A Review: Application of Microwave Techniques for Environmental Analytical Chemistry

Abstract

The acceptance of microwave digestion technique is based on procedures successfully carried out for mist different kinds of samples. The goals of this paper are to gather all information concerning applications of microwave digestion methods to analytical chemistry. Some applications of microwave techniques to sample digestion, solvent extraction, sample drying, the measurements of moisture, analyte desorption and adsorption, sample clean up, chromomeric reaction, speciation, and nebulization of analytical samples are presented.     

Development of magnetic dispersive microsolid-phase extraction using lanthanum phosphate nanoparticles doped on magnetic graphene oxide as a highly selective adsorbent for pesticide residues analysis in water and fruit samples

Magnetic graphene oxide/lanthanum phosphate nanocomposite (MGO@LaP) was synthesized and used as an efficient adsorbent for magnetic dispersive microsolid-phase extraction (MD-µ-SPE) of pesticides before gas chromatography–electron capture detector (GC–ECD) analysis. The adsorbent was thoroughly characterized with scanning electron microscopy, vibrating sample magnetometer, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Optimized extraction conditions were investigated concerning extraction time, adsorbent amount, sample pH, and salt amount as well as desorption conditions (type and volume of desorption solvent and desorption time). Under the optimal conditions, the method demonstrated good linearity (3–1500 µg L^?1) with satisfactory determination coefficients of >?0.997 and low detection limits for both chlorpyrifos (0.67 µg L^?1) and hexaconazole (0.89 µg L^?1). Finally, the method showed high analyte relative recoveries in the range of 78–120% for the determination of the selected pesticides in water and fruit juice samples.

     

磁性多壁碳纳米管固相萃取-气相色谱-质谱法检测水样中的13种邻苯二甲酸酯类化合物

建立了磁性多壁碳纳米管(MWCNTs)固相萃取结合气相色谱-质谱检测水样中13种邻苯二甲酸酯类化合物(PAEs)的方法。优化了萃取时间、水样pH值、解吸溶剂的种类和用量、解吸时间等影响萃取效率的主要条件。最终确定萃取时间为10 min,水样pH 5～7,解吸溶剂为2 mL丙酮,解吸时间为5 min。在优化的条件下,各组分的萃取回收率为89.7%～100.5%。方法具有较高的灵敏度,检出限(信噪比(S/N)为3)为0.08～0.47 μg/L。3种实际样品的加标回收率为84.5%～107.5%,相对标准偏差为1.9%～12.8%。该方法操作简便、省时,准确、灵敏、环保,可用于水样中PAEs的检测,并成功地应用于自来水、瓶装饮用水和湖水样品的分析,13种PAEs均未检出。     

Trace Analysis of Hydrocarbons in Air Using Standard Gas Chromatographic and Personal Sampling Equipment

Abstract

Unmodified standard gas chromatographs are reported to be useful for the determination of a large number of ambient hydrocarbons. Packing of standard injector glass liners with an adsorbent permits thermal desorption in the injector on to the chromatographic column. Coupling to a personal sampling pump permits exposure-related sampling. The potential of the technique is illustrated by applications with the Tenax GC adsorbent. Precautions required to avoid artifacts when working in the subnanogram range are described.     

Comparaison de Differentes Methodes Analytiques Appliquees au Dosage des Hydrocarbures Dissousdans L'Eaua L'etatde Traces

Abstract

Many physical-chemical methods are employed for the evaluation of trace hydrocarbons dissolved, in underground or surface waters.

Comparison is done of three techniques chosen amongst the most commonly used in the studies conducted on water pollution caused by oil products:

infrared spectroscopy;

ultraviolet spectrofluorimetry;

gas chromatography.

To enable the application of these techniques to very low concentrations of hydrocarbon all these techniques require a concentration step.

This can be carried out, either by the liquid-liquid extraction of the hydrocarbons with the assistance of an organic solvent and in this case, the concentration ratios are poor, or by the trapping technique, where the hydrocarbon concentration is effected by adsorption on a resin, followed by desorption by a relatively small amount of an appropriate organic solvent. The water amounts so treated can be 10 to 100 larger than those treated by a liquid-liquid extraction.

A trapping system is described which has been used in an initial phase for the detection and quantitation of aromatic hydrocarbons up to C₉. The operational conditions are described for the measurement of heavier hydrocarbons (sampled water quantity and flow, desorption solvent, amount of resin).

The importance of the concentration method and of the sensitivity of the analytical techniques chosen for the definition of the detection threshold of the dissolved hydrocarbons is pointed out.

In addition to the detection level problems for certain types of hydrocarbons, the selectivity of these techniques is considered.

