This article throws light upon the ten modern techniques used to control pollutants discharged from industries. Some of the techniques are: 1. Capillary Isatochophoresis 2. Cryogenic Gas Chromatography 3. Closed Loop Stripping Analysis 4. Inductive Coupled Plasma Instrumentation 5. Continuous Flow-Wet Analyser 6. Dual-Ion Chromatography 7. Gas-Chromatography-Mass Spectrometry-Data Programme System and Others.
Technique # 1. Capillary Isatochophoresis:
It is a technique of separating a mixture of substances in capillary but without the use of any support or packing. This technique has been used very successfully in quality control, process control and control of pollutants discharged from chemical industry.
ADVERTISEMENTS:
Sulfur oxide and other sulphur compounds (such as, thiocyanate, thiosulphate etc.) nitrates and nitrites and also some EDTA-chelates, constitutes the major effluents of some chemical industries. Capillary isatochophoresis has been applied for monitoring drainage and for treatment of such waste-water, containing similar compounds. The sample requirement is low about 2pl and the technique does not require any pretreatment procedure.
By using leading electrolyte of 10 mH histidine-HCL+10 mH histidine 50% acetone and terminal electrolyte of 0.01 Mn-caproic acid, in a capillary tube of 0.5 mm i.d of 20 cm long. A mixture of waste water from industry effluents was successfully treated for analysis and separation of inorganic pollutant ions viz., SO4—; SO3–“; EDTA; EDTA-fe and also SO3NH2~. The mixture of these pollutants from water was separated under temperature conditions of 20°C with the use of 50 p current.
Technique # 2. Cryogenic Gas Chromatography:
Cryogenic gas chromatography is a technique of focusing or trapping the substance, either by cooling or by concentrating on the adsorbent, as the case may be. The cryogenic focusing is helpful in separation of pollutants such as polycyclic aromatic hydrocarbons, tri-halo methane and poly-chlorinated biphenyls from effluents, there by facilitating in pollution control and monitoring. It has been successfully applied for detection of gasoline in water at the level of 4 ppm. Besides, cryofocussing has also been employed for thermal desorption of organic compounds from ultra-low tar cigarette smoke.
Other applications of cryofocusing includes, study of volatile sulphur compounds, the determination of monoterpenes hydrocarbons in the atmosphere and analysis of human auxilliary volatiles. Cryofocussing have also been used for identification of off-flavour compounds, analysis of volatile aroma components in fruits and vegetable juice, analysis of volatiles released from disintegrating fruits and analysis of volatile compounds from wine and brandies.
Cryogenic trapping is oldest and best known of cryogenic techniques. The use of cryogenic trapping has been established in modern environmental analysis as a satisfactory sampling procedure prior to the determination of volatile pollutants in air and water samples.
Many of the applications of cryogenic trapping have been, in conjugation with the sampling of air, for specific analytes such as, as methyl-bromide, methyl-chloride, vinyl-chloride, phosphine, chloroprene, hydrocarbons, chlorinated hydrocarbons, halocarbons, Freon, nitrous oxide, tetralkyl-lead compounds, nitrosamines and other pollutants. Ethylene has been reported to be trapped by this technique up to and extent of 100% from a large volume of air.
ADVERTISEMENTS:
The air samples containing methyl-cyclo-penta-dienyl-maganese-tricarbonyl, sulphur compounds in urban atmosphere and the lower aliphatic carbonyls in exhaust gases have been successfully analysed and separated by this. Some other environmental applications are, determination of alkyl-arsenic acids in pesticides, analysis of fish and sediments for volatile priority pollutants, sampling of stack gas for SO2 etc.. Recently cold cryotrapping has been employed for air monitoring of nicotine contaminators and nitrated PAHs in diesel particulates. Other areas which have used cryogenic trapping includes foods sciences, analytes for manufacturing processes and some other miscellaneous applications.
