Volatile Analytes Research Articles

Derivatization of small biomolecules for optimized matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is a powerful tool for the measurement of low molecular mass compounds of biological interest. The limitations for this method are the volatility of many analytes, possible interference with matrix signals or bad ionization or desorption behavior of the compounds. We investigated the application of well-known and straightforward one-pot derivatization procedures to circumvent these problems. The derivatizations tested allow the measurement and the labeling of alcohols, aldehydes and ketones, carboxylic acids, alpha-ketocarboxylic acids and amines.

A microporous membrane interface for the monitoring of dissolved gaseous and volatile compounds by on-line mass spectrometry

Membrane contactors have been used in a wide range of applications, since they offer a number of advantages over the conventional dispersed phase contactors, such as the absence of emulsions, no flooding at high flow rates or unloading at low flow rates. Besides, they provide a very high and constant specific interfacial area. Hollow fibre modules have been the preferred geometry when liquid–liquid and gas–liquid interfaces are involved. This paper addresses a novel application for hollow fibre membrane contactors. A microporous hydrophobic hollow fibre membrane module is used as an interface for membrane inlet mass spectrometry (MS). The module acts as a gas contactor between the liquid phase in which a gaseous or volatile analyte is dissolved and a stripping gas that is analysed by MS. The signal of the mass spectrometer is thus correlated to the concentration of the analyte in the liquid phase. The performance of the developed system was tested by measuring the concentration of dissolved oxygen, propane and ethanol in water. Linear correlations were obtained between the mass spectrometer signal and the concentration of the dissolved analytes. The effect of operation parameters such as liquid and gas flow rates and membrane area on the module performance and on the mass spectrometer signals was studied. This type of interface, by enabling liquid phase analysis, might prove an useful and low cost upgrade of instruments designed and constructed to exclusively analyse gas phases.

Traditional sampling with laboratory analysis and solid phase microextraction sampling with field gas chromatography/mass spectrometry by military industrial hygienists.

The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the United States Department of Defense or the Uniformed Services University of the Health Sciences. Rapid on-site detection and identification of environmental contaminants to which personnel may be exposed is often needed during military deployment situations. The availability of military industrial hygienists with capabilities for "complete" on-site exposure assessment of chemical species should allow detection and identification of a number of important stressors almost immediately following sample collection. Portable gas chromatography/mass spectrometry (GC/MS) provides a rapid and efficient separation of volatile and semivolatile organic analytes, accompanied by sensitive electron impact ionization-mass spectrometry (EI-MS) detection. The use of GC/MS in the field is limited, however, by equipment cost, complexity of the equipment, and the analytical process. Additionally, a skilled operator is needed to obtain useful separations and to interpret mass spectral data. To demonstrate benefits and limitations of "complete" exposure assessment capabilities, a previously unidentified complex mixture, produced by thermal dispersion of riot control agents, was examined. Established active sampling methods were used with laboratory analyses. Solid phase microextraction, a passive sampling method that simplifies preparation for GC/MS analysis, also was used with a field-portable GC/MS system. Both sampling/analysis methods were used to detect CS riot control agent-derived air contaminants dispersed from riot control type canisters through oxidizer-supported combustion of a chemical fuel.

Optimisation of solid-phase microextraction of volatiles

The results of a systematic study on the precision and repeatability of measurements of the headspace solid phase micro-extraction (SPME) with open-cap vials in combination with capillary gas chromatography in comparison with septum-sealed vials are reported. Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) were used as the target analytes in the investigation of spiked water samples at concentration levels of 42.5 μg l −1. The dependence of a sample volume versus peak area showed maximum SPME recovery. The influence of sample volume on the precision and the time of taking the sample on the losses of volatile analytes was examined.

