sequential injection lab on valve

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Sequential injection lab-on-valve:the third generation of flowinjection analysisJianhua Wang, Elo Harald Hansen

Termed the third generation of flow-injection analysis, sequential injec-

tion (SI)-lab-on-valve (LOV) has specific advantages and allows novel,

unique applications not least as a versatile front end to a variety of

detection techniques. This review presents and discusses progress to date

of the SI-LOV approach as well as its applications in the automation andthe micro-miniaturization of on-line sample pre-treatment. Special

emphasis is placed on using SI-LOV in conjunction with bead injection

(BI) for on-line separation and pre-concentration of ultra-trace levels of

metals by exploiting the renewable micro-column approach. With detec-

tion by ETAAS and ICP-MS, it is shown, as illustrated by recent results in

the authors laboratory, that this methodology eliminates the problems

encountered in conventional on-line column pre-concentration systems,

improves the overall operational efficiency and yields the robustness

necessary for routine assays. Also discussed is the future potential of the

SI-LOV approach as a front end to various analytical protocols.

# 2003 Published by Elsevier Science B.V.

Keywords: Bead injection (BI); Electrothermal atomic absorption spectrometry(ETAAS); Inductively coupled plasma mass spectrometry (ICP-MS); Lab-on-valve

(LOV); Renewable micro-column; Separation and pre-concentration; Sequential

injection (SI)

1. Introduction

Appropriate sample pre-treatment prior

to analysis remains inevitably the bottle-

neck of the entire analytical procedure

with modern instrumentation [1,2].

Flow-injection analysis (FIA) has led tosignicant progress in this eld, not only

in terms of eciency, but also in relia-

bility, rapidity and robustness. Since its

introduction in 1975[3], this technique,

or rather analytical concept, has grown

into a discipline covered by a series of

monographs and more than 12,500 sci-

entic publications [4]. All this clearly

shows that in the past 27 years FIA has

grown almost exponentially. In fact, it

has been characterized as having gone

through three generations[5,6], that is:

(1) ow injection (FI); (2) sequential

injection (SI)[7]; and, (3) laboratory-on-

valve (lab-on-valve, LOV) [8].

The rst and the second generations ofow injection and their hyphenations

have played, and indeed continue to play,

important roles in the automation and

the miniaturization of on-line sample pre-

treatment, resulting in the acceleration of

analysis with considerable reductions in

sample/reagent consumption and waste

production [1,2,6,7]. However, even

more importantly, they have allowed

implementation of procedures that used

to be dicult or even not feasible by con-

ventional approaches [9].

It is especially noteworthy that these

rst two generations have been the main

tools for replacing labor-intensive man-

ual operations in various separation/pre-

concentration techniques through clever

on-line manipulations. However, in

reagent-limited assays, in handling

highly hazardous chemicals, or where

waste production is a critical parameter,

further downscaling of solution handling

is warranted [8]. In addition, the most

widely employed on-line, sample-proces-

sing approach (i.e., solid-phase extrac-tion (SPE) based on liquid^solid

interactions) is often impaired by the irre-

versible changes of the reactive surface of

the solid phase and/or the creation of ow

resistance in the packed reactor. In order

to overcome these drawbacks, the third

generation of ow injection techniques,

SI-LOV, was introduced [8]. The minia-

turized LOV system potentially oers

facilities to allow any kind of chemical

and physical processes, including uidic

Jianhua Wang,

Elo Harald Hansen*

Department of Chemistry,

Technical University of

Denmark, Building 207,

Kemitorvet, DK-2800

Kgs. Lyngby, Denmark

*Corresponding author.

Tel.:+45-4525-2346;

Fax:+45-4588-3136;

E-mail: [email protected]

Trends in Analytical Chemistry, Vol. 22, No. 4, 2003 Trends

0165-9936/03/$ - see front matter# 2003 Published by Elsevier Science B.V. doi:10.1016/S0165-9936(03)00401-1 225
http://-/?-


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and microcarrier bead control, homogenous reaction,

liquid-solid interaction and in-valve, real-time optical

detectionofvariousreactionprocesseswithopticalbers.

