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Determination of small amounts of boron by radiation decomposition of chloroacetic acid solution
Talanta, Vol. 26. pp. 705 to 711 {3 Pergamon Press Ltd 1979. Printed in Great Britain
0039-9140/79/0801-0705502.00/0
DETERMINATION OF SMALL AMOUNTS OF BORON BYRADIATION DECOMPOSITION OF CHLOROACETIC ACID SOLUTION* M. H. YANO and C. L. TSENG Institute of Nuclear Science, National Tsing Hua University, Taiwan, Republic of China and G. Ti3LG Max-Planck-lnstitut f'tir Metailforschung, Laboratorium ftir Reinststoffe, 7070 Schw~ibisch Gmiind, FRG
(Received 1 November 1978. Accepted 20 November 1978) Summary--For the determination of boron in the/~g/g range in aqueous solution by activation analysis an indirect method is proposed, based .on the liberation of chloride ions from chloroacetic acid by the primary reaction !°B(n, ~)TLi. The sample solution, to which is added 0.01-0.5M choroacetic acid, is irradiated with reactor neutrons. The concentration of the chloride ions liberated from the chloroacetic acid is directly proportional to the boron content of the irradiated sample. It is determined potentiometrically with a chloride-sensitiveelectrode. By this method boron contents > 10-s g can be detected with good reProducibility. Interference from other ionic species has been investigated and can be neglected. The method is suitable for the determination of'boron in biological matrices.
Many chemical methods, with various sensitivities, have been reported for the determination of boron. These are based on spectrophotometric, 1~ fluorimetric, 5'6 atomic absorption7-9 and emission~°'t2 spectrometric techniques. Owing to the non-availability of suitable radionuclides of boron, nuclear techniques have seldom been used for the determination of boron. A radio-reagent method based on the reaction of boric acid with hydrofluoric acid labelled with fluorine-18 was, however, reported to b e suitable for the determination of boron in the submicrosram range, t 3 The present study was initiated to~ develop a new method for the indirect determination of boron based on the measurement of a specific product of the radiation decomposition of a chemical system. The principle of this method lies in the fact that when a sample containing boron and chloroacetic acid is subjected to neutron irradiation, the charged particles (TLi and 4He) resulting from the nuclear reaction t°B(n, 4He)~Li, will immediately interact with chloroacetic acid, forming radiation decomposition products such as chloride. It is well known that the concomitant radiation (fast neutrons and y-rays) axising during reactor neutron irradiation can also lead to such reaction products. The radiation decompo-
* Presented at the International Symposium on Microchemical Techniques, Davos, 22-27 May 1977, Switzerland. 705
sition process can be expressed as CH2CICOOH
"He. TLi , C I (nr. 7)
+ other radiolytic fragments. By measurement of the halide ions produced, with a chloride-sensitive electrode, the boron content in the sample can be deduced from the relationship between the boron concentration and the halide concentration induced by fission radiation. It is of primary importance that the effect of the concomitant radiation on the formation of chloride ions during neutron irradiation should be taken into account. Other factors which influence the usefulness and applicability of this method to the determination of small amounts of boron must also be investigated.
EXPERIMENTAL
Reagents and apparatus All chemicals used in this study were of analytical-reagent grade. An lonanalyzer Chloride Electrode Model 94-17 coupled with an Orion Model 701 Specific Ion Meter (Orion Research Inc.) was used to measure chloride ion concentrations. Pretreatment of sample for analysis A pretreatment which includes separation and enrichment steps is needed in the method. Various interfering ions which might influence the result of the analysis should be removed prior to the determination. Halide ions are
M . H . YANG,C. L. TSE~O and G. TbLG
706
eliminated by adding concentrated nitric acid to the sample and evaporating to dryness. The metal ions (Hg 2+, Ag +, Cu 2+, etc.) which form complexes with chloride are extracted with sodium diethyldithiocarbamate in chloroform before adjustment of the pH to 2-3. The aqueous phase is then evaporated to dryness after addition of nitric acid. Another method of separation and enrichment is to distil the boron as methyl borate, which is absorbedin a mixture of glycerol and aqueous alkali. 1'*
Preparation of solution for irradiation The pretreated samples were dissolved along with enough chloroacetic acid to produce a final concentration between 0.01 and 0.3M. Five ml of this solution were sealed in a quartz tube (5 cm x 2 cm diameter) for irradiation.
Neutron irradiation Sample solutions were irradiated with thermal neutrons in the THOR reactor of National Tsing Hun University for times ranging from 10 sec to 2 min. The thermal-neutron flux at the irradiation position was about 2.1 × 10 '2 n.cm-Z.sec - t and the ionizing radiation was estimated to be about 4.5 x 103 tad/see. The irradiation temperature was about 30°.
Measurement of chloride After irradiation the sample was cooled for I hr to allow for the decay of short-lived nuclides. The concentration of chloride ions produced was then measured with a chloridesensitive electrode.
