Determination of iodide formed from inorganic iodine in aqueous solution

Anat’ytzca Chlmtcu Acta, 248 (1991) 595-602 Elsevter Science Pubhshers B V , Amsterdam

Determination

595

of iodide formed from inorganic iodine in aqueous solution Ronald 0. Rahn

School

ofPublrc Health, Umuersrty of Alabama at Bwmmgham, Btrmmgham, AL 35294 (USA) (Recetvcd 22nd August 1990)

The analysis of the conversion of todme (I*) mto todrde (II) m borate buffer (0 23 M, pH 8) was exammed usmg a variety of methods Reversed-phase hquid chromatography (LC) with an Ion-paumg mobde phase employing either electrochemical (EC) or ultraviolet (UV) detectton was employed and the results were compared wtth those obtamed etther electrochemcally using an todide-selectrve electrode or spectroscopically by measurmg the absorbance increase at 226 nm due to I- The results were exammed m the hght of the two-step model of rapid I, hydrolysis to yreld equal amounts of I- and hypomdous acid (HOI), followed by a slow disproporttonatton of HOI to I- and iodate (IO,), giving a fmal ratio of I- to IO, of 5.1. Independent of the method of analysts, the final yield of I- was 84 + 5% of the mttial amount of I, on a gram-atom basis, consrstent with the expected stotchtometry HOI and IO,- were determined spectroscopically by measunng their conversion to truodlde (I;) at the appropnate pH m the presence of excess of I-. The ttme-dependent yrelds of HOI and IO; were followed and the results were consistent with the two-step model except for the fact that the yteld of IO; at completton was 11 + 2% Instead of the predicted 17% At reaction ttmes less than completton, the yield of I- vaned, depending on the method of measurement. Only absorbance measurements gave an accurate or true picture of the I- concentration at a gtven pomt m time. LC-UV or LC-EC showed no change m I- wtth time, always givmg the m-urn, consrstent aslth the mobde phase acting as a catalyst In contrast, the I- electrode gave I- values too low (tmtially by a factor of 2) when HOI was present, presumably owmg to the mteractton of HOI wrth the ion electrode. The sensrttvity of the LC-EC measurement was 5 X 10p8 M, which, taken together with the selectivity and reproducibihty of the method, makes LC-EC suitably reliable for conductmg these types of measurements Keywords

Liqutd chromatography,

Iodide

Photolysis of halogenated pyrimidines results in homolytic splitting of the carbon-halogen bond and liberation of the free halogen [l]. Previously, the loss of iodine atoms from UV-irradiated DNA substituted with either iododeoxycytidine (IdCyd) [2] or tododeoxyuridine (IdUrd) [3], was measured using iodine-125 as a radioactive label and measuring the loss of counts from immobihzed DNA. It was of interest to determine whether the formation of I- in solution could also serve as a means of followmg this reaction. Such a measurement would be intrinsically sensitive to low levels of 0003-2670/91/$03

50

0 1991 - Elsevter Science Pubhshers B.V.

change because it is a null-point measurement (i.e., it measures the change in iodide against a background of zero). Also, by utilizing chemicalanalytical techniques for measuring iodide, radiolabelhng could be avoided. Photoinduced iodide formation can occur according to the followmg scheme. Homolytic splitting of the carbon-iodine bonds of the absorbing molecule leads to iodine atoms, which then recombine to form molecular iodine (I*):

596

R.0

The I, then reacts rapidly with water via a hydrolysis step to form iodide and hypoiodous acid: I, + H,O = II+

H++ HOI

(2)

According to Eigen and Kustm [4] and Palmer and van Eldik [5], this reaction goes to completion within a few seconds. The hypoiodous acid then undergoes disproportionation according to a second step to form iodide and iodate: 3HOI = 2II+

IO;

+ 3H+

(3)

This reaction may take hours or days, depending on the pH, temperature, concentration and the presence of other solute molecules [6,7]. The overall stoichiometry of the reaction is given by 31, + 3H,O = 51-i

