Gas Chromatograph-mass Spectrometer System Research Articles

Hydrogen or Helium Conservation in Gas Chromatography Mass Spectrometry: How We Chose What Was Right for Our Laboratory

Helium is getting more and more difficult to obtain, and it does not look like that will change anytime soon. The only alternative carrier gas to helium that Agilent recommends for gas chromatography mass spectrometry is hydrogen. Converting a gas chromatograph mass spectrometer (GCMS) to use hydrogen presents additional safety concerns and may not be possible for some systems. Helium conservation, having the GCMS system use nitrogen as a carrier gas when idle, may be a viable alternative when conversion to hydrogen is not possible.

Investigation of Volatile Compounds in Combination with Multivariate Analysis for the Characterization of Monofloral Honeys

Lately there has been a growing demand for monofloral honeys with distinctive properties. Considering the limitations of pollen analysis, the volatile profile of honey has been proposed as a helpful supplementary tool for the confirmation of monoflorality; however, research remains regarding the volatile markers that may characterize the monofloral honey types. Therefore, in this study, we tried to expand the research by investigating the aroma profiles of five monofloral honey types (fir, pine, erica, thyme, cotton) and discriminate them through chemometric approach. A purge and trap–gas chromatograph–mass spectrometer system was used for the extraction, separation, and identification of volatile and semi-volatile compounds. Thyme honey had the richest quantitatively aroma profile, with 97 volatile compounds, whereas fir and cotton honeys had 65 and 60 volatile compounds, respectively. From a total of 124 compounds, the 38 were detected in all the studied honey types. Thyme honey was distinguished by the presence (or percentage participation) of benzeneacetaldehyde, benzealdehyde, and benzyl nitrile; erica honey of isophorone and furfural; cotton honey of 1-butanol, 2-methyl, 1-pentanol, and 4-methyl-; and honeydew honeys of α-pinene, octane, and nonanal. The discriminant analysis confirmed that the percentage participation of volatile compounds may lead to the discrimination of the studied monofloral honey types.

Probing the low-temperature chemistry of methyl hexanoate: Insights from oxygenate intermediates

Understanding the combustion of methyl esters is crucial to elucidate kinetic pathways and predict combustion parameters, soot yields, and fuel performance of biodiesel, however most kinetic studies of methyl esters have focused on smaller, surrogate model esters. Methyl hexanoate is a larger methyl ester approaching the chain length of methyl esters found in biodiesel and has not received as much research attention as other smaller esters. The purpose of this work is to present the first atmospheric pressure combustion data of methyl hexanoate, CH3CH2CH2CH2CH2COOCH3. Mixtures of 2% methyl hexanoate in O2 and N2 are studied using a plug flow reactor at atmospheric pressure, wall temperatures from 573 to 973 K, residence times from roughly 1-2 s., and fuel equivalence ratios of 1, 1.5, and 2. Exhaust gases are analyzed by a gas chromatograph-mass spectrometer system and species mole fractions are presented. The literature model shows satisfactory agreement with the experimental species profiles and improvements for future mechanistic studies are suggested. In particular, this work proposes new unimolecular decomposition pathways of methyl hexanoate to form methanol or methyl acetate. Furthermore, the experiment detected three unsaturated esters that are direct products of the low temperature oxidation chemistry and it provides more insight into branching ratios for the formation of methyl hexanoate radicals and for the decomposition of hydroperoxyalkyl radicals.

Online fast pyrolysis of cellulose over titanium dioxide using tandem micro-reactor-GC-MS

In this work, the catalytic effect of titanium dioxide (TiO2) on the online fast pyrolysis of cellulose was investigated using a tandem micro reactor coupled to a gas chromatograph-mass spectrometer (GC-MS) system. This system was used in the following two different modes: in-situ and ex-situ. The results obtained with TiO2 were compared with those of zeolite (HZSM-5) under identical pyrolysis conditions. Levoglucosan was the major product in the non-catalytic pyrolysis of cellulose. As for the catalytic pyrolysis of cellulose at 500 °C with TiO2 (in-situ), the peak of levoglucosan disappeared whereas aromatic hydrocarbons such as benzene, toluene and naphthalene were newly detected. In this case, oxygenated compounds such as furfural, furan, methylfuran were still observed for TiO2 whereas oxygenated compounds (i.e, furan, benzofuran, methylbenzofuran, acetone and 2-butanone) with low yields were observed for in-situ catalytic pyrolysis with HZSM-5. For ex-situ catalytic pyrolysis of cellulose at 500 °C using TiO2, oxygen-containing compounds were hardly formed, while various aromatic hydrocarbons were detected. When the ex-situ pyrolysis of cellulose with HZSM-5 was carried out, the yields of the aromatic hydrocarbons were comparable to those with TiO2.

