Skip to main content

Automated analysis

 

Clinical courses

About Authors:
Patelia emanual michael*, Keyur B Ahir
Department of Pharmaceutical Chemistry and Analysis,
Indukaka Ipcowala College of Pharmacy,
New Vallabh Vidyanagar – 388121, Gujarat, India.
*ricky.emanual@gmail.com

Abstract:
Ethane, cyclohexane, SO2, ethylene and other gaseous components. Liquid solutions also can be monitored by the analyzers. Near IR measurements using tungsten filaments lamps as sources are often used to monitor water concentrations. IR reflectance can be used to monitor water concentration in some solids, such as in paper. If moisture is present some of the incident radiation is observed and less is reflected at the wavelengths characteristics of water.
Gas chromatography is the most used process control chromatographic technique. Process control gas chromatographs are generally capable of automatic column switching and back flushing. Back flushing eliminates from the column those long retention time components in the sample which are not assayed. The sample is automatically injected in to the proper column and partially or completely separated in to its components. After the component of interest has reached the detector, the flow of carrier gas through the column is reversed to remove the long retention time components from the column and thereby minimize the analytical dead time prior to injection of the next sample.

REFERENCE ID: PHARMATUTOR-ART-1631

Introduction:
Both liquids and gases have been monitored by process control gas chromatography. Gaseous sample volumes are normally in the range form 0.5-100 ml and liquid sample volume range from 0.5-5µl. In order to minimize dead time, the gas chromatograph is placed as near to the sampled stream as possible. Generally it is advisable to keep the total sampling and assay time less than 4 or 5 minutes. The controller is often well removed from the instrument, in the laboratory or control room of the industrial plant. Timing sequences during sample injection, development, back flushing and switching can be controlled mechanically with rotating cams or servo motors, or electronically. Micro computers are often used for instrumental control and to perform peak integrations and calculations. Liquid chromatographs have also been used as process control analyzers.


Of the electro analytical process control techniques, potentiometry has been used most often. The pH meter is probably the most used of the process control electro analyzers. Ion selective electrodes have been used in process control with flow through cells to monitor H+, s2-, CN-, Na+, Ag+, water hardness, F-, and other ions. Amperometry is commonly used to monitor dissolved O2. Other electro analytical techniques which have been used in process control include coulometry, conductometry, and automated potentiometric titrimetry. In some process control applications it has been possible to use radio chemical analyzers, which monitor the radio activity of the sample.

1. Centrifugal force analyzer
*    A centrifugal force analyzer consists of a wheel containing                             compartments for samples, reagents, and the detector measurement.
*    As the wheel rotates, the solutions in the compartments closer  to the center of the wheel are moved by centrifugal force through connecting channels to the outer compartments, which contain other solutions.
*    During the process the sample and reagents are mixed and then forced into the outermost compartment, where a detector measures the concentration of the reaction product.
*    Because many samples can be assayed both simultaneously and rapidly with a centrifugal analyzer, the device is sometimes referred to as a parallel-fast analyzer.
*    Centrifugal analyzers vary in the number of samples that can be simultaneously assayed and in various operating parameters.
*    The best known of the centrifugal analyzers is the GeMSAEC analyzer that is manufactured by Electro-Nucleonics.
*    GeMSAEC is an acronym for the National Institute of General Medical Sciences and the Atomic Energy Commission.
*    A side-view sketch of the rotor used in the GeMSAEC analyzer is shown in fig.


*    Sample solutions are loaded into the compartments located nearest to the center of the wheel. Reagents are loaded in the reagent compartments and the wheel is rotated about its axis. Centrifugal force from the rotation moves the sample over the barrier separating the sample from the reagent, and eventually through a capillary and into a cuvet at the outer edge of the wheel.
*    Mixing is accomplished by the rapid change in rotation rate as the wheel accelerates.
*    Radiation from a monochromator passes vertically through the quartz windows of the cuvets to a photomultiplier tube which measures the transmittance of each sample as it rotates past the spectrophotometric detector.
*    The tansmittances of the sample are displayed on an oscilloscope, where each sample appears as a negative peak. The peaks are separated by flat portions.
*    The rotors used in centrifugal analyzer have positions for between 15 and 30 samples. The results are monitored by a computer, which calculates concentrations and averages results after many rotations.

