PINSTECH/HPD-142

ICP-MS as advantageous analytical technique for the determination of long-lived "Tc in the environment.

HEALTH PHYSICS DIVISION Pakistan Institute of Nuclear Science and Technology

Nilore, Islamabad. December, 1992

PINSTECH/HPD-142

ICP-MS as advantageous analytical technique for the determination of long-lived "TC in the environment.

IHSANULLAH

HEALTH PHYSICS DIVISION

Pakistan Institue of Nuclear Science and Technology

Nilore, Islamabad.

December, 1992

CONTENTS

ABSTRACT

1. INTRODUCTION

2. TECHNETIUM-99

2.1 SOURCES OF T c

22 IMPORTANCE OF T c IN THE ENVIRONMENT

23 ENVIRONMENTAL CHEMISTRY OF Tc

3. DOSES OF T c

4. ANALYTICAL TECHNIQUES

5. INDUCTIVELY COUPLED PLASMA

MASS-SPECTROMETRY (ICP-MS)

5.1 PLASMA

5.2 PRINCIPLE OF ICP-MS17

5.3 APPLICATIONS OF ICP-MS

5.4 ANALYSIS OF T c BY ICP-MS

5.5 INTERCOMPARISON STUDIES BY ICP-MS

5.6 ELECTROTHERMAL VAPORIZATION (ETV)

REFERENCES

TABLES

FIGURES

ABSTRACT

Technetium (Tc) was the first artificially created by man and has no stable isotope. The most crucial

technetium isotope environmentally, "Tc, is a pure beta emitter with a half-life of 2.1 X 10* years. The

main source of "Tc to the environment is the disposal of liquid wastes from nuclear installations or

during separation and recovery of spent nuclear fuels. Because of its long half-life, high fission yield,

mobility and current interest in the collective long-term doses, it is necessary to establish a knowledge

of the behaviour of "Tc in the environment for complete assessment of the impact of nuclear industry.

Due to various analytical difficulties however, data on the behaviour of Tc in the environment are

limited. In the literature, many techniques are reported for the analysis of Tc. A very sensitive, precise

and powerful technique is required which can be applied to environmental samples in order to gain

information by obtaining more precise data to assess the impact of Tc releases on man. Attention has

been focussed for this purpose on a new powerful technique i.e. inductively coupled plasma mass

spectrometry (ICP-MS).

This report has been directed towards the development of ICP-MS. The technique gives a very high

sensitivity enabling long-lived radionuclides including ̂ Tc to be measured directly down to pg ml'1 levels

in solutions. Because of its versatility ICP-MS is finding applications for trace multielement analysis and

low detection limits in almost all fields.

1. INTRODUCTION

Monitoring radioactivity for safe operation of nuclear facilities involves measurement of many

radionuclides especially those which are long-lived. The fate of long-lived radionuclides released from

nuclear installations is of radiological interest because of the possibility of eventual intake by man long

after discharges may have ceased. The measurement of environmental samples provides essential

information for radiological assessments as to quantity and the behaviour of the radionuclide in question.

Desmet and Myttenaere (1986) acknowledged that our knowledge of the environmental behaviour of

Tc is at an immature stage, lagging behind knowledge of other, chemically more predictable,

radionuclides (such as caesium). Investigations of the behaviour of "Tc in the environment arc essential

for a comprehensive assessment of the environmentat impact of the nuclear fuel cycle. The increasing

use of the element as " T c in nuclear medicine has resulted in many gaps in Tc chemistry being filled.

Clearly, hitherto there was no means of obtaining this information as Tc was not readily available since

it has no stable isotopes. In general, very sensitive analytical techniques are required for comprehensive

investigations because of low environmental concentrations.

2. TECHNETIUM-99

The element with atomic number 43 was the first artificially produced by man and was given the name

technetium (from the Greek word, technetos) meaning artificial (Pcrricr & Scgrc 1937 & 1947). There

are twen:y-one radioactive isotopes and seven isomers. Among the long-lived isotopes i.e. "Tc(ti/j = 2.6

x 10s y),"Tc(ti/? = 4.2 x 10* y) and Tc(ti/j = 2.1 x 10s y), only "Tc is a fission product with 6.06% yield

and most important isotope environmentally with specific activity 630 kBq mg'1 (Rioscco, 1987, Long &

Sparkcs, 1988 and Robb, 1983).

2

" T c is an ideal radionuclide for diagnostic purposes as it

- has a short half-life (6 hrs)

- is a pure gamma emitter (140 keV)

- is convenient for clinical use

- gives minimum radiation dose to the patient

- has high detection efficiency by scintillation counting

- has different compounds to allow different compounds to be

targeted

• commercially available in the form of "Mo generators

A high proportion (85 %) of the "Mo decays via the metastable nuclide **Tc and then to the ground

state "Tc (Keller, 19S9):

-YdtO keV),

2.1x105y

V 6 - 0 h

99m!

2.1. SOURCES OF T c

T c has principally been introduced into the environment as waste discharge from nuclear reprocessing

facilities and from previous nuclear atmospheric detonation tests. A minor source is th" use of the

isomer W n T c in medicine which rapidly decays to the ground stale. Since 1945, thousands of kilograms

of "Tc have been produced artificially ns a result of worldwide nuclear power programmes. Naturally,

3

"ft: is produced i: ry small quantities by the fission of actinides.

Technetium discharges occur during the following steps of the nuclear fuel cycle:

- reactor operation

- nuclear fuel reprocessing

- conversion of recy d uranium into UF4

- enrichment of recycled uranium

- fuel fabrication

- waste treatment

Several nuclear fuel reprocessing plants discharge mixed products to the sea at coastal locations in

Western Europe and constitute significant sources of "Tc. The principal source of discharged fission

products in the UK is the reprocessing plant at Sellafield which discharges to the Irish sea (Hunt, 1978-

1989). Low-level radioactive wastes from Dounreay Nuclear Power Development Establishment

(DNPDE) are discharged to the Pentland Firth. The scale of reprocessing and other activities on 'he

site results in levels of discharges to the sea which are considerably smaller than those from Sellaficld.

The releases of *Tc in liquid effluent from the enrichment plant at Capenhurst (UK) are less in

comparison with reprocessing discharges by a factor of 1000 (Camplin & Aarkrog, 1989). Technetium

discharges in liquid effluents from the Sellafield and Capenhurst plants are shown in Table 1. The

French reprocessing plant at Cap de la Hague released 11.7 TBq into the sea in 1983. The quantity of

*Tc over a six month sampling period (September 1983 - March 1984) in the distillate discharged from

the evaporator of the German reprocessing plant at Karlsruhe was 2.5 X 10s Bq. In the reprocessing off-

gas, concentrations of up to 0.3 Bq m'3 have been detected (Luykx, 1986).

The liquid wastes containing "̂ Tc generated by reprocessing plants and other activities at the sites arc

released to the aquatic environment. Examples of discharges are those from Sellaficld to the Irish sea,

4

from Dounrey to the Penlland Firth and liquid effluents from Cap de la Hague to the English Channel.

Mackenzie and Scott (1984) have reviewed the quantities and composition of low level liquid radioactive

waste discharged to the marine environment.

22. IMPORTANCE OF "Tc IN THE ENVIRONMENT

Interest in "Tc from an environmental point of view stems from its high fission yield, its long half life

and its high solubility and mobility in nature tRioscco, 87 and Long & Sparkcs, 1988). **Tc releases to

the atmosphere are discussed by Till ct al, (1978). Kirchner (1990) has recently developed a new hazard

index, on the basis of a discussion of the advantages and limitations of hazard calculations of nuclear

waste. He concluded that T c will be a most significant component of high-level radioactive waste at

the 105 year post-disposal time point.

Ths effect of Tc in the environment are largely controlled by its source, chemistry and biological

interactions. The behaviour of Tc in terrestrial and aquatic environments were reported in a symposium

held 5-10 May 1986 in Seattle to compile the latest results. These results are published in a special issue

of Health Physics Vol. 57(2), 1989.

23. ENVIRONMENTAL CHEMISTRY OF Tc

Technetium exists in the valency states (C), (II), (HI), (IV), (V), (VI) and (VH) in aqueous solutions.

Of these only Tc (II) is stable in the form of a complex. Under oxidizing conditions, Tc (VII) as the

pertechnetate ion, Tc0'4, is the dominanl oxidation state in the absence of complcxing agcnls (Sparkcs

& Long, 1988).

5

The pertechnetate represents the most likely soluble form of this radioelcment and is considered to be

the major Tc species in low level liquid effluent from fuel reprocessing installations (Beasley Sc. Lorz,

1986). The pertechnetate ion is considered to be the most stable chemical form in the em-ironment over

a wide range of both pH and Eh (Figure 1).

3.DOSESOF*Tc

As increasing presence of "Tc in the environment is foreseen, hence its contribution has therefore to

be taken into account in calculations of (he future long-term collective dose to the population.

The major pathways by which Tc can be taken in by man are via drinking water, fish, food crops, egg,

milk and meat and the air (inhalation). Technetium is assumed to be uniformly distributed throughout

all organs and tissues of the body other than the thyroid, stomach wall and liver (Hoffman et al, 1984

and Garcia-Leon & Madvirga, 1985). To assess the dose to man from releases of "Tc into a small river,

the major pathways of exposure to man identified by Zeevcrt et al. (1989) are demonstrated

diagrammatically in Figure 2. For "Tc, the external irradiation hazard is not taken into account since

it leads to a negligible dose, because of the weak beta particle of 0.292 MeV emitted by this isotope.

Zeevert et al. (1989) summarized the biospheric transfer parameters to which the first year doses were

the most sensitive, the committed dose equivalent are given in Table 2. The estimated doses to the

critical group from marine pathways in recent years are shown in Table 3. The committed effective dose

equivalent rate (from 1983 to 1986) was 6.6 X10 2 Sv / ' as a result of "Tc discharge of 1.2 X 10" Bq

y' to a local critical group near Cap de la Hague. A routine liquid discharge of 4.54 X 10'° Bq y' will

lead to 5 j&v y> to individuals (Campiin & Aarkrog, 1989).

6

Technetium is uniformly distributed tbroughout all organs and tissues of the body other than thyroid,

stomach wall and liver. *Tc is classified into toxicity group III by International Atomic Energy Agency,

(IAEA, 1985a). The derived air concentration (DAC) n obtained by dividing the annual limit of intake

(ALT) by the air breathed:

DAC * AU/2.4 X It? Bq m *

The ICRP (International Commission on Radiological Protection) Task Group on Lung Dynamics

assigned oxides, hydroxides, halides and nitrates of Tc to inhalation class W and all other compounds

of the element to inhalation class D. The ALI (Bq) and the DAC Bq m' for "Tc are as follows (ICRP,

1975, ICRP, 1983):

Inhalation

Class D Class W

ALI 2 X10* 2 X10 7

DAC 8 X10 4 1X10*

4. ANALYTICAL TECHNIQUES

Various physical and chemical properties of technetium such as its ̂ -radioactivity, complex iormation;

absorption bands of X-rays and UV and IR light; mass to charge ratio etc, can be used for its

qualitative, as well as its quantitative analysis. Many papers and reports (Kotego et al., 1968; Lavrukhina

& Pozdnyakov, 1970 ; Robb, 1983 and Long & Sparkes, 1988) reviewed the available methods.

7

In general, the different techniques can be arranged in the following order of sensitivity:

Method Wt. or Tc nu;isur.>!>kfg)

1. X-rays fluorescence 1 0 5

2. Gravimetry/classical NT*

3 Infra-red spectrometry 10"

4. Spectrophotometry 10 - i t ) 7

5. Emission spectrometry 10"*

6. Polarography KT'-IO*

7. Atomic absorption 10 4 -i() '

8. Radiomctry (^-counting) ifr*

9. Mass spectromefy 10 w -10 '"

10. Response mrltiplioton l(r"-l(r' 2

ionization MS

11. Neutron activation 10 "iff 1 3

12. ICP-MS 10 "

13. ICP-MS-ETV 10"-10"

In literati;; c, classical and el'-mical .'.:.'!' Js are descried in enr!v work on Tc for its determination

while more recently physical and instrumental techniques have become available and have proved

suitable for (he analysis of Tc.

The determination of the mass abwdancc of hng-Iivcd radionuclides, such as a 7 Np, ""Pu, ""Pu, M U ,

" H i z,*Th, I W I and T c , have some advantage in sensitivity over conventional radiometric methods of

analysis according (o f fatverson, 1934 .ind Hislop cl a!. 1987. In conventional radiometric methods, the

8

main interference is the presence of similar decay products in impure samples. ICP-MS is claimed to

be less susceptible to spectral interferences than inductively coupled plasma optical emission

spectrometry (1CP-OES) and certainly in the present work no problem was encountered.

Although the neutron activation method has been developed to determine T c in environmental

samples, there are still some problems which make the measurement of the short-lived > wTc (15.8 s)

difficult in the case of (n,y) reaction, and the detection limit (10* g) is rather poor when using the (n,n')

reaction which gives ""Tc (Robb et al., 1985 and Kim et al., 1989).

In mass spectrometry (MS) charged particles consisting of the parent ion and ionic fragments of the

original molecule are produced and passed through magnetic and electric fields, where they arc

separated according to their mass/charge ratio. A mass spectrum can be detected after separation and

provides a record of the number of different ions characteristic of individual elements or compounds.

MS can be used for stable isotopes across the mass range and can also be applied for some long-lived

radio-isotopes which have sufficient numbers of atoms available for detection. The new technique of

1CP-MS can achieve sufficient sensitivity for determination of U, Pu, Th and **Tc etc.

A large number of different mass-spectrometric devices are available for the determination of suitably

long-lived radionuclides (Hursthouse, 1990). They include thermal ionization mass spectrometry (TIMS),

resonance ionization mass spectrometry (RIMS), spark source mass spectrometry (SSMS), microwave

induced plasma mass spectrometry (MIP-MS), glow discharge mass spectrometry (GDMS) and ICP-MS,

with important implications for the long-li/ed nuclides. The main advantage of the ICP-MS over other

mass spectrometric methods is that its ior. source operates outside the vacuum system, enormously

simplifying sample introduction and eliminating interference from species characteristic of the vacuum

system (VG Isotopes, 1987). A future development, which holds great potential for radionuclide studies,

is the use of microwave induced plasma(MlP)-MS, glow discharge sourcc(GDS)-MS and electrothermal

9

vaporization(ETV)-MS.

ICP-MS was used along with ICP-OES, ion exchange/liquid scintillation counting (IEX/LSC) and

graphite furnace atomic absorption spectrometry (GFAAS) for direct measurement of *Tc in aqueous

samples. ICP-MS is considered to be the most sensitive of these four techniques, having the potential

to detect Tc below 0.1 ppb (Brown et at., 1985).

The precise and accurate measurements of trace elements in different materials are essential. In this

regard, a rapid, versatile and sensitive tool such as ICP-MS is an ideal analytical technique for such

studies. Gray & Date (1983) compared ICP-MS, inductively coupled plasma-atomic emission

spectrometry (ICP-AES) and flame atomic absorption spectrometry (FAAS) for detection limits and

concluded that ICP-MS has very low detection limits for most of the elements.

The limit of detection (LOD) achieved by ICP-MS in ng g'J (6a blank) for various elements are

compared to in Table 3 with other widely used techniques (Date & Gray, 1989). FAAS shows good

LOD but for a limited number of elements. While ICP-AES has excellent detection for only light

elements and is less effective for heavy elements i.e. Pb and U. Another precise method such as X-ray

fluorescence (XRF) has determination limit poorer to that of ICP-MS. Tool et al. (1990a) used ICP-MS

along with alpha spectrometry and found ICP-MS has very low LOD. The ICP-MS exhibits excellent

detection limits over the complete Periodic Table. Further, the lin.its mentioned here for ICP-MS may

be improved in future.

5. INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (ICP-MS) •

The original concept of inductively coupled plasma-mass spectrometry (ICP-MS) developed from a

requirement, expressed in 1970, for the next generation of multielement instrument systems to follow

the rapidly developing technique of ICP-AES. After a survey of available and emerging techniques,

10

including atomic fluorescence spectrometry (AFS), instrumental neutron activation analysis (INAA),

atomic absorption spectrometry (AAS) and XRF, the conclusion made by Date and Gray (1989) was

that atomic mass spectrometry was the only basic spectrometry technique that had the potential for

the wide element coverage, clement specificity and relatively uniform sensitivity for almost all the

elements of the periodic table tc provide a good successor to the powerful tool that ICP-AES was

promising to become.

Since the ICP-MS technique is based on the measurement of the mass of an element, any interferences

must be eliminated as far as possible. For "Tc, two isobaric nuclides are important. "Mo is a radioactive

nuclide which decays with a half-life of 67 hours and which after few days will have gone. The other

isobaric nuclide is wRu. wRu is stable and 12.7% abundant in natural ruthenium and so will interfere.

The average amount of Ru in crustal rocks is 10 ppb (Masson & Moore, 1982), whereas the levels of

**Tc in most of the environmental samples is only just above the LOD (0.004 ppb), therefore, samples

have to be decontaminated from Ru before analysis. Some workers have used the wRu/'°'Ru and

w Ru/ I M Ru ratios for the elimination of "Ru (Bullivant ct al. 1990) but these ratios are not constant at

low concentrations, hence this method can not be applied for eliminating the Ru contribution to the T c

peak.

5.1. PLASMA

The use of an atmospheric pressure plasma as an ion source for atomic mass spectrometry is an

attractive concept, not least because of (he ease and rapidity of sample introduction and exchange,

normally a difficult and restricting aspect of inorganic mass analysis. When an ICP is used as the plasma

it offers the additional possibility of high sensitivity and freedom from matrix and intcr-clcmental effects,

making the ICP a useful source.

11

Inorganic samples, in the form of simple molecules, requl.c complete vaporization and dissociation

before 'heir constituent atoms can be ionized for mass analysis. Relatively large amounts of energy arc

thus required to bring inorganic samples into a suitable state of ionization. The most difficult part of

the process is the initial volatilization and dissociation of the sample, after which ionization is easy. A

clue to the solution to this problem was presented during a seminar in iManchester at which ion

extraction from flames and plasmas, at gas pressures up to atmospheric, was described. "It was realized

that although a chemical flame, at a gas temperature of up to 3000*K, was probably not hot enough for

most material, and constituted an undesirably reactive environment, the atmospheric pressure arcs and

plasmas then being explored as atomic emission sources were almost certainly much more suitable"

(Date & Gray, 1989). In plasmas operating at atmospheric pressure, gas temperatures of 50OO*K or

more were achieved and, because of the relatively long dwell time of a few milliseconds, energy transfer

to the sample was very efficient as it attained equilibrium with the plasma gas (Alkemadc, 1973 and

Date & Gray, 1989).

5.2. PRINCIPLE OF ICP-MS

ICP-MS consists of two techniques, an ICP for ion generation and a quadrupolc mass analyzer for the

separation and detection of these ions. "Samples are introduced into the central channel of the plasma

as a finely dispersed mist, which is rapidly dissolved and vaporized. Dissociation is virtually complete

during transit through the plasma core and elements with a first ionization energy of less than 10 cv,

are fully ionized. Ions are extracted from the central channel of the plasma through a sampling apsrture

into the quadrnpole mass analyzer, where they are separated on the basis of their mass-to-charge ratio

prior to detection by an electron multiplier. These pulses arc amplified, accumulated in a high capacity

multi-channel analyzer and then subsequently processed by a powerful microcomputer" (VG Isotopes,

1937).

12

The operation and the advantages of ICP-MS arc discussed by Fasscl (1977) and Boumans (1978).

Figure 3 shows the schematic diagram of the VG PlasmaQuad used for the determination of T c . It can

be divided into four sections: (i) sample introduction, (ii) ICP torch/ion gcnera'or, (iii) plasma/mass

spectrometer interface and (iv) quadrupolc mass analyzer.

S3. APPLICATIONS OF ICP-MS

Many features which make ICP-MS an attractive instrument for trace element studies arc discussed

(Date & Gray, 1989 and Gray & Date, 1983). Date & Gray (1989) reviewed in detail the applications

of ICP-MS in various fields i.e. earth sciences, food sciences, water rcourccs, petroleum and

metallurgical industries and environmental analyses. Many workers this technique in biomedical studies

(Lyon et al. 1988, Lyon, 1990, Tothil rt al. 1990). The ICP-MS was used for trace elements analysis in

natural water, ground water, drinking water and in wastes (Hcnshaw ct al. 1989, dc Boer et al. 1990 and

Tool et al. 1990b). Dale (1990) and Yamasaki & Tsumura (1990) applied it for the determination of

mercury in marine biota and trace elements in plant tissues respectively. Tool et al. (1990a) used ICP-

MS for (he determination of actinides in environmental samples.

5.4. ANALYSIS OF "Tc BY ICP-MS

High temperature plasmas have recently been recognized as a sensitive source for emission

spectrometry. In order to avoid the lengthy route (i.e. extraction, precipitation, prior to ^-counting),

Brown and Pickford (1984) found that inductively coupled plasma optical emission spectrometry (ICP-

OES) could be applied to the determination of Tc in aqueous solution down to 4 ppb (4 ng ml'). The

determination of Tc was investigated by Karnowski (1981) in an assessment of the ICP for nuclear fuel

analysis and a detection limit of 20 ppb was achieved (Long & Sparkcs, 1987). Long et al. (1987) used

the relatively new technique of ICP-MS for the determination of Tc in environmental samples. A

13

detection limit of 10-20 ppt (10-20pg ml"1) was quoted (Long & Sparkes 1987).

Kim et al. (1989) applied ICP-MS to the determination of *Tc in soil samples. A detection limit of 3.2

ppt (3.2 pg ml"') was reported. Nicholson et al. (1990) used ICP-MS for soil samples with a detection

limit of 0.01 ppb, while Bullivant et al. (1990) used ICP-MS for the determination of T c in Springficlds

effluent. A detection limit of 0.006 ppb was obtained. The Springfields effluent arose from two sources.

Firstly, the disposal of washings from the decommissioning of the gaseous diffusion plant at Capenhurst

and secondly, the handling of reprocessed uranium from the Sellaficld plant A comprehensive

radiochemical method has been developed for T c which can be applied to all types of low level samples

as a preparation for ICP-MS analysis (Ihsanullah & East, 1991a).

The authorized discharges to the Irish sea of artificial radionuclides including "Tc, from the nuclear

facilities provides a unique opportunity to study the behaviour of "Tc in the marine environment.

Particular attention was given to the marine ecosystems, where different samples from the coast of the

Irish sea extending towards the North sea and a silt sample from Ravenglass (Figure 4) were collected

and analyzed for the determination of "Tc using iCP-MS. Due to the significance of the Chernobyl

accident as a source of environmental pollution, terrestrial samples from a site known as "the Forest of

Miracles", 1 km to the east of the damaged reactor were also collected for analysis by ICP-MS. The

results obtained for the determination of "Tc in these samples are given in Table 4 (Ihsanullah & East,

1991b). Due to continuous growth and death of plants and changes in the chemical states of the

radionuclide in question, Tc might have been transported from the samples. Another reason was that

very snail quantities of each sample were available for analysis. A factor which might explain the

Unavailability to observe Tc in the Porphyra is that Porphyra is not a good bioindicalor compared lo

other species. The level of Tc concentration in water sample was below detection limit due to the low

specific radioactivity and the distance (about 700 km) from Scllaficld.

14

In conclusion, this review shows the applicability of the ICP-MS method to "Tc analysis in seaweeds and

other media. The new technique of ICP-MS offers significant advances and advantages over previous

methods for the measurement of this radionuclide. The long radioactive half-life of T c means that its

direct measurement is possible by ICP-MS because of the very high sensitivity of the technique. Thus

ICP-MS measurements of **Tc are based on the direct detection of its atoms rather than the

measurements of its radioactivity. Along with superior sensitivity, ICP-MS takes less time for analysis

and offers potentially very low limits of detection compared with other techniques.

5.5.INTERCOMPARISON STUDIES BY ICP-MS.

In a study two intercompari&on algal (Fucus vesiculosus) materials were analyzed by ICP-MS

(Ihsanuilah, 1991). The results obtained for IAEA marine alga sample (IAEA, 1985b) along with the

certified values of other are given in Table 5. The results for the second reference material (Bates, 1988)

obtained are compared with the results reported using other techniniques in Table 6. Ridout et al,

(1988) determined various trace elements in a marine reference material for Lobster hepatopancreas

(TORT-1) using ICP-MS.

5.6. ELECTROTHERMAL VAPORIZATION (ETV)

In principle, any method developed for use with ICP-AES may be transferred with little change to ICP-

MS. For exampJe ETV has been used in ICP-AES for many years but since the majority of AES users

had scanning monochromators rather than multichannel polychromators, ETV was largely considered

to be a single element technique (Date & Gray, 1989). The most exciting feature of the ETV-1CP-MS

combination is that multielement analysis can be carried out.

15

The new sample introduction system for ICP-MS the electrothermal vaporization (ETV) furnace, will

probably be extremely useful to improve the performance of the system as it could offer an increase of

up to 100 times in sensitivity. Recently an ETV unit was installed at the SURRC but was not used for

the determination of **Tc in the present study. Because of the improved sensitivity much lower limits

down to concentrations of, for example, sub ppt levels should be possible and much smaller sample

volumes (SO *d) adequate for analysis. The ETV has already found some applications in the Held (2nd

International Conference on Plasma Source Mass Spectrometry, University of Durham, UK.,Septembcr,

1990). However the ICP-MS and ETV-ICP-MS techniques have just become available commercially, and

work continues to assess the reliability of measurement with these techniques.

The principle of operation is that 10-100 jd sample solutions are injected into the graphite furnace. The

furnace is then sealed with a carbon rod and is resistively heated in three steps as follows:

a) 75*C for 2 min to evaporate water from the sample

b) 350'C for 1 min to ash organics in the sample

c) and then to 2850*C in 5 seconds to vaporize the residual

trace elements.

The vaporized trace elements are rapidly transported from the furnace to the plasma where they are

atomized, ionized and detected by the mass spectrometer (Gray & Date, 1983; Gray, 1986; Date et al,

1987; Park & Hall, 1988; Park et al, 1987 and Gregoirc, 1988).

The advantages of the ETV method include: high sensitivity; ability to analyze small samples; solid and

liquid : Tiples can be introduced; multielement and isotope ratio measurements can be made; and a

high sample throughput is possible.

16

Because the furnace allows volatile matrices to be evaporated and ashed from the sample, this can help

to overcome isobaric molecular interferences and improve limits of detection. In general a 100-1000

times improvement in L.O.D is achieved by ETV over nebulization. These improvements arc achieved

because the water and organic matrix, which would cool the plasma, is removed during the drying and

ashing stages and the analyte enters the plasma as a concentrated plug. Due to its versatile features,

ETV is being applied in numerous areas like ICP-MS.

17

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Bates, T.H. (1988). An intercomparison exercise on technetium-99 in seaweed. Envron. Int. 14,283-288.

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Bullivant, D.P., John, M. & Makinson, P.R. (1990). A preliminary investigation into the determination of **Tc and B 7 Np in Simulated Springfields Effluent: A comparison of LSC and ICP-MS techniques. 2nd Int. Conf. on "Plasma Source Mass Spectrometry", Durham.

Camplin, W.C. & Aarkrog, A. (1989). Radioactivity in north European waters. MAFF, Report No. 20, Lowestoft, 120p.

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18

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21

TabklrDisduigtsoT^cfronScllafieirartCa^^ BNFL report, 1989).

Year SeUafieid plaat Capeahnrst plaat

TBq GBq

1978 178.0 Ua 1979 433 122 1980 56.8 113 1981 5.8 63 1982 3.6 20.4 1983 4.4 3.4 1984 43 1985 1.9 1986 6.6 1987 3.6 1988 42

22

Table 2: Committed efTective dose equivalents from first year exposure of tin individual in routine release of T c (Zeevert et al., 1989).

Exposure pathway Dose equivalent Contribution (nSvGBq1 to total dose T c y ) (%)

Ingestion of: Drinking water 1.07 18 Fish 0.105 1.7 Grain 259 43 Green vegetables 0.174 2.9 Root crops 0.516 8.5

Milk contaminated by: -irrigation of pasture 0.885 -watering of cow 0324

Meat contaminated by: •irrigation of pasture 0.278 •watering of cow 0.101

Inhalation of air 0.015

Total 6.06

0.2

100

Table 3: Estimated doses from different sources. (Camplin & Aakrog, 1989).

Direct inputs into the marine environment

Annual individual effective dose equivalent (mSv)

Sellafield Dounreay Cap de la Hague other nuclear sites Solid waste disposal Chernobyl Fallout from weapons testing Naturally-occurring radiation

0.3-3.5 0.03 o.l 0.0001-0.3 0.00002 0.08 0.001-0.01 <2

23

Table 4: Concentration of "To in environmental samples using ICP-MS.

Sample Location Date of Drywt "1c activity sampling taken Bq g'(dry month/yr (gms) weight) ± S.D.

Fucus ColwynBay 9/89 24 0.74 ± 0.05 vesiculosus Ravenglass 10/89 25 10.18 ± 0.53

Whitehaven 10/89 23 1.98 ± 0.06 Sandyhill 10/89 24 1.78 ± 0.09 Ettrick Bay 4/90 25 0.49 ± 0.04 Tongue 4/90 24 0.14 ± 0.02 Aberdeen 4/90 25 0.10 ± 0.05

AscophyDum Ettrick Bay 4/90 20 1.06 ± 031 nodosum Porphyra Dounreay 7/90 5 < Z5 x 10* (Sloke) sat Ravenglass 11/86 30 0.025 ± 0.001 Moss ( Chernobyl' 10/89 1 < 12.6 x Iff3

Lichen 1« 10/89 0.2 < 6 3 . 0 x l 0 3

Water Tongue 3/90 15" < 17 Bq l1

(Forest of MLade) & " (litres).

Table 5: T c measurements in IAEA reference sample (AG-B-1).

Lab Code No. T c , mBq g., (no. of observations)

2 5 6 27 28

11.4 ± 0.5 (2) 11.1 ± 1.5 (5) 14.7 ± 0.2 (2) 13.3 ± 1.2 11.5 ± 1.5

Overall median of 2,5 & 6 results, Md 11.5

Confidence interval (« = 0.05) 11.1 -14.7

Present work: (Ihsanullah & East, 1991)

12.5 ± 1.5 (2)

24

Table 6: Intercomparison studies of T c in BNFL seaweeds.

Lab gms method *Tc taken

2 2 2 1

used Bq g-* ± a

1 , 2 3A

B

taken

2 2 2 1

L.S spectrometry L.S. spectrometry 0-counting Ga;,-f!ow Geiger

434 ± 031 4.42 ± 020 338 ± 0.25 4.60 2 0.43

4 5

1 2-3

counting 0-counting ICP-MS

4.99 ± 0.19 4.0

6 2-3 ICP-MS < 4.40

The overall mean (1-6 sa mples) = 4.64 ± 0.25

Present <0.1 ICP-MS 431 ± 0.45 work (IhsanuUah & East 1991)

25

1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH

Figure 1: Chemical forms of Tc over a wide range of Eh and pH.

26

WELL

RIVER

r FILTRATION DRINKING WATER I INGESTION

FOOD CROPS INGESTION

M

IRRIGATION T

r

SOIL]--

I PASTURE WA7EF!NG

SEDIMENT

EXTERNAL IRRADIATION

INHALATION

CATTLE x

1 HM

\ MILK INGESTION

MEAT INGESTION

•*; FISH INGESTION

EXTERNAL IRRADIATION

N

Figure 2: The possible pathways from a radionuclide's release into a freshwater system 'Zeevert et al, 1989).

27

Tvtyut:

Dounreay

North Sea

Sampling Sites * Discharge Sites

F igure 3 : Sampling s i t es (UK) ,

28

Quad. RF

0 ^ 1

bias voltage

>ol L 2 J —

Hl,Fi Quad. RF control

1 vac, pumps

PlasmaOuad control m.c.s.

ICP RF

oi_-| {j=r r w

computer

9»* control]

sample

Figure 4: The schematic diagram of the ICP-MS,

29

ICP-Mass Spectrometer (PlasmaQuad PQI.VG Elemental) installed at Scottish Univer­sities Research & Reactor Centre, East Kilbride, Glasgow, U.K.