I
L.
V
L I
A
A
1 '1
On-site automated FI monitors provide near-continuous, reliable, and low-cost data for assessing water quality Reagent consumption is generally low in FI systems (an important consideration for field applications) and can be reduced still further by using reagent injection manifolds, as shown in Figure 2. Reverse FI, as this configuration is often called, is suitable for applications in which the sample is in abundant supply (as is the case in many environmental situations) and is particularly useful when extransported to a flow-through detector for pensive reagents are necessary. Reverse FI also minimizes the quantity of remeasurement. The response is in the form of a peak, the height of which is usu- agent($ discharged to waste, which is advantageous if environmentally questionally directly related to analyte concentration. The degree of sample dispersion is able reagents are used. highly reproducible and is controlled by SimultaneousFI can be performed by factors such as flow rate, manifold geome- designing split-linemanifolds in which the sample is injected into more than one try,and tubing length and diameter. flow channel and undergoes a different A simple FI manifold p i r e 1)typically consists of a propulsion unit (such as reaction in each channel. This can be achieved either by splitting the carrier a peristaltic pump), a six-port rotary sample injection valve, and a flow-through de- stream after injection or by connecting two tector (such as a spectrophotometer). injection valves in series in two separate Narrow-bore poly (tetrafluoroethylene) reaction systems. Other components that can easily be incorporated into FI systems (PTFE) tubing (typically 0.8 mm i.d.) is used for sample and reagent transport, and include gas dialysis units, for the diffusion of a gaseous analyte from a carrier tightly wound coils are often included to aid mixing. A number of options are avail- (donor) stream through a microporous membrane into a reagent (acceptor) able for the basic FI components (Table stream, and solid-phase reaction columns, 1). The manifold shown in Figure 1 is a in which the injected sample reacts with single-channel system in which the car(or selected components are retained by) a rier stream (which can also contain a recolumn packed with solid material. agent) transports the sample to the detector. If the method requires more than one reagent, additional streams can be Process FI merged with the carrier stream at suitRecently there has been considerable inable points in the manifold. terest in process analytical chemistry.The ability to acquire analytical information Basic principles during the various stages of an industrial FI was first described by Ruzicka and process is seen as a means of increasing Hansen (5)as an unsegmented flow techKevin N. Andrew efficiency and maximizing economic pernique in which a volume of liquid samNicholas J. Blundell formance ple (typically W200 pL) is inserted into a (6).Process analytical chemisDavid Price try can also play a role in the environmoving liquid carrier stream, where it Paul J. Worsfold mental control of industrial processes undergoes physical dispersion as it is University of Plymouth
ince its developmentin the mid1970s, flow injection (FI) has become a routine laboratory technique for sample analysis and on-line sample treatment (1,Z). It is capable of a fast response (typically 10-120 s) and a high sample throughput (typically 30120/h) with low reagent consumption (typical flow rates are 0.5-2.0 mL/min) and low operational costs and is easily adapted to automated analysis. Such features are well suited to the requirements of industrial process analysis, and the potential of FI for on-line process monitoring has been discussed (3,4). Recently, interest has also focused on the use of FI for in situ monitoring of environmental matrices, particularly natural waters. With the trend toward increasingly stringent legislation pertaining to the quality of surface water and groundwater, the incidence of transient pollution events, and the desire to understand complex biogeochemical cycling processes, there is a growing need to obtain reliable quantitative analytical data in situ. Automated FI monitors operating in the field represent a lowcost option for obtaining nearcontinuous, quantitative data for a wide range of dissolved aquatic chemical parameters. In this Report we outline the basic features of FI that have made it so attractive for laboratory and process analysis and discuss how these characteristics are applicable to monitoring natural and polluted waters.
