- Email: [email protected]
The prevention of radiocarbon loss in liquid scintillation counting of solutions containing 14CNaHCO3
Technical International Journal ol Applied Radiation and Isotopes. pp. 795-796. Pergamon Press. Printed in Great Britain
1977. Vol.
28.
The Prevention of Radiocarbon Loss in Liquid Scintillation Collating of Solutions Containing ’ 4C-NaHC03
A METHOD is proposed for determination of the exact amount of 14C introduced in the incubation flasks for primary productivity studies: vigorous shaking, in a tightly closed vial, and instantaneous counting during a short period. Nearly 100% of the activity is counted in these conditions.
IOnoduction The note by hERsoN et al. (1976) is very interesting, because it deals with an important problem which concerns all aquatic ecologists involved in primary productivity studies: the knowledge of the exact amount of “C activity initially introduced in the incubation flasks. This apparently simple problem has not been definitively solved.
Medmds and Resulta I have performed the same experiment as Iverson et al., with a different premixed cocktail: Instagel, a product of
lOOp,-
21 t
z
‘x .j t
c-
60
i 1 ‘9
75 70
Inlticl
14C
795
notes
counted activity, instead of 66% found by Iverson et al. (computed from their Fig. 1). Therefore, the results are very similar from one cocktail to the other. But after 5 hr. the- scintillation vial was vigorously shaken and radioactivity immediately recounted for a short period (0.1 mink 96% of tbe initial “C activity was then recovered. There would be a rapid, nearly total redissolution of the “CO, in Instagel. In order to be quite clear on this phenomenon, another experiment was done. Two series of triplicates, with the same amount of radioactivity, were counted every 2 min. A regular decrease was found, as in the first experiment. In series a, 100% of the initial “C activity was recovered after 12 min. with vigorous shaking (Fig. 2). In series b, after 10 min, the vials were opened, ventilated to renewing the air above the cocktail, closed again and vigorously shaken: only 40% of the initial activity was recovered (Fig. 2). The vials were stored for I month. After this period, a new count was made; 61.9 and 22.9% of the initial activity were found in the vials of series a and b respectively, before shaking. After shaking, 100% of the radioactivity was recovered in series a and 37% in series b (against 40% a month before). Discussion Therefore, there are two ways for standardizing “CNaHCO, solutions for primary productivity measure merits. (1) The method recommended by Iverson et al. is to add redistillkd phenethylamine to a xylene-based cocktail, and phenethylamine + methanol to toluene-based cocktail. (2) Our method is to shake vigorously the mixture
activity After
wgorous
shaking
4
++ +++t+
+++ ++++++
+
+
t
+
+
t
t
t
60
I
FIG.
1. The evolution with time of an aqueous solution (0.5 ml of seawater) of “C-NaHCOs of In&gel.
Packard Instrument, instead of Aquasol (New England Nuclear Corporation). The initial “C-NaHCOs solution was dissolved in seawater (p? = 8) and an aliquot part (0.5 ml) was mixed with 6.5 ml Instagel. In these proportions the mixture is clear. As Iverson et al. did. we obtained a regular decrease of the “C activity with time (Fig. 1). After 5 hr. the sample contained 68% of the initial
in 6.5 ml
in a tightly closed scintillation vial; this point is extremely important in order to avoid the loss by the screw cap (series b). However, the last procedure makes automatic counting of a large number of samples impossible; but standardization seldom requires a great number of samples. On the other hand. it presents the advantage of simplicity and eludes the problems of solubilization.‘2)
796
Technical notes International Journal of Applied Radiation and Isotope pp. 796-799. Pergamon Press. Printed in Great Britain
1977. Vol. 28.
Method for Visualizing Water Sorbed on Metal Surfaces shaken
Intradnction
in the form of an electrolyte layer on metal surfaces is well-known as an important parameter in atmospheric corrosion processes.“) Atmospheric contaminants, especially sulphur dioxide, are known to accelerate the corrosion of many metals. ‘*’ In this laboratory, we have been attempting to establish the role of sulphur dioxide sorption on metal surfaces as the initial step of accelerated atmospheric corrosion. On the important industrial metal, iron, sulphur dioxide uptake has been shown to be non-uniform, being confined to points of up to 0.5mm in diameter.‘3’ It has also been established that the rate of sulphur dioxide sorption is increased with increasing humidity.“’ In an attempt to implicate water vapour in the activation of the sites, we have developed a technique to locate water sorption sites on iron surfaces using tritiated water (THO) and autoradiography. WATER
2
4
6
6
IO 12 14 I6
ml”
0
2
4
6
8
IO 12 14 I6 ‘16
ml”
Method
FIG. 2. Comparison of 14C activity evolution with time using series a (vials closed) and series b (vials opened).
