Determination of size of starch grains

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BACKGROUND

Measurement of crystals using stage and eyepiece micrometers.¹

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REQUIREMENTS

Microscope with mechanical stage

Eyepiece and stage micrometer

Calibration of eyepiece micrometer with the help of stage micrometer:

1. Stage micrometer
   
   1. Take the micrometer slide in hand and feel the sides of the slide.
      
   2. The correct sides shows a slight elevation on one side.
      
   3. Place it on the stage of the microscope. View the scale through the eyepiece at 10 x 10 magnification to find the position of the scale on the micrometer.
      
   4. To locate the scale, start viewing from the edge of the cover glass containing the engraved micrometer scale and then move to the centre and locate the scale on the equatorial plane.
      
2. Eyepiece micrometer
   
   1. Remove the eyepiece and unscrew the part A
      
   2. Place the eyepiece micrometer at level B of the eye piece where there is a hinge or diaphragm (it is the support on which the eyepiece micrometer rests).
      
   3. Screw part A back and see whether the numbering on the eyepiece micrometer is in correct position, i,e zero to hundred. If numbers are reverse, remove the scale and place it in a correct manner.
      
   4. The eye-piece can be rotated to make adjustments.
      
   5. Do not introduce the eyepiece micrometer into the draw tube.
      
3. Calibration of eyepiece micrometer
   
   1. View through the eyepiece with the required optical combinations.
      
   2. Adjust the scales of the two micrometers such that both the scales are superimposed. Rotate the eyepiece to place the scales in a parallel position or remove the stage micrometer till the lines coincide with eyepiece scale.
      
   3. Move the stage micrometer such that the “0” readings of both the micrometer scales coincide or one of the larger division of the stage micrometer coincides with one of the lines of the eyepiece micrometer scale. Note the initial readings.
      
   4. Carefully scan the scales to see, which of the two scale readings exactly coincide on the right side. Note the final readings and calculate the factor for 1 division of the eyepiece micrometer.
      

Now the microscope is ready for taking measurements

Compound microscope

Eyepiece micrometer

Stage micrometer

Glycerin water

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PROCEDURE

Calibrate eyepiece micrometer by using stage micrometer and calculate the factor. Mount a little quantity of powdered sample in glycerin water and measure the length and breadth of 25 calcium oxalate crystals. Multiply the values by the factor for the next dimensions of the crystals.

Calculate the average value and give the range for the dimensions.

In case of cascara bark the calcium oxalate crystals range from 10-25-45 µm, while in case of frangula bark, they measure up to 15 µm.

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CONCLUSION

Size of calcium oxalate crystals of the given sample is __________

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REFERENCES

1. Kokate CK, Practical Pharmacognosy, 4^th edition, Vallabh Prakashan. Delhi; 1994: 112-114.
2. Joshi S, Aeri V. Practical Pharmacognosy, 1^st edition, Frank Bros. & Co. New Delhi; 2009: 203-204.