Analysis of samples Attempts were made to determine the boron content in water and biological samples. For the analysis of boroncontaminated waste-water, a 100-ml water sample was taken and its pH adjusted to 2-3 with nitric acid. It was then extracted with 0.1M sodium diethyldithiocarbamate in chloroform. The aqueous phase was added to nitric acid and slowly evaporated to dryness. The residue was dissolved in 0.2M chloroacetic acid to give a final volume of 5 ml for neutron irradiation. The loss of boron for the whole process was shown to be negligible by an atomicabsorption spectrometric analysis. As a model for the analysis of biological material, a sample of orchard leaves (NBS S R M 1571) was digested in a mixture of nitric acid and hydrogen peroxide and evaporated to a small volume to expel excess of water, After addition of methanol and concentrated sulphuric acid, the solution was heated to 80 ° to distil the methyl borate, which was carried in a nitrogen stream to the collecting solution containing glycerine and I% sodium hydroxide. The solution was treated further by evaporation and addition of chloroacetic acid for subsequent neutron irradiation.
RESULTS AND DISCUSSION 'In the determination of boron by the radiationinduced decomPosition of chloroacetic acid, two sources of radiation are responsible for the formation of chloride ions. One consists of the high-energy charged particles resulting from the fission reaction t°B(n, 4He)TLi, while the other is the concomitant radiation (fast neutrons and 7-rays) accompanying thermal neutrons in the nuclear reactor. Each type of radiation has a different efficiency in the radiolysis of chloroacetic acid and a quantitative assessment of the relative doses of the two radiations is required to establish the feasibility and limits of detection of the method. An estimation of the fission radiation dose from the nuclear reaction '°B(n, "He)TLi can be made from the following data: t°B abundance 18.7%, fission cross-section 3990 barn, fission energy 2.973 MeV. If the thermal-neutron flux is taken as 2.1 x 1 0 " n . c m - 2 . s e c -1 (corresponding to the flux at the irradiation position of the T H O R reactor) and the boron content in the sample solution as 0.01%, the total fission radiation dose is calculated to be 4.2 x l0 s rad/sec. The reactor radiation dose at a fixed irradiation position in a reactor can be determined experimentally) s The radiation dose in T H O R was determined to be 1.9 x 10 ~ rad/hr for 7-rays and 6.7 x 106 rad,qu" for fast neutrons. The radiation doses for samples with various boron contents are given in Table i. It is seen that the fission radiation dose decreases with decreasing boron concentration, in contrast to the constant reactor radiation dose under the fixed irradiation condition. As the concentration of boron decreases to 0.01%, the two radiation doses attain nearly equal levels. Obviously the halide ions estimated at lower boron concentrations (<0.001%) are due predominantly to the effect of reactor radiation rather than to that of fission radiation. The limit of detection for boron can be estimated to be around 10 ppm under the present experimental conditions. The measured chloride concentration for chloroacetic acid solutions containing boron will contain contributions resulting from both fission radiation and reactor radiation. The chloride concentration due solely to the effect of fission radiation by '°B(n,
Table 1. Comparison of the radiation dose rate for samples with various boron contents Fission radiation dose,
Reactor radiation dose,
tad/see
rad/sec
4.2 ×
0.1 O.O1
10~ 4.2 × 104 4.2 × tO3
4.5 x 103 4.5 x 103 4.5 × 103
0.001 0.0001
4.2 × 102 4.2 x tO ~
4.5 × 10 3 4.5 × 103
B concentration, % 1
707
Determination of boron
20
40
60
80
I00
o o' NoCl IN H'zO 160
A, NoCl IN IxlO'~M QCDROACETIC (CONTAINING I00 ugB/ml)
180
KP
~2
KY
Q-LORtDE CONCENTRATION, M
Fig. 1. Calibration curve of chloride concentration v s . electrode potential. O NaCI in water; A NaCI in 0.1M chioroacetic acid containing 1(30/~g g boron per ml.
4He)TLi can be obtained by subtracting the chloride concentration in the blank (boron-free chloroacetic acid solution) from that in the sample (chloroacetic acid solution containing boron). To achieve an accurate determination of chloride by using the chloride-selective electrode, the influence of Chloroacetic acid and boron on the measurement must first b e assessed. Figure 1 shows the relationship between chloride concentration and electrode potential. Clearly no interference can be observed in the presence of chloroacetic acid (0.1M) and sodium borate (B 100/~g/ml). A plot of boron concentration against the concentration of chloride ions produced by fission radiation was constructed. Figure 2 demonstrates the relationship between the yield of chloride ions by fission radiation and the boron content in irradiated solutions containing various concentrations of chloroacetic acid. The results show that the yield of chloride ions by fission radiation is linearly proportional to the
concentration of boron down to 10- 5 g/ml. The figure also shows that the yield of chloride ions by fission radiation increases with increasing concentration of chloroacetic acid solution. A concentration around 0.1M is suitable for practical purposes. The effect of irradiation time on the response curve was also examined. From Fig. 3 it can be seen that longer irradiation times are more favourable than shorter ones for the production of chloride. They will, however, create more complications in tl/e system owing to the subsequent reactions of the radiolysed products. An irradiation time of around 1 rain was considered to be suitable in this study. The limits of detection and the precision of determination of boron must be considered. Table 2 summarizes the results for both samples (with various boron contents) and blanks (withoutboron) in 0.3M chloroacetic acid; irradiated for 30 sec. It can be seen from Table~2 that the potential reading for the blank is low compared with that for the samples, owing
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708
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BORON CONTENT. rng/ml Fig. 2. Relationship between the yield of chloride ions by fission radiation and the boron in the irradiated solutions containing various concentrations of chloroacetic acid: A, 0.2M; B, 0.1M; C, 0.01M. Irradiation time 1 rain.
