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IS 5258:1969 is the Indian Standard (BIS) for determination of particle size of powders by optical microscope method. This standard specifies a method for determining the particle size and size distribution of powders using an optical microscope. It covers the apparatus, sample preparation, measurement procedure, and the calculation of results for particles typically in the 1 to 150 micrometre range.
Determination of particle size of powders by optical microscope method
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Sieves, Sieving and Other Sizing Methods
! Proper sample dispersion on the slide is critical to prevent particle agglomeration, which leads to inaccurate, oversized measurements. Using a suitable dispersing agent is often necessary.
! The choice of mounting medium should ensure good optical contrast and chemical inertness, so it does not react with or dissolve the powder particles.
! A statistically significant number of particles (typically over 600) must be measured across multiple fields of view to obtain a representative size distribution.
ISO 13322-1:2014International Organization for Standardization (ISO), International
HighCurrent
Particle size analysis — Image analysis methods — Part 1: General principles
Covers the general principles of determining particle size distribution using modern digital image analysis, the successor to manual optical microscopy.
USP <776>United States Pharmacopeia (USP), USA
HighCurrent
Optical Microscopy
Provides procedures for particle size determination by optical microscopy, with a focus on pharmaceutical applications.
ASTM E20-96American Society for Testing and Materials (ASTM), USA
HighWithdrawn
Standard Practice for Particle Size Analysis of Particulate Substances in the Range of 0.2 to 75 Millimeters by Optical Microscopy
Directly covered manual optical microscopy for particle size, making it a very close historical equivalent to the IS method.
Ph. Eur. 2.9.37European Pharmacopoeia (Ph. Eur.), Europe
HighCurrent
Optical microscopy
Defines the method for particle sizing using optical microscopy, largely harmonized with the USP <776> method.
Key Differences
≠IS 5258 specifies a manual measurement technique using an eyepiece graticule (e.g., Filar micrometer). Modern standards like ISO 13322-1 are based on automated or semi-automated digital image analysis using software.
≠The Indian standard was published in 1969 and reflects the technology of that era. International standards are regularly updated to include advancements in digital cameras, computer processing power, and statistical analysis software.
≠IS 5258 recommends specific diameter definitions like Martin's or Feret's. While modern standards also define these, they formalize a much wider array of size descriptors (e.g., area-equivalent circular diameter) and place strong emphasis on explicitly reporting the chosen descriptor.
≠While IS 5258 mentions sample preparation, modern standards like ISO 13322-1 provide more extensive and detailed guidance on sample dispersion, handling of touching particles (segmentation), and dealing with artifacts from lighting and focus.
Key Similarities
≈The fundamental principle of measuring a 2D projection of particles to infer size distribution remains the same across both the IS standard and its international counterparts.
≈All standards emphasize the critical importance of proper sample preparation to ensure particles are well-dispersed and individually measurable, avoiding agglomerates.
≈The requirement to calibrate the measurement system using a certified stage micrometer is a core, unchanged principle essential for measurement traceability in both manual and automated methods.
≈Both the Indian standard and international equivalents acknowledge the statistical nature of the measurement, requiring a sufficiently large number of particles to be counted to achieve a representative distribution.
Parameter Comparison
Parameter
IS Value
International
Source
Primary Measurement Method
Manual counting and sizing using a Filar micrometer eyepiece or a Patterson-Globular graticule.
Automated digital image capture and software-based analysis of particle characteristics.
ISO 13322-1:2014
Minimum Particle Count
At least 600 particles shall be examined.
Sufficient to ensure statistical validity; often thousands for automated systems, with guidance based on desired precision.
ISO 13322-1:2014
Calibration Standard
Stage micrometer.
Certified length scale standard (e.g., stage graticule or stage micrometer).
ISO 13322-1:2014
Recommended Particle Diameters
Martin's Diameter or Feret's Diameter.
Defines a wide range including Area-Equivalent Diameter, Feret's Diameter, Martin's Diameter, etc., with emphasis on clear reporting.
ISO 13322-1:2014
Handling of Overlapping Particles
Overlapping particles should be disregarded.
May be disregarded or separated using software-based watershed segmentation algorithms.
ISO 13322-1:2014
Reporting of Results
Tabulation of particle counts in size classes and calculated mean diameters (number, surface, weight).
Full distribution data (histogram, cumulative curve), statistical parameters (mean, median, mode), and comprehensive report of measurement conditions.
ISO 13322-1:2014
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Applicable particle size range1 to 150 micrometres (µm)
Minimum number of particles to be measured for routine analysis625 particles
Maximum number of particles per field of view for countingapproximately 60 particles
Recommended number of particles for high accuracy work2500 particles
Required microscope magnificationSuch that the image of the particle is at least 10 divisions of the eyepiece graticule
Key Formulas
Arithmetic Mean Diameter (d_mean) = (Σ n_i * d_i) / Σ n_i, where n_i is the number of particles of size d_i
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 4 - Apparatus
Clause 5 - Sampling and Preparation of Mount
Clause 6 - Procedure
Clause 7 - Calculation and Expression of Results
Frequently Asked Questions4
What particle size range is this method suitable for?+
It is primarily used for particles in the range of 1 to 150 micrometres (µm).
How many particles should be measured for a reliable result?+
A minimum of 625 particles should be measured for routine analysis to ensure statistical validity (Clause 7.1).
What is the key principle of measurement?+
The method involves comparing the magnified image of a particle with a calibrated scale (eyepiece graticule) within the microscope's eyepiece.
How should the sample be prepared?+
A representative sample of the powder is dispersed in a suitable liquid medium and mounted as a thin layer between a microscope slide and a cover slip (Clause 5).