IO,

+ 6H+

(4)

and predicts that for every six atoms of iodine present initially in the form of molecular iodme, five iodide ions are ultimately formed, provided that the reaction goes to completion. Initial attempts to measure iodide generated photochemically from DNA substituted with IdUrd led to the question of whether the quantitative conversion of iodme to iodide in aqueous solution takes place according to the predicted stoichiometry and under what conditions A review of the literature revealed that although extensive studies have been done on the kinetic aspects of iodine hydrolysis, particularly under strongly alkaline conditions, very little has been done on the quantitative conversion to iodide following completion of the reaction, particularly under conditions approaching neutrality. It was therefore decided to study the quantitative conversion of molecular iodine into iodide using several available methods and to compare the results obtained with the stoichiometry predicted by Eqn. 4. The methods used here to measure iodide meluded UV spectrophotometry of the intact reaction mixture using the absorbance maxtmum of iodide at 226 nm, liquid chromatographic (LC) separation (reversed phase ion-pair), using UV detection at 226 nm or electrochemical detection, and electropotential measurements using an iodide-selective electrode. Previous studies using these techniques to measure iodide have been carried out by the follow-

RAHN

ing: Reeve [8], who first used an ion-pairing mobile phase with LC to separate iodide; Hurst et al. [9], who applied electrochemical detection with ion-pair LC to obtain a sensitivity of 4 ng I- ml-’ (3 x lo-* M); and Han et al. [lo], who coupled ion chromatography with electrochemical detection to measure iodide with a reported sensitivity of 10 ng mlli (8 X lo-’ M). A comparison of the merits of UV, electrochemical (EC) and conductimetnc detection for measuring iodide has been presented by Lookabough et al. [ll].

EXPERIMENTAL

Apparatus Absorbance measurements were made with a Guilford Response scanning UV-visible spectrophotometer An Orion iodide-selective electrode with a single-junction reference electrode (Model 90-01) and an Orion Research Model 601 A/digital Ionanalyzer was used to measure iodide m solution. The output was monitored with a Houston Omnigraph chart recorder. LC with UV detection (LC-UV) was done using a Waters Model 6000A chromatograpmc pump and a Hitachi L4200 UV-visible detector with a reversed-phase cartridge column from Scientific Glass Engineering (5 pm; 50 X 4 mm t.d., Model GLC4-ODS28/5). LC with EC detection (LC-EC) was done using a PM-30A dual-piston pump and a Model LC-4B amperometric detector (equipped with a silver electrode), both from Bioanalytical Systems, together with an Alltech/Applied Science Econosphere Cl8 column (5 pm; 250 X 4.6 mm id). The chromatograms were recorded with a Hitachi D-2000 Chromato Integrator, which allowed the area under the iodide peak to be calculated Measurement of lodzde All samples were prepared in 0.23 M borate buffer (pH 8) unless stated otherwise. A stock solution of iodide (0.01423 M) was made from potassium iodide. Aliquots (10-100 ~1) were then placed m volumetric flasks ranging from 5 to 1000 ml and diluted to volume with borate buffer. These solutions were then used as standards to cahbrate the various methods employed in this