In conclusion, the various methods are compared amongst themselves from the point of view of their application, of the quality of the results which are obtained and of their applicability to the different real water samples polluted by hydrocarbons.     

Modern Analytical Methods for Monitoring Workplace Atmospheres

Abstract

Since measurements of exposure to hazardous substances were made obligatory in Germany under the Hazardous Material Regulation and Regulations for Accident Prevention there has been a need for widely-applicable, economic methods for determining airborne organic substance concentrations at workplaces. The relevant limits, which are based on toxicological and industrial hygiene data, are drawn up annually by the German Science Foundation and published as “Technische Regel für gefährliche Arbeitsstoffe” (TRgA 900) by the Ministry of Employment and Welfare.

Most organic substances, that have been assigned limits can be determined by gas liquid chromatography. The system described here is based on multicomponent GLC analysis. It has been used at BASF, the chemical-manufacturing company, where since 1979 approximately fifteen thousand workplaces have been evaluated. Hazardous substances have been detected at levels down to a few micrograms per cubic meter.

The standard system encompasses:

–-personal air samplers operating for 8 h;

–-adsorption by a solid sorbent;

–-desorption by solvent;

–-simultaneous GLC-separation on two different capillary columns;

–-computer correlation of the qualitative and quantitative data of the two chromatograms (plausibility check);

–-automatic print-out of the analytical report;

–-transfer of the results to a data bank for documentation.

Details are given of the method involving adsorption on activated charcoal and desorption with carbon disulfide. Benefits, cost advantages, and limitations are discussed.

Special sampling by means of other adsorbents (e.g. silica gel) in conjunction with special desorption, formation of derivatives, headspace analysis, and adsorption by liquids are techniques used to supplement the standard method of organic trace analysis in the field of industrial hygiene.     

Modifications of Adsorbent,Sample and Solvent in Thin Layer Chromatography

Abstract

This review covers, from a practical point of view, the modifications of the sample, adsorbent and solvent, which are available to achieve the separation of complex chemical mixtures by thin layer chromatography.     

Optimisation of a Gas Stripping Concentration Technique for Trace Organic Water Pollutants

Abstract

The application of gas stripping for the concentration prior to analysis of organic water pollutants at the parts per million and parts per billion level has been studied. Solutes are stripped from solution by a stream of inert gas and subsequently adsorbed onto active carbon from which surface they are taken up in a solvent for analysis.

The method is shown to be applicable to the analysis of a wide range of compounds including pesticides and polychlorinated biphenyls. The effect of gas flowrate, the time of stripping, adsorbent particle size, and desorbing solvent on the percentage recovery of a range of organic compounds has been measured.

Problems of contamination of aqueous solutions by absorption of atmospheric vapours prior to analysis are considered, and the analysis of a typical water sample is demonstrated.     

Graphene‐coated magnetic‐sheet solid‐phase extraction followed by high‐performance liquid chromatography with fluorescence detection for the determination of aflatoxins B1, B2, G1, and G2 in soy‐based samples

A new method named graphene‐coated magnetic‐sheet solid‐phase extraction based on a magnetic three‐dimensional graphene sorbent was developed for the extraction of aflatoxins prior to high‐performance liquid chromatography with fluorescence detection. The use of a perforated magnetic‐sheet for fixing the magnetic nanoparticles is a new feature of the method. Hence, the adsorbent particles can be separated from sample solution without using an external magnetic field. This made the procedure very simple and easy to operate so that all steps of the extraction process (sample loading, washing, and desorption) were carried out continuously using two lab‐made syringe pumps. The factors affecting the performance of extraction procedure such as the extraction solvent, adsorbent dose, sample loading flow rate, ionic strength, pH, and desorption parameters were investigated and optimized. Under the optimal conditions, the obtained enrichment factors and limits of detection were in the range of 205–236 and 0.09–0.15 μg/kg, respectively. The relative standard deviations were <3.4 and 7.5% for the intraday (n = 6) and interday (n = 4) precisions, respectively. The developed method was successfully applied to determine aflatoxins B₁, B₂, G₁, and G₂ in different soy‐based food samples.     

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

Rapid and Simple Technique for the Quantitation of Polyamines in Biological Samples

Abstract

A rapid and simple technique has been developed to quantify putrescine, spermidine, and spermine in biological tissue. The method, based upon several published procedures, involves protein precipitation with perchloric acid followed by dansylation with 5-dimethylamino-1-naphthalenesulfonyl chloride (dansyl chloride). After extraction on a Waters C₁₈ Sep-Pak cartridge, the samples are analyzed by high pressure liquid chromotography using a step solvent change and a 3μ C₁₈ reverse phase column. The chromotographic conditions allowed complete analysis of the three polyamines within 10 min with a total run time of 13 min (sample injection and re-equilibrium of column). Standard curves were linear up to 1 μg polyamine and the coefficient of variation for the assay ranged from 4% at l μg polyamine per sample to 11% at 50 ng polyamine per sample. The assay is therefore both rapid and simple. Moreover, unlike other available methods, the present technique does not require duel pumps, ion pairing agents, solvent extraction or a gradient control system. The concentrations of putrescine, spermidine and spermine in rat lung, liver and kidney are reported.     