to the strong concomitant radiation field in the reactor. The difference in potential readings between sample and blank is very small when the boron content is low. Since the ion-selective electrode gives a logarithmic relation of response to concentration (as can be seen from Fig. 1), a very small change in chloride ion concentration at a high chloride ion concentration can not be determined with high precision. The standard deviation (Table 2) increases with decreasing concentrations of boron. With the present experimental conditions boron concentrations down to 20 #g/ml can be determined with reasonable precision (relative standard deviation 16%). . The interference of halides and some common ions in the determination of chloride ions is summarized in Table 3. As can be seen, for some common ions such as Na +, K*, Mg 2+, N O j , Ca 2+, PO~-, no interference is observed at concentrations up to 0.1M. Halide ions, (except F=), show serious interference even at concentrations as low as 10-'*M. Metal ions, such as Hg 2+, A g ' , Cu 2+, which form strong complexes with chloride, ~ interfere to some extent in the precise determination of chloride ions as can be seen
from Fig. 4. The interference from Hg 2+ and Ag + begins at the /zg/m] concentration level, while that from Cu 2+ begins at about 102/zg/ml. No interference can be observed for Cd 2+, Zn 2+, Ni 2 + or other ions with less tendency to complex with chloride. Several attempts have been made to eliminate the interfering ions mentioned above. Experimental evidence shows that the interference of halide ions can be eliminated either by the addition of a substoichiometric amount of silver nitrate prior to the irradiation, or by evaporating the sample t o dryness in the presence of nitric acid. The interference of metal ions can be eliminated by extracting the sample solution with sodium diethyidithiocarbamate in chloroform at pH 2-3. Table 4 shows evidence of the elimination of the interferenc~ of Hg 2+, Ag +, CI- and Br-, each ion being present at a concentration of 50 #g/ml in the solution for pretreatment. The applicability of:the method to the determination of boron has been tested with natural water samples and biological materials. Pretreatment of the water sample was by sodium diethyldithiocarbamate extraction followed by addition of chloroacetic acid,
Determination of boron !
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B01~N (~IWENT. mg/~ Fig. 3. Relationship between the yield of chloride ions by fission radiation and the boron content in the irradiated solutions for different irradiation times: A, 2 min; B, 1 rain, C, 0.5 rain. Chloroacetic acid concentration 0.2M. Table 2. Precision of the method B content,
Electrode rending,
r~/mi
mV
0 (Blank)
139.2 139.5 140.2
Total ['C1-], 10- 3M
Net ECI-] produced by fision radiation, 10-4M Individual determination Average Standard deviation*
0.963 0.940 0.892 Av. 0.932
0.892flh9
5.0
99.2
5.26
42.1
1.0
120.5
2.13
12.3
0.25
128.5 128.7 129.8 12&8
1.51 1.41 1.50 1.45
5.84 5.68 4.82 5.18
5.42
0.47 (9%)
0.10
132.0 133.4 131.8 133.0
1.28 1.21 1.29 1.23
3.48 2.82 3.62 3.00
3.20
0.39 (12%)
0,02 '
135.5 135.8 136,5 135,8
1.11 1.08 1.05 1.08
1.78 1.52 1.20 1.52
1.48
0.24 (16%)
0.01
138.0 136.5 137.8 138.0
1.00 1.05 0.99 1.00
0.71 1,18 0.60 0.71
0.81
0,31 (35%)
* Relative standard deviation in brackets.