Although still in its infancy, SI-LOV has already

proved to be an attractive, eective front end to various

detection devices with micro-miniaturized sample pro-

cessing along with improved eciency and ruggedness.

The present review presents a brief outline of progress

in development of SI-LOV, with special emphasis on the

application of SI-LOV-bead injection (BI) to on-line

separation/pre-concentration of ultra-trace levels of

metals by means of the renewable micro-column con-

cept, as used in conjunction with detection by electro-

thermal atomic absorption spectrometry (ETAAS) and

inductively coupled plasma mass spectrometry

(ICP-MS).

2. Micro SI-LOV (SI-LOV) system

The rst LOV microsystem was a single, monolithic

fabricated Perspex component mounted atop a six-port

selection valve (hence the name lab-on-valve).

Designed to integrate all necessary laboratory facilities

for a variety of analytical schemes, it is made to include

connecting ports, working channels and a ow-

through cell. The conduits are situated in three layers

in order to facilitate as many uidic operations as

possible [8,10]. The central ow-through channel, via

which the other individual ports are connected, is used

to communicate with a syringe pump.

A multi-purpose ow cell, which is permanently

incorporatedinto port 2 (Fig. 1, close up), allows a series

of miniaturized uidic operations to be performed,

including in-valve sampledilution and reagent addition/

mixing, as well as incubation. The ow cell is furnished

with optical bers, communicating with an external

light source anda detection device to facilitate real-time

monitoring of the reactions taking place inside the cell.

The ow cell can also be congured as a jet-ring-cell,

to execute BI and real-time monitoring of the changes

in the optical properties of the beads after liquid-solid

interaction by means of absorbance, uorescence and/

or reectance spectroscopy.

This version of the LOV system is operated with

microliter and sub-microliter levels of sample and

reagents. Therefore, this approach is also known as the

micro sequential injection (mSI) protocol [8,11,12].

Fig. 1shows a typical mSI-LOV system with a close-up

of the multi-purpose ow cell congured for real-time

measurement of absorbance.

3. Applications ofSI-LOV system

The mSI-LOV system has been employed in a variety of

applications of micro-miniaturized in-valve uids and

micro-carrier beads, as well as appropriate in-valveinteractions followed by real-time detection. It has also

been used as a front end to capillary electrophoresis

(CE). Table 1 summarizes various applications of the

mSI-LOVto date.

In the mSI-LOV system, the multi-purpose ow cell

depictedin Fig.1 is employedto accommodatethe sample/

reagent zone and to facilitate real-time detection by

recording the absorbance (facing bers, as shown in

Fig.1)oruorescence(bersat90,notshownin Fig.1).

To increase the sensitivities for kinetically slow reac-

tions, selected segments of the sample zone can be mon-

itored by adopting the stopped ow technique. The

eectiveness of the stopped ow technique in mSI-LOV

systems has been illustrated in the determination of

phosphate[8,12], enzymatic assays[8], and monitor-

ing of ammonia, glycerol, glucose and free iron in fer-

mentation broths [11].

To carry out on-line measurement of nitrate and

nitrite, a cadmium reduction column can be incorpo-

rated into the LOV system to reduce nitrate to nitrite

before merging the stream of nitrite with chromogenic

reagents (sulfanilamide and N-(1-naphthyl)ethylene-

diamine) [12]. With a miniaturized column, an appro-

priate period of stopped ow of the sample zone in the

cadmium column is employed to increase the contacttime and thus improve reduction eciency.

In the mSI-BI-LOV mode, the ow cell is congured

into the jet-ring-cell approach, or more precisely an

adaptation of the renewable column concept, in order

to perform bioligand-interaction assays. In this case, an

appropriate suspension of beads is injected into the ow

cell, whereupon the beads are trapped and then per-

fused with analyte solution. Afterwards, the loaded

beads are exposed to various stimuli, and the (bio)-

chemical reactions taking place on the bead surface are

recorded in real time. This has been demonstrated by

Figure 1. Schematic diagram of a SI-LOV microsystem incorporating a

multi-purpose flow cell configured for real-time measurement of

absorbance (adapted from[11],with permission of The Royal Society of

Chemistry).

