OBJECTIVE:
To lay down the procedure for operation of operation of Densimat.
SCOPE:
This SOP is applicable for the procedure for operation of operation of Densimat at {Company Name} {Location}.
RESPONSIBILITY:
In charge- Microbiology- is responsible to ensure compliance as per SOP.
Head/Designee Quality Control – Shall be responsible for ensuring compliance as per SOP.
ACCOUNTABILITY:
QA Head shall be Accountable for implementation of SOP.
About Densimat:
Densitometry in the pharmaceutical industry is a technique used to measure the density of substances, often in the context of Thin-Layer Chromatography (TLC). It helps quantify the amount of a particular compound present in a sample by measuring the intensity of a spot on a TLC plate. This technique is valuable for quality control, research, and development in various pharmaceutical applications, including drug discovery, formulation development, and stability testing. Densitometry provides accurate and reliable data, aiding in the development and manufacturing of safe and effective pharmaceutical products.
PROCEDURE:
Preparation of the densimat for measurement:
Densimat is designed to measure the optical density of a bacterial inoculum produced in an ampoule of liquid medium.
The operating temperature range is not more than 30°C.
Electrical Characteristics:
Automatic switching “ON” when an ampoule is inserted in the optical block.
The densimat goes into the automatic standby mode after 30 seconds if there is no change in the optical density.
The Standby mode is indicated by “McF” on the display.
The Densimat comes out of standby mode when the ampoule is removed.
The Densimat is designed to run on 2 sonneschein batteries or equivalent, connected series.
The Densimat can also be supplied with current by one of the following AC power supply adapters or equivalent ones.
Optical Characteristics:
The light source is LED 950 nm.Central photo sensor and lateral photo sensor are used for measurement.
Logarithmic display in McFarland units – 0.5McF to 7.5 McF.
Principle:
Densimat enable precise determination of bacterial density by two measurements.
An incident beam of light is passed through the ampoule and two subsequent measurements are obtained:
Scattered light S (two photo sensors).
Transmitted light (one photo sensor).
The ratio S/T is directly proportional to the density of the bacterial suspension.
The results are displayed on the mobile graduated scale on the liquid crystal display.
| Standard McFarland Scale | Bacterial concentration 1×108 / mL | Theoretical Optical density at 550nm |
| 0.5 | 1.5 | 0.125 |
| 1.0 | 3.0 | 1.25 |
| 2.0 | 6.0 | 1.50 |
| 3.0 | 9.0 | 0.75 |
| 4.0 | 12.0 | 1.00 |
| 5.0 | 15.0 | 1.25 |
| 6.0 | 18.0 | 1.50 |
| 7.0 | 21.0 | 1.75 |
The Bacterial Concentration Varies according to the size of the microorganisms.
Densimat is designed to be used on laboratory bench top, but may be moved depending on the needs of the user.
Densimat shall be placed on a flat, horizontal surface.
Procedure for density measurement:
Before starting of the operation, the densimat shall be connected with AC power adapter.
Use laminar air flow unit to minimize the extraneous contamination.
Prepare a homogenous bacterial suspension in the ampoule recommended in the procedure for reagent used.
Wipe the ampoule clean and Place the ampoule in the densimat well.
DENSIMAT comes on automatically.
Turn the ampoule until you obtain the minimum stable reading on the scale.
Only the minimum value is obtained is of significance.
If the density is higher than the standard required, the bacterial suspension shall be diluted by adding a certain volume of the medium.
If the density is less than the standard required, add more inoculum.
The McFarland units/reading should be 0.5 to 0.63 for bacteria (color strips) and 2.0 for Candida /Bacillus or prepare as per manufacturer instructions given in the leaflet.
Note: In order to save the batteries, it is recommended to remove the ampoule from the Densimat to adjust the inoculum.
It is important that the ampoules shall be used are clean. Ampoules shall be cleaned before use with 70% v/v IPA.
The results obtained below 0.5 McFarland units or higher than 7.5 McFarland units are less significant and shall be considered with caution.
Enter the reading in the user logbook of SOP.
Cleaning Procedure:
Take a readymade swab (preferably, pre-sterilized).
Cut the desired length of the swab bud with the length of scissors.
Take the stainless steel device and insert the swab bud into it.
Dip the Swab bud into 70% v/v IPA/ 2-propanol or equivalent.
Clean the photo sensors with alcohol impregnated swab by rotating inside the reading block.
Preventive maintenance of the optical block shall be carried out once in three months.
Cleaning shall be performed, if an ampoule has been broken inside the reading block of the densimat.
Cleaning shall be performed, if the results are obtained more than the recommended McF units.
Use of different type of batteries shall damage the densimat.
If any discrepancy, immediately inform to the in charge microbiology or his designee.
REFERENCE:
Not applicable
ANNEXURES:
Not applicable
ENCLOSURES: SOP Training Record.
DISTRIBUTION:
- Controlled Copy No. 01 : Head Quality Assurance
- Controlled Copy No. 02 : Head Quality Control (Micro.)
- Master Copy : Quality Assurance Department
ABBREVIATIONS:
| No. | : | Number |
| SOP | : | Standard Operating Procedure |
| QC | : | Quality Control |
| AC | : | Alternate current |
| nm | : | Nanometer |
| McF | : | McFarland |
REVISION HISTORY:
CHANGE HISTORY LOG
| Revision No. | Details of Changes | Reason for Change | Effective Date |
| 00 | New SOP | Not Applicable | To Be Written Manual |