710
M.H. YANG,C. L. TSENGand G. T~LG
Ni ~'~"
140
i 180
CATION CONCENTRATION,/.i.g/ml Fig. 4. Effect of concentration of metal ions fforming negatively-charged complex ions with chloride) on the measurement of electrode potential. Concentration of chloride ion 1 x 10-3M in 0.1M chloroacetic acid.
while that of the orchard leaves (NBS standard reference material) was by digestion with nitric acid and hydrogen perioxide followed by distillation of boron as methyl borate. The boron content of the two samples is given in Table 3. Effect of various ions on the determination of halide ion with the chloride-selective electrode (chloroacetic acid 0.2M, irradiation time 2 min; boron 100 gg/ml)
Ion
Concentration, M --
-M g 2÷ Na + K +
1 x 10 -2 2 x I0 -l 2 x I0 -l
Ca 2+ NO~" S042-
1 × 10 - 2 2 × 10-2 1 × 10 - 2
PO~-
I × 10 -2
FCI-
1 x 10 - 2 1 x 10-s 1 x 10 -4 1 x 10-5 1 x 10 -4 1 x 10-5 I x 10-4
Br1-
* Interference is observed
Electrode reading, mV 95.6 96.1 95.8 95.7
95.4 96.1 95.4 96.0 95.6 95.1 88.4* 94.8 88.8* 94.2 89.3*
Table 5. The same samples were analysed for boron content by the standard colorimetric method using carmine) 7 The values obtained by the two methods are, found to be in good agreement. The accuracy of this method is confirmed by the good agreement between the experimental data and the NBS certified value for orchard leaves. Two factors dominate the present method for the determination of boron: the amounts of thermal-neutron flux effective for the irradiation of the sample and the ratio of the thermal-neutron flux to the concomitant radiation dose in the reactor. An increase in thermal-neutron flux of an order of magnitude would, in principle, increase tenfold the concentration of chloride ions produced by the fission radiation and thus decrease the detection limit for Table 4. Elimination of the interference of Hg 2+, Ag2+, CI- and Br- (chloroacetic acid 0.2M; boron 100 /~g/mi, interfering ion 50/zg/ml; irradiation time 2 min) Analysis No. 1 2 3 Blank
Each interfering ion added, ltg/rnl
Potential reading, m V
50 50 50 0
95.5 96.0 96.2 95.6
Determination of boron
711
Table 5. Determination of boron in waste-water and NBS orchard leaves Sample
Boron, ppM Individual
Analytical method Present*
Waste-water Colorimetric Orchard leavest (NBS SRM 1571)
1.19 1.68 1.46
1.51 1.31 !.38
1:58 1.26 1.59
Average 1.42 -+ 0.13 1.48 + 0.08
Present:~
28.1
35.6
29.8
31.2 _ 2.8
Colorimetric
33.2
31.8
32.5
32.5 _ 0.50
* 100 ml of water taken and concentrated to 5 ml for neutron irradiation. t NBS certified value is 33 ___3 ppM (ng/g). :~2 g of orchard leaves taken for each analysis.
boron. Decreasing c o n c o m i t a n t radiation, o n the other hand, will lower the chloride concentration of the blank and increase the difference in chloride concentration between blank and sample, consequently increasing the precision of the determination. Both t h e r m a l - n e u t r o n flux and concomitant radiation dose are, however, characteristic of a nuclear reactor. In our present study, under the fixed irradiation condition, (thermal-neutron flux 2 x 1012 n . c m - 2 . s e c -1, c o n c o m i t a n t radiation dose 4.5 x 103 rad/sec), b o r o n d o w n to a b o u t 10-Sg/ml can be determined with good reproducibility.
Acknowledgement--One of the authors (M.H.Y.) is indebted to the National Science Council of the Republic of China for a research grant to finish this work. REFERENCES 1. A. R. Eberle and M. W. Lerner, Anal. Chem., 1960, 32, 146. 2. L. Ducret, Anal. Chim. Acta, 1957, 17, 213.
3. L. Pasztor and I. D. Bode, Anal. Chem., !960, 32, 1531. 4. W. T. Dible, K. C. Berger and E. Truog, ibid., 1954, 26, 418. 5. J. C. Landry, M. F. Landry and D. Monnier, Anal. Chim. Acta, 1972, 62, 177. 6. Z. Skorko-Trybula and Z. Boguszewska, Mikrochim. Acta, 1976 II, 335. 7. R. R. Eltonbott, Anal. Chim. Acta, 1976, 86, 281. 8. J. C. M. Pau, E. E. Pickett and S. R. Koirtyohann, Analyst, 1972, 97, 860. 9. G. I. Spielholtz, G. C. Toralballa and J. J. Willsen, Mikrochim. Acta, 1974, 649. 10. E. H. Daughtrey, Jr. and W. W. Harrison, Anal. Chim. Acta, 1974, 72, 225. 11. ldem, ibid., 1973, 67, 253. 12. R. M. Dagnall, D. J. Smith, T. S. West and S. Greenfield, ibid., 1971, 54, 397. 13. M. P. Menon, J. Radioanal. Chem., 1973, 14, 63. 14. G. S. Spicer and J. D. H. Striekland, Anal. Chim. Acta, 1958, 18, 523. 15. G. Ahnstr6m, Neutron Irradiation of Seed II, IAEA, p. 107, 1968. 16. C. C. Wu and M. H. Yang, Anal. Chim. Acta, 1976, 84, 335. 17. D. F. Boltz, Colorimetric Determination of Nonmetals, Interscience, New York, 1958.