Investigations into the generation of Ag, Au, Cd, Co, Cu, Ni, Sn and Zn by vapour generation and their determination by inductively coupled plasma atomic emission spectrometry, together with a mass spectrometric study of volatile species. Determination of Ag, Au, Co, Cu, Ni and Zn in iron

Vapour generation–inductively coupled plasma atomic emission spectrometry has been successfully extended to the determination of silver, gold, cadmium, cobalt, copper, nickel and zinc using sodium tetrahydroborate(III). Mass spectroscopic studies suggest that volatile analyte species are unstable relative to analyte atoms. Detection limits are superior to nebulization for Ag, Au, Cu and Cd, whereas for Co, Ni and Zn detection limits are slightly worse. Matrix interferences were investigated from a variety of elements, including As, Cr, Pb, Mo, Pt, Pd, Ti, Al, Ca, Mg and Sn. Memory effects were reduced by use of a rinse solution of thiourea in hydrochloric acid. Reduction of solution-based interference from iron was accomplished by the use of 2% (v/v) phosphoric acid for the determination of Ag, Au and Cu. Potassium fluoride was necessary to reduce interferences from iron in the determination of Co and Ni. The technique was applied to the determination of Ag, Au, Co, Cu and Ni in low alloy steel standard reference materials. Excellent agreement was found between experimental and certified values.

Feasibility of eliminating interferences in graphite furnace atomic absorption spectrometry using analyte transfer to the permanently modified graphite tube surface

A procedure is proposed to avoid spectral and/or non-spectral interferences in graphite furnace atomic absorption spectrometry (GF AAS) by transferring the analyte during the pyrolysis stage from a solid sampling platform to the graphite tube wall that has been coated with a permanent modifier, e.g. by electrodeposition of a platinum-group metal. The direct determination of mercury in solid coal samples was chosen as a model to investigate the feasibility of this idea. The graphite tube surface was coated with palladium and the analyte was transferred from the solid sampling platform to the tube wall at a temperature of 500±50 °C. A characteristic mass of m 0=64 pg Hg was obtained for an atomization temperature of 1300 °C, proposing a quantitative transfer of the analyte to the tube wall. Calibration against aqueous mercury standards was not feasible as this element was lost in part already during the drying stage and could not be trapped quantitatively on the modified graphite tube surface. However, the results for all except one of the coal reference materials were within the 95% confidence interval of the certificate when the slope of a correlation curve between the integrated absorbance, normalized for 1 mg of sample, and the certified value for mercury was used for calibration. A detection limit of 0.025–0.05 μg g −1 Hg in coal, calculated from three times the standard deviation of the investigated coal samples, could be obtained with the proposed method. The spectral interference due to excessive background absorption in the direct determination of mercury in coal could be eliminated completely. It is expected that this analyte transfer can be used in a similar way to eliminate other spectral and/or non-spectral interferences in the GF AAS determination of other volatile analytes.

Development of microwave-assisted drying methods for sample preparation for dried spot micro-X-ray fluorescence analysis.

Although dried spot micro X-ray fluorescence (MXRF) is an effective analytical technique for trace elemental analysis, the sample preparation procedures currently used suffer from a number of drawbacks. These drawbacks include relatively long preparation times, lack of control of the sample preparation environment, and possibility of loss of volatile analytes during the drying process. Microwave-assisted drying offers several advantages for dried spot preparation, including control of the environment and minimized volatility because of the differences between microwave heating and conventional heating. A microwave-assisted drying technique has been evaluated for use in preparing dried spots for trace analysis. Two apparatus designs for microwave drying were constructed and tested using multielement standard solutions, a standard reference material, and a "real-world" semiconductor cleaning solution. Following microwave-assisted drying of these aqueous samples, the residues were redissolved and analyzed by ICPMS. Effective recovery was obtained using the microwave drying methods, demonstrating that the microwave drying apparatus and methods described here may be more efficient alternatives for dried spot sample preparation.

EN CORE® Sampler Performance: Storing Soil for VOC Analysis

The En Core® sampler is designed to collect and store soil samples in a manner that minimizes loss of contaminants due to volatilization and/or biodegradation. Use of this device is described in American Society for Testing and Materials (ASTM) Practice D 6418, Standard Practice for Using the Disposable En Core Sampler for Sampling and Storing Soil for Volatile Organic Analysis. Two studies were performed to evaluate the performance of the En Core sampler to store VOC-contaminated soil for analysis. One study involved spiking soil samples with low concentrations of VOCs (less than 200 µg/kg) and storing them under various conditions prior to analysis. Results from this study show that the En Core sampler gives 80% or greater recoveries of low concentrations of VOCs from soil samples stored under a number of conditions. The second study was performed to generate data on the performance of the 25-g En Core sampler to store soil samples spiked with EPA Method 1311, Toxicity Characteristic Leaching Procedure (TCLP), volatile organic analytes. Results show that the En Core device gives 80% or greater recoveries of most of the Method 1311 volatile organic analytes from soil stored under various conditions for 14 days.