DETERMINATlON

OF IODIDE

IN AQUEOUS

597

SOLUTION

study to measure iodide. The average molar absorptivity for iodide determined from the absorbance at 226 nm of these solutions was 13 540 1 which is within 1% of the value mol-’ cm-‘, obtained by Toth et al. [6] of 13 500 1 mole1 cm-‘. A stock solution of molecular iodine (1.03 x 10e3 M) was made by weighmg out crystals of inorganic iodine and dissolvmg them in a fixed volume of ethanol. Samples for studymg the chemistry of iodine in water were prepared by using a syringe to deliver 50 ~1 of iodine stock solution to 2 ml of borate buffer. The concentration of the resulting iodine solution is expressed on a gramatom basis except where noted, so as to simplify the stoichiometric relationsmp between the imtial concentration of iodine and the resulting concentration of iodide. Quantitative conversion of iodine to triiodide was accomplished by addmg iodine to a solution containmg 0.5 M potassium iodide. Based on the addition of a known amount of I, to the solutions, the absorbance at 353 nm gave a molar absorptivity for I; of 26400 1 mol-’ cm-‘, m complete agreement with Toth et al. [6] and Awtrey and Connick [12]. This agreement confirms the use of the 50-pl syringe, which had been calibrated with water to deliver known amounts of I, in ethanol. If the potasstum iodide solution was made 0.1 M rather than 0.5 M, the absorbance was observed to be 4% lower. Hence, 0.5 M potassium iodide is necessary to a&eve complete conversion of iodine to triiodide. Iodide electrode measurements were done using l-2-ml volumes contained in a shallow plastic dish (a small magnetic stir bar was used to minimize drifting of the electrode potenttal). The slope of the calibration graph was usually in the vicinity of 59 mV per decade concentration change but did tend to vary slightly from day to day and even during the same experiment. Ion-pair LC was done using a mobile phase as described by Lookabaugh et al. [ll], consisting of 0.005 M tetrabutylammonium hydrogensulfate in a solution of methanol-phosphate buffer (15 : 85) (pH 7.0) EDTA was added (as recommended in the manual for the LC 4B detector; BAS, West Lafayette, IN) to passivate the detector and reduce baseline noise. For UV detection, a wave-

length of 226 nm was used. The iodide eluted after 5 min using a flow-rate of 0.5 ml min-‘. A background signal overlaps slightly where iodide elutes, resulting in the calibration graph having a non-zero intercept. However, the calibration graph based on the area under the iodide peak was linear, allowing concentrations of iodide to be determmed easily down to the lop6 M level. For electrochemical detection following LC, an applied potential of 0.01 V was used as recommended by Hurst et al. [9]. With a flow-rate of 1 ml mu-l, iodide eluted after 3.8 min. According to Lookabaugh et al. [ll], it is necessary to precondition the electrode with injections of concentrated iodide m order to maxirmze the repeatability of response. As found here, non-linear calibration graphs also resulted when preconditioning was omitted. However, continuous use of the column under ordinary operating conditions negates the necessity for repeating this treatment. With electrochermcal detection, a blank control gave an area corresponding to 3 X lo-*-4 X lo-’ M at the location where iodide elutes. If one assumes a detection limit corresponding to a signal-to-background ratio of 2 : 1, then the detection limit based on the area under the peak is about 10 ng ml-‘, similar to values reported by other workers Measurement of hyporodous acid (HOI) and lodate (IO,-) The species HOI and IO; were deternnned sequentially in the same solution by their reaction with iodide to form triiodtde. It was found that at pH 7 m the presence of excess of iodide the following reaction takes place: HOI + 21-

‘-,

I; + OH-

(5)

which 1s essentially the reverse of Eqn. 2 and allows one to measure HOI in the presence of iodate Then, by lowering the pH to 2.6, iodate can be measured according to the Dushman reaction [13]: 6H++

IO,

+ 51-

%

31, + 3H,O

(6)

The procedure used was as follows. To 2 ml of reaction mixture were added 40 ~1 of 5 M potas-

598

RO RAHN

sium iodide solution and the absorbance of the triiodlde formed from HOI was read at 353 nm. Then 37 pl of 1.8 M sulfuric acid were added to lower the pH to 2.6. The absorbance increase at 353 nm then corresponds to the formation of triiodlde from iodate. The method was calibrated using a standard solution of iodate, and exactly 3 mol of triiodide were formed per mole of iodate reacted. Reactions carried out in the absence of iodate were used as controls and the resulting absorbance was subtracted from the sample absorbance to give a final corrected value The above method differs from that of Habersbergerova [14], who measured iodate after first complexing HOI with phenol so as to prevent its subsequent conversion to tniodide Then, in the absence of phenol, both HOI and lodate were measured by their conversion to triiodlde. Seal [15] also reversed Eqn. 1 usmg excess of iodide but added thiosulfate to titrate the iodine formed instead of measuring it spectroscopically as done here.