0039-9140/79/0801-0705502.00/0
DETERMINATION OF SMALL AMOUNTS OF BORON BYRADIATION DECOMPOSITION OF CHLOROACETIC ACID SOLUTION* M. H. YANO and C. L. TSENG Institute of Nuclear Science, National Tsing Hua University, Taiwan, Republic of China and G. Ti3LG Max-Planck-lnstitut f'tir Metailforschung, Laboratorium ftir Reinststoffe, 7070 Schw~ibisch Gmiind, FRG
(Received 1 November 1978. Accepted 20 November 1978) Summary--For the determination of boron in the/~g/g range in aqueous solution by activation analysis an indirect method is proposed, based .on the liberation of chloride ions from chloroacetic acid by the primary reaction !°B(n, ~)TLi. The sample solution, to which is added 0.01-0.5M choroacetic acid, is irradiated with reactor neutrons. The concentration of the chloride ions liberated from the chloroacetic acid is directly proportional to the boron content of the irradiated sample. It is determined potentiometrically with a chloride-sensitiveelectrode. By this method boron contents > 10-s g can be detected with good reProducibility. Interference from other ionic species has been investigated and can be neglected. The method is suitable for the determination of'boron in biological matrices.
Many chemical methods, with various sensitivities, have been reported for the determination of boron. These are based on spectrophotometric, 1~ fluorimetric, 5'6 atomic absorption7-9 and emission~°'t2 spectrometric techniques. Owing to the non-availability of suitable radionuclides of boron, nuclear techniques have seldom been used for the determination of boron. A radio-reagent method based on the reaction of boric acid with hydrofluoric acid labelled with fluorine-18 was, however, reported to b e suitable for the determination of boron in the submicrosram range, t 3 The present study was initiated to~ develop a new method for the indirect determination of boron based on the measurement of a specific product of the radiation decomposition of a chemical system. The principle of this method lies in the fact that when a sample containing boron and chloroacetic acid is subjected to neutron irradiation, the charged particles (TLi and 4He) resulting from the nuclear reaction t°B(n, 4He)~Li, will immediately interact with chloroacetic acid, forming radiation decomposition products such as chloride. It is well known that the concomitant radiation (fast neutrons and y-rays) axising during reactor neutron irradiation can also lead to such reaction products. The radiation decompo-
* Presented at the International Symposium on Microchemical Techniques, Davos, 22-27 May 1977, Switzerland. 705
sition process can be expressed as CH2CICOOH
"He. TLi , C I (nr. 7)
+ other radiolytic fragments. By measurement of the halide ions produced, with a chloride-sensitive electrode, the boron content in the sample can be deduced from the relationship between the boron concentration and the halide concentration induced by fission radiation. It is of primary importance that the effect of the concomitant radiation on the formation of chloride ions during neutron irradiation should be taken into account. Other factors which influence the usefulness and applicability of this method to the determination of small amounts of boron must also be investigated.
EXPERIMENTAL
Reagents and apparatus All chemicals used in this study were of analytical-reagent grade. An lonanalyzer Chloride Electrode Model 94-17 coupled with an Orion Model 701 Specific Ion Meter (Orion Research Inc.) was used to measure chloride ion concentrations. Pretreatment of sample for analysis A pretreatment which includes separation and enrichment steps is needed in the method. Various interfering ions which might influence the result of the analysis should be removed prior to the determination. Halide ions are
M . H . YANG,C. L. TSE~O and G. TbLG
706
eliminated by adding concentrated nitric acid to the sample and evaporating to dryness. The metal ions (Hg 2+, Ag +, Cu 2+, etc.) which form complexes with chloride are extracted with sodium diethyldithiocarbamate in chloroform before adjustment of the pH to 2-3. The aqueous phase is then evaporated to dryness after addition of nitric acid. Another method of separation and enrichment is to distil the boron as methyl borate, which is absorbedin a mixture of glycerol and aqueous alkali. 1'*
Preparation of solution for irradiation The pretreated samples were dissolved along with enough chloroacetic acid to produce a final concentration between 0.01 and 0.3M. Five ml of this solution were sealed in a quartz tube (5 cm x 2 cm diameter) for irradiation.
Neutron irradiation Sample solutions were irradiated with thermal neutrons in the THOR reactor of National Tsing Hun University for times ranging from 10 sec to 2 min. The thermal-neutron flux at the irradiation position was about 2.1 × 10 '2 n.cm-Z.sec - t and the ionizing radiation was estimated to be about 4.5 x 103 tad/see. The irradiation temperature was about 30°.
Measurement of chloride After irradiation the sample was cooled for I hr to allow for the decay of short-lived nuclides. The concentration of chloride ions produced was then measured with a chloridesensitive electrode.
