. When this switch is set to "mV", mV measurement or mV end point setting or mV pre-control point setting can be performed.

9) "Function" selector switch. When this switch is set to "Manual", manual titration can be performed; when "Automatic" is set, the preset end point titration is performed. After the end point, the titration is terminated and the titration light is on. When the switch is placed in "Control", the pH or mV control titration is performed. After reaching the end point pH or mV value, the instrument is still ready for titration and the titration lamp is always off.

10) "Endpoint potential" adjustment knob. Used to set the end point potential or pH value.

11) "Pre-control point" adjustment knob. It is used to set the pre-control point mV or pH, the size of which depends on the nature of the chemical reaction, ie the size of the titration jump. Generally, redox titration, strong acid and strong base neutralization titration and precipitation titration can choose smaller pre-control point values; weak acid strong base, strong acid weak base can choose intermediate pre-control point value; and weak acid weak base titration needs to choose large pre-control point value .

12) "Titration start" button. When the "Function" switch is placed in "Auto" or "Control", click this button and the titration starts. When the "Function" switch is set to "Manual", press this button to titrate. Release this button and the titration stops.

13) Power switch.

14) Fuse holder.

15) Power outlet.

16) Solenoid valve interface.

17) Ground terminal. Can be connected to the reference electrode.

18) Electrode socket.

19) Recorder output: for use with (0-1)V recorders. The output voltage is as follows:

mV file

Instrument display value (mV)

-500

Connection and installation

1 titration device installation

The titration device was mounted on a JB-1A blender. The installation steps are as follows (see Figure 2):

1) JB-1A type agitator 2) Electrode holder 3) Solenoid valve 4) Solenoid valve screw 5) Rubber tube 6) Dropper holder

7) Burette 8) Dropper clamp fixing screw 9) Curved pipette holder (2) 10) Tubular pipette holder (1)

11) Nut 12) Jacket 13) Sandwich 14) Head screw 15) Mounting thread 16) Close ring

1) Screw the pipette holder (1) of serial number 10 onto the mounting thread (15) of the agitator;

2) Align the holes of the core (13) and the jacket (12), pass the dropper holder (1) of the serial number 10, adjust to the appropriate position, and tighten the nut (11) to fix it;

3) Insert the end of the solenoid valve (3) into the core (13) and tighten the screw (14) to fix it;

4) Install the dropper clamp (6) on the pipette holder (2) of No. 9 and adjust it to the appropriate position. Tighten the dropper holder fixing screw (8) to fix it;

5) Clamp the burette (7) on the pipette holder (6), and insert the rubber tube above the solenoid valve into the end of the burette (7);

6) Install the electrode holder (2) at the lower end of the serial number 9 dropper holder (2). Install the electrode and capillary, and insert the rubber tube under the solenoid valve into the capillary. Electrode and capillary installation are shown in Figure 3.

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1) Electrode rod jaw 2) Spring ring 5) Calomel (reference) electrode holder

3) Drip tube (glass capillary) jaw 4) Glass (pH, pNa) electrode holder

2 Solenoid valve structure, adjustment and installation or replacement of pipes.

Before use, the head screw (4) should be adjusted so that when the solenoid valve is de-energized, there is no drop of liquid droplets; when the solenoid valve is opened, the droplets are dropped and the appropriate flow rate is adjusted.

Installation or replacement of pipes.

First unscrew the nut in Figure 4 and pull out the base. Then unscrew the two screws on the base and loosen the compression screw. The pipe can be replaced.

3 Insert the electrode plug into the electrode socket (18) on the rear panel of the instrument. If the electrode used is divided into the measuring electrode and the reference electrode, connect it to the electrode socket converter. The specific method is as follows (see Figure 5):

Insert the converter plug (22A) into the instrument electrode socket; the measuring electrode plug is inserted into the converter socket (22B) and the reference electrode plug is connected to the instrument's rear panel terminal (17). Some electrodes need to be connected by a contactor (such as a 213 platinum electrode), the electrode is connected to the contactor, and the contactor is inserted into the converter socket (22B).

4 Insert the solenoid valve plug into the solenoid valve port (16) on the rear panel of the instrument.

Instructions

After the instrument is installed and connected, plug in the power cord, turn on the power switch, and the power indicator lights. Use after 15 minutes of preheating.

1 mV measurement

1.1 "Setting" switch to "Measure", "pH/mV" selector switch to "mV";

1.2 Insert the electrode into the solution to be tested, stir the solution evenly, then read the electrode potential (mV) value;

1.3 If the measured signal is beyond the measuring range of the instrument, the display will not light and an overload alarm will be issued.