RESULTS

AND DISCUSSION

Absorbance measurements Iodzde. The absorption spectra of an aqueous solution of iodine are shown in Fig. 1 as a function of time after the addition of molecular iodine.

075

/

1

200 0

300 0

Wavelength (nm)

Fig. 1 UV spectral changes as a function of time followmg the addltlon of lodme to borate buffer (0 23 M, pH 8) Iodine (0.05 ml of a 1.03 X 10m3 M stock solution) was added to 2 ml of buffer to give a concentration of 5.03X10e5 g-atom 1-l Absorption spectra were recorded after the followmg times (a) 2, (b) 10, (c) 25, (d) 39, (e) 310 and (f) 310 mm plus heatmg at 90 QC for 30 mm The absorbance was zeroed at 350 nm.

TABLE

1

Percentage conversIon (on a gram-atom basis) of Iodine mto I-, HOI, and IO; as a function of time a Time (Mm)

HOI

10;

I_

“HOI” (talc )

_

1

48

0 28

2 10 15

_ _ 26

_ _ 5.9

53 66 _

46 26 _

25 30

13

_ 10 5

72 _

17 _

_ 10 1 10 6

77 _

10 _ _

_

78

8

12.3

83

0

39 45 60 310 + 90* c for 30 mm

_ 9.9 8.3 _ 1.2

a Absorbance measurements were made on solutrons prepared as described for Fig. 1 IO&de was determmed from the absorbance at 226 nm HOI and lodate were determined by theu conversion to trnodlde as discussed under Expenmental The percentage yields are based on the initial concentration of lodme being 5 03 X lo- 5 g-atom 1-l “HOI” was calculated from the iodide data usmg Eqn. 7

The time-dependent increase in absorbance with a maximum at 226 nm 1s due to the formation of iodide. From these data the percentage of total iodine (as iodine atoms) initially added that is converted on a gram-atom basis into iodide was calculated and 1s presented inTable 1. Extrapolation to t = 0 indicates that mitially 50% of the iodine added is converted into iodide owing to rapid hydrolysis (Eqn. 2). The disproportionation reaction (Eqn. 3) then takes place over the next several hours, resultmg in further iodide formation A final heating step IS required for completion of this second step. The spectra shown in Fig. 1 are identical with those of postassium iodide itself (not shown), which indicates that only Icontributes to the absorbance. Hyporodous acid and lodute. As indicated in eqns. 2 and 3, both HOI and iodate are also formed from iodine in aqueous solution. According to Eqn. 2, the initial concentration of hypoiodous acid should be 50% of the initial iodine added to solution. At the end of the reaction, HOI goes to zero, and according to Eqn. 4, the yield of iodate should be close to 1/6th or 17% of the

DETERMINATION

OF IODIDE

IN AQUEOUS

SOLUTION

599

initial iodine added. The yields of HOI and iodate were measured at various times following the addition of iodine to the buffered solution and are presented in Table 1. Clearly, HOI starts very close to 50% and decreases to zero, as expected, but even after heating the iodate concentration never exceeds 12%. Similar results were obtained for concentrations ranging from 10e5 to lop4 M as shown in Table 2. In all instances, the final yields of iodate were lo-12% instead of 17%, a result that 1s inconsistent with the predicted stoichiometry, and for which there is no apparent explanation (see note added m proof ). The yield of HOI could also be calculated from the concentration of iodide using the followmg expression, which is derived m the Appendix: “HOI”

= 5/4[1,],

- 3/2[1I]