’
0003-2700/94/0366-916A/$04.50/0 0 1994 American Chemical Society
Analytical Chemistry, Vol. 66, No. 18, September 15, 1994 917 A
when applied to the on-line monitoring of gaseous and liquid emissions. The requirements of an on-line process monitor include rapid analysis and high samplingfrequency;robust construction to withstand harsh chemical matrices; a simple design that can be easily maintained; the ability to perform automated, unattended analyses and undertake regular self-calibration;and minimal capital and operating costs. FI can meet all of these requirements and can be applied to a wide range of chemical parame-
ters. In addition to single-parameter monitoring, FI has the potential for multicomponent process monitoring (7), particularly in combination with multichannel detection systems and chemometric software routines. Figure 3, a typical on-line process FI monitor, shows how each component is controlled automatically by a simple single-board computer, which in turn communicates with a central process control computer. This arrangement allows appropriate adjustments to be made to process
Savple
]eager
+Waste
Results Figure 1. Simple single-channel FI manifold.
Description
Set of rollers on a revolving drum that squeezes flexible tubing to produce a constant, pulsing flow Cam-driven piston that produce! variable pulseless flow Pressurized inert gas vessel connected by a flow regulator to each reagent or carrier reservoir, producing pulseless flow Six-port unit with sample loop; electronic or pneumatic operation tdrodynamic injection Selective stopping and starting of both sample and reagent pumps; sample enters reagent stream while the reagent pump is stopped and is then transported to the detector when it is restarted Manual injection through sep' UV-vis, diode array, and IR spectrophotometry; solid-sta' photometry (LED source, phc diode detector); fluorometry; chemiluminescence;atomic spectrometry Potentiometry (ion-sehecnve ana p n electrodes), conductimetry, amperometry, coulometry, voltammetr
918 A Analytical Chemistry, Vol. 66, No. 18, September 15, 1994
variables in response to feedback from the on-line monitor. The monitor can be designed to incorporate sample pretreatment procedures such as filtration, dilution, and preconcentration. Solenoid valves can also be incorporatedto switch between the sample and standards for regular self-calibration. Process FI applications that use molecular spectroscopic detection (Table 2) have been discussed in a number of publications (8-24). The primary applications, which demonstrate both the versatility of FI and its ability to withstand harsh sample matrices, are in the areas of biotechnology, industrial chemistry processes, and water quality. One of the most promising new applications of FI is its use for f r o n t a d sample treatment and delivery for spectroscopic detection (e.g., inductively coupled plasma MS). Environmentalmonitoring The traditional approach to monitoring dissolved chemical species in natural waters involves periodic manual sample collection followed by laboratory analysis. However, this approach is susceptibleto errors arising from contamination and/or degradation of the sample during collection, transportation, and storage (25).In addition, it is very time consuming and labor intensive, particularly when large numbers of samples are involved, and only provides intermittent data, which may exclude short-term fluctuations of environmental significance. The ability to conduct analyses in situ and provide a pseudocontinuous profile of chemical fluxes is therefore important, not only because of the limitations of the conventional approach but also because of escalatinglegislative restrictions and the increasing need for greater management and control of industrial, environmental, and agricultural processes. Approaches to in situ monitoring
Syringebased, fixed-site monitors that incorporate wet chemistries and spectrophotometric detection are commercially available for the determinationof a variety of chemical species. Deployment of this type of instrumentationis restricted, however, by its power requirements and lack of portability. Consequently, the majority