The metal surface to be examined was attached to the internal base of a 15-ml nickel crucible by means of a cellulose adhesive strip. The crucible was then inverted over a flat surface which contained a saturated salt solution made up in THO in its centre. The humidity within the crucible was thus maintained by the saturated salt solution which was known to provide a given relative humidity at a specific temperature. Is) The salt solution was held in a 2-ml glass beaker containing: (a) 100~1 of 5 Ciml-’ THO, (b) 0.2-1.0 g salt, (c) a varying volume of unlabelled distilled water, which was determined by the solubility of the salt being used. Stopcock grease (Apiezon M) spread over the flat surface prior to the inversion of the crucible provided a seal which isolated the system from the laboratory atmosphere. The system was then allowed to stand for a minimum of 24 h while exchange took place between water molecules on the iron surface and THO in the surrounding atmosphere. Following removal from the radioactive atmosphere, the crucible containing the metal sample was partly immersed in liquid nitrogen to “freeze” the water bound to the metal surface in position. Simultaneously, a cotton wool pad soaked in A.R. benzene was held at the mouth of the crucible, thereby allowing a thin layer of benzene to condense on to the sample. (PRYDZet al.‘“’ have shown that benzene at 77 K is an efficient fluor.) After the sample had been exwsed to benzene vaoour for 5 s, the crucible and samole w&e completely imm&ed in liquid nitrogen. A sheet-of X-rav film Uafa Gevaert. Curix RPl-PE-NISI was then laid -on top gf the sampie and held in position with a brass weight (70g). The film was left in contact with the sample for approximately 72 h and then developed in the usual manner. Figure 1 is an example of an exposure of
quenching and chemiluminescence due to the diverse. bases used to retain 14C CO, in liauid scintillation cocktails.‘3*4’ The counting must &z ins&taneous to obtain the correct signal. This would not be a problem, because if radioactivity in the incubation flasks is high enough to be detected through organism’s uptake, it is necessarily high enough to be counted during a short period. Centre de Recherches Okanographiques BP V18, Abidjan, Ivory Coast.
A. HERBLAND
References 1. IVERSON R. L., BITTAKER H.
F. and MYERS V. B. L.imnol. Ocean&r. 21, 756-758 (1976). 2. SMITHD. W., FLIERMANS C. B. and BROIZK T. D. Appl. Microbial. 23, 595-600 (1972). 3. FRANCIS G. E. and HAWKINS J. D. Int. J. appl. Rudiat. Isotopes 18, 223-230 (1976). 4. WAITE D. T., DIJTHIE H. C. and MATTHEWS J. R. Hydrobiology 43, 231-234 (1973).
1977. Vol.
28.
The Prevention of Radiocarbon Loss in Liquid Scintillation Collating of Solutions Containing ’ 4C-NaHC03
A METHOD is proposed for determination of the exact amount of 14C introduced in the incubation flasks for primary productivity studies: vigorous shaking, in a tightly closed vial, and instantaneous counting during a short period. Nearly 100% of the activity is counted in these conditions.
IOnoduction The note by hERsoN et al. (1976) is very interesting, because it deals with an important problem which concerns all aquatic ecologists involved in primary productivity studies: the knowledge of the exact amount of “C activity initially introduced in the incubation flasks. This apparently simple problem has not been definitively solved.
Medmds and Resulta I have performed the same experiment as Iverson et al., with a different premixed cocktail: Instagel, a product of
lOOp,-
21 t
z
‘x .j t
c-
60
i 1 ‘9
75 70
Inlticl
14C
795
notes
counted activity, instead of 66% found by Iverson et al. (computed from their Fig. 1). Therefore, the results are very similar from one cocktail to the other. But after 5 hr. the- scintillation vial was vigorously shaken and radioactivity immediately recounted for a short period (0.1 mink 96% of tbe initial “C activity was then recovered. There would be a rapid, nearly total redissolution of the “CO, in Instagel. In order to be quite clear on this phenomenon, another experiment was done. Two series of triplicates, with the same amount of radioactivity, were counted every 2 min. A regular decrease was found, as in the first experiment. In series a, 100% of the initial “C activity was recovered after 12 min. with vigorous shaking (Fig. 2). In series b, after 10 min, the vials were opened, ventilated to renewing the air above the cocktail, closed again and vigorously shaken: only 40% of the initial activity was recovered (Fig. 2). The vials were stored for I month. After this period, a new count was made; 61.9 and 22.9% of the initial activity were found in the vials of series a and b respectively, before shaking. After shaking, 100% of the radioactivity was recovered in series a and 37% in series b (against 40% a month before). Discussion Therefore, there are two ways for standardizing “CNaHCO, solutions for primary productivity measure merits. (1) The method recommended by Iverson et al. is to add redistillkd phenethylamine to a xylene-based cocktail, and phenethylamine + methanol to toluene-based cocktail. (2) Our method is to shake vigorously the mixture
activity After
wgorous
shaking
4
++ +++t+
+++ ++++++
+
+
t
+
+
t
t
t
60
I
FIG.
1. The evolution with time of an aqueous solution (0.5 ml of seawater) of “C-NaHCOs of In&gel.
Packard Instrument, instead of Aquasol (New England Nuclear Corporation). The initial “C-NaHCOs solution was dissolved in seawater (p? = 8) and an aliquot part (0.5 ml) was mixed with 6.5 ml Instagel. In these proportions the mixture is clear. As Iverson et al. did. we obtained a regular decrease of the “C activity with time (Fig. 1). After 5 hr. the sample contained 68% of the initial
in 6.5 ml
in a tightly closed scintillation vial; this point is extremely important in order to avoid the loss by the screw cap (series b). However, the last procedure makes automatic counting of a large number of samples impossible; but standardization seldom requires a great number of samples. On the other hand. it presents the advantage of simplicity and eludes the problems of solubilization.‘2)
796
Technical notes International Journal of Applied Radiation and Isotope pp. 796-799. Pergamon Press. Printed in Great Britain
1977. Vol. 28.
Method for Visualizing Water Sorbed on Metal Surfaces shaken
Intradnction
in the form of an electrolyte layer on metal surfaces is well-known as an important parameter in atmospheric corrosion processes.“) Atmospheric contaminants, especially sulphur dioxide, are known to accelerate the corrosion of many metals. ‘*’ In this laboratory, we have been attempting to establish the role of sulphur dioxide sorption on metal surfaces as the initial step of accelerated atmospheric corrosion. On the important industrial metal, iron, sulphur dioxide uptake has been shown to be non-uniform, being confined to points of up to 0.5mm in diameter.‘3’ It has also been established that the rate of sulphur dioxide sorption is increased with increasing humidity.“’ In an attempt to implicate water vapour in the activation of the sites, we have developed a technique to locate water sorption sites on iron surfaces using tritiated water (THO) and autoradiography. WATER
2
4
6
6
IO 12 14 I6
ml”
0
2
4
6
8
IO 12 14 I6 ‘16
ml”
Method
FIG. 2. Comparison of 14C activity evolution with time using series a (vials closed) and series b (vials opened).
The metal surface to be examined was attached to the internal base of a 15-ml nickel crucible by means of a cellulose adhesive strip. The crucible was then inverted over a flat surface which contained a saturated salt solution made up in THO in its centre. The humidity within the crucible was thus maintained by the saturated salt solution which was known to provide a given relative humidity at a specific temperature. Is) The salt solution was held in a 2-ml glass beaker containing: (a) 100~1 of 5 Ciml-’ THO, (b) 0.2-1.0 g salt, (c) a varying volume of unlabelled distilled water, which was determined by the solubility of the salt being used. Stopcock grease (Apiezon M) spread over the flat surface prior to the inversion of the crucible provided a seal which isolated the system from the laboratory atmosphere. The system was then allowed to stand for a minimum of 24 h while exchange took place between water molecules on the iron surface and THO in the surrounding atmosphere. Following removal from the radioactive atmosphere, the crucible containing the metal sample was partly immersed in liquid nitrogen to “freeze” the water bound to the metal surface in position. Simultaneously, a cotton wool pad soaked in A.R. benzene was held at the mouth of the crucible, thereby allowing a thin layer of benzene to condense on to the sample. (PRYDZet al.‘“’ have shown that benzene at 77 K is an efficient fluor.) After the sample had been exwsed to benzene vaoour for 5 s, the crucible and samole w&e completely imm&ed in liquid nitrogen. A sheet-of X-rav film Uafa Gevaert. Curix RPl-PE-NISI was then laid -on top gf the sampie and held in position with a brass weight (70g). The film was left in contact with the sample for approximately 72 h and then developed in the usual manner. Figure 1 is an example of an exposure of
quenching and chemiluminescence due to the diverse. bases used to retain 14C CO, in liauid scintillation cocktails.‘3*4’ The counting must &z ins&taneous to obtain the correct signal. This would not be a problem, because if radioactivity in the incubation flasks is high enough to be detected through organism’s uptake, it is necessarily high enough to be counted during a short period. Centre de Recherches Okanographiques BP V18, Abidjan, Ivory Coast.
A. HERBLAND
References 1. IVERSON R. L., BITTAKER H.
F. and MYERS V. B. L.imnol. Ocean&r. 21, 756-758 (1976). 2. SMITHD. W., FLIERMANS C. B. and BROIZK T. D. Appl. Microbial. 23, 595-600 (1972). 3. FRANCIS G. E. and HAWKINS J. D. Int. J. appl. Rudiat. Isotopes 18, 223-230 (1976). 4. WAITE D. T., DIJTHIE H. C. and MATTHEWS J. R. Hydrobiology 43, 231-234 (1973).