Mechanistic studies on the trapping and desorption of volatile hydrides and mercury for their determination by electrothermal vaporization-inductively-coupled plasma mass spectrometry

Metallic coatings in the pyrolytic graphite furnace have been used for the pre-concentration of Hg (using electrochemically reduced Au) and AsH 3 (using both thermally and electrochemically reduced Ir and Pd/Ir) prior to electrothermal volatilization. The analyte trapping efficiency during accumulation and the analyte and modifier release processes during volatilization were monitored in real time. This was achieved by using the fast response capability of inductively-coupled plasma-mass spectrometry to determine simultaneously both the analyte and modifier elements as a function of time. The temperature dependence of the analyte trapping process points to contrasting mechanisms for Hg adsorption on Au (reversible, physical adsorption/amalgamation) and for AsH 3 adsorption on Pd, Ir or Pd/Ir (physical adsorption followed by an irreversible hydrogen abstraction reaction at active sites). Results also indicate that only minor volatilization of modifier occurs at the temperature required for volatilization of analyte from the furnace.

Coupling pervaporation to AAS for inorganic and organic mercury determination. A new approach to speciation of Hg in environmental samples

The design and development of a new approach for Hg speciation in environmental samples is described in detail. This method, consisting of the coupling of pervaporation and atomic absorption spectrometry, is based on a membrane phenomenon that combines the evaporation of volatile analytes and their diffusion through a polymeric membrane. It is proposed here as an alternative to gas chromatography for speciation of inorganic and organic Hg compounds, as the latter compounds are volatile and can be separated by applying the principles mentioned above. The interest of this method lies in its easy handling, low cost, and rapidity for the analysis of liquid and solid samples. This method has been applied to Hg speciation in a compost sample provided by a waste water treatment plant.

Feasibility study on in situ microwave digestion prior to analysis of biological samples by total reflection X-ray fluorescence

A microwave-assisted, micro-digestion procedure was developed and evaluated for analysis of solid samples by total reflection X-ray fluorescence spectrometry. Digestion of a 1.1-mg sub-sample of the NIST Bovine Liver (1577a) standard reference material was performed directly on the surface of common, siliconized quartz reflectors with a 20-μl H 2O 2+20 μl HNO 3 mixture. The method was evaluated in terms of variations in the peak-to-background ratio (detection limits) and on the recovery rates for various volatile and non-volatile analytes. The characteristics of the reflector surface, the order of addition of the digestion reagents as well as the microwave power must be carefully controlled for successful application of the methodology.

Moderate volatility analyte transport behavior with membrane desolvation reversed-phase liquid chromatography-helium microwave-induced plasma atomic emission spectroscopy

The transport behavior of moderately volatile analyte in a membrane desolvation system is examined. With the goal of atomic emission determination of liquid chromatographic analytes, a tubular polytetrafluoroethylene membrane desolvator interface was used to enhance the performance of a 120 W helium microwave-induced plasma atomic emission detector. To monitor organo-chlorine compounds, Cl emission was observed at 479.5 nm. Membrane desolvator conditions such as temperature, solvent composition and counter current gas flow were optimized. Converse to required conditions for non-volatile inorganic compounds, semi-volatile organic compound transport was maximized at lower membrane desolvator temperatures. Analyte transport was enhanced by modifying the solvent with dilute H 2SO 4. Low vapor pressure H 2SO 4 minimized analyte diffusion across the membrane and helped linearize the calibration plot. The detection limit of 2,6-dichlorobenzamide in pure methanol using ultrasonic nebulization and membrane desolvation with microwave-induced plasma detection was 2 ppm. Chromatographic separation and detection was demonstrated with 2,6-dichlorobenzamide and 4-chlorobenzamide.

Development of a simple gradient LC–IR interface for the detection of terpenoids from the α-pinene–ozone reaction

The development of a simple interface between liquid chromatography and infrared spectroscopy (LC–IR) using a coaxial sprayer is described for less volatile analytes. The system consists of a transfer capillary, in which the analytes are transported from the separation column of the gradient-LC to the outlet of the sprayer. This transfer capillary is coaxially surrounded at the outlet by a stainless steel sprayer capillary, which is resistively heated and flushed with nitrogen gas. The samples are sprayed in the manner that the eluent is vaporized by the heated nitrogen when exiting the capillary, while the analytes are deposited on a moving slide made of infrared transparent material (ZnSe or CaF 2). Afterwards the deposited compounds are analyzed with an infrared microscope in transmission. First results from reaction products of the gas phase reaction of α-pinene with ozone are presented.