of currently available portable instrumentation for monitoring chemical water quality parameters in situ is based on coupling ion-selective electrodes with datalogging devices. The ion-selective electrode approach has recently been used by the U.K. National Rivers Authority to develop small, hand-held meters and larger monitors intended for long-term field deployment (26). However, the sensing surface is prone to biological fouling, and electrodes are available only for a limited number of chemical species. Biological early warning systems (i.e., monitors incorporatingliving organisms) have also been proposed for fixed-site deployment. Their operation is based on a pollutant-induced change in the status of the organism, such as enhanced movement or ventilatory frequency, and these monitors can be useful as general indicators of water quality. However, they are not sufficiently selective to provide the specific chemical information that is often required. FI, particularly in conjunction with solid-state detection systems, can potentially offer a rugged, portable, and selective alternative to the approaches mentioned. In situ FI instrumentation Solid-state photometric detectors (27) incorporate light-emitting diodes as sources (and photodiodes as detectors) and are now available at minimal cost for most of the visible region of the electromagnetic spectrum. These low-power, lowcost detectors have enabled standard FI spectrophotometric methods to be adapted for field applications. Power consumption is an important consideration for an in situ monitor. For deployments of up to 30 days, batteries provide the most rugged and reliable power supply. A range of nonrechargeable cells, such as zinc-carbon, lithium, and alkaline manganese, and rechargeable cells, such as nickel-cadmium and lead-acid, are commercially available. Rechargeable cells based on the traditional lead-sulfuric acid cell are the most widely used in field-based equipment because of their low cost, large range of available power capacities, and excellent recharging capability. Their main limitation is their power-to-weight ratio, which reduces
portability for longer term deployments (e.g., more than one week of intermittent operation). In some remote locations, solar panels are a cost-effective and reliable power supplement to batteries. The microcomputercontrol/data acquisition system can be a significant part of the total cost and power requirement of an in situ monitor. However, modern CMOSbased microcontrollershave an average power consumption in the microamp range, which is negligible in compari-
son to the power required by the system’s components (typically 200-400 mA). Sample delivery to and data transmission from the monitor are important aspects of in situ measurement; biofouling and suspended solids are the two most significant problems. Sample delivery and data transmission generally involve the incorporation of commercially available inline filtration devices; biofouling can be managed by including biocides in the r e agent streams. Various options are avail-
Sample
Figure 2. Four-channel FI manifold with reagent injection.
Figure 3. Process FI monitor. Solid lines represent the flow of liquid. Dotted lines represent communication links. Analytical Chemistry, Vol. 66, No. 18, September 15, 1994 919 A
able for remote communication: satellite, land-line, VHF/UHF radio, and cellular telephone. The particular method used depends on the specificrequirements of a given application,such as cost, monitor location, and frequency of transmission. The industry standard output from on-line monitoring devices is a 4-20-mA loop, but an RS-232 interface can also be used.
monitoring scheme may not detect shortterm changes, such as those caused by storms, between sampling intervals. A battery-powered, microcontrollerbased FI monitor has been shown to provide a versatile and reliable system for the determination of chemical parameters in natural waters (28)and, when used in conjunction with a miniature microporous suction cup, has the potential for measurFreshwater monitoring ing chemical fluxes in soil cores. Figure 4 Within the freshwater environment, key shows the monitor and a concentration application areas for in situ FI monitoring profile that depicts the passage of nitrate include effluent discharges (point and fertilizer through a core of saturated clay diffuse sources), supply intake, data acqui- soil. The detector incorporates a green sition for environmental databases, nutrilight-emitting diode (Ama = 565 nm) to ent budget studies, and leachate monitor- detect the pink diazo compound (I.” = ing of soils and landfills. Each of these de542 nm) formed from the reaction of niployment scenarios places different trite (produced by the reduction of nitrate requirements on the design considerusing a copperized cadmium column) ations of any monitoring system. For exwith sulfanilamide and N-l-naphthylethylample, if fixed-sitemonitoring is appropri- enediamine. ate for a point discharge into a river or within a water treatment plant, ac power is Marine monitoring likely to be available. The in situ monitoring of marine environIn contrast, for nutrient budget studies ments (estuarine, coastal, and open ocean at remote locations or for soil leachate waters) can involve shipboard techmonitoring, a portable battery-powered niques or remote instrumentation, includmonitor would be essential. In the latter ing submersible and buoy-mounted decontext, in situ monitoring is particularly vices. As mentioned earlier, the major important for those species that are highly problem with the conventional “send-it-tomobile and pass relatively easily between the-lab” approach is contamination soil water, groundwater, and surface wa- and/or degradation of the sample prior to ter, because a conventional (manual) analysis. This is generally more serious
Azo dyes Morphine ron(ll and 111) luminum in steel Paper production alcium Fish farming mmonia and nitrite Hydroponic cultivation Nitrate Wastewater monitoring Phosphate, ammonia, and nitrate Total phosphorus I reated water monitoring Fluoride Aluminum and iron Biotechnology L- Phenylalanine Glucose, lactic acid, and protein Ammonium, glucose, and protein Acetate and phosphate P-Galactosidase Penicillin V
Spectrophotomet Chemiluminescence Spectrophotometry Spectrophotometry Spectrophotometry Spectrophotometry LED photometry Spectrophotometry
___ Diode array Spectrophotometry Spectrophotometry LED photometry
920 A Analytical Chemistry, Vol. 66, No. 18, September 15, 1994
for marine samples than for freshwater samples because of the lower concentrations of analytes and the high and variable dissolved solids content of the matrix (29).The refractive index of the matrix can also be particularly problematic for wet chemical methods that use optical detection. The remoteness of open ocean locations also means that sampling is particularly expensive. Real-time data s u p plied by in situ monitoring can maximize the spatial and temporal information obtained. FI techniques therefore offer the same advantages for marine sample analysis as they do for freshwater sample analysis. Applications for laboratory and ship board monitoring have been comprehensively reviewed (30,31). Since the early 1980s, a wide variety of analytes have been successfully determined by FI with optical detection onboard research vessels (32-40),as shown in Table 3. The first shipboard application was a reverse FI method (reagent injection) for the determination of nitrate or nitrite, in which seawater was pumped directly into the manifold (32).Since that time, several wet chemical procedures based on UV-vis, fluorescence, and chemiluminescence detection have been reported. The logical progression from shipboard monitoring is the deployment of submersible systems. This approach has been pioneered by Johnson (41) via the use of “scanners” (submersible chemical analyzers) capable of housing continuous flow (as opposed to FI) manifolds (e.g., for the determination of silicate and sulfide in the Rose Garden hydrothermal vent field of the Galapagos Rift). The manifolds were pressure compensated and oil filled to withstand depths of up to 2500 m. Submersible monitors such as these prevent contamination and/or sample degradation by eliminating sample transportation to the ship. The main advantage, however, is the much greater number of samples that can be analyzed in situ as compared with the limited number of samples that can be collected and returned to the ship in a single day. This has been demonstrated by another sub mersible continuous flow analyzer (42) used for the determination of nitrate. The analyzer used positive displacement pumps rather than peristaltic pumps. The
highdefinition depth profile data obtained from a cruise in the Sargasso Sea are in excellent agreement with data obtained from bottle-collected samples from the same location. Groundwater monitoring
FI instrumentation can potentially be used for in situ groundwater monitoring, provided the sample is pumped to the surface. However, there is a growing demand for monitoring devices that are physically located within boreholes. At present, FI monitors cannot meet this requirement because of their physical size (the typical diameter of an inspection borehole is 2 in.). Nonetheless, recent advances in the miniaturization of FI components (e.g., micromachined silicon structures incorporating pumps and flow manifolds) suggest the feasibilityof in situ FI monitoring within boreholes in the foreseeable future (43). Conclusions
Figure 4. Determinationof nitrate concentration gradient in soil. Top: Battery-powered microcontroller-based monitor. Bottom: Concentration profile depicting the passage of nitrate fertilizer through a core of saturated clay soil.
rabie 3. ShipnoPr4 ana sunmersinie =wiicawons of Fl 4rea of deployment
3alifornia coast riaco and Manus
Analyte
Jetection method
Nitrate and nitrite Ammonia Hydrogen peroxide Cobalt Manganese and : Manganese Copper Iron and manganese Silicate ' iosy"-te
Spectrophotometry Spectrophotometry Spectrophotometry Chemiluminescence Spectrophotometry 2hemiluminescence 2hemiIuminescence Spectrophotometry Spectrc-"-'-metry
Jeference
FI is now accepted as a powerful, routine tool for the automation of wet chemical methods in the laboratory and is being increasingly used in process situations. The full potential of the technique for in situ environmental monitoring, however, has yet to be realized. Novel chemistries are required to provide lower detection limits and information on chemical speciation. Nonetheless, advances in computer hardware, software, power sources, communication systems, solid-state light sources, detectors, and other hardware, together with the proven versatility and reliability of FI, have made such deployments feasible for the monitoring of natural and polluted waters. We would l i e to thank the following organizations in the U.K. for their support: IC1 Chemicals and Polymers, Runcom; IC1 Engineering, Winnington; Brixham Environmental Laboratories (Zeneca plc) ,Brixham; Institute of Freshwater Ecology, Wareham; and Plymouth Marine Laboratory, Plymouth. We'd also like to thank AFRC/NERC (grant number GST/O2/ 587) and NERC (reference number GT4/91/ AAPS/43).
References (1) Ruzicka, J. Fresenius. 2.Anal. Chem. 1986,324,745.
(2) Valcarcel, M.; Luque de Castro, M. D. Flow Injection Analysis: Principles and Application; Ellis Horwood: Chichester, U.R, 1987.
Analytical Chemistry, Vol. 66, No. 18, September 15, 1994 921 A
A
Data
Selected Reprints EDITED BY
Howard J. White, Jr.
1
- A
This practical guide will tell you everything you need to know about the vdata. Compiled from widely scattered sources, Reporting Experimental Data is a definitive reference volume which offers information on coordinating data from many disciplines. The volume gathers the recommendations for publication of data for measurements of a physical chemical nature together with current IUPAC recommendations for quantities, symbols, and units. A unified reference source for all authors of scientific publications!
Contents: Describing and Presenting Measurements Items of General Use in Chemistry Thermodynamics Including Biothermodynamics Chemical Kinetics and Transport Properties Electrochemistry Colloid and Surface Chemistry Photochemistry Analytical Chemistry Crystallography and Electron Diffraction Spectroscopies Automated Products
.
.
Howard j . White, Jr.. Editor
360 pages (1993) Clothbound ISBN 0-8412-2529-X-$89.95
Order from: American Chemical Society Distribution Office, Dept. 74 1155 Sixteenth Street, NW Washington,DC 20036
Or CALL TOLL FREE AT 1-800-227-5558(in Washington, DC, 202-872-4363) and use your credit card!
ACS IIIPUBUCKITONS Essential Resourcesfor the Chemical Sciences
(3) Benson, R L.; Worsfold, P. J.; Sweeting, F. W. Anal. Proc. 1989,26,385. (4) Luque de Castro, M. D. Talanta 1989, 36,591. (5) Ruzicka, J.; Hansen, E. H. Anal. Chim. Acta 1975, 78,145. (6) Callis, J. B.; Illman, D. L.; Kowalski, B. R Anal. Chem. 1987,59,624A. (7) MacLaurin, P.; Worsfold, P. J. Microchem. J. 1992,45,178. (8) Gisin, M.; Thommen, C. Trends Anal. Chem. 1 9 8 9 , 4 6 2 . (9) Barnett, N. W. et al. Anal. Chim. Acta 1993,282,551. (10) Lynch, T. P.; Kernoghan, N. J.; Wilson, J. N. Analyst (London) 1984,109,843. (11) Bergamin, H. et al. Anal. Chim. Acta 1986,190,177. (12) Nyman, J.; Ivaska, A Talanta 1993,40,95. (13) Ariza, A. C. et al. J. Autom. Chem. 1992, 14,181. (14) Clinch, J. R et al. Anal. Proc. 1988,25,71. (15) Pedersen, K M.; Kummel, M.; Sheberg, H. Anal. Chim. Acta 1990,238,191. (16) Benson, R. L. et al. Anal. Chim. Acta 1994,291,233. (17) Chen, D.; h q u e de Castro, M. D.; Val&cel, M. Anal. Chim. Acta 1990,230,137. (18) Benson, R L.; Worsfold, P. J. Sci. Total Environ. 1993,135, 17. (19) Nalbach, U. et al. Anal. Chim. Acta 1988, 213,55. (20) Nikolajsen, K.; Nielsen, J.; Villadsen, J. Anal. Chim. Acta 1988,214,137. (21) Chung, S. et al. Anal. Chim. Acta 1 9 9 1 , 249,77. (22) Forman, L. W.; Thomas, B. D.; Jacobson, F. S.Anal. Chim. Acta 1991,249,101. (23) Kracke-Helm, H-A. et al. J. Biotechnol. 1991,20,95. (24) Carlsen, M. et al. Anal. Chim. Acta 1993, 279,51. (25) Hunt, D.T.E.; Wilson, A. L. The Chemical Analysis of Water: General Principles and Techniques; Royal Society of Chemistry: London, 1986. (26) Adams, J.RW.; Dolby, J. C.; Williams, P. N.J. Inst. Water Environ. Manage. 1992,6,64. (27) Dasgupta, P. K et al. Talanta 1993,40,53. (28) Blundell, N. J. et al. J. Autom. Chem. 1993,15,159. (29) Johnson, K. S.; Coale, K. H.; Jannasch, H. W. Anal. Chem. 1992,64,1065. (30) Atienza, J. et al. Cw't. Rev. Anal. Chem. 1991,22,331. (31) Atienza, J. et al. Crit. Rev. Anal. Chem. 1992,23,1. (32) Johnson, K. S.; Petty, R L. Limnol. Oceanogr. 1983,28,1260. (33) Willason, S. W.; Johnson, K. S. Mar. Biol. 1986,91,285. (34) Johnson, K. S. et al. Anal. Chim. Acta 1987,201,83. (35) Johnson, K S. et al. Natlcre 1988,332,527. (36) Kolotyrkina, I. Y.; Shpigun, L. K.; Zolotov, Y. A. J. Anal. Chem. (USSR) 1988, 43,223. (37) Chapin, T. P.; Johnson, K S.; Coale, K. H. Anal. Chim. Acta 1991,249,469. (38) Coale, K. H. et al. Anal. Chim. Acta 1992, 266,345. (39) Coale, K H. et al. Nature 1991,352,325. (40) Shpigun, L K.; Kolotyrkina, I. Y.; Zolotov, Y. A Anal. Chim. Acta 1992,261,307.
922 A Analytical Chemistry, Vol. 66, No. 18, September 15, 1994
(41) Johnson, K. S.; Beehler, C. L;Sakamote Arnold, C. M. Anal. Chim. Acta 1986,179, 245. (42) Taylor, C. D.; Howes, B. L.; Doherty, K. W. Mar. Technol. Soc. J. 1993,27,32. (43) van der Schoot, B. H. et al. Anal. Method Instrumen. 1 9 9 3 , I , 38.
r i Paul J. Worsjbld (left) is a professor of analytical science at the University of Plymouth (Department of Environmental Sciences, Drake Circus,Plymouth, PIA 8AA, U.K.). He received his B.Sc. degreefiom Loughborough University of Technology (U. K.) and his Ph.D. from the University of Toronto (Canada). His research interests are the application of FI techniques, molecular spectroscopy, and environmental analysis. Kevin N . Andrew (rZght) received his B.Sc. degree in environmentalscience in 1992fiom the Universityof Plymouth and is working on his doctorate there. His research concerns the application of FI and chemometrictechniques to the on-line monitom'ng of industrial liquid efluent streams.
NicholasJ. Blundell (left) is a postdoctoral fellow at the University of Plymouth and received his Ph.D. in inorganic chemistry fiom the Universityof Leicester (U.K.) in 1991. His research interests are in the design and deployment of FI instrumentation for remote environmental monitoring and in the use of computers in analytical chemistry. David Price (right) is a postgraduate student workingjointly at the University of Ply mouth and Plymouth Marine Luboratory. He received a B.Sc. degreefiom the University of Liverpool (U.K.) in 1991. His research is in the area of marine analytical chemistry and specifically the application of FI with chemiluminescencedetection to the shipboard monitoring of H,O,.