2 pH calibration and measurement

2.1 Calibration: The instrument should be calibrated before pH measurement. In general, the instrument is calibrated once a day when it is used continuously. The steps are as follows:

a) "Setting" switch to "Measure", "pH/mV" switch to "pH";

b) Adjust the "Temperature" knob so that the white line of the knob points to the corresponding solution temperature value;

c) Turn the "Slope" knob clockwise (100%);

d) insert the cleaned electrode into a buffer solution with a pH of 6.86;

e) Adjust the "Positioning" knob so that the instrument display reading is consistent with the pH of the buffer solution at the current temperature (see Appendix 1);

f) Rinse the electrode with distilled water, insert a standard buffer solution with a pH of 4.00 (or pH 9.18), and adjust the slope knob to match the instrument display reading to the pH of the buffer solution at the current temperature (see Appendix 1). ;

g) Repeat (e)~(f) until you no longer need to adjust the "Positioning" or "Slope" adjustment knob. At this point, the instrument completes the calibration. After the calibration is complete, the "Positioning" and "Slope" knobs should not be moved until the next calibration.

2.2 pH measurement

The calibrated instrument can be used to measure pH as follows:

a) "Setting" switch to "Measure", "pH/mV" switch to "pH";

b) Wash the electrode head with distilled water and wash it once with the solution to be tested;

c) measuring the temperature value of the measured solution with a thermometer;

d) Adjust the "Temperature" knob so that the white line of the knob points to the corresponding solution temperature value;

e) Insert the electrode into the solution to be tested, stir the solution to make the solution uniform, and read the pH of the solution.

3 Preparation before titration

3.1 Install the titration device according to Section 5, place a stir bar in the test cup, and place the test cup on the JB-1A blender.

3.2 Electrode selection: depending on the chemical reaction of the titration, if it is a redox reaction, a platinum electrode and a calomel electrode and a tungsten electrode can be used; if it is a neutralization reaction, a pH composite electrode or a glass electrode and a calomel electrode can be used; The silver salt reacts with the halogen, and a silver electrode and a special calomel electrode can be used.

Application example

Redox titration, heavy chromium ion titration of ferrous ions:

Electrode: 213 type platinum electrode

217 type calomel electrode

Electrode connection: Connect the 213 platinum electrode to the contactor, insert the contactor into the "measuring electrode" socket of the electrode socket converter, and connect the 217 type calomel electrode to the "reference electrode" terminal of the converter. Instrument electrode socket. Dropping solution: 0.0167mol/L Â± 10% potassium dichromate

To be dripped: 10 ml of ammonium ferrous sulfate having a concentration of 0.1 mol/L Â± 10%, 10 ml of sulfuric acid having a concentration of 15%, and dissolved in 50 ml of distilled water.

The "pH/mV" switch is set to "mV", the "set" switch is set to "end point", and the "end point potential" potentiometer is adjusted so that the instrument displays 590 mV. Set the "pre-control point" to the "set" switch and adjust the "pre-control point" potentiometer so that the instrument displays "90mV". The "Function" switch is set to "Automatic". When the "Titration Start" switch is clicked, the instrument starts titration. Reading burette reading after the "end point" light is on

Troubleshooting

The titration lamp is shining, but there is no drop under the droplet, and the solenoid valve plug is connected correctly, then the solenoid valve can be adjusted.

The head screw (4), so that the drip can not drip when the solenoid valve is not open, and adjust to the appropriate flow rate (see section 5, section 2)

2 When the solenoid valve is closed, there are still drops under the droplets, and the head screw (4) on the solenoid valve can be re-adjusted. If the fault cannot be eliminated, the rubber pipe will be deformed for a long time, the elasticity will be deteriorated, or the rubber pipe installation position is not suitable. . At this time, according to the second section of Section 5, disassemble the solenoid valve, change the upper and lower positions of the rubber tube or replace the rubber hose. The rubber tube is preferably cooked in a slightly alkaline solution for several hours before being exchanged.

Precautions

1 The input (electrode socket) of the instrument must be kept dry and clean. When the instrument is not in use, insert the Q9 shorting plug into the socket to prevent dust and moisture from entering.

2 When measuring, the lead wire of the electrode should be kept still, otherwise it will cause unstable measurement.

3 When using the buffer solution to calibrate the instrument, ensure the reliability of the buffer solution. Do not mismatch the buffer solution, otherwise the measurement will be inaccurate.

4 After removing the electrode sleeve, the sensitive glass bulb of the electrode should be avoided from contact with the hard object, because any damage or rubbing will invalidate the electrode.

5 The external reference (or calomel electrode) of the composite electrode should always be noted that there is a saturated potassium chloride solution, and the replenishing solution can be added from the upper hole of the electrode.

6 Electrodes should be protected from long-term immersion in distilled water, protein solutions and acidic fluoride solutions.

7 The electrode should be protected from contact with silicone oil.

8 It is best to rinse the solenoid valve hose several times with the drip before titration.

9 After reaching the end point, you cannot press the "Trip Start" button, otherwise the instrument will start titrating again.

10 Do not use a solution such as potassium permanganate that works with a rubber hose.

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