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pH Meter


PH Meter

Question 1) What is full form of pH?

 Answer) pH is denoting, potential of hydrogen or power of hydrogen

Question 2) what is pH value or pH scale.?

Answer) pH is a scale used to specify the acidity or basicity of an aqueous solution:

  •  lower pH values correspond to solutions which are more acidic in nature while higher values  correspond to solutions which are more basic or alkaline.
  • pH is the negative of the base 10 logarithm of the activity of the hydrogen ion the pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution.
  • A lower pH indicates the higher concentration of hydrogen ions at 25 C° solutions with the pH less than seven are acidic and solutions with the pH greater than seven are basic.
Question 3) what is equation of pH?
Answer) PH is defined as the negative logarithm of the hydrogen ion activity.
pH=-log10 (H+)
Question 4) How to measure pH?
Answer) Answer) Primary pH standard values are resolute using a concentration cell with transmission, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be precise with a glass electrode and a pH meter, or a colour changing indicator.

Question 5) Electrode potential follow which rules.?
Answer) Electrode potential follows the Nernst equation which for the hydrogen ion can be written as:
E=E0+RT/F ln(H+)
    E= measured potential
    E0= standard electrode potential
    R= gas constant
    T= temperature in kelvins
    F= faraday constant

Question 6) What are pH indicators.?
Answer) Indicators may be used to measure pH by making use of the information that their colour changes with pH
  • Visual judgment  of the color of a test solution with a standard color map.
  • Provides a means to measure pH accurate which is gives more specific measurements to nearest number are possible. 
  • Universal indicator consists of a mixture of indicators which has a continuous colour change from about pH 2 to pH 10. 
  • Universal indicator made from one type of absorbent paper who lives with universal indicator.
Question 7) What is principle of measurement of pH by pH meter or potentiometric pH meter? AnswerThe pH meter measures the difference in electrical potential between a pH electrode and a reference electrode. So the pH meter is sometimes referred to as a potentiometric pH meter.
  • Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the equivalent Ph value.
  • They consist of a simple electronic amplifier and a pair of electrodes or alternatively a combination electrode. Which is display calibrated in pH units. It usually has a glass electrode and reference electrode or a combination electrode.
Question 8) What is the design of electrode.?
Answer)The design of the electrodes is the key part:
  • These are rod-like structures usually made of glass with the bulb containing the sensor at the bottom.
  • The reference electrode is insensitive to the pH of the solution being collected of a metallic conductor which connects to the display.
  • The display consists of a voltmeter which shows voltage in units of pH.
  • On captivation of the glass electrode and the reference electrode in the test solution an electrical circuit is completed in which there is a potential difference created and detected by the voltmeter now a day many ph meters use a combination probe constructed with the glass electrode and the reference electrode contained within a single probe.
Question 9) How to store the electrode?
Answer) The best solution for electrode storage is 3M potassium chloride solution.

Question 10) What is minimum instrument requirement for pH measurement?
Answer)The measurement system shall be capable of performing a two point or more pH calibration.
  • The accuracy of the pH measurement system is calibrated slope of should be between 90 to 105 and an offset of zero ±30 millivolt (0.5 pH units at 25 )
  • As per united states pharmacopoeia the instrument shall be capable of temperature compensating
  • The pH sensor convert the pH unit to the millivolt signal at any temperature.
  • The precision of the temperature measurement system shall be ± 1 C° the declaration of the temperature measurement system shall be at least 0.1 C°
 Question 11) What is ideal requirement of buffer solutions?
Answer)Buffer salts of expected purity can be obtained from the national institute of standards and technology (NIST) other national authorities.
Buffer solutions should be stored in suitable containers that ensure stability of the pH through the expiry date and fitted with a tight closure.

Question 12) How long store buffer pH more than 11?
Answer) For buffer solutions greater than 11 the storage should be in suitable containers that are resistant to reduce carbon dioxide interference which would lower the pH of the buffer.
For buffer solutions greater than 11 they should typically be prepared and used fresh unless carbon dioxide entrance is restricted.

Question 13) How long store buffer pH less than 11?
Answer)For buffer solutions lower than 11 they should typically be prepared at intervals not to exceed 3 months.

Question 14) How many methods to calibrate the pH meter.
Answer) pH meter calibration shall be performed by:
  • Two point calibration
  • Multiple point calibration and
  • Multiple segment calibration
Question 15) Which buffer shall be used for pH meter calibration?
Answer) For two point calibration  method:
Calibrate the pH measurement system select three buffer solutions for calibration such that the expected pH of the material under test falls within their range. Two of the buffers are used for the calibration process and the third buffer is used for verification. The value of the verification buffer shall be between two of the calibration buffers.
For multiple point calibration process:
Three or more calibration buffers plus at least one verification buffer is used.
For multiple segment calibration process:
Three or more calibration buffers with at least two slopes and offsets plus at least one verification buffer for each segment are used.

Question 16) What is temperature range to calibration or verification done.?
Answer) Typically as per united states of pharmacopoeia temperature should be 25 C°± 2 C°, While as per British pharmacopoeia and European pharmacopoeia temperature should be between 20 to 25 C°.

Question 17) What are acceptance criteria of pH meter calibration.?
Answer) Typically acceptance criteria as per united states of pharmacopoeia are:
( a) Slope of 90 %  to 105 %
(b) Offset of 0 ± 30 mV (0.5 pH units at 25 C°.
As per British pharmacopoeia and European pharmacopoeia slope of 95 % to 105 %.

Question 18) What is acceptance criteria for pH verification?
Answer) The pH reading shall be within ±  0.05 pH of the value at the buffer solution temperature.

Question 19) What precaution should be taken for test sample sensitive to ambient carbon dioxide? Answer) If the pH of the chest sample is sensitive to ambient carbon dioxide then use purified water that has been recently boiled and subsequently stored in a container designed to minimize ingress of carbon dioxide.
Question 20) How often do need to calibrate my pH meter?
Answer)Typically before each time use it or each set of uses.
              Based on the risk can be verified before each time use it or each set of uses.

Question 21) Should stir sample during pH measurement?
Answer) Yes there are two main advantages to slowly stirring or gently agitating the sample during a pH measurement.
  • The increased flow of the sample across the electrode, results in a faster response time.
  • The solution is properly homogenate so no areas of increased or decreased pH exist.
Question 22) When is a pH reading stabilized?
Answer) It is difficult to know the exact time to take a pH reading. In general, one minute is required to measured for a stable reading.
If a reading is taking an exceptionally long time to stabilize, this can indicate several conditions:
  • Clogged electrode junction.
  • Non-homogeneous solution.
  • Troublesome sample with low ionic strength.
  • Non-aqueous sample.
Question 23) Can measure the pH of a gas?
Answer) The only way to measure the pH of gas is to dissolve it into distilled water and measure the mixture.

Question 24) What is ideal requirement of commercially available buffer solution?
Answer) Commercially available buffer solutions for pH measurement system:
  • Calibrated by methods traceable to national institute of standards and technology (NIST) or other national authorities.
  • Labeled with a pH value accurate to 0.02 pH units may be used.
  • Solutions prepared from ACS reagent grade materials or other suitable materials. The solution prepared from the national institute of standards and technology or other national authorities certified material.
  • Buffer solutions that are greater than 12 should be used immediately or should be prepared using freshly boiled water and they should be stored under conditions to minimize carbon dioxide absorption and ingress.
Question 25) What is the best way to remove air bubbles from inside a pH probe?
Answer) Air bubbles can get trapped in the electrolyte solution of the reference system. This results in variable and unstable readings and may make it impossible to achieve a reading. Remove to air bubbles shake the probe strongly using a downward motion so that the air bubbles move to the upper end of the probe.

Question 26) Why pH value between 0 to 14?
Answer) No the pH value can be less than zero for very strong acids or greater than 14 for very strong bases.


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