Trends Trends in Analytical Chemistry, Vol. 22, No. 4, 2003

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the bioligand-interaction assay of immunoglobulin

(IgG) on protein G immobilized Sepharose beads [8].Very recently, the mSI-LOV system was interfaced to

CE for anion separation. In this case, the multi-purpose

ow cell was recongured as a front end between the

mSI-LOV system and the CE system [13]. The micro-

uidic property of the mSI-LOV system not only provided

an ecient means of delivering sample to the CE system

with various sample-injection modes, including

electrokinetic, hydrodynamic and head column eld

amplication (HCFA) sample stacking, but also served

as a versatile means of sample pre-treatment to facil-

itate the ensuing CE separation.

4. Solving a dilemma

Column-based SPE is among the most ecient and

widely employed on-line separation/pre-concentration

techniques[6,14,15], and the interfacing of SPE with

detection by ETAAS and ICP-MS has received extensive

attention.

In conventional FI, on-line column, pre-concen-

tration systems, the column is used as a permanent

component. For reliable application, the break-through

capacity of the column, the extent of interfering eects

and the particle size of the sorbent material must becarefully balanced. Although smaller particle sizes

result in higher break-through capacities, ner parti-

cles tend to cause progressively tighter packing and

hence create ow resistance in the column. Moreover,

some sorbent materials undergo volume changes, i.e.,

swelling or shrinking, at dierent experimental condi-

tions, which make the situation even worse, not to

mention complicated [16].

Although some approaches to alleviate the ow resis-

tance have been quite successful, such as use of bi-

directional ows during loading and elution sequences

[16^18], it is very dicult to eliminate its adverse

eects completely. Besides, the deterioration of the ana-lytical results of an on-line column, pre-concentration

procedure may also be associated with the malfunction

of the reactive surface of the sorbent itself. This can be

attributed to contamination or deactivation of the sur-

face after processing a large number of samples, and/or

even the loss of some of the functional groups or active

sites present.

In this respect, a superb alternative for eliminating

anyproblems associated with the changes of the surface

properties of the sorbent materials and/or the creation

of ow resistance in a column reactor is a surface-

renewal scheme, i.e., the column is simply renewed or

replaced for each analytical run. The renewable-sur-

face concept, proposed by Ruzicka, has been well estab-

lished by using the jet-ring-cell in a variety of

(bio)chemical studies [19^21]. This concept is well

suited to on-line SPE separation/pre-concentration in a

LOV incorporating a miniaturized renewable column,

i.e., SI-BI-LOV [22].

5. The SI-BI-LOV system

This version of the LOV is fabricated using hard PVC

containing (1 + 6) channels and is mounted atop a6-port selection valve, as shown inFig. 2. Two of the

channels, including the central one, are used as micro-

column positions (C1and C2). To trap the beads within

the channel cavities serving as micro-columns and to

prevent the beads from escaping during the operations,

the outlets of these two channels are furnished with

small pieces of PEEK tubing, which t into, and are

axed by the screws in, the outlets. The diameter of this

tubing is slightly smaller than the diameters of the

columns; it provides an internal channel which thus

allows liquid to ow freely through the channel and

Table 1. The applications of mSI-LOV system for micro-miniaturized in-valve fluid and microcarrier bead handling as well as appropriate in-valveinteractions followed by real-time monitoring and/or as a front end to CE

LOV system Applications Detection Ref.

mSI-LOV Phosphate assay Absorbance [8,12]Enzymatic activity assay of proteinSavinase Fluorescence [8]Fermentation monitoring of ammonia,glycerol, glucose and free iron Absorbance [11]

mSI-LOV with Environmental monitoring of NO3 and

reduction column NO2 (NO3

on-line reduced to NO2) Absorbance [12]

mSI-BI-LOV Bioligand interaction assay of(jet-ring-cell) immunoglobulin (IgG) on protein G Fluorescence [8]

immobilized Sepharose beads Absorbance [8]

mSI-LOV-CE Separation of anions. The mSI-LOV is usedas a sample pre-treatment unit and a sampleintroduction system to CE

Absorbance [13]


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along the walls, but entrap the beads. A close-up of thepacked renewable micro-column is shown in Fig. 2.