Polypyrrole‐magnetite dispersive micro‐solid‐phase extraction combined with ultraviolet‐visible spectrophotometry for the determination of rhodamine 6G and crystal violet in textile wastewater

Polypyrrole‐magnetite dispersive micro‐solid‐phase extraction method combined with ultraviolet‐visible spectrophotometry was developed for the determination of selected cationic dyes in textile wastewater. Polypyrrole‐magnetite was used as adsorbent due to its thermal stability, magnetic properties, and ability to adsorb Rhodamine 6G and crystal violet. Dispersive micro‐solid‐phase extraction parameters were optimized, including sample pH, adsorbent amount, extraction time, and desorption solvent. The optimum polypyrrole‐magnetite dispersive micro‐solid phase‐extraction conditions were sample pH 8, 60 mg polypyrrole‐magnetite adsorbent, 5 min of extraction time, and acetonitrile as the desorption solvent. Under the optimized conditions, the polypyrrole‐magnetite dispersive micro‐solid‐phase extraction with ultraviolet‐visible method showed good linearity in the range of 0.05–7 mg/L (R ² > 0.9980). The method also showed a good limit of detection for the dyes (0.05 mg/L) and good analyte recoveries (97.4–111.3%) with relative standard deviations < 10%. The method was successfully applied to the analysis of dyes in textile wastewater samples where the concentration found was 1.03 mg (RSD ±7.9%) and 1.13 mg/L (RSD ± 4.6%) for Rhodamine 6G and crystal violet, respectively. It can be concluded that this method can be adopted for the rapid extraction and determination of dyes at trace concentration levels.     

Reversed-Phase High-Performance Liquid Chromatographic Determination of Nicotine in Pesticide Formulations

Abstract

A simple and rapid reversed-phase high-performance liquid chromatographic procedure is described for the determination of nicotine in liquid formulations. Samples are diluted with methanol, and naphthalene is added as the internal standard. Peak height ratios obtained from injections of standard and sample filtrates are used for quanti-tation. An eluting solvent of 0.05M (NH₄)₂ HPO4 (pH 7.5) -methanol (40/60, v/v) at a flow of 2 mL/min gives retention times of 3.13 and 6.88 min respectively for nicotine and naphthalene. Sample analysis can be completed in approximately one hour by the method described as compared to 1.5 days required by the Official AOAC gravimetric method (6.176–6.177).     

ICP-AES and Colorimetry as Analytical Tools for the Determination of Phosphorus Containing Compounds,Including Phosphine

Abstract

The direct quantitative determination of phosphine in gaseous mixtures or in air samples is associated with a number of difficulties. the paper describes an alternative technique based on the oxidation of phosphine to phosphate. Phosphate can be analysed either by inductively coupled plasma-atomic emission spectrometry (ICP-AES) or by a colometric method.

Because the problem of a proper (quantitative) sampling of phosphine in the air of working environments and/or in gaseous mixtures is still unsolved, standard solutions of KH₂PO₄ have been used as analytes (“artifical samples”) in the ICP-AES method.

The statistics concerning the sample variances, obtained from the 2 methods mentioned above, indicate no differences.     

A New Method for the Measurement of Airborne Formaldehyde Using Derivatization with 3,5-Bis(Trifluoromethyl) Phenylhydrazine and Analysis by GC-ECD and GC-MS/SIM

Abstract

A new method was developed and described for the measurement of airborne formaldehyde using derivatization with 3,5-bis(trifluoromethyl)phenylhydrazine (TFMPH) coated onto silica solid phase extraction cartridges. Analysis by GC-ECD provides a detection limit of 74 ng formaldehyde per sample. A field study was conducted to compare the use of TFMPH to 2,4-dinitrophenylhydrazine (DNPH) and NIOSH method 3500 (chromotropic acid, CTA). Samples were collected from indoor and outdoor environments known or suspected to contain formaldehyde. Use of TFMPH with GC-ECD analysis correlates well with both methods (R²=0.93, slope=1.07 vs. DNPH; R²=0.99, slope=1.06 vs. CTA). Spiked samples were shown to be stable at least 7 days when stored at –20 °C. Analysis of samples by GC-MS with selected ion monitoring (GC-MS/SIM) also proved feasible. Laboratory and field results show the use of TFMPH to be viable for quantifying airborne formaldehyde in occupational and environmental samples.     

