33A-1 Advantages and Disadvantages of Automatic Analyses33A-2 Unit Operations in Chemical Analysis33A-3 Types of Automatic Analytical Systems33B FLOW-INJECTION ANALYSISSample and Reagent Transport SystemSample Injectors and DetectorsSeparations in FIADialysis and Gas DiffusionExtraction33B-2 Principles of Flow-Injection AnalysisDispersion33B-3 Applications of Flow-Injection AnalysisLimited-Dispersion Applications33C DISCRETE AUTOMATIC SYSTEMS33C-1 Automatic Sampling and Sample Definition of Liquids and Gases33C-2 Robotics33D ANALYSES BASED UPON MULTILAYER FILMS.Chemistry 331Chapter 33 Automated Methods of Analysis.33A AN OVERVIEW OF AUTOMATIC INSTRUMENTS AND INSTRUMENTATIONBy IUPAC terminology, automatic devices do not modify their operation as a result of feedback from an analytical transducer. For example, an automatic acid/base titrator adds reagent to a solution and simultaneously records pH as a function of volume of reagent. In contrast, an automated instrument contains on or more feedback systems that control the course of the analysis. Thus, some automated titrator compare the potential of a glass electrode to its theoretical potential at the equivalence point and use the difference to control the rate of addition of acid or base.33A-1 Advantages and Disadvantages of Automatic AnalysesIn the proper context, automated instruments offer a major economic advantage because of their savings in labor costs. A second major advantage of automated instruments is their speed, which is frequently significantly greater than that of manual devices. The third advantage of automation is that a well-designed analyzer can usually produce more reproducible resultsover a long period of time than can an operator employing a manual instrument. The reasons for this are machines do not suffer from fatigue, which has been demonstrated to adversely affect the result obtained manually, particularly near the end of a working day. The second reason is the high reproducibility of the timing sequences of automated instruments.33A-2 Unit Operations in Chemical AnalysisAll analytical methods can be broken down into a series of eight steps, or unit operations, any one of which can be automated. The table below list the steps in the order in which they occur in a typical analysis.33A-3 Types of Automatic Analytical SystemsAutomatic analytical systems are of two general types: discrete analyzers and continuous-flow analyzers; occasionally, a combination of the two is encountered. In a discrete instrument, individual samples are maintained asseparate entities and kept in separate vessels throughout each unit operation listed on the table. In continuous-flow systems, in contrast, the sample becomes a part of a flowing stream where the several unit operations take place as the sample is carried from the injection or sample introduction pointto a flow-through measuring unit, and thence to waste. Both instruments are computer controlled.33B FLOW-INJECTION ANALYSISFlow-injection methods, in their present form, were first described in the mid 70s. Flow-injection methods are and outgrowth of segmented-flow procedures, which were widely used in clinical laboratories in the 1960s and 1970s for automatic routine determination of a variety of species in blood and urine samples for medical diagnostic purposes. The discoverers of flow-injection analysis found, however, that excess dispersion and cross-contamination are nearly completely avoided in a properly designed system without air bubbles and that mixing of samples and reagents could be easily realized.33B-1 InstrumentationSample and Reagent Transport SystemOrdinarily, the solution in a flow-injection analysis is moved through the system by a peristaltic pump, a device in which a fluid ( liquid or gas) is squeezed through plastic tubing by rollers.Sample Injectors and DetectorsThe injectors and detectors employed in flow-injection analysis are similar in kind and performance requirements to those used in HPLC. For successfulanalysis, it is vital that the sample solution be infected rapidly as a pulse or plug of liquid; in addition, the injections must not disturb the flow of the carrier stream. Detection in flow-injection procedures has been carried out by atomic absorption and emission instruments, fluorometers, electrochemical systems, refractometers, spectrophotometers, and photometer.Separations in FIASeparations by dialysis, by liquid/liquid extraction, and by gaseous diffusionare readily carried out automatically with flow-injection systems.Dialysis and Gas DiffusionDialysis is often used continuous-flow methods to separate inorganic ions, such as chloride or sodium or small organic molecules, such as glucose, from high-molecular-weight species such as proteins.ExtractionAnother common separation technique readily adapted to continuous-flow methods is extraction. It is important to reiterate that none of the separation procedures in FIA methods is ever complete. The lack of completeness is of no consequence, however, because unknowns and standards are treated an identical way.33B-2 Principles of Flow-Injection AnalysisDispersionDispersion D is defined by the equationD = co/c Where co is the analyte concentration of the injected sample and c is the peak concentration at the detector. Dispersion is influenced by three interrelated and controllable variables: sample volume, tube length, and pumping rate.33B-3 Applications of Flow-Injection AnalysisIn the flow-injection literature, the terms limited dispersion, medium dispersion, and large dispersion are frequently encountered where they refer to dispersions of 1 to 3, 3 to 10, and greater than 10, respectively.Limited-Dispersion ApplicationsLimited-dispersion flow-injection techniques have found considerable application for high-speed feeding of such detector systems as flame atomic absorption and emission as well as inductively coupled plasma. It is also used with electrochemical detectors such as specific-ion electrodes and voltammetric microelectrodes.33C DISCRETE AUTOMATIC SYSTEMSA wide variety of discrete automatic systems are offered by numerous instrument manufacturers. Some of these devices are designed to perform one or more.33C-1 Automatic Sampling and Sample Definition of Liquids and GasesSeveral dozen automatic devices for sampling liquids and gases are currentlyavailable from instrument manufactures. This device consists of a movable probe, which is a syringe needle or a piece of fine plastic