*    ADVANTAGE: results obtain with high speed
*    DISADVANTAGE: each sample and reagent compartment must be individually loaded prior to the analyses.
*    A centrifugal analyzer can do only a single type of analysis on a loaded series of samples.
*    Different types of analyses are performed by changing the reagents and the wavelength at which the detector is adjusted.

NOW YOU CAN ALSO PUBLISH YOUR ARTICLE ONLINE.

SUBMIT YOUR ARTICLE/PROJECT AT articles@pharmatutor.org

Subscribe to Pharmatutor Alerts by Email

FIND OUT MORE ARTICLES AT OUR DATABASE

2. Automatic titrators
*    An entire titration can performed automatically by titrators equipped with microcomputer and analog-to-digital converter, and using dedicated software. Digitally controlled stepper motors permit precise control of the titrant.
*    A fully automatic unit accepts, serially, samples placed on a turntable.
*    After each titration the turnable rotates, indexes the next sample beneath the electrode assembly, and actuated the titration switch.
*    This type of instrumentation is ideal for performing multiple analyses in which the fundamental analytical procedure remain fixed, as in a quality control situation.
*    Automatic titrators can also be used to measure the volume of titrant required to maintain the indicator electrode at a constant potential. The volume added is plotted automatically versus time and becomes useful in kinetic studies.
*    Since many enzymatic reactions result in the release or consumption of hydrogen ion, the amount of acid or base required to maintain a constant pH versus time gives a measure of the enzyme activity.

3. Laboratory robots
*    In most analytical laboratories concerned with automated analysis there is a large deficiency, the automation of physical manipulation. These manipulation may include several of the following operation:
-    Sample identification
-    Extraction of aliquots,
-    Concentration,
-    Extraction,
-    Crushing,
-    Grinding,
-    Weighing,
-    Addition of reagents.

*    Important consideration in the use of  laboratory robots are coordinate system, drive system,  hand, sensors and programming.
*    In addition to reducing the cost of performing such operations by a factor of four compared with human labor, the use of robots frees the chemist from many tedious tasks.
*    The typical laboratory robot consists of a body, an arm, and a hand or gripper.
*    Movement of the body or arm allow the hand to sweep out a space that can be viewed as Cartesian, cylindrical, or spherical. Joints may be added to the arm to allow more flexibility. At a minimum, the hand must contain a pair of fingers to grasp an object.
*    The parts of the robot are moved by electrical servo or stepper motors.
*    Servo motors are more reliable under mechanical torque, whereas stepper motors provide low cost and an easy interface to digital microcomputers.
*    Regardless of the type of motor used, the mechanical properties of the drive train between the motor and the robot component are important to precise, reliable robot operation.
*    The robot is only one components of a robotic laboratory work station, other components are a microcomputer and the instrumentation required for the analysis.
*    The three components are linked by a hardware-software interface and by the devices that are required to give the robot precise and reliable mechanical coupling to the elements at the work station.
*    Because of the limited sensory input available with current robots, precise mechanical interfaces between the robot and each work station component are necessary.
*    The environment around the robot must be designed so that the robot can find and grasp the desired component.
*    Mechanical devices used to accomplish the required task include a mobile base for the robot, gripper fingers or hands for handling test tubes, beakers, or flasks, sample racks and empty container magazines, and holders for electrodes and pipet tips.
*    Although most commercially available robot can be programmed using a hand-held training pendant, the capabilities of many robots can be extended by interfacing them to microcomputers. Comprehensive robotic work station software can be developed using high-level languages such as BASIC or FORTH.

4. Automatic organic elemental analysis
*    Several manufacturers produce automatic instruments for analyzing organic compounds for one or more of the common element including carbon, hydrogen, nitrogen, oxygen, and sulfur.
*    All of these instrument are based upon high-temperature oxidation of the organic compound, which convert the element of interest to gaseous molecules.
*    In some instrument, the gases are separated on a chromatographic column, while in others separations are based upon specification absorbents.
*    In most instrument, thermal conductivity detection server to complete the determinations. These instruments are equipped with devices that automatically load the weighed sample into the combustion area.