The sorbent beads are suspended in an appropriate

amount of water or buer solution, usually within the

range of 1:10^1:20(m/v).In operation, thesuspension is

rst aspirated into a 1.0 ml plastic syringe that is after-

wards mounted on port 6 of the LOV. To pack thecolumn

precisely and reproducibly for each analytical run, the

aspiration rate of the suspension of beads from the plastic

syringe into micro-column position C1 should be carefully

controlled (2^5 ml/s is appropriate). After aspiration into

the LOV system, the beads can then be readily transferred

back and forth between the two micro-column positions

(C1 and C2), as the protocol requires. These manipu-

lations facilitate bothsample loading and the treatment of

the analyte-loaded beads according to the scheme that is

to be followed for the post-analysis, as illustrated in the

followingexamplestakenfromtheauthorsownwork.

6. Trace-metal examples

In the experiments described below, an aqueous suspen-

sion of SP Sephadex C-25 cation-exchange resin (dry-

beadsize40^125 mm; H+-o rK+-form)wasemployed[22].

When using ETAAS as the detection device, two dif-ferent schemes for dealing with the analyte loaded

beads can be exploited (Fig.3) [22^24]:

1. after the resin beads have been exposed to a cer-

tain amount of sample solution, the loaded beads

are eluted with a small, well-dened volume of

an appropriate eluent, which is ultimately

transported into the graphite tube for quanti-

cation, whereupon the used beads are discarded.

New beads are aspirated and fresh columns are

generated for the ensuing sample cycles.

2. alternatively, as a novel, unique approach, the

loaded beads can be transported directly into the

graphite tube, where advantage can be taken of

the fact that the beads primarily comprise

organic materials, that is, they can be pyrolyzed,

thereby allowing ETAAS quantication of the

analytes. While the former approach can be used

with ICP as well, the latter is obviously prohibi-

tive for this detection device. Outlines of opera-

tional sequences for these approaches are given

below.

To execute on-line separation/pre-concentration in

the renewable column, a set volume of sample solution

is rst aspirated and stored within the holding coil (HC),

followed by aspiration of a small amount of the suspen-

sion of beads, usually 15^20 ml, which is initially cap-

tured in column position C1. Thereafter, the central

channel is directed to communicate with column posi-

tion C2, and, while the syringe pump moves slowly for-ward, the beads are thereby transferred to C2 followed

by sample solution, i.e., separation/pre-concentration

takes place in this column position (Fig. 4, top). After-

wards, the analyte retained within the micro-column

can be dealt with according to the two schemes men-

tioned above for post-analysis.

In the rst scheme (Fig. 4, top), both sample-loading

and analyte-elution processes take place in the same

column positionC2,theeluenthavingbeenaspiratedfrom

port 2 in an intermediate step and stored in HC, before

being pumped forward and through C2. Eventually, via

Figure 2. Diagram of a LOV system for bead injection (BI) incorporating

two micro-column positions (C1 and C2), along with a close-up of a

packed renewable micro-column.

Figure 3. Illustration of the two possible schemes for dealing with ana-

lyte-loaded beads in the renewable micro-column approach. (a) The

analyte-loaded beads are eluted and the eluate is exploited for quanti-

fication by ETAAS and/or ICP-MS. (b) The analyte-loaded beads are

transported directly into the graphite tube of the ETAAS, where, fol-

lowing pyrolysis of the beads, the analyte is quantified.