Investigations on the use of chemical modifiers for the direct determination of trace impurities in Al2O3 ceramic powders by slurry electrothermal evaporation coupled with inductively-coupled plasma mass spectrometry (ETV-ICP-MS).

The direct determination of trace impurities in Al2O3 ceramic basic powders by ICP-MS using electrothermal evaporation (ETV) with slurry sampling has been investigated. To increase interference-free analyte volatilization, the use of the palladium-group modifiers (PGM) IrCl3, Pd(NO3)2, and PdCl2 for the determination of Ca, Fe, Ga, Mg, Mn, Na, Ni, and V in Al2O3 powders was studied. Their role, which in ETV-ICP-MS and ETV-ICP-OES is to stabilize the investigated analyte during the ashing phase, to increase vaporization of the matrix, and to reduce transport losses was investigated. Optimum analysis results were obtained with PdCl2 modifier when 500 ng Pd was used for a sample weight of 100 microg Al2O3 injected into the ETV. Calibration was performed by standard addition with aqueous solutions of the analytes. The RSDs calculated from triplicate analysis ranged form 5 to 10%. Detection limits between 0.07 microg g(-1) (Ga) and 1.1 microg g(-1) (Na) were achieved. The accuracy was proven for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V by analyzing an NIST standard reference Al2O3 material (SRM 699) with a middle grain size of 16.4 microm. The analytical method was used for the analysis of Al2O3 powder (AKP 30, Sumitomo, Japan) with impurities in the low microg g(-1) range and a middle grain size of 1.1 microm. The results obtained for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni, and V were comparable with those obtained by ICP-MS subsequent to conventional decomposition with hydrochloric acid at high pressure.

Semiautomatic multiresidue gas chromatographic method for the screening of vegetables for 25 organochlorine and pyrethroid pesticides

A method for multiresidue screening of lyophilised vegetables for up to 25 pesticides (16 pyrethroids and 9 OCPs) permitted in the European Union was systematically developed on the basis of solid-phase extraction and gas chromatography with electron capture detection. The residues of pesticides were extracted from the lyophilised sample with n-hexane by mechanical shaking; the organic phase containing the pesticides was aspirated into a continuous module which comprises a laboratory-made silica column for analyte preconcentration and sample matrix clean-up. The method provides excellent clean-up despite the complexity of the matrices involved thanks to the lyophilisation process which also helps to sample preservation without losses of the selected relatively non volatile analytes. Detection limits were about 1–10 ng/g, except for lindane and captan (30 ng/g) thus allowing their determination at concentrations lower than their maximum residue limits with good precision (ca. 5%). The accuracy of the quantitative determination measured in terms of average percentage recovery of the 25 compounds in eight different vegetables was 93±3, bifenthrin and deltamethrin excepted. The proposed method was applied to the screening of about 100 vegetables for the selected pesticides, being the positive findings further confirmed by GC/MS.

Use of a PTV injector to achieve inverse-large volume injection: Injection of volatile analytes in a semi-volatile solvent

Large volume injection of volatile analytes in a semi-volatile solvent, termed inverse-LVI, has been accomplished using a programmable-temperature vaporizing (PTV) injector. It was found that simple optimization of the time the split valve remained closed allowed complete analyte transfer to the column, while venting most of the solvent. Increasing the PTV temperature ramp from 10 K/s to 15 K/s was found to improve peak shapes, especially of the early eluting peaks, by decreasing the injection bandwidth. In addition, the optimum splitless time was found to be independent of injection volume (up to solvent limits) meaning only a single optimization was necessary for quantitative analyte transfer from each solvent. The ability to quantitatively transfer the analyte to the column was also found to be solvent independent (propylene carbonate, tridecane, and Butyl CARBITOL® Solvent were evaluated). Excellent data were obtained for injection volumes up to 15 μL of propylene carbonate and 36 μL of tridecane using an unpacked fritted PTV liner.