(7)

where [12],, corresponds to the initial concentration of todme and is expressed in gram-atoms per liter. This relationship is based on the fact that disproportionation results in the formatron of two iodide atoms formed per three molecules HOI lost. The values of HOI obtained from Eqn. 7 are presented in Table 1 as “HOI.” Because the disproportionatton reaction (Eqn. 3) IS second order [16], where initially two intermediates (HOI) interact wtth each other, the rate of HOI loss should be proportional to the square of the intermediate concentration, d[“HOI”]/ d t = - K[“HOI”12. The products of the initial disproportion reactions are HIO, and HI. HIO, then undergoes rapid disproportionation to form HIO, and HI. Therefore, a plot of the reciprocal of HOI concentratton vs. time (according to classical second-order kinetics) should give a straight hne. Such is the case, as shown m Fig. 2 using HOI values determined by conversion to tritodide or calculated from the iodide concentration using Eqn. 7. The rate constant calculated from the slope is 2.6 X lo3 1 mol-r mini’ at pH 8. The fact that determinations of the HOI data in two different ways give results that fall on the same curve in Fig. 2 provides confirmanon of the two-step reaction model and supports the use of the triiodtde method for measunng HOI. Also shown in Fig. 2 are results obtained at pH 10, which show that disproportion is 4-5 times

“r

0

10

20

30 Time

40

50

60

(mm)

Fig. 2. Second-order plots (l/[HOI] vs. time) for the &sproportlonatlon of hypomdous acid at pH 8 as compared wth pH 10; “HOI” calculated from lodlde values at pH 8 usmg Eqn 7 (o), and HOI obtained by measunng its conversion to trnodlde at either (0) pH 8 or (0) pH 10. All data obtamed for total lodme concentration of 5 03 x 10m5 g-atoms 1-l.

faster at thts pH than at pH 8, a result consistent with that observed by Toth et al. [6] at the same temperature (25°C). Thts acceleration in the rate of disproportionation on raising the pH is presumably due to the fact that hydrogen ions are a product of the forward reaction. Thomas et al. [7] and Buxton and Sellers [17] also observed an increase in the rate of disproportionation with increasing pH, and the latter presented an expression for the rate constant in which a term is included contaming the hydroxyl ion concentration implicitly. However, on raising the pH to 11 or higher, the rate duninishes (results not shown), consistent with the deprotonation of HOI to form IO-, which, according to Paquette and Ford [18], occurs with a pK, of ca. 11 [17]. It is expected that the rate of disproportionation involving IO- ions would be reduced owing to the electrostatic repulsion of the two negatively charged species. Iodide-selectwe electrode measurements An electrode specific for iodide was used to measure iodide formation following the addition of various amounts of I, to buffer (pH 8). Samples were heated at 90 o C for 30 min prior to measurement in order to complete the reaction. The results presented m Fig. 3 demonstrate a linear relationship from 1 x 10e4 to 5 x lop6 M with a slope of

600

RO

TABLE

RAHN

2

Percentage of total iodine on gram-atom basis found as iodate following heatmg iodme solutions of various concentrations at 90°C for 30 mm Initial concentration of iodine (10-s M) 2 4 5 10

9.7 9.3 10 6 12.2 11

Average

10 5

1

lo-’

K

, ,, , , , , , , , ,

10-7

10-s

10-s

Percentage as iodate

10.'

Concentratron of lnltlal lodme (gram atoms per liter) Fig. 3. FormatIon of iodide as a function of centration of iodme as determined either with tive electrode (D), average of three samples heatmg to 90 o C for 30 mm, or by by LC-EC three samples measured without heatmg

the mmal conan iodide-selecmeasured after (o), average of

0.83, consistent with the predicted stoichiometry. The time dependence of the formation of iodide from iodine at 25 o C was followed using the probe

100

r

90

d

80

-

b

z ; 70

+A

g -80

; 50 a

E 40

8 $ 30

:$ , , 0

5

, ,

10 15 Time (mm)