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air segmentation, the eluate is transported into the gra-

phite tube [23].

In the second approach (Fig. 5), the separation/pre-

concentration is carried out in column position C2, and,

on completion, the analyte-retaining beads are, along

with a certain amount of carrier solution, usually

30^40ml, transferred back to column position C1. (This

is necessary because all external communication is

eected via syringe pump SP). Afterwards, via air seg-

mentation and through port 4, the beads and the car-

rier zone are transported to the graphite tube of the

ETAAS instrument, where the beads are pyrolyzed and

the analytes quantied [22]. The validity of both

schemes has been demonstrated by the determination

of Ni in biological and environmental samples.

It should be emphasized that, in the bead-pyrolysis

scheme, a temperature of more than 1000C and a

holding time of ca. 40 s is required to pyrolyze the

beads. These conditions are obviously not applicable forthe determination of metals with a low atomization

temperature, particularly Cd, Bi and Pb. In such cases,

it is necessaryto make use of the rst approach compris-

ing an elution step, since the eluate can be pyrolyzed at

substantially lower temperatures as compared to the

beads themselves, which helps to avoid analyte loss

before atomization. This was demonstrated by the

determination of trace levels of Bi in biological and

environmental samples [24].

Table 2 clearly shows that the procedures based on

the employment of renewable columns give much

better precisions (relative standard deviations, RSDs)

and lower limits of detection (LODs) than those of the

conventional processes, i.e., by using a permanent

column either with repetitive uni-directional or bi-

directional operations. While the two schemes for

employing renewable columns exhibit comparable per-

formance, the precision of the elution-based procedure

is much better than that of pyrolyzing the beads

directly, because it is easier to handle and transport

homogeneous solutions than heterogeneous ones.

The interface of the SI-BI-LOV on-line, renewable

column, pre-concentration system to ICP-MS is, in

principle, quite straightforward as compared to that to

ETAAS. In addition, considering that nitric acid can

be used as an eluent for the retained analytes, the pro-

tocol used for ETAAS is, after appropriate modi-cation, readily transferable for interfacing with ICP-

MS, with due consideration to the continuous feature

of the ICP-MS system and the characteristics of the

renewable micro-column and the LOV system. The

manifold is illustrated in Fig. 6. The interface of the

renewable column-based pre-concentration protocol

to ICP-MS opens a route to multi-element screening of

ultratrace metals in complex matrices, such as saline

samples, as demonstrated in the simultaneous deter-

mination of Ni and Bi in biological and environmental

samples (Table 2).

Figure 4. The SI-BI-LOV on-line renewable column pre-concentration

system. The beads are eluted and the eluate is introduced into the

graphite tube for quantification. SP: syringe pump; HC: holding coil;

IV: two-position injection valve.Figure 5. The process of the SI-BI-LOV on-line renewable column

pre-concentration system: Transportation of the analyte-loaded beads

into the graphite tube followed by pyrolysis and quantification.

IV: two-position injection valve.




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The micro-miniaturized renewable column volume in

the LOV results in a correspondingly smaller break-

through capacity for the analytes, and consequently a

very limited amount of eluent suces for the complete

elution of the retained analytes. It is, therefore, critical

to minimize the dispersion of the eluate zone during its

transport to the ICP, as this might cause severe loss of

sensitivity. The introduction of small air segments at

both ends of the eluate zone, as used successfully with

detection by ETAAS, might help to minimize the disper-

sion [25^27]. Yet, in the experience of the present

authors, with interfacing FI/SI on-line sample pre-

treatment systems with an ELAN 5000 ICP-MS

[28,29], the use of air segments tend to extinguish the

plasma.

However, dispersion is particularly critical when

using a conventional nebulization system. The low

sample transport eciency of a cross ow nebulizer,

typically 1^2%, might cause an unduly large dis-

persion of the eluate zone. Therefore, it is clearly not

appropriate for delivering such a small volume of

eluate.

