Electrochemistry - Chromservis.cz

GMP, GLP, ISO 9001, EN 45000, Calibration, Verification, Traceability, and Certification from an accredited organization: Key words those are increasingly important. The calibration of pH and Redox electrodes has never been easy. All calibration procedures assume that the labelled values of the calibration buffers are correct. But buffer values can change over time and so can your results

A complete range of patented buffer solutions provides never before achieved pH stability. Hamilton guarantees DURACAL pH buffers for 5 years after the date of manufacture. The pH 9.21 and pH 10.01 buffers are even stable in air. See the diagram below for details. High buffering capacity provides rapid, stable calibration. Preservatives are added to prevent microbial and mold growth.

Traceability

An important issue for the production of Certified Reference Material is to ensure the traceability through an unbroken chain of comparisons to reference mate­rial of the highest metrological quality (Primary Reference Material).

• Closed Loop Traceability: Unlike other manufacturers where only a top-down traceability is applied, Hamilton is work­ing with circular or closed loop traceability. The closed loop traceability ensures the users of Hamilton DURACAL buffer a unique reliability!


• Top-down traceability: At Hamilton, the pH value of DURACAL buffers is de­termined by comparison against two Sec­ondary Reference Buffer Solutions. These are purchased from accredited suppliers for Secondary Reference Materials. The so­lutions themselves are compared against Primary Reference Solutions from PTB¹⁾ or NIST ²⁾.


• Bottom-up traceability: To ensure the highest possible accuracy and full reliability of the pH value, a representa­tive number of samples from every single production lot is sent to a German DKD³⁾ laboratory (DKD-K-06901) for an external, independent and impartial verification. In this laboratory, the DURACAL samples are compared against Secondary Reference Solutions from DKD-K-06901.

The Secondary Reference Solutions are of course compared against Primary Refer­ence Solutions from PTB. At this stage, the loop is closed: the PTB Primary Refer­ence Solution is the starting and ending point of the traceability loop. DKD provides Hamilton with a calibration certificate for every DURACAL production lot.

Often the pH meters are used in applications, which require regular cleaning of the electrode. These applications involve very hard waters, dirty samples like soil slurries, viscous materials or samples with high oil and protein content. We do not recommend these procedures for persons unfamiliar with or unable to use safe techniques involving these chemicals: Detergents, HCl (Hydrochloric Acid), and NaOH (Sodium Hydroxide).

Method 1

Soak the electrode in a 0.4 molar concentration of HCl (hydrochloric acid) for 10 minutes, then rinse the electrode with deionized or distilled water. This should remove any organic protein from the glass  electrode and the surface of the reference electrode.

Method 2

Soak the electrode in a 3.8 or 4.0 molar KCl (potassium chloride) solution heated to 50°C for 1 hour. Allow the KCl solution to cool down to room temperature, then rinse the electrode with deionized or distilled water. This will open and clean the reference electrode of all contaminants.

Method 3

Soak the electrode in a 4.01 pH buffer solution (EC-BU-4BT), heated to 50°C for 1 hour. Allow the buffer to cool down to room temperature, then rinse the electrode with deionized or distilled water. This will open and clean the reference electrode.

Method 4

After each use, rinse the electrode in 0.5 N or 1% HCl. If you have a build-up of oil or protein contaminants, try soaking the electrode in warm detergent and water solution. Degreasing dishwashing detergents or stain removing pre wash pretreatment are ideal for this: any brand will do. An overnight soak may be needed if build-up is heavy. Then rinse the pH sensor in deionized or distilled water and soak for 10 minutes in 1% HCl. Rinse the pH sensor in deionized or distilled water and check in buffers. If the pH sensor calibrates to buffers it can be used in tests. When the pH electrode cannot be calibrated even after attempts to clean it, it must be replaced.

Method 5

For protein removal, soak the pH electrode in contact lens enzymatic cleaner solution overnight. The enzymes will remove proteins from glass and plastic.

Physical properties measurement is mostly based on sensors with limited life time. So that these sensors give precise and accurate data, you have to properly use and store them. This website should help you in this point.

• Can you trust your buffer solution?


• Cleaning & reconditioning pH electrodes


• Colorimetric measurement


• Maintenance and storage of pH electrodes


• pH measurement


• Turbidity measurement

Optical sensors for DO measurement

Classical oxygen sensors are based, as is common in the industry, on Clark Cell technology, in which oxygen diffuses through a membrane and is reduced electrochemically on a precious metal. The electrons involved in this process generate a very small current (nanoamperes) which is converted to an oxygen measurement signal by a measurement amplifier. Sensors such as these have served well for decades, but have their limitations.

Measurement principle

While other suppliers of optical oxygen sensors utilize fragile optical fibers, a single light channel, or two different LEDs, Hamilton prefers a mechanically and thermally stable symmetrical design. The unique design of the VISIFERM™ DO enables to monitor the status of the sensor's blue LED using one of the photodiodes. The photodiode with the red filter measures the oxygen-dependent red light generated on the luminophore through luminescence (fluorescence) caused after exitation by the blue light. Electrons are excited to a higher energy level, and return to their original level after emission of red light. When the luminophore comes into contact with elemental oxygen, the O2 molecules absorb the energy, resulting in reduced intensity of red light emission. This difference in intensity is analyzed by the instrument's self-monitoring system to pinpoint photobleaching (bleaching of the luminophore).

High precision measuremet of the optical phase shift between the blue and red light pulses provides accurate indication of oxygen concentration. Normally, the luminophore's excited electrons remain in this state for some time. However, in the presence of oxygen they return to their ground state more quickly. Between the pulsed excitation of the luminophore with blue light and the emission of red light, there is an oxygen-dependent time shift which can be measured as an angle of phase. Measurement, calculation, and output of the measured value occur entirely inside the sensor.

Notice that VISIFERM™ DO sensors measure the partial pressure of oxygen (pO2) just as classical sensors do. This can be displayed as % air saturation, concentration in mg/l, ppm, or even as ppb. The measurement range is currently limited to 0.05% to 300% air saturation (4 ppb to 25 ppm). For most applications this measurement range is more than adequate. When calibrating the sensor well, the limit is even below 1 ppb.

Maintenance and storage of pH electrodes

pH electrodes are delicate sensors that require proper care and maintenance to produce accurate and reliable results, and to prolong useful life. When the pH electrode is not used for a period of time, always keep it moist. Store the pH electrode in storage solution or in a pH 7 buffer. DO NOT store the electrode in distilled or deionised water as this will cause ions to leach out of the glass bulb and reference eledtrolyte, causing slow and sluggish response.

pH electrodes may be shipped with either protective caps or in electrode soaking bottles to prevent cracking or scratching, and to keep the glass bulbs moist. Remove the electrode gently from the storage bottle and rinsse it with distilled water before use. For long-term storage, always keep the pH electrode in the bottle, filled with sufficient storage solution to cover the glass bulb. Replenish the bottle as needed.

Physical properties measurement is an area covering various electrochemical and spectrophotometric methods. The most commonly measured parameters are: pH, redox-potential (ORP), conductivity, dissolved oxygen concentration (DO), salinity, total dissolved solids (TDS) and turbidity. Area of Physical Properties Measurement also includes colorimetry, which is uses mostly for:total and free chlorine, cyanuric acid, pH, chlorine dioxide, bromine and ozone.

This section includes interesting information in following areas

• Laboratorny applications
• Optical method for dissolved oxygen measurement
• Process measurement
• Useful information (hints and tips)

If you are interested in our products, please look at our laboratory product line or products for process measurement.