Analysis of samples Attempts were made to determine the boron content in water and biological samples. For the analysis of boroncontaminated waste-water, a 100-ml water sample was taken and its pH adjusted to 2-3 with nitric acid. It was then extracted with 0.1M sodium diethyldithiocarbamate in chloroform. The aqueous phase was added to nitric acid and slowly evaporated to dryness. The residue was dissolved in 0.2M chloroacetic acid to give a final volume of 5 ml for neutron irradiation. The loss of boron for the whole process was shown to be negligible by an atomicabsorption spectrometric analysis. As a model for the analysis of biological material, a sample of orchard leaves (NBS S R M 1571) was digested in a mixture of nitric acid and hydrogen peroxide and evaporated to a small volume to expel excess of water, After addition of methanol and concentrated sulphuric acid, the solution was heated to 80 ° to distil the methyl borate, which was carried in a nitrogen stream to the collecting solution containing glycerine and I% sodium hydroxide. The solution was treated further by evaporation and addition of chloroacetic acid for subsequent neutron irradiation.
RESULTS AND DISCUSSION 'In the determination of boron by the radiationinduced decomPosition of chloroacetic acid, two sources of radiation are responsible for the formation of chloride ions. One consists of the high-energy charged particles resulting from the fission reaction t°B(n, 4He)TLi, while the other is the concomitant radiation (fast neutrons and 7-rays) accompanying thermal neutrons in the nuclear reactor. Each type of radiation has a different efficiency in the radiolysis of chloroacetic acid and a quantitative assessment of the relative doses of the two radiations is required to establish the feasibility and limits of detection of the method. An estimation of the fission radiation dose from the nuclear reaction '°B(n, "He)TLi can be made from the following data: t°B abundance 18.7%, fission cross-section 3990 barn, fission energy 2.973 MeV. If the thermal-neutron flux is taken as 2.1 x 1 0 " n . c m - 2 . s e c -1 (corresponding to the flux at the irradiation position of the T H O R reactor) and the boron content in the sample solution as 0.01%, the total fission radiation dose is calculated to be 4.2 x l0 s rad/sec. The reactor radiation dose at a fixed irradiation position in a reactor can be determined experimentally) s The radiation dose in T H O R was determined to be 1.9 x 10 ~ rad/hr for 7-rays and 6.7 x 106 rad,qu" for fast neutrons. The radiation doses for samples with various boron contents are given in Table i. It is seen that the fission radiation dose decreases with decreasing boron concentration, in contrast to the constant reactor radiation dose under the fixed irradiation condition. As the concentration of boron decreases to 0.01%, the two radiation doses attain nearly equal levels. Obviously the halide ions estimated at lower boron concentrations (<0.001%) are due predominantly to the effect of reactor radiation rather than to that of fission radiation. The limit of detection for boron can be estimated to be around 10 ppm under the present experimental conditions. The measured chloride concentration for chloroacetic acid solutions containing boron will contain contributions resulting from both fission radiation and reactor radiation. The chloride concentration due solely to the effect of fission radiation by '°B(n,
Table 1. Comparison of the radiation dose rate for samples with various boron contents Fission radiation dose,
Reactor radiation dose,
tad/see
rad/sec
4.2 ×
0.1 O.O1
10~ 4.2 × 104 4.2 × tO3
4.5 x 103 4.5 x 103 4.5 × 103
0.001 0.0001
4.2 × 102 4.2 x tO ~
4.5 × 10 3 4.5 × 103
B concentration, % 1
707
Determination of boron
20
40
60
80
I00
o o' NoCl IN H'zO 160
A, NoCl IN IxlO'~M QCDROACETIC (CONTAINING I00 ugB/ml)
180
KP
~2
KY
Q-LORtDE CONCENTRATION, M
Fig. 1. Calibration curve of chloride concentration v s . electrode potential. O NaCI in water; A NaCI in 0.1M chioroacetic acid containing 1(30/~g g boron per ml.
4He)TLi can be obtained by subtracting the chloride concentration in the blank (boron-free chloroacetic acid solution) from that in the sample (chloroacetic acid solution containing boron). To achieve an accurate determination of chloride by using the chloride-selective electrode, the influence of Chloroacetic acid and boron on the measurement must first b e assessed. Figure 1 shows the relationship between chloride concentration and electrode potential. Clearly no interference can be observed in the presence of chloroacetic acid (0.1M) and sodium borate (B 100/~g/ml). A plot of boron concentration against the concentration of chloride ions produced by fission radiation was constructed. Figure 2 demonstrates the relationship between the yield of chloride ions by fission radiation and the boron content in irradiated solutions containing various concentrations of chloroacetic acid. The results show that the yield of chloride ions by fission radiation is linearly proportional to the
concentration of boron down to 10- 5 g/ml. The figure also shows that the yield of chloride ions by fission radiation increases with increasing concentration of chloroacetic acid solution. A concentration around 0.1M is suitable for practical purposes. The effect of irradiation time on the response curve was also examined. From Fig. 3 it can be seen that longer irradiation times are more favourable than shorter ones for the production of chloride. They will, however, create more complications in tl/e system owing to the subsequent reactions of the radiolysed products. An irradiation time of around 1 rain was considered to be suitable in this study. The limits of detection and the precision of determination of boron must be considered. Table 2 summarizes the results for both samples (with various boron contents) and blanks (withoutboron) in 0.3M chloroacetic acid; irradiated for 30 sec. It can be seen from Table~2 that the potential reading for the blank is low compared with that for the samples, owing
M.H. YANG,C. L. TS~NGand G. T(SLG
708
. . . . . .