To overcome these drawbacks, a direct-injection,

high-eciency nebulizer (DIHEN) was found to be eec-

tive [30]. The eluate zone was sandwiched between

carrier segments, and transport was eected by a con-

tinuous infusion pump (IP). Under such conditions, no

signicant dispersion was encountered.

7. Conclusions and future outlook

The SI-BI renewable micro-column, pre-concentration

scheme using a m iniaturized LOV system is proposed as

preferable to the conventional procedure employing a

permanent column. Interfacing this approach to both

ETAAS and ICP-MS has been shown to have a number

of merits in comparison with its traditional counter-

part, including the complete elimination of ow resis-

tance, high precision and a low LOD. In addition, the

expense of column renewal for each analytical cycle

is very limited, i.e., the bead suspension obtained from

Table 2. Comparisons of the performance data for the pre-concentration of Ni and Bi in the SI-BI-LOV system using a renewable column or a permanentcolumn with uni-directional and bi-directional repetitive operation

With detection by ETAAS

Conventional

Bead pyrolysis Elution uni-direct. bi-direct.

Ni Ni Bi Ni NiRSDH

a (%, 0.3 mg/l) 1.5 2.3b 5.8 4.9RSDK (%, 0.3 mg/l) 3.4 1.7LODH (ng/l) 9

c 10.2, 11.4c 27.0 42.0 24.0Enrichment factor 72.1 71.1 33.4

With detection by ICP-MS (Elution)

Ni BiRSDH(%, 0.8 mg/l) 2.9 1.7LODH (ng/l) 15.0 4.0Enrichment factor 35.2 28.4 (1.63.2 mg/l)

9.1 (0.041.6 mg/l)

aThe subscript stands for the form of ion exchanger;bRSD value obtained at the 2.0 mg/l level;cLOD value obtained with the K+ form of ion exchanger.

Figure 6. The SI-BI-LOV on-line renewable column pre-concentration

system with detection by ICP-MS: The beads are eluted and the eluate

is introduced into the ICP v ia a DIHEN. SP: syringe pump; HC: holding

coil; IV: two-position injection valve; SL: sample loop; IP: infusion pump;

DIHEN: direct injection high efficiency nebulizer.




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1 gram of dry bead of SP Sephadex C-25 can be used for

ca. 500 operations.

The studies based on the miniaturized SI-BI-LOV

renewable column approach have focused on pre-con-

centration of trace metals and its interfacing with

ETAAS and ICP-MS. However, this scheme is equally

applicable to virtually any kind of liquid-solid inter-

actions, including SPE as well as precipitation/copre-

cipitation separation/pre-concentration protocols with

detection by various techniques. Further investigations

are required in this eld. In particular, the LOV-based

SI-BI surface-renewal approach has opened a promis-

ing avenue for immunoassay and/or bio-chemical

assays employing immobilized enzymes, although

rather few studies hitherto have been directed to this

subject by employing the BI scheme [19^21,31^33].

However, considering its vast potential, it is expected

that the SI-BI-LOV protocol will gain considerable

momentum in the very near future.

References

[1] J. Ruzicka, E.H. Hansen, Flow Injection Analysis, 2nd Edn,

John Wiley & Sons, Chiche ster, Susse x, UK, 1988.

[2] Z. Fang, Flow Injection Separation and Pre-concentration,

VCH Publishers Inc., New York, USA, 1993.

[3] J. Ruzicka, E.H. Hansen, Anal. Chim. Acta 78 (1975) 145.

[4] E.H. Hansen, Flow injection bibliography, http://www.

owinjection.com/

[5] J. Ruzicka, J. Flow Inject. Anal. 15 (1998) 151.

[6] E.H. Hansen, J.-H. Wang, Anal. Chim. Acta 467 (2002) 3.

[7] J. Ruzicka, G.D. Marshall, Anal. Chim. Acta 237 (1990) 329.

[8] J. Ruzicka, Analyst (Cambridge, UK) 125 (2000) 1053.[9] E.H. Hansen, Anal. Chim. Acta 308 (1995) 3.

