New automatic potentiometric titrator use conditions and panel description
The automatic potentiometric titrator is a common analytical instrument for capacity analysis designed according to the principle of potential method.
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.
Instrument use
1 for laboratory application of potentiometric titration for capacity analysis;
2 controlled titration of pH or electrode potential;
Automatic potentiometric titrator (professional)
Automatic potentiometric titrator (professional)
3 automatic potentiometric titration for capacity analysis;
4 pH determination - for laboratory sampling to determine the pH of the aqueous solution, or the PH value of the cosmetic;
5 Potential measurement - measuring the potential of the electrode or other millivolts
Panel description
among them:
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 “Measureâ€, 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.
Characteristics
The instrument adopts touch screen control and Chinese operation interface, which is easy to understand;
The instrument adopts modular design, consisting of three parts: volumetric titration device (can be replaced by Coulomb titration device), control device (can be replaced by PC titration software) and measuring device (including potential measurement, conductance measurement and permanent stop measurement). Realize potentiometric titration, coulometric titration, conductometric titration and permanent stop titration;
The instrument is controlled by titration software and can perform various operations;
The instrument has the functions of pre-titration, preset end point titration, blank titration or manual titration to generate a special titration mode, which expands the scope of use of the instrument;
The titration system uses materials resistant to perchloric acid corrosion and can be used for non-aqueous titration;
principle
Potentiometric titration is a method for determining the end point of titration by measuring the change in potential during the titration. Compared with the direct potentiometric method, the potentiometric titration method does not need to accurately measure the electrode potential value. Therefore, the influence of temperature and liquid junction potential is not important. The accuracy is better than the direct potential method. The ordinary titration method relies on the color change of the indicator to indicate the end point of the titration. If the solution to be tested has color or turbidity, the indication of the end point is more difficult, or no suitable indicator can be found at all. . Potentiometric titration is based on a sudden jump in the electrode potential to indicate the end point of the titration. Titrated to
Potentiometric titrator operation
Potentiometric titrator operation
Before and after the end point, the concentration of the ions to be measured in the drip is continuously changed by n orders of magnitude, causing a sudden jump in the potential, and the content of the measured component is still calculated by consuming the amount of the titrant.
Potentiometric titration can be used for acid-base titration, redox titration, titration and precipitation titration using different indicator electrodes. The acid-base titration uses a PH glass electrode as an indicator electrode, and in a redox titration, a platinum electrode can be used as an indicator electrode. In the titration, if EDTA is used as the titrant, a mercury electrode can be used as the indicator electrode. In the precipitation titration, if the halide ion is titrated with silver nitrate, a silver electrode can be used as the indicator electrode. During the titration process, as the titrant is continuously added, the electrode potential E changes continuously, and when the electrode potential suddenly jumps, the titration reaches the end point. It is easier to determine the end point of the titration with a differential curve than a normal titration curve.
If an automatic potentiometric titrator is used, the titration curve can be automatically drawn during the titration process, the titration end point is automatically found, the volume is automatically given, and the titration is quick and convenient.
Conductor titration is performed, a reference electrode is inserted into the solution to be tested, and an indicator electrode constitutes a working battery. With the addition of the titrant, the concentration of the measured ions changes continuously due to the chemical reaction, and the potential of the indicating electrode also changes accordingly. A sudden jump in potential occurs near the equivalence point. Therefore, by measuring the change in the electromotive force of the working battery, the end point of the titration can be determined.
The basic instrumentation for potentiometric titration includes a burette, a titration cell, an indicator electrode, a reference electrode, a stirrer, and an instrument for measuring the electromotive force.
How does the potentiometric titration determine the endpoint of the titration? The method of plotting the potential to determine the curve.
The potentiometric titration curve is a graph in which the electrode potential value (battery electromotive force) E is plotted against the addition volume V of the standard solution as the titration progresses.
According to different methods of drawing, there are three types of potentiometric titration curves, EV curve, ordinary potential titration curve, and the inflection point e is the equivalent point.
Determination of the inflection point: Make two 45° oblique lines tangent to the titration curve, and the intersection of the bisector and the curve is the inflection point.
Ee is the equipotential point potential.
Ve is the volume of the standard solution to be added to the equivalence point.
The larger the potential jump range and slope, the smaller the analysis error.
Curve, one derivative curve, first derivative curve.
The e point at the top of the curve is the equivalent point (you need to find it first when drawing)
Use the E and V values ​​of two adjacent:
.
=0 is the equivalent point
In the formula, V1 and V2 are the calculated values ​​of the values.
Folding and editing this paragraph features and applications
Potentiometric titration has many advantages over volumetric analysis with indicators. It can be used first for the titration of colored or turbid solutions. It is not acceptable to use indicators; in the absence or absence of indicators, this method is used; It can also be used in cases where the concentration of the test solution or the titration reaction is not complete enough; sensitivity and accuracy are high, and automation and continuous measurement can be realized. Therefore, the use is very extensive.
According to the type of titration reaction, potentiometric titration can be used for neutralization titration (acid-base titration) precipitation titration, complexometric titration, redox titration
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