*    An automatic C, H, and N analyzer
*    In this instrument, sample are oxidized at 900 0C under static conditions in pure oxygen environment that produces a gaseous mixture of carbon dioxide, carbon monoxide, water, elemental nitrogen, and oxide of nitrogen.
*    After 2 to 6 min in the oxygen environment, the products are swept with a stream of helium through a 750 0C tube furnace where hot copper reduces the oxides of nitrogen to the element and also removes the oxygen as copper oxide.
*    Additional copper oxide is also present to convert carbon monoxide to the dioxide. Halogen are removed by a silver wool packing.
*    The product from the reaction furnace pass into a mixing chamber where they are brought to a constant temperature.
*    The resulting homogeneous mixture is then analyzed by passing it through a series of three precision thermal conductivity detector, each detector consisting of a pair of sensing cells.
*    Between the first pair of cells is a magnesium perchlorate absorption trap that removes water. The differential signal then server as a measure of the hydrogen in the sample.
*    Carbon dioxide is removed in a second absorption trap. Again, the differential signal between the second pair of the cell is a measure of carbon in the sample.
*    The remaining gas, consisting of helium and nitrogen, passes through the third detector cell.
*    The output of this cell is compared to that of a reference cell through which pure helium flows. The voltage differential across this pair of cells is related to the amount of nitrogen in the sample.

NOW YOU CAN ALSO PUBLISH YOUR ARTICLE ONLINE.

SUBMIT YOUR ARTICLE/PROJECT AT articles@pharmatutor.org

Subscribe to Pharmatutor Alerts by Email

FIND OUT MORE ARTICLES AT OUR DATABASE

For oxygen analysis,
*  The reaction tube is replace by a quartz tube filled with platinized carbon. When the sample is pyrolyzed in helium and swept through this tube, all of the oxygen is converted to carbon monoxide, which is then convert to carbon dioxide by passage over hot copper oxide. The remainder of the procedure same, with the oxygen concentration being related to the differential signal before and after absorption of the carbon dioxide.

For sulfur analysis,
*  The sample is combusted in an oxygen atmosphere in a tube packed with tungsten(VI) oxide or copper oxide. Water is removed by a dehydrating reagent located in the cool zone of the same tube. The dry sulfur dioxide is then separated and determined by the differential signal at what is normally the hydrogen detection bridge. In this instance, however, the sulfur dioxide is absorbed by a silver oxide reagent.

