(i) Analysis of HTO

Water samples from oilfields may be of various qualities, ranging from relatively pure water (transparent liquid) via samples which contain some degree of oil to samples where the water exists mainly in an oil-water emulsion as illustrated in Fig. 23. Thus, pretreatment of the samples is needed before instrumental analysis of the beta emission (by liquid scintillation counting). The form of the pretreatment varies with the composition of the sample.

In general, for samples of type A and B, a combination of oil phase removal by pipetting and filtration followed by a distillation process is common. For samples of type C, an emulsion breaking step has to be included in the beginning before oil-water separation and eventual distillation of the resulting relatively small water volume (in most cases). Details on the analytical protocols, including pretreatments, are given in Appendix III.

(ii) Analysis of HTO and 14C labelled alcohol in mixture

The analysis of HTO and 14C labelled alcohol in water samples from the oilfield cannot be carried out directly by liquid scintillation counting, as purification somewhat different from the procedure described above for HTO is required. The following equipment parts and the purification procedure are proposed:

Equipment and reagents:

(1) Round flask 500 mL, connection size 24/40;

(2) Fractional distillation Vigreux column, 31 cm long, cs 24/40;

(3) Dean & Stark collector, volume 10 mL;

(4) Water cooling system;

(5) Heating mantle for the round flask;

(6) Magnetic stirrer;

(7) Liquid scintillation counter with standard vial of volume 22 mL;

(8) Methanol and toluene reagent grade;

(9) Scintillation cocktail, e. g. Instagel or Ultima Gold.

Procedure:

(1) Sample treatment: Add 10% v/v of toluene to a water aliquot in a separation funnel and shake to extract any dispersed oil droplets into the toluene.

(2) Transfer a maximum 10 mL aliquot of the water phase to a standard counting vial and mix with 10-12 mL of an appropriate scintillation cocktail. Shake vigorously to create a stable gel.

(3) Store the sample in the dark at least 1 h before starting the count.

(4) Count the sample in the liquid scintillation counter in dual label mode with the windows set at 3H and 14C. Calculate the tritium activity by correcting for the contribution of 14C in the tritium window.

(5) To another 10 mL of the purified water phase add 3 mL of methanol and 1.3 mL of toluene and transfer the mixture into the round flask. This volume ratio of methanol and toluene creates an azeotrope.

(6) Heat the sample very gently at low power (a few hours) to distil off the azeotrope.

(7) Collect the distillate (about 4 mL) into the vial.

(8) Add cocktail (10 mL) and count in dual label mode with the windows set at 3H and 14C. Calculate the 14C activity by correcting for the tritium activity in the 14C window.