Dispersive solid-phase extraction based on mesoporous melamine-formaldehyde polymer for sensitive determination of five chlorinated herbicides residues in water by high-performance liquid chromatography

ABSTRACT

In this work, a low-cost melamine-formaldehyde polymer with large-surface-area mesoporous structure was prepared and applied as an efficient solid sorbent for pre-concentration of five kinds of chlorinated herbicides including fomesafen, atrazine, pyrithiobac-sodium, benazolin and acifluorfene from water samples. Extraction parameters such as pH of the sample solution, amount of mesoporous melamine-formaldehyde polymer (mMFP), extraction time, type of desorption solv-ent and volume of the sample were systematically investigated. Combining dispersive solid-phase extraction with high-performance liquid chromatography (HPLC), the detection limits (S/N = 3) of the five herbicides were ranged from 0.04 to 0.18 μg L^?1 with good linearity (R² ≥ 0.9908). Then the tap water and river water samples were analysed by the developed method, and the obtained results indicated that this method provides acceptable recoveries and precisions. mMFP can be prepared through one-pot catalyst-free polymerisation from low-cost starting materials, so that they could be easily scaled up for the sample pre-treatment and have the powerful potentiality in purification of contaminated water.     

Automatic thermal desorption in GC analysis of dairy product volatiles

Summary Automatic thermal desorption (ATD) has been evaluated for the analysis of volatile components from dairy products. It has resulted in a fast and reproducible method which needs only a low amount of sample. Volatile components from milk are collected by off-line purging and trapped on cartridges packed which a suitable adsorbent. Cheese samples are submitted to the same process or directly introduced into the cartridges. The desorption step that follows is carried out automatically and on-line with the chromatographic analysis. Repeatability and sensitivity were satisfactory for both types of products.     

Chromatographic Separation of Closely Related Dyes on Metal Salt-Impregnated Thin Layers

Abstract

The chromatographic characteristics of 42 dyes belonging to different groups have been studied on metal salt-impregnated plates. A suitable separation scheme for the dyes studied and suitable adsorbent system as well as solvent system have been developed.     

Development and validation of a magnetic solid‐phase extraction with high‐performance liquid chromatography method for the simultaneous determination of amphetamine and methadone in urine

The simultaneous determination of amphetamine and methadone was carried out by magnetic graphene oxide nanoparticles, a magnetic solid‐phase extraction adsorbent, as a new sample treatment technique. The main factors (the amounts of sample volume, amount of adsorbent, type and amount of extraction organic solvent, time of extraction and desorption, pH, the ionic strength of extraction medium, and agitation rate) influencing the extraction efficiency were investigated and optimized. Under the optimized conditions, good linearity was observed in the range of 100–1500 ng/mL for amphetamine and 100–1000 ng/mL for methadone. The method was evaluated for determination of AM and methadone in positive urine samples, satisfactory results were obtained, therefore magnetic solid‐phase extraction can be applied as a novel method for the determination of drugs of abuse in forensic laboratories.     

Graphene oxide reinforced polyamide nanocomposite coated on paper as a novel layered sorbent for microextraction by packed sorbent

ABSTRACT

In this work, a novel layered sorbent for microextraction by packed sorbent (MEPS) was introduced, which has been prepared by coating graphene oxide/polyamide (GO/PA) nanocomposite (NC) onto cellulose paper through solvent exchange method. Scanning electron microscopy (SEM) was applied to investigate the surface characteristic and morphology of PA and GO/PA NC coated on cellulose paper. The prepared MEPS device was used for extraction of organophosphorous pesticides (OPPs) including chlorpyrifos, fenthion, fenithrothion, ethion, edifenphos and phosalone in environmental aqueous samples followed by detection using gas chromatography-flame ionisation detector (GC-FID). Important parameters affecting the MEPS method including pH of sample solution, extraction draw-discard cycles, sorbent layers, desorption solvent volume and desorption draw-eject number were studied and optimised using central composite design (CCD). Based on the method validation, limits of detection (LODs) were in the range of 0.2–1 µg L^?1. The calibration graphs for chlorpyrifos, fenthion and edifenphos are linear in the concentration range of 1 to 500 µg L^?1; for ethion and phosalone are linear in the range of 1–1000 µg L^?1 and for fenithrothion is linear in the range of 3–1000 µg L^?1. The method precision (RSD %) with six replicates determinations was in the range of 3 to 9.4 % and 3.9 to 11.9% for distilled water and spiked river water sample, respectively, at the concentration level of 300 µg L^?1 . The developed method was applied successfully to determine OPP compounds in river, dam and tap water samples; accordingly, the relative recoveries (RR%) were obtained in the range of 77.8 to 113.3%.