5. Process-control analyzers
*    Because process-control analyzers must function without constant human supervision, they must be more stable and more rugged than the corresponding laboratory instruments.
*    Sometimes process control analyzers are categorized as either nonspecific analyzers or as specific analyzers.
*    Nonspecific analyzers measure a physical property such as temperature, pressure, or thermal conductivity. Such analyzers do not directly provide information about a specific chemical component of the system.
*    Specific analyzers assay one or more individual components of the system. Instruments such as spectrophotometers and chromatographs are specific analyzers.
*    Specific analyzers must be calibrated in much the same manner in which laboratory instruments are calibrated. Usually calibration is done by performing a laboratory assay on the sample assayed with the process- control analyzer and adjusting the process-control analyzer to yield the value obtained in laboratory. The process is periodically repeated to ensure that the process-control analyzer has not drifted from its calibrated position.
*    The more popular analyzers use a spectroscopic, chromatographic, or electroanalytical technique.
*    Among the spectroscopic instruments used for process control are ultraviolet, visible, and infrared absorptive instruments.
*    Turbidimetry, flame emission, fluorescence, chemiluminescence, and refraction have also been used in process control.
*    Refractive-index and infrared-absorptive measurements are used more often in process control than other spectral methods.
*    Refractive index measurement, differential refractive-index measurements, and critical-angle measurements can be used to measure the concentration of one component in a two-component mixture.
*    The concentration of one component in more complex solutions generally cannot be determined from refractive-index measurements.
*    The refractive index and the critical angle can be measured directly in the process stream.
*    Other uses, the measurements have been used for process-control assay of sugar in beverages, Alcohol in beverages, Dissolved solids in beverages, Ketchup, jam and jelly, and saturated hydrocarbons in fats and oils.
*    Dispersive infrared spectrophotometers are occasionally used, the infrared analyzers that are used for process control are normally nondispersive.
*    The detector contains the same substance that is assayed. Interferences in the measurements that are made by some instrument that use traditional infrared detectors are eliminated by passing radiation from the source through filters that contain a high concentration of the interference. Essentially all of that portion of the infrared spectrum that could be absorbed by the interference is absorbed by the filter, thereby eliminating the effect of the interference on the detector.
*    Infrared absorbance measurements have been used to monitor CO2 , CO , CH4 ,H2O(g), NH3 , Ethane, cyclohexane, SO2, ethylene and other gaseous components.
*    Liquid solutions also can be monitored by the analyzers.
*    Near IR measurements using tungsten filaments lamps as sources are often used to monitor water concentrations.
*    IR reflectance can be used to monitor water concentration in some solids, such as in paper.
*    If moisture is present some of the incident radiation is absorbed and less is reflected at the wavelengths characteristics of water.
*    Gas chromatography is the most used process control chromatographic technique.
*    Process control gas chromatographs are generally capable of automatic column switching and back flushing.
*    Back flushing eliminates from the column those long retention time components in the sample which are not assayed.
*    The sample is automatically injected in to the proper column and partially or completely separated in to its components.
*    After the component of interest has reached the detector, the flow of carrier gas through the column is reversed to remove the long retention time components from the column and thereby minimize the analytical dead time prior to injection of the next sample.
*    The back flushed components generally flow to the detector in a single block and appear as a single chromatographic peak.
*    Injection in to process  control gas chromatographs is usually accomplished with an automatic sampling valve which is designed in a manner similar to that of the sample introduction valves used for HPLC.
*    The GC detectors most often used with process control chromatographs are the thermal conductivity detector and the flame ionization detector.
*    Gas chromatographic process control analyzers have proved to be especially useful in the control of distillation columns.
*    Process control gas chromatographs can be operated either with or without temperature programming.
*    Both liquids and gases have been monitored by process control gas chromatography. Gaseous sample volumes are normally in the range form 0.5-100 ml and liquid sample volume range from 0.5-5µl.
*    In order to minimize dead time, the gas chromatograph is placed as near to the sampled stream as possible.
*    Timing sequences during sample injection, development, back flushing and switching can be controlled mechanically with rotating cams or servo motors, or electronically.
*    Micro computers are often used for instrumental control and to perform peak integrations and calculations. Liquid chromatographs have also been used as process control analyzers.
*    Of the electroanalytical process-control techniques, potentiometry has been used most often.
*    The pH meter is probably the most used of the process control electroanalyzers.
*    Ion selective electrodes have been used in process control with flow through cells to monitor H+, s2-, CN-, Na+, Ag+, water hardness, F-, and other ions
*    Amperometry is commonly used to monitor dissolved O2.
*    Other electroanalytical techniques which have been used in process control include coulometry, conductometry, and automated potentiometric titrimetry.
*     In some process control applications it has been possible to use radio chemical analyzers, which monitor the radio activity of the sample.

Conclusion:
Specific analyzers assay one or more individual components of the system. Instruments such as spectrophotometers and chromatographs are specific analyzers. Specific analyzers must be calibrated in much the same manner in which laboratory instruments are calibrated. Usually calibration is done by performing a laboratory assay on the sample assayed with the process- control analyzer and adjusting the process-control analyzer to yield the value obtained in laboratory. The process is periodically repeated to ensure that the process-control analyzer has not drifted from its calibrated position.

The more popular analyzers use a spectroscopic, chromatographic, or electroanalytical technique.

References
1)    Principles of instrumental analysis; By D.A.Skoog, F.J.Holler, T.A.Nieman; Fifth  edition; 2005; Page no-842 to 845.
2)    Introduction to instrumental analysis; By R.D.Braun; Publiched by pharmamed press; Page no-963-964 & 970 to 975.
3)    Instrumental methods of analysis By H.H.Willard, L.L.Merritt, J.A.Dean, F.A.Settle; 7th edition, CBS Publishers and Distributors, Page no. 694, 824-826.

NOW YOU CAN ALSO PUBLISH YOUR ARTICLE ONLINE.

SUBMIT YOUR ARTICLE/PROJECT AT articles@pharmatutor.org

Subscribe to Pharmatutor Alerts by Email

FIND OUT MORE ARTICLES AT OUR DATABASE