• British Pharmacopoeia Volume V
  • Appendices

Appendix V C. Determination of Distillation Range

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(Ph. Eur. method 2.2.11)
bp2013_v5_47_2009_[appendix_v_c] 2211distillationrange_1_2012_70_fig.png


The distillation range is the temperature interval, corrected for a pressure of 101.3 kPa (760 Torr), within which a liquid, or a specified fraction of a liquid, distils in the following conditions.

Apparatus The apparatus (see Figure 2.2.11.-1) consists of a distillation flask (A), a straight tube condenser (B) which fits on to the side arm of the flask and a plain-bend adaptor (C) attached to the end of the condenser. The lower end of the condenser may, alternatively, be bent to replace the adaptor. A thermometer is inserted in the neck of the flask so that the upper end of the mercury reservoir is 5 mm lower than the junction of the lower wall of the lateral tube. The thermometer is graduated at 0.2 °C intervals and the scale covers a range of about 50 °C. During the determination, the flask, including its neck, is protected from draughts by a suitable screen.

Method Place in the flask (A) 50.0 mL of the liquid to be examined and a few pieces of porous material. Collect the distillate in a 50 mL cylinder graduated in 1 mL. Cooling by circulating water is essential for liquids distilling below 150 °C. Heat the flask so that boiling is rapidly achieved and note the temperature at which the first drop of distillate falls into the cylinder. Adjust the heating to give a regular rate of distillation of 2-3 mL/min and note the temperature when the whole or the prescribed fraction of the liquid, measured at 20 °C, has distilled.

Correct the observed temperatures for barometric pressure by means of the formula:

bp2013_v5_47_2009_[appendix_v_c] 2211distillationrange_2_2012_70_eq.png


t1

=

the corrected temperature,

t2

=

the observed temperature, at the barometric pressure b,

k

=

the correction factor taken from Table 2.2.11.-1 unless the factor is given,

b

=

the barometric pressure, expressed in kilopascals, during the distillation.

bp2013_v5_47_2009_[appendix_v_c] 2211distillationrange_3_2012_70_tb.png