The chemical structure of a 30 cm methanol pool fire

SummaryThis study documents a series of time‐averaged gas species measurements made along the centerline of a 30 cm methanol pool fire steadily burning in a quiescent environment. All gas species measurements were obtained using a gas chromatograph/mass spectrometer system (GC/MS). Measurements were made at different heights along the centerline of the fire and repeated at least twice for each location. Gas species volume fractions were determined via the GC/MS using predetermined calibration factors. The gas species volume fractions were compared at different heights within the methanol fire.

Discrimination of Red Wines with a Gas-Sensor Array Based on a Surface-Acoustic-Wave Technique.

We applied a thermal-desorption gas-chromatograph mass-spectrometer (TD-GC–MS) system to identify the marker volatile organic compounds (VOCs) in the aroma of red wine. After obtaining the marker VOC, we utilized surface acoustic waves (SAWs) to develop a highly sensitive sensing system as ‘electronic nose’ to detect these marker VOC. The SAW chips were fabricated on a LiNbO3 substrate with a lithographic process. We coated sensing polymers on the sensing area to adsorb the marker VOC in a sample gas. The adsorption of the marker VOC altered the velocity of the SAW according to a mass-loading effect, causing a frequency decrease. This experiment was conducted with wines of three grape varieties—cabernet sauvignon, merlot and black queen. According to the results of TD-GC–MS, the King brand of red wine is likely to have unique VOC, which are 2-pentanone, dimethyl disulfide, 2-methylpropyl acetate and 2-pentanol; Blue Nun-1 probably has a special VOC such as 2,3-butanedione. We hence used a SAW sensor array to detect the aroma of red wines and to distinguish their components by their frequency shift. The results show that the use of polyvinyl butyral (PVB) as a detecting material can distinguish Blue Nun-2 from the others and the use of polyvinyl alcohol (PVA) can distinguish King from the others. We conducted random tests to prove the accuracy and the reliability of our SAW sensors.

An aircraft gas chromatograph–mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow

Abstract. Volatile organic compounds (VOCs) are important for global air quality and oxidation processes in the troposphere. In addition to ground-based measurements, the chemical evolution of such species during transport can be studied by performing in situ airborne measurements. Generally, aircraft instrumentation needs to be sensitive, robust and sample at higher frequency than ground-based systems while their construction must comply with rigorous mechanical and electrical safety standards. Here, we present a new System for Organic Fast Identification Analysis (SOFIA), which is a custom-built fast gas chromatography–mass spectrometry (GC-MS) system with a time resolution of 2–3 min and the ability to quantify atmospheric mixing ratios of halocarbons (e.g. chloromethanes), hydrocarbons (e.g isoprene), oxygenated VOCs (acetone, propanal, butanone) and aromatics (e.g. benzene, toluene) from sub-ppt to ppb levels. The relatively high time resolution is the result of a novel cryogenic pre-concentration unit which rapidly cools (∼ 6 °C s−1) the sample enrichment traps to −140 °C, and a new chromatographic oven designed for rapid cooling rates (∼ 30 °C s−1) and subsequent thermal stabilization. SOFIA was installed in the High Altitude and Long Range Research Aircraft (HALO) for the Oxidation Mechanism Observations (OMO) campaign in August 2015, aimed at investigating the Asian monsoon pollution outflow in the tropical upper troposphere. In addition to a comprehensive instrument characterization we present an example monsoon plume crossing flight as a case study to demonstrate the instrument capability. Hydrocarbon, halocarbon and oxygenated VOC data from SOFIA are compared with mixing ratios of carbon monoxide (CO) and methane (CH4), used to define the pollution plume. By using excess (ExMR) and normalized excess mixing ratios (NEMRs) the pollution could be attributed to two air masses of distinctly different origin, identified by back-trajectory analysis. This work endorses the use of SOFIA for aircraft operation and demonstrates the value of relatively high-frequency, multicomponent measurements in atmospheric chemistry research.

Comparative study of ferrate and thermally activated persulfate treatments for removal of mono- and dichlorobenzenes from groundwater

The removal of mono- and dichlorobenzenes from model solutions containing four chlorobenzene compounds separately or all four mixed, as well as mixed but with the addition of groundwater matrix was studied applying ferrate and thermally activated persulfate treatments. The concentration of target molecules were determined by gas chromatographmass spectrometer system following the enrichment of analytes by solid phase micro-extraction. At optimized experimental conditions and with the same concentration of oxidative agents, the removal efficiency values were the highest for the 1.2-dichlorobenzene (1.2-DCB) and monochlorobenzene (MCB) in case of ferrate and persulfate treatment, respectively. At nearly the same molar ratios, the persulfate treatments in comparison to the ferrate technology resulted in a higher average removal efficiency for the four target molecules in the model solutions (39 vs. 19%). However, in the presence of groundwater matrix with a given bicarbonate and chloride ion content, the average removal efficiency values reached only 14% for both treatment procedures. This means that the persulfate treatment is more sensitive to the presence of interfering ions existing in groundwater.

SF<sub>6</sub> gas decomposition analysis under point-to-plane 50 Hz AC corona discharge

As one of the most commonly used insulating mediums, in electrical discharge, sulfur hexafluoride (SF6) will decompose in the presence of water vapor and oxygen, producing various gaseous by-products. It is shown that the concentrations and production rates of SF6 gaseous decomposition by-products heavily depend on electrical field to gas density ratio (E/N) under corona discharge. Regarding the difficulty in measuring E and N, applied voltage and the SF6 pressure, are proposed in this paper to describe E and N, respectively. Several experiments of 50-Hz AC discharges were carried out under different applied voltages and different SF6 pressures using point-to-plane electrodes. The concentrations of SF6 gaseous by-products were measured by a gas chromatograph-mass spectrometer system (GS/MS). Experimental data show that the concentrations of SF6 gaseous by-products increase while the ratio (SOF2+SO2)/SO2F2 decreases, with increasing applied voltage. The concentrations decrease with increasing pressure of SF6. The formation mechanisms of SF6 gaseous by-products with the variations of applied voltage and the SF6 pressure are discussed, such as SO2F2, SOF2+SO2, CF4, and CO2 and so on. An experimental expression is derived which connects the SF6 pressure with the concentration of the decomposition by-products.

Relationships between volatile compounds and sensory characteristics in virgin olive oil by analytical and chemometric approaches

The volatile fraction of virgin olive oil is characterised by low molecular weight compounds that vaporise at room temperature. In order to obtain an aroma profile similar to natural olfactory perception, the composition of the volatile compounds was determined by applying dynamic headspace gas chromatography, performed at room temperature, with a cryogenic trap directly connected to a gas chromatograph-mass spectrometer system. Samples were also evaluated according to European Union and International Olive Council official methods for sensory evaluation. In this paper, the composition of the volatile fraction of 25 extra virgin olive oils from different regions of Italy was analysed and some preliminary considerations on relationships between chemical composition of volatile fraction and sensory characteristics are reported. Forty-two compounds were identified by means of the particular analytical technique used. All the analysed samples, classified as extra virgin by the panel test, never present peaks whose magnitude is important enough in defected oils. The study was focused on the evaluation of volatile compounds responsible for the positive impact on olive odour properties ('green-fruity' and 'sweet') and olfactory perception. Chemometric evaluation of data, obtained through headspace analysis and the panel test evaluation, showed a correlation between chemical compounds and sensory properties. On the basis of the results, the positive attributes of virgin olive oil are divided into two separated groups: sweet types or green types. Sixteen volatile compounds with known positive impact on odour properties were extracted and identified. In particular, eight compounds seem correlated with sweet properties whereas the green sensation appears to be correlated with eight other different substances. The content of the compounds at six carbon atoms proves to be very important in defining positive attributes of extra virgin olive oils and sensory evaluation.

Halocarbons in the marine atmosphere and surface seawater of the south Yellow Sea during spring

The concentrations of eight halocarbons, including methyl chloride (CH3Cl), methyl bromide (CH3Br), trichloroethene (C2HCl3), tetrachloroethene (C2Cl4), methyl chloroform (CH3CCl3), and three chlorofluorocarbons (CFCs) (CFC-11, CFC-113, and CFC-114), were measured using a canister sampling technique and an automated preconcentration gas chromatograph–mass spectrometer system in the marine atmosphere of the south Yellow Sea (SYS) in May 2012. The atmospheric concentrations of these halocarbons ranged from single digits to hundreds of pptv. Our results revealed elevated regional mixing ratios for most halocarbons (particularly C2HCl3 and C2Cl4) compared with the levels found in literature, thus suggesting substantial releases of C2HCl3 and C2Cl4 from anthropogenic sources in China. By contrast, the mean concentration of CFC-11 in the present study was lower than the global average value. The diffusion and transportation of terrestrial pollutants from coastal areas are important sources of halocarbons in the SYS, whilst terrestrial sources contribute to elevated concentrations of the selected halocarbons in coastal water. The sea-to-air fluxes of CH3Cl and CH3Br were estimated based on the simultaneous measurement of the atmospheric and seawater concentrations of these two gases. By simple extrapolation, the emissions of CH3Cl and CH3Br from the study area could account for 0.04% and 3% of the global oceanic emissions, respectively, thus indicating that the coastal area constituted important sources of atmospheric CH3Cl and CH3Br.

An ionic liquid modified dummy molecularly imprinted polymer as a solid-phase extraction material for the simultaneous determination of nine organochlorine pesticides in environmental and food samples

In this research, a novel dummy molecularly imprinted polymer (DMIP) was prepared through a sol–gel process using bisphenol A as the dummy template and the synthesized 1-(triethoxysilyl) propyl-3-aminopropyl imidazole bromide (SilprImN) as the functional monomer. The prepared SilprImN-DMIP was characterized by FT-IR and verified with a satisfied identification and penetration performance to bisphenol A in static and kinetic adsorption tests. Furthermore, this novel DMIP was applied as a solid-phase extraction (SPE) material to develop a method for the simultaneous determination of nine organochlorine pesticides (OