Automatic analytical methods for environmental monitoring and control

(Table III.2.2. continued)

(Table III.2.2. continued)

While the “classic” or continuous flow systems can operate well without the aid of a computer, they are uneconomical in terms of reagent consumption and waste generation, because of the continuous pump of all solutions. In contrast, the recently designed variants of FIA, SIA and BIA, are based on discontinuous flow and consumes reagents only when the sample is treated, the reagent being injected not pumped into the carrier stream. Nowadays, the use of personal computers and the availability of dedicated and object-orientated software make SIA and BIA widely accessible, although these new variants impose some constraints on the versatility of operation as compared to FIA. The principles of FIA and SIA are discussed in Chapter III.2.1. BIA combines the advantages of solid-phase chemistry with the novelty of fluidic handling of microcarrier beads (beads diameter of 30 – 150 m), allowing automated surface renewal and post-analysis manipulations. It operates in SIA mode but instead of reagent solutions, bead suspensions are used as reagent carrier. The injected bead suspension is trapped in a flow-through detector in FIA manifold, where it is subsequently perfused by the analyte solution, buffers, or auxiliary reagents. Chemical reactions occur at the bead surface and can be analyzed in “real-time” directly on the solid phase or within the eluting liquid phase. Monitoring simultaneously the changes in solid and liquid phase, a multi-parameter assay is possible. At the end of an analysis cycle, the beads can be automatically discarded, collected, or rerouted. BIA is applicable in diverse fields of research, including chemical sensors, bioassay, affinity chromatography, spectrophotometry and electrochemistry.

Flow-based analytical techniques fall into one of four categories: air-segmented, unsegmented continuous flow; flow injection analysis and sequential injection analysis. Multi-commutation and binary sampling can be implemented in both unsegmented and segmented flow systems and potentialities and limitations have been pointed out by B.F. Reis et al.

Automated flow systems are intended to analyze multiple samples, either for a single analyte or for several analytes. Automated instruments perform the following operations:

1. 
   Sampling (from a small cup on auto-sampler, or assembly line);
   
2. 
   Sample dispensing;
   
3. 
   Dilution and reagents adding;
   
4. 
   Chemical reaction development;
   
5. 
   Directing the reaction product in the detection system;
   
6. 
   Reading the recorded data;
   
7. 
   Processing the data.
   

In some cases, new pumps are becoming available. The time of multichannel peristaltic pump is gone and a new alternative in the use of individual computer-controlled peristaltic pump appears on the horizon. LACHAT Instruments affirms that: “A system can be set up with four chemistries, and you can select any one, two, three or all four to be run on different batches of samples”. Therefore, these new devices make possible to run each analytical channel under full computer control and to select individual methods to be run on a sample batch.

Besides the above-mentioned essential aspects, it is important also to provide the main figures of merit for a proper description of an automated flow analyzer:

1. 
   Sample throughput – the number of samples processed per unit of time should be estimated in association with specified carry-over level. It is also recommended to specify the consumption of sample and/or reagents when sample throughput is calculated.
   
2. 
   Analytical characteristics – accuracy, sensitivity, detection limit, selectivity, dynamic range of concentration and precision should be calculated from the data according to the IUPAC regulations. The analyzer should be validated using a standard method with confidence limits and tests of significance.
   
3. 
   Robustness – is discussed from two points of view: the dependence of the analytical signal on the variation of system parameters (temperature, reagent concentrations, flow rates, etc.) and the instrumental stability, which is manifesting it-self as a shift and/or drift in baseline and/or analytical signal. The stability of the analytical curve, cost and maintenance requirements should be specified.
   
4. 
   Portability – to another operational environment and consequent suitability for in situ, in vivo or on –site analyses, as process analyzer for on-line monitoring.
   

The series 2000 analyzer analyses ions, nutrients and metals down to ppb levels. Both discrete laboratory applications and on-line process control are catered for in single or multi-channel configurations. The systems are modular allowing the user to purchase only what they need, from a basic single channel analytical system with manual or automatic sample presentation through to multi-channel systems with computer control and data processing. The analyzers offer a wide range of applications based on continuous flow technologies including segmented flow (SFA), flow injection (FIA) and ion selective electrode (SIA). Techniques include on-line distillation and UV digestion, on-line automatic calibration and standards preparation, over-range dilution and re-analysis.

The instrument comprises three separate units and these are basic analytical modules, automatic sample presentation and data capture. The analysis can start immediately with the analytical module consisting of a manifold constructed for the plug-in chemistry. Ready assembled units are available for the most commonly used methods and where is possible a single manifold can mount two related chemistries. The pump tube and valve connections are conveniently positioned and colored for identification. It takes only a few minutes to change the analytical method. BURKARD methods combine the latest improvements in performance with low reagent consumption. FIA_flo 2000 offers fully automatic sampling with a choice of carousel or XYZ sample changer. Automatic dilution of over-range samples is available as an option on the XYZ. However to alleviate the need for dilution the MicroStream data-processor has an extended concentration range enabling the results to be printed out at up to 10 times the normal calibration standard. When the instrument is not used with a sample changer a low-cost manual injection timer is available to ensure precise loop filling. In addition, each valve has a manual injection button as standard to assist the analyst with setting up of the individual chemistries. The standard high sensitivity colorimetric and UV detectors coupled to FIA_flo use filter technology and flow through cells with a rage of path lengths from 3-50 mm. Free standing alternative detectors for Chemiluminescence, Fluorescence, and Ion Selective Electrode interface with the chemistry manifold using the appropriate couplings. FIA_flo 2000 comes with MicroStream, a powerful multi-tasking system based on Windows^® software. MicroStream will speed up your calculating and reporting. Starting with a low-cost package for single-channel use, this system can be expanded to run up to four independent multi-channel analyzers. New quality control software checks the accuracy of analysis and all results can be downloaded to other software packages and LIMS. MicroStream is compatible with Windows^® based networks. FIA_flo 2000 analyses nutrients, ions and metals and the most popular applications include: waters; soil samples; landfill samples; fertilizers; food and drinks; chemicals/pharmaceuticals; quality control.

The SIA2000-S automatic chemistry analyzer is a low cost and versatile instrument for a range of applications based on ion selective electrode technology. It is ideal for the laboratory with small sample numbers that arrive on irregular basis. The modular design of SIA2000-S system allows the individual purchase of sampler, analytical chemistry unit, data processor or recorder to better meet the exact analyst requirements. The “add-on” potential means that options may be acquired as the work load increases and the chemistry module interfaces with other manufacturers instruments. The analysis module comprises a multi-channel fixed or variable speed peristaltic pump, an injection valve (valves), heating bath fitted with two PTFE coils and a dual flow cell carrying the ion selective and reference electrodes. An interface is fitted to enable the electrode response to be amplified, linearized and output to a chart recorder or data handling system. Ionic species, both monovalent and divalent, may be determined over a wide concentration range giving an excellent linear calibration. BURKARD SCIENTIFIC method sheets provide information on flow rate, regents, sample loop sizes and manifold configurations for standard or specific determinations. The laboratory based analyzer handles with up to 40 samples per hour. The simple construction enables quick interchange of electrode and flow-cells. When the method incorporates a flow injection valve, reproducible timing of the loop volume can be accomplished using the Burkard BT2000 loop timer with pencil switch.

Originally designed for fluoride determination in water, this technology has been extended to include applications in clinical, agricultural and industrial science. The following species are of typical uses for SIA: ammonia, nitrate and nitrite in soil sample; sodium and chloride for clinical methods; fluoride in soil and waters; total and free SO₂ in beer and wines; pH and conductivity.

The ALERT 2000-S is a chemical analyzer for continuous on-line monitoring of industrial processes, water (drinking water, rivers, sea-water, sewage) and effluents. It offers a flexible system that can be supplied for local measurement of a single chemical, or as a much larger network of multi-channel systems for remote monitoring over a wide geographical area. The analytical unit comprises a multi-port valve precision pump unit, chemistry manifold, a choice of detector and a pre-programmed database providing a range of control options and graphical indicators. The sample is continuously introduced via a diaphragm pump of suitable flow-rate into a weir. At intervals the sample and calibration standards are pumped at selected flow rates into the chemistry stream, where they may be diluted and mixed with reagents to form a colored complex which is measured at either visible or UV wavelengths in a colorimetric detector. The analogue amplifier signal is received by the Data A-D converter, analyzed, and continuously printed out showing sample concentration levels. From the processed data received, if concentration limits are exceeded, corrective measures will be taken by the process pumps to restore acceptable operating conditions. The analyzer has main isolations switches situated inside each cabinet. The chemistry module has a main ON-OFF switch and additional switches for the chemistry pump and sample pump. The pH-meter has a separate power source requiring a low voltage supply. At the heart of all ALERT 2000-S systems is an industrial computer. This is an all-solid state system consisting of a single board computer together with one or more intelligent analogue cards and a mix of other industry standard input/output, control and communication interface cards, depending on the application. Solid state relays and optional opto-isolated digital inputs and outputs allows the computer to operate valves, pumps and power supplied to directly control the analyzer, activate alarms, etc. For controlling industrial processes, three-term or PID functions may be added. Each ALERT 2000-S is designed to satisfy individual requirements and it is available in three configurations:

• 
  Monitoring locally with ALERT 2000 having built-in keypad and VDU.
  
• 
  Monitoring locally with connection to Homebase computer via RS232 (single ALERT 2000 over distances of up 100 meters) or RS422/RS485 (multi-drop over distances up to 1200 meters).
  
• 
  Monitoring over long distance using single or multiple ALERT 2000 systems connected to a Homebase via telephone links.
  

Other options of the system include self-diagnostics tests, reagent level monitoring and leak detection. On the communications side it offer a radio links to the telephone network. ReMAC allows access into the analyzer's data logs and audit trails. Files of data can be downloaded to Homebase, and graphic displays of past and current test levels may be displayed and plotted. ReMAC also allows complete control of the remote site by re-setting limits, and enabling and disabling of functions etc.

The ALERT 2000-S has a wide range of applications in the field of the on-line monitoring of wastewater; effluents; industrial process monitoring; food and drinks; pharmaceuticals, quality control.

All BURKARD analyzers can be fitted with the computer controlled automatic start-up and shut-down. A motorized wash/reagent changeover system ensures that all reagent lines are automatically connected to a water-wash on completion of analysis. The computer returns the valve to reagents for restart. Other computer control options are possible, e.g. reagent level sensing, special functions and interfacing to other instruments.

The CHEMLINE is the ALLIANCE Instruments’ first on-line monitor and it gives a correct answer to the problems of reliability, accuracy and low maintenance.

1. 
   The sample is admitted into the reactor by opening a specific valve and moving down the piston. A precise volume is admitted into the reactor by programming and then the valve is closed.
   
2. 
   The first reagent is admitted into the reactor by opening the second dedicate valve. The piston moves down in order to admit the right volume of reagent then the second valve is closed.
   
3. 
   The mixing of sample with the reagent is performed by moving the piston and admitting a gas (air or nitrogen) with the third valve. The step can be operated one or more times.
   
4. 
   The chemical reaction takes place in the reactor for some minutes. During this step all the valves are closed and piston is stopped.
   
5. 
   If necessary, a second reagent can be added or dilution performed by using the same principle.
   
6. 
   The last step is to take the measurement by pushing the solution to the detector, which can be a colorimeter, an infrared detector, a UV photometer or selective electrode. Another valve, at the top of the reactor is used.
   
7. 
   After closing this valve, there are three possibilities:
   

A complete washing operation is performed;

Calibration is performed

8. 
   If it is important to accelerate the development of the reaction product by heating, to distillate the sample or to use a UV digester, another valve will be selected in order to send the solution to a specific module: heating-bath, distillation unit, UV lamp, etc. The same valve will permit the return to the reactor if another reaction has to be done.
   

All the operations: step number of the motor, opening and closing of the valves are controlled by a microprocessor, each step is fully programmable. This patented principle allows a very high accuracy of volume insertion and guarantees very good quality of the analysis. Before or during the analysis, an automatic dilution can be programmed. The level and the factor of dilution are programmable. The analytical section does not require a regular maintenance. Only, some seals and o-rings can be replaced every six month. This new way of mixing samples and reagents without using a peristaltic pump offers a significant advantage to the user: a very low maintenance (no change of tubes, nothing to maintain regularly). It is not required to stop the analyzer the user must only refill the CHEMLINE with reagents.

In most cases, colorimetric detection is performed in the range 400-800 nm. The colorimeter includes a tungsten-halogen lamp, lenses which focus the light in a 10, 30 or 50 mm flow-cell. The detection is dichromatic: the transmitted light is divided in 2 equivalent beams by a prism and analyzed at two different wavelengths. The final measurement is obtained by difference. This type of detection cancels matrix effects like color of the sample especially important when it is changing.