[F18. PROCEDURE U.K.
All steps of the preparation must be carried out without any significant ethanol loss through evaporation that would change the isotopic composition of the sample.
The following description refers to the procedures generally used for ethanol sample combustion using commercial automated combustion systems. All other methods that ensure that all of the ethanol sample is converted into carbon dioxide without any loss of ethanol through evaporation may be used for the preparation of carbon dioxide for isotopic analysis.
Experimental procedure based on the use of an elemental analyser:
placing the samples in capsules:
use capsules, tweezers and a preparation tray, all of which must be clean,
take an appropriate-sized capsule using the tweezers,
introduce an appropriate amount of liquid into the capsule using a micropipette,
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Note: 3,84 mg of absolute ethanol or 4,17 mg of distillate with an alcohol strength of 92 % m/m are necessary to obtain 2 mg of carbon. The appropriate quantity of distillate must be calculated on that basis, according to the quantity of carbon necessary given the sensitivity of the mass spectrometry apparatus, U.K.
close the capsule with the tweezers,
each capsule must be completely sealed. If not, it must be discarded and a new capsule prepared,
two capsules must be prepared for every sample,
place the capsules in the appropriate place on the tray of the automatic sampler of the elemental analyser. Every capsule must be carefully identified by a serial number,
systematically place capsules containing working references at the beginning and the end of the sample series,
regularly insert control samples in the sample series;
checking and adjusting the elemental analysis and mass spectrometry apparatus:
adjust the temperature of the elemental analyser furnaces and the helium and oxygen flows for optimal combustion of the sample,
check the elemental analysis and mass spectrometry system for leaks (for example by checking the ionic current where m/z = 28 for N 2 ),
adjust the mass spectrometer to measure the ionic currents where m/z = 44, 45 and 46,
check the system using known control samples before starting to measure the samples;
carrying out a series of measurements
The samples placed on the automatic sampler of the elemental analyser (or of the chromatograph) are introduced in turn. The carbon dioxide from each sample combustion is eluted towards the mass spectrometer which measures the ionic currents. The interfaced computer records the ionic currents and calculates the δ value for each sample (point 9).]