20

,

and the results are shown m Fig. 4. Immediately following the addition of molecular iodine to the buffer solution, the initial iodide concentration as measured with the probe is 25-308 of the initial iodine instead of the expected 50% consistent with Eqn. 2. It is speculated that the presence of HOI interferes with the electrode measurement because HOI is the only other species present at t = 0. {Thomas et al. [7] obtained a similar result which they interpreted, however, in terms of the hydrolysis of I, (Eqn. 2) at this pH being incomplete.} Using the electrode to measure iodide in the presence of HOI, therefore, gives an apparent reading of I- which appears to be less than the true value except at the end of the disproportionation reaction when HOI is zero. As shown m Fig. 4, the rate of apparent Iformation as measured with the probe is enhanced by the presence of EDTA such that the yield of iodide reaches a plateau within 30 mm at 25°C. Also shown in Fig. 4 is the acceleration of the rate of disproportionation on raismg the pH from 8 to 10, consistent with the results obtained spectrophotometrically.

25

Fig. 4 Time course for iodide formation as measured with an todide-selective electrode following the addition of 50 ~1 of molecular todme (1 03 X lo-’ M) to 2 ml of the followmg solutions (a) borate buffer pH 8; (b) same as (a) except 4 pl of 05 M EDTA added; (c) same as (a) except 30 ~1 of concentrated NaOH added to raise the pH to 10; (d) LC mobile phase, such that the total concentration of iodine is 5 03 x 10e5 g-atom 1-l Data are presented as a percentage of initial iodine although this is an apparent percentage because the electrode is affected by HOI present to reduce observed readings

Ion-pairing IL Solutions of iodine m buffer (pH 8) were analyzed by ion-pair LC and the peak correspondmg to iodide was measured using either UV detection at 226 nm or electrochemical detection. Six different samples, all having an imtial iodine concentration of 5.02 X lop5 M, were heated at 90 o C for 30 mm and the iodide concentration was determined from a calibration graph. The average

DETERMINATION

OF IODIDE

IN AQUEOUS

SOLUTION

100 r

601

Assistance m some of the early stages of this work was provided by Blake Otwell and Trish Harris. Support of this research by NC1 Grant R01 CA43847 is gratefully acknowledged.

APPENDIX:

ol

/

0

20

I

I

I

40

I

_/

1

60

Time (min) Fig. 5. Tune course of lodlde formatIon as measured by LC-IzC (---•---) followmg addition of 50 ~1 of Iodine (1.03 x 10e3 M) to 2 ml of borate buffer (pH 8, 0 23 M). The area under the peak was used as a measure of the concentration The sohd curve corresponds to the absorbance changes observed for the same solution as measured at 226 nm

proportion of iodine converted to iodide as determined by either LC-UV or LCEC was 83 + 3%, consistent with the expected stoichiometry. The LC-EC results as plotted in Fig. 3 fit a straight line with a slope of 0.83 over a concentration range from lo-’ to 10. 4 M. The time dependence for the disproportionation of HOI to iodide at 25 o C as measured using electrochemical detection is shown m Fig. 5. As demonstrated previously using the ion-selective electrode (Fig. 4), the presence of the ion-pairing mobile phase catalyzes the rate of disproportionation such that a maximum yield of 83% is reached withm lo-20 min or less. Both phosphate and EDTA are present m the mobile phase and are likely candidates for enhancing thts reaction. It is clear that the final Iodide yields resultmg from the hydrolysis of I, 1. J subsequent disproportionation of HOI are cc.,rsistent with the predicted stoichiometry independent of the method of measurement. However, it is concluded from the standpoint of sensltivlty and reproducibility that the LC-EC method is the most suitable for making these types of measurements. Application of this methodology to the analysis of the photochemistry of halogenated pyrunidmes is m progress.

DERIVATION

OF EQN

7

If the initial concentratton of I, on a gram-atom basis is denoted by [I,],, and if I, undergoes complete hydrolysis in accordance with Eqn. 2, then the sum of the concentrations of the reaction products at any time following the rapid hydrolysis step 1s given by [I,],

= [I-l

+ [HOI] + [IO;]

(Al)

or [HOI] = [I,],

- [I-]

- [IO;]

(A2)

where [I,], is a constant and [II] is the experimentally determined iodide concentration. From Eqn 3 it is seen that during disproportionatron 2 mol of iodide are formed per mole of iodate. Based on this relationship, [IO;]

= 1/2[II],

(A3)

where [I-Id 1s the concentration of iodide attributed to disproportionation. If the total amount of iodide [I-] is given by the sum

11-I= [IPlil+ r1,

(A4)

where [IIlh is the concentration of iodide attributed to hydrolysis, then Eqn. A3 can be written as [IO,]

= l/2{

[1-l - rid

(A9

Accordmg to Eqn. 2,

(Ah)

[IPlil= MJ/2 which allows Eqn. A5 to be rewritten as [IO,]

=

1/N-1 - M”P)

Substitutmg A2 gtves [HOI] = [IJo

this expression - [II]

= 5/4[1,]

(A7) for [IO,]

- 1/2[II]

- 3,‘2[II]

into Eqn.

+ 1,‘4[1,], (A81

602

RO

Note added in proof

The lower than expected yields of iodate reported here (11 + 2%) can be explained by the presence of 2.5% ethanol m the reaction mixture, a consequence of using a stock solution of iodine in ethanol to prepare the reaction mixtures. It has been found that ethanol suppresses iodate formation such that the yield is less than 6% in the presence of 16% ethanol. In contrast, the addition of iodine crystals directly to aqueous buffer results in the iodate yield reaching the expected limit of 17 * 1%.

REFERENCES S Y. Wang, m S.Y Wang (Ed ), Photochemrstry and Photobiology of Nuclac Actds, Vol I, Academtc Press, New York, 1976, p. 295 R 0 Rahn and R.S. Stafford, Photochem. Photobtol, 30 (1979) 449. RO. Rahn and H G. Selhn, Photochem Photoblol, 35 (1982) 459. M. Eigen and K Kustm, J Am. Chem. Sot, 84 (1962) 1355

RAHN

5 DA Palmer and R. van Eldtk, Inorg. Chem, 25 (1986) 928. 6 L M. Toth, K.D Pannell and 0 L. Irkland, Oak Ridge National Laboratory/Techmcal Memorandum NUREG/ CR-3514 ORNL/TM-8664, Dtvlsion of Techmcal Informatron and Document Control, US Nuclear Regulatory Commtsston, Washmgton, DC, 1984. 7 T.R Thomas, D.T Pence and RA Hasty, J Inorg. Nucl Chem., 42 (1980) 183. 8 R.N Reeve, J Chromatogr., 177 (1979) 393 9 W.J Hurst, J.W. Stefovtc and W.J. White, J. Chromatogr, 7 (1984) 2021. 10 K. Han, W.F Koch and K W Pratt, Anal. Chem., 59 (1987) 731 11 M Lookabaugh, I S KruII and W.R LaCourse, J Chromatogr , 387 (1987) 301 12 A.D Awtrey and R.E. Conmck, J Am. Chem. Sot., 73 (1951) 1842. 13 S. Dushman, J. Phys Chem., 8 (1904) 453 14 A. Habersbergerova, Radtochem RadIoanal Lett , 28 (1977) 439-444 15 KC Seal, J Indtan Chem Sac , 36 (1961) 811. 16 J C. Wren, J. Paquette, S Sunder and B.L. Ford, Can. J. Chem., 64 (1986) 2284 17 G V Buxton and R M Sellers, J Chem Sot., Faraday Trans. 1, 81 (1985) 449 18 J Paquette and B.L. Ford, Can J Chem , 63 (1985) 2444