Muffle Furnace – Operation and Calibration SOP

Standard Operating Procedure (SOP) for Operation and Calibration check of muffle furnace installed in quality control lab for analysis of sulfated ash, loss on ignition (LOI), etc.

SOP for Muffle Furnace

1.0   PURPOSE:

    • The purpose of this SOP is to describe the procedure for Operation and Performance Check procedure of Muffle Furnace and general practices for Loss on Ignition and Residue on Ignition test.

2.0   SCOPE:

    • This procedure is applicable to the following muffle furnace installed in the Quality Control Department at the pharmaceutical plant.


    • The instruction manual of muffle Furnace.
    • URS and analytical instrument/equipment qualification (SOP)
    • Maintenance of laboratory instruments (SOP)
    • Instrument/Equipment usage log book. (SOP)
    • Preparation of Internal and External Calibration Schedule and Calibration Practices (SOP)
    • USP 32 General chapter <733> Loss on Ignition


    • Analyst :

    • To operate the instrument as per SOP.
    • To calibrate the instrument as per SOP.
    • Recording all documents related to calibration and preventive maintenance.
    • Quality Control Head or Designee :

    • Training to the concern before the implementation of SOP.
    • To verify the calibration and preventive maintenance followed as per schedule.
    • To ensure proper documentation as per SOP.
    • Quality Assurance :

    • To ensure the implementation of the system as per SOP.
    • Quality Head and Plant Head :

    • To review and approve the SOP.Muffle Furnace


    • LOI: Loss on ignition
    • NA: Not Applicable
    • QA: Quality Assurance
    • QC: Quality Control
    • SOP: Standard Operating Procedure
    • USP:  United States Pharmacopoeia


    • Constant Weight: The difference between two consecutive weights, which does not differ by more than 0.5 mg per gm. of the substance taken.


  • Procedure for Operation of Muffle Furnace :

    • Keep the Muffle on a leveled and firm platform.
    • Ensure that the instrument is connected with the main power supply.
    • Both the ON/OFF power switch and digital display illuminate.
    • The door safety switch removes power from the heating elements when the door is open.
    • The single set point model w/OTP furnace controller is a single setpoint controller that provides single display to indicate the current chamber temperature or setpoint temperature.
    • When the controller is turned ON it will perform a short self-test and then display a default page.
    • The measured value is found in the upper display and the setpoint is found in the lower display.
    • Button and indicator
      • OP1: Illuminate when the output is ON (normally heating)
      • OP2: Illuminate when the output is ON (normally Cooling)
      • OP4: Illuminate when the AA relay output is ON (Will go on during an alarm situation)
      • PAGE Button: Allow you to select a new list of parameters.
      • Scroll Button: Allows you to select a parameter within a list of parameters.
      • Down Button: allow you to decrease a value
      • UP Button:  Allow You to Increase a value
    • Then set the required temperature by pressing {▲} or {▼} arrow key Until the desired setpoint value is displayed and then release the button.
    • A few seconds after the button is released the controller will accept the new value and Indicated by a brief flash of the display.
    • Press the PAGE button to return to HOME
    • To view the display “UNITS” press SCROLL until Units is displayed.
    • Temperature units can be changed by Pressing up and down buttons.   
    • The controller will flash an alarm message in the home display when an alarm condition is detected.
    • The working temperature range is 300 to 1100°C.
  • General Procedure for Handling of Muffle Furnace :

    • In case of any maintenance of the instrument, follow the procedure as per SOP “Maintenance of Laboratory Instruments” SOP.
    • For the entry of usage of the instrument follow the procedure as per SOP “Instrument/Equipment usage logbook” SOP.
    • Affix the calibration label on the instrument as per SOP “Authorized personnel list and status labeling in the working area” SOP.
    • Maintain the third party calibration schedule and the Internal calibration schedule for the instrument as per SOP “Preparation of Internal and External (Third Party) Calibration Schedule and Calibration Practices” SOP.
  • Calibration/ Validation of Muffle Furnace:

    • Frequency: Yearly ± 30 days by an external agency.
  • Precautions during handling of Muffle Furnace:

    • Conduct the ignition in a well-ventilated hood, but protected from air currents, and at  As low a temperature as is possible to affect the complete combustion of the carbon.
    • Take care of nothing is falling inside the muffle furnace.
    • If something falls inside during the analysis immediately switch “ OFF ”
    • Allow it to cool and then clean it with the dry cloth.
    • Do not open the door without cooling of the chamber
    • Do not open the door frequently at higher temperature as it may damage the heaters
    • Handle hot sample/container carefully using personnel protective equipment.
    • Avoid operating the furnace at a lower temperature


    • Quality Assurance
    • Quality Control




Janki Singh is experienced in Pharmaceuticals, author and founder of Pharma Beginners, an ultimate pharmaceutical blogging platform. Email: [email protected]

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