Use of a PTV injector to achieve inverse-large volume injection: Injection of volatile analytes in a semi-volatile solvent

Large volume injection of volatile analytes in a semi-volatile solvent, termed inverse-LVI, has been accomplished using a programmable-temperature vaporizing (PTV) injector. It was found that simple optimization of the time the split valve remained closed allowed complete analyte transfer to the column, while venting most of the solvent. Increasing the PTV temperature ramp from 10 K/s to 15 K/s was found to improve peak shapes, especially of the early eluting peaks, by decreasing the injection bandwidth. In addition, the optimum splitless time was found to be independent of injection volume (up to solvent limits) meaning only a single optimization was necessary for quantitative analyte transfer from each solvent. The ability to quantitatively transfer the analyte to the column was also found to be solvent independent (propylene carbonate, tridecane, and Butyl CARBITOL® Solvent were evaluated). Excellent data were obtained for injection volumes up to 15 μL of propylene carbonate and 36 μL of tridecane using an unpacked fritted PTV liner.

Fast GC instrumentation and analysis for field applications

AbstractEnvironmental contaminants are found in a wide variety of molecular shapes and sizes, with organic pollutants exhibiting vapor pressures in the 103–10−6 torr range. This translates into a need for chemical analyzers that are capable of analyzing both volatile compounds (i.e., those compounds that have high vapor pressures at ambient temperatures) as well as semivolatile substances (i.e., those compounds that must be heated before they exhibit substantial vapor pressures). Volatile environmental analytes are found in gaseous, liquid, or solid sample matrices, whereas semivolatile analytes exist as either liquids or solids, including aerosol dispersions. Unfortunately, conventional field‐portable GC analyzers are only capable of analyzing for volatile analytes. A small, fast, dual‐high‐resolution‐column GC instrument that is capable of analyzing both volatile and semivolatile analytes has been developed and patented. As typically configured, it uses two narrow‐bore, 100‐micron ID separation columns, is temperature programmable at rates of 5–20 °C per second, and uses less than 150 W of dc power. Typical separation times for compounds with Kovatt's retention indices of <1000 are 10–15 s, and compounds with retention indices of up to 2500 are separated in <1min. Because the instrument has dual columns and detectors, analytes are simultaneously analyzed on columns with different liquid phases, thus providing added confidence in the quality of the analytical data. Because this fieldable GC device uses a solid‐sorbent trapping system with a conventional heated injector inlet system, it can analyze a wide variety of sample matrices, including gases, dilute gases, thermal extracts from VOS tubes, purge‐and‐trap water/soil extracts, headspace samples, membrane extracts, SPME, thermal and SCF extracts, liquid organic solvent extracts, and direct aqueous samples. This report describes this new instrument and presents typical data from analysis of volatile and semivolatile analytes in a variety of sample matrices. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 97–105, 2001

About the Plate Model of Chromatomembrane Gas Extraction

Two models of gas extraction (network and plate ones) proposed in different works were compared. It was shown that the main relationships used for calculating the concentration of a volatile analyte and its portion in the solution after gas extraction are identical.

Analytical methods for water disinfection byproducts in foods and beverages

The determination of exposure to drinking water disinfection byproducts (DBPs) requires an understanding of how drinking water comes into contact with human through multiple pathways. In order to facilitate the investigation of human exposure to DBPs via foods and beverages, analytical method development efforts were initiated for haloacetonitriles, haloketones, chloropicrin, and the haloacetic acids (HAAs) in these matrices. The recoveries of the target analytes were investigated from composite foods and beverages. Individual foods and beverages used to investigate the general applicability of the developed methods were selected for testing based on their watercontent and frequency of consumption. The haloacetonitriles, the haloketones, and chloral hydrate were generally well recovered (70-130%), except for bromochloroacetonitrile (64%) and dibromoacetonitrile (55%), from foods spiked after homogenization and following extraction with methyl-t-butyl ether (MTBE); the addition of acetone was found to be necessary to improve recoveries from beverages. The process of homogenization resulted in decreased recoveries for the more volatile analytes despite the presence of dry ice. The HAAs were generally well recovered (70-130%), except for trichloroacetic acid (58%) and tribromoacetic acid (132%), from foods but low recoveries and emulsion formation were experienced with some beverages. With both groups of analytes, certain matrices were more problematic (as measured by volatility losses, emulsion formation) than others with regard to processing and analyte recovery.