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BORON CONTENT. rng/ml Fig. 2. Relationship between the yield of chloride ions by fission radiation and the boron in the irradiated solutions containing various concentrations of chloroacetic acid: A, 0.2M; B, 0.1M; C, 0.01M. Irradiation time 1 rain.
to the strong concomitant radiation field in the reactor. The difference in potential readings between sample and blank is very small when the boron content is low. Since the ion-selective electrode gives a logarithmic relation of response to concentration (as can be seen from Fig. 1), a very small change in chloride ion concentration at a high chloride ion concentration can not be determined with high precision. The standard deviation (Table 2) increases with decreasing concentrations of boron. With the present experimental conditions boron concentrations down to 20 #g/ml can be determined with reasonable precision (relative standard deviation 16%). . The interference of halides and some common ions in the determination of chloride ions is summarized in Table 3. As can be seen, for some common ions such as Na +, K*, Mg 2+, N O j , Ca 2+, PO~-, no interference is observed at concentrations up to 0.1M. Halide ions, (except F=), show serious interference even at concentrations as low as 10-'*M. Metal ions, such as Hg 2+, A g ' , Cu 2+, which form strong complexes with chloride, ~ interfere to some extent in the precise determination of chloride ions as can be seen
from Fig. 4. The interference from Hg 2+ and Ag + begins at the /zg/m] concentration level, while that from Cu 2+ begins at about 102/zg/ml. No interference can be observed for Cd 2+, Zn 2+, Ni 2 + or other ions with less tendency to complex with chloride. Several attempts have been made to eliminate the interfering ions mentioned above. Experimental evidence shows that the interference of halide ions can be eliminated either by the addition of a substoichiometric amount of silver nitrate prior to the irradiation, or by evaporating the sample t o dryness in the presence of nitric acid. The interference of metal ions can be eliminated by extracting the sample solution with sodium diethyidithiocarbamate in chloroform at pH 2-3. Table 4 shows evidence of the elimination of the interferenc~ of Hg 2+, Ag +, CI- and Br-, each ion being present at a concentration of 50 #g/ml in the solution for pretreatment. The applicability of:the method to the determination of boron has been tested with natural water samples and biological materials. Pretreatment of the water sample was by sodium diethyldithiocarbamate extraction followed by addition of chloroacetic acid,
Determination of boron !
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B01~N (~IWENT. mg/~ Fig. 3. Relationship between the yield of chloride ions by fission radiation and the boron content in the irradiated solutions for different irradiation times: A, 2 min; B, 1 rain, C, 0.5 rain. Chloroacetic acid concentration 0.2M. Table 2. Precision of the method B content,
Electrode rending,
r~/mi
mV
0 (Blank)
139.2 139.5 140.2
Total ['C1-], 10- 3M
Net ECI-] produced by fision radiation, 10-4M Individual determination Average Standard deviation*
0.963 0.940 0.892 Av. 0.932
0.892flh9
5.0
99.2
5.26
42.1
1.0
120.5
2.13
12.3
0.25
128.5 128.7 129.8 12&8
1.51 1.41 1.50 1.45
5.84 5.68 4.82 5.18
5.42
0.47 (9%)
0.10
132.0 133.4 131.8 133.0
1.28 1.21 1.29 1.23
3.48 2.82 3.62 3.00
3.20
0.39 (12%)
0,02 '
135.5 135.8 136,5 135,8
1.11 1.08 1.05 1.08
1.78 1.52 1.20 1.52
1.48
0.24 (16%)
0.01
138.0 136.5 137.8 138.0
1.00 1.05 0.99 1.00
0.71 1,18 0.60 0.71
0.81
0,31 (35%)
* Relative standard deviation in brackets.
710
M.H. YANG,C. L. TSENGand G. T~LG
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CATION CONCENTRATION,/.i.g/ml Fig. 4. Effect of concentration of metal ions fforming negatively-charged complex ions with chloride) on the measurement of electrode potential. Concentration of chloride ion 1 x 10-3M in 0.1M chloroacetic acid.
while that of the orchard leaves (NBS standard reference material) was by digestion with nitric acid and hydrogen perioxide followed by distillation of boron as methyl borate. The boron content of the two samples is given in Table 3. Effect of various ions on the determination of halide ion with the chloride-selective electrode (chloroacetic acid 0.2M, irradiation time 2 min; boron 100 gg/ml)
Ion
Concentration, M --
-M g 2÷ Na + K +
1 x 10 -2 2 x I0 -l 2 x I0 -l
Ca 2+ NO~" S042-
1 × 10 - 2 2 × 10-2 1 × 10 - 2
PO~-
I × 10 -2
FCI-
1 x 10 - 2 1 x 10-s 1 x 10 -4 1 x 10-5 1 x 10 -4 1 x 10-5 I x 10-4
Br1-
* Interference is observed
Electrode reading, mV 95.6 96.1 95.8 95.7
95.4 96.1 95.4 96.0 95.6 95.1 88.4* 94.8 88.8* 94.2 89.3*
Table 5. The same samples were analysed for boron content by the standard colorimetric method using carmine) 7 The values obtained by the two methods are, found to be in good agreement. The accuracy of this method is confirmed by the good agreement between the experimental data and the NBS certified value for orchard leaves. Two factors dominate the present method for the determination of boron: the amounts of thermal-neutron flux effective for the irradiation of the sample and the ratio of the thermal-neutron flux to the concomitant radiation dose in the reactor. An increase in thermal-neutron flux of an order of magnitude would, in principle, increase tenfold the concentration of chloride ions produced by the fission radiation and thus decrease the detection limit for Table 4. Elimination of the interference of Hg 2+, Ag2+, CI- and Br- (chloroacetic acid 0.2M; boron 100 /~g/mi, interfering ion 50/zg/ml; irradiation time 2 min) Analysis No. 1 2 3 Blank
Each interfering ion added, ltg/rnl
Potential reading, m V
50 50 50 0
95.5 96.0 96.2 95.6
Determination of boron
711
Table 5. Determination of boron in waste-water and NBS orchard leaves Sample
Boron, ppM Individual
Analytical method Present*
Waste-water Colorimetric Orchard leavest (NBS SRM 1571)
1.19 1.68 1.46
1.51 1.31 !.38
1:58 1.26 1.59
Average 1.42 -+ 0.13 1.48 + 0.08
Present:~
28.1
35.6
29.8
31.2 _ 2.8
Colorimetric
33.2
31.8
32.5
32.5 _ 0.50
* 100 ml of water taken and concentrated to 5 ml for neutron irradiation. t NBS certified value is 33 ___3 ppM (ng/g). :~2 g of orchard leaves taken for each analysis.
boron. Decreasing c o n c o m i t a n t radiation, o n the other hand, will lower the chloride concentration of the blank and increase the difference in chloride concentration between blank and sample, consequently increasing the precision of the determination. Both t h e r m a l - n e u t r o n flux and concomitant radiation dose are, however, characteristic of a nuclear reactor. In our present study, under the fixed irradiation condition, (thermal-neutron flux 2 x 1012 n . c m - 2 . s e c -1, c o n c o m i t a n t radiation dose 4.5 x 103 rad/sec), b o r o n d o w n to a b o u t 10-Sg/ml can be determined with good reproducibility.
Acknowledgement--One of the authors (M.H.Y.) is indebted to the National Science Council of the Republic of China for a research grant to finish this work. REFERENCES 1. A. R. Eberle and M. W. Lerner, Anal. Chem., 1960, 32, 146. 2. L. Ducret, Anal. Chim. Acta, 1957, 17, 213.
3. L. Pasztor and I. D. Bode, Anal. Chem., !960, 32, 1531. 4. W. T. Dible, K. C. Berger and E. Truog, ibid., 1954, 26, 418. 5. J. C. Landry, M. F. Landry and D. Monnier, Anal. Chim. Acta, 1972, 62, 177. 6. Z. Skorko-Trybula and Z. Boguszewska, Mikrochim. Acta, 1976 II, 335. 7. R. R. Eltonbott, Anal. Chim. Acta, 1976, 86, 281. 8. J. C. M. Pau, E. E. Pickett and S. R. Koirtyohann, Analyst, 1972, 97, 860. 9. G. I. Spielholtz, G. C. Toralballa and J. J. Willsen, Mikrochim. Acta, 1974, 649. 10. E. H. Daughtrey, Jr. and W. W. Harrison, Anal. Chim. Acta, 1974, 72, 225. 11. ldem, ibid., 1973, 67, 253. 12. R. M. Dagnall, D. J. Smith, T. S. West and S. Greenfield, ibid., 1971, 54, 397. 13. M. P. Menon, J. Radioanal. Chem., 1973, 14, 63. 14. G. S. Spicer and J. D. H. Striekland, Anal. Chim. Acta, 1958, 18, 523. 15. G. Ahnstr6m, Neutron Irradiation of Seed II, IAEA, p. 107, 1968. 16. C. C. Wu and M. H. Yang, Anal. Chim. Acta, 1976, 84, 335. 17. D. F. Boltz, Colorimetric Determination of Nonmetals, Interscience, New York, 1958.