[10] J. Ruzicka, in: A. van den Berg, W. Olthuis, P. Bergveld,

(Editors), Micro Total Analysis Systems 2000, Kluwer

Academic Publishers,Dodrecht,The Netherlands,2000, pp.1^10.

[11] C.-H. Wu, L. Scampavia, J. Ruzicka, B. Zamost, Analyst

(Cambridge, UK) 126 (2001) 291.

[12] C.-H. Wu, J. Ruzicka, Analyst (Cambridge, UK) 126 (2001)

1947.

[13] C.-H. Wu, L. Scampavia, J. Ruzicka, Analyst (Cambridge, UK)

127 (2002) 898.

[14] E.V. Alonso,A.G. Torres,J.M.C.Pavon, Talanta 55(2001)219.

[15] J.L. Burguera, M. Burguera, Spectrochim. Acta Part B 56

(2001) 1801.

[16] Z.-L. Fang, J. Ruzicka, E.H. Hansen, Anal. Chim. Acta 164

(1984) 23.

[17] Z.-R. Xu, S.-K. Xu, Z.-L. Fang, Atom. Spectrosc. 21 (2000) 17.

[18] Z.-R. Xu, H.-Y. Pan, S.-K. Xu, Z.-L. Fang, Spectrochim. Acta

Part B 55 (2000) 213.

[19] P.S. Hodder, J. Ruzicka, Anal. Chem. 71 (1999) 1160.[20] J. Ruzicka, L. Scampavia, Anal. Chem. 71 (1999) 257, A.

[21] J. Ruzicka, Analyst (Cambridge, UK) 123 (1998) 1617.

[22] J.-H. Wang, E.H. Hansen, Anal. Chim. Acta 424 (2000) 223.

[23] J.-H. Wang, E.H. Hansen, Anal. Chim. Acta 435 (2001) 331.

[24] J.-H. Wang, E.H. Hansen, Atom. Spectrosc. 22 (2001) 312.

[25] K. Benkhedda, H.G. Infante, E. Ivanova, F. Adams, J. Anal. At.

Spectrom. 15 (2000) 1349.

[26] K. Benkhedda, H.G. Infante, E. Ivanova, F. Adams, J. Anal. At.

Spectrom. 16 (2001) 995.

[27] V. Stefanova, V. Kmetov, L. Futekov, J. Anal. At. Spectrom. 12

(1997) 1271.

[28] J.-H. Wang, E.H. Hansen, J. Anal. At. Spectrom. 17 (2002)

1284.

[29] J.-H. Wang, E.H. Hansen, J. Anal. At. Spectrom. 17 (2002)

1278.[30] J.-H. Wang, E.H. Hansen, J. Anal. At. Spectrom. 16 (2001)

1349.

[31] B. Willumsen, G.D. Christian, J. Ruzicka, Anal. Chem. 69

(1997) 3482.

[32] J. Ruzicka, A. Ivaska, Anal. Chem. 69 (1997) 5024.

[33] I. La hdesma ki, L.D. Scampavia, C. Beeson, J. Ruzicka, Anal.

Chem. 71 (1999) 5248.

Elo Harald Hansen, who is one of the two inventors of FI, is Pro-

fessor of Analytical Chemistry at the Department of Chemistry, Tech-

nical University of Denmark. His research interests are instrumental

and automated analysis with special emphasis on the development

and application of procedures based on FI/SI. In recent years, he has

focused particularly on developing FI/SI schemes for the determina-

tion of trace levels of metals in complex matrices by hyphenation withatomic spectrometric techniques and ICP-MS.

Jianhua Wang obtained his MSc from Nankai University, China.

After employment at Yantai Normal University, he spent one year at

the University of Delaware, USA, before commencing his PhD studies

at the Technical University of Denmark in 1999. He was awarded the

PhD degree in 2002. He is currently pursuing his interests in the

development and use of FI/SI procedures at Northern University,

Shenyang, China, where he has joined Professor Zhaolien Fangs

researchgroup.


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