Technique # 3. Closed Loop Stripping Analysis:
Closed loop stripping analysis is an electro chemical sampling concentration technique capable of concentrating up to one million fold thereby, facilitating detection and separation of organics up to very low-level. The technique is applicable to a range of compounds including fuels, chlorinated hydrocarbons, substituted aromatics.
It has also been widely used for monitoring of water samples, industrial effluents, river water, tap and normal water. The closed loop stripping analysis have been applied for analysis of fuels in water. The detection limit is less than 1 ppb.
Technique # 4. Inductive Coupled Plasma Instrumentation:
Inductive coupled plasma instrumentation is a technique for multi-elemental screening of environmental samples. This is an effective technology for trace metal screening of hazardous material to assess the toxicity potential of sites. By inductive-coupled plasma instrumentation at least 26 elements can be analysed from a sample mixture at a time.
ADVERTISEMENTS:
The analytical accuracy is within the limit of (±) 25%. Range of metals detected includes, Al, Sb, As, Ba, Be, B, Cd, Ca, Cr, Co, Cu, Fe, Pb, Mg, Mn, Hg*, Mo, Ni, Sc, Ag, Na, TI, Sn, Ti, V and Zn etc. By this technique analyst can currently scan 30-40 samples each for 26 elements and report data in less than eight hour.
Technique # 5. Continuous Flow-Wet Analyser:
It is a reliable process for close monitoring and control of process, as well as analysis of pollutants such as cyanides, metals and phenols’ in effluents. Atypical application of this technique is the on-line monitoring of total organic carbon (TOC), which is effectively analysed using low temperature photochemical oxidation which generate carbon dioxide. Any CO2 generated is separated and finally analysed colorimetrically giving TOC-value. Inorganic ions can be removed up to 1000 ppm level.
Cyanide present as main pollutant up to limit of 10-500 pg/L can be successfully analysed. Survey reveals that metal cyanide of cobalt, nickel, silver, cadmium and ferric cyanide and also thiocyanide have been recovered by this technique.
Silica in boiler water up to the limit of 1.5 ppb, have been successfully analysed. Besides this, analysis of ammonia, hexavalent chromium, sulfates, copper, nitrates, hardness and phenol includes its other applications.
Technique # 6. Dual-Ion Chromatography:
ADVERTISEMENTS:
This technique determines cations and anions simultaneously, using a complexing agent, to complex the divalent metals, which are finally separated and also detected. The analysis time for the determination of the ion is considerably less. For monovalent cation and anion, it is less than 15 minutes, whereas for divalent cation and anion, it is less than 30 minutes. The detection limit approaches 1 ppm for most of the species.
It determine a diverse range of environmentally critical compounds in sub ppb-level, in almost any sample of matrix, which includes, organic and inorganic cations and anions, organic acids, organic amines, transitional metals, carbohydrates and alcohols.
Recently, amerometric detection technique have made a revolutionary change in the field of ion chromatography. It is basically an electro-chemical phenomenon, which is used for detection of specific substances, that are easily oxidizable or reduceable.
Environmental and industrial samples containing iodides, cyanides and sulfites sulfides, bromide, thiocyanate etc., have been successfully screened by this technology. Soil samples and environmental water samples containing cyanides even up to the limit of 1.2 ppm can be detected by this instrument.
The sulfite contaminated in food is dangerous to public health. The amero-metric ion chromatography is a suitable technology for detection of sulfites, even in the presence of sulphate, formed due to its oxidation.
Thus it provides detection limit far superior than any other alternative technique. Recently ion chromatography has been applied for separation of anions in shale products, organic carboxylic acids in waste water. This method has been, also applied for detection of formaldehyde in water, ammonia and ethanol-amine in refinery water.
Technique # 7. Gas-Chromatography-Mass Spectrometry-Data Programme System:
In recent years, the analysis of air and water have become very essential to estimate the level of environmental pollutants for maintenance of proper hygienic conditions and materiology. GC-MS-DP system is basically a chromatographic, resolution, mass- spectrometric identification and data-interpretation, all three combined into one.
The device helps in identifying more than 150 compounds in air, including saturated hydrocarbons (from butane to tridecane) and their isomers, olefins, aromatic compounds, naphthalene (methyl-cyclobutane, cyclopentane, cyclohexane etc.), ether, ester, aldehydes, ketone, alcohol, organochlorine compounds, terpenes. The analysis sensitivity is 1 µg/m3.
The device also helps in analysing water samples containing more than 70 compounds, including organohalogen compounds (chloroform, bromo-dichloro methane, tri-chloroethylene, tetra-chloro-ethylene), aromatic hydrocarbons (from pentane to tri-decane) and their isomers, napthalene (methyl-cyclo-pantone, methyl-cyclo hexane, dimethyl-cyclo-hexane, propyl-cyclo hexane) and terpene (bornanone-2, ƴ-pipene limonene compounds etc.), dimethyl-ether, acetal- dehyde and 2-ethyl-4-methyl 2 pentanol.
Technique # 8. Low Temperature-UV Promoted Chemical Oxidation TOC-Analysis:
High temperature oxidation method has been used since 1963, for determination of total organic carbon (TOC- value), but it has one major disadvantage attached to it i.e. its low sensitivity. The demand for better drinking water quality and industrial ultra-pure water have contributed to the need for a method of measuring organic carbon at very low parts per billion (ppb) concentration. Low temperature ultra-violet (UV)-promoted chemical oxidation TOC-analyzers, provided better results.
The low-temperature-instrument provide continuous flow of per sulfate solution to promote oxidation prior to UV-irradiation since reactions take place in the liquid phase, disadvantage of catalyst poisoning, reactor corrosion and high temperature element burnouts are completely ruled out.
By this technique samples of naturally occurring water, including waste water, sludge’s and brine were analysed. The error was within the limit of ± 2% (for sample containing small amount of suspended particles and + 6% for samples containing high levels of suspended particles). It has also analysed successfully several samples of sea water.
This improved combustion technique offers several advantages over other conventional high temperature techniques. The technique’s capability of handling large sample volumes, up to 1000 µL, enhances sensitivity for trace level analysis. Particulate and salt containing samples can be routinely analysed very successfully by this technology.
Technique # 9. Slotted Tube-Atom Trap-Flame Atomic Absorption Spectrophotometry:
Slotted tube atom trap-AAS is a new technique for determination and monitoring of elements such as lead, cadmium, arsenic, copper, zinc and thallium in environment and water-treatment plants. This STAT-AAS provide results within 10 seconds even for a very low concentrations of elements (up to sub ppm levels).
Application of STAT, includes, the determination on lead, cadmium, zinc and copper in portable and waste waters, the determination of copper and zinc in serum, the determination of lead in whole blood and determination of lead and cadmium in urine.
It has also been used for detecting toxicological effects of lead in tinned food. Thus STAT, provides a simple and in-expensive technique for the determination of low levels of a number of important elements in environment.
Technique # 10. Zeeman Electro Thermal Atomic Absorption Spectrophotometer:
Electro-thermal AAS is currently the method of choice for high sensitivity trace metals analysis, water treatment plants, hazardous waste sites, forensic, clinical and semiconductor, industries.
High sensitivity makes it ideal for measuring trace metal pollutants in water and wastewater. Various pollutants detected and monitored are Al, As, Cd, Cr, Cu, Pb, Se in effluent water and Ag, As, Cd, Cr, Hg, Pb, reported in municipal digested sludge.
Many metals contaminated in the soil, causes its pollution. By this AAS technique, arsenic, cobalt, copper, chromium, silver, gold, nickel and zinc were successfully analysed.
The analysis of elements such as arsenic, selenium and antimony is greatly simplified since no hydrine generation accessory is required.