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Titration is a typical measurement technique categorized as a quantitative analytical method commonly used for quality control and R&D analyses. Lately, the analytical instrument marketplace has been dominated by application-driven techniques such as HPLC and LC/MS while titration applications are very mature and well-documented. To perform a titration, one requires only the principal apparatus which largely consists of burets, beakers, standardized solutions, reagents and indicators. Due to this simplicity, titration methods are very widely used for measuring , for instance, hardness in drinking water, chloride ions in food, metal ions in plating solutions, quantification analyses in petrochemicals and water determinations by Karl Fischer titration.
In general, the end point of a manual titration is detected visually by a color change in the colorimetric indicator and the results may vary considerably both individually and by operator to operator. On the contrary, using automatic potentiometric titrators produces measurements with high accuracy and precision because the titrant is dispensed precisely with an automatic buret and the end point is defined and determined automatically with an electronic sensor.
The COM-1700 series titrators have been recently designed and developed and are being introduced as the next generation of automatic titrators that will provide outstanding features and benefits. |
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The configuration of the COM 1700 generally consists of an arithmetic and control unit (ACU) equipped with a controller, color display and printout measurement results (referred to as the “titrator main unit”), burets controlled by the titrator main unit, and a stirrer to mix the sample with the added titrant in a beaker during the titration. (see Figure 1 below) |
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The titrator main unit is equipped with a 7.5-inch color touch screen to improve both the ease of viewing the display and the overall operability when compared to the previous model. Furthermore, thanks to a built-in thermal printer (paper width: 58 mm) and a USB flash memory port, a smaller footprint was achieved. To expand the capability of the titrator, optional units can be added easily so that one can control up to four titrator workstations independently and in parallel.
The new buret has been completely re-engineered and will provide a much longer operational life and a much easier reagent exchange operation. More details about the buret are described in the next section. |
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(1) Principle of the Buret |
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A plunger moves up and down inside the buret and is driven by a gear-driven stepping motor.
A selector valve shifts the direction of flow path; from the reagent bottle to the syringe and from the syringe to the buret tip.
When the plunger moves downward, the valve is switched to the reagent bottle side to fil the syringe with the reagent. When moving upward, the valve is switched to the buret tip side to dispense a certain amount of the reagent (titrant) which fills the syringe.
This dispensing operation is carried out by a stepping motor controlled by the main unit as described above. |
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(2) Conventional Buret |
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Since the plunger of a conventional buret is positioned on the lower side and fixed on completion of measurement as shown in Figure 3, the glass syringe is always filled with reagent (titrant) and the life of the syringe and the buret may be reduced due to the constant contact with the chemicals in the reagent.
Generally, very alkaline reagents and potassium permanganate solutions are commonly used in a number of titration applications. When using alkaline solutions, the glass wall inside of the syringe may corrode. When using potassium permanganate, manganese dioxide may crystallize inside the wall of the syringe and these crystals may score the plunger and glass wall during the up and down movement thus causing a leak and permanent damage.
In addition, a conventional buret has a dead space at the very top of the syringe as shown in figure 2. The process of detaching the syringe from the buret, attaching a push rod to the plunger, and repeatedly aspirating and discharging the reagent using the plunger is required to exchange the reagent completely. |
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(3) The New Buret |
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The syringe for the newly developed buret is designed with a special head shape to fit a conicallyshaped plunger thus reducing the head space and minimizing the dead volume as much as possible. (see Figure 5 below). This innovative design change completely eliminates the disadvantages of the conventional buret. |
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1) Longer life of syringe by upper limit standby position of plunger
The new buret design results in the extended lifetime of the syringe by setting the standby position of plunger to the upper limit after the measurement has been completed (see Fig. 5 above). Due to this improvement, the remaining reagent between the plunger and the syringe is very small thus reducing any potential corrosion on the inside wall of the syringe by alkaline solutions. This upper resting position also prevents the plunger from bonding with crystallized manganese dioxide. |
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2) Reagent exchange greatly facilitated
The new buret does not require several repeat operations to aspirate and discharge the reagent by manually detaching the syringe and using a push rod to accomplish this task. The end user can simply exchange the reagent by just pressing keys on the keyboard to move the plunger repeatedly up and down several times to replace the reagent entirely (refer to Figure 5).
The test result of exchanging reagents in the syringe by the newly-designed syringe is shown below to indicate the considerable increase in efficiency. |
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[Measurement condition]
The new buret B-1700-20 (20 ml syringe) is filled with pure water and then the water was replaced with 1 mol/L hydrochloric acid solution until the syringe and the flow path to the buret tip was completely exchanged.
The volume of 0.1 mol/L NaOH solution used to titrate 1 mL of 1 mol/L HCl dispensed from the buret tip by moving the plunger up and down for one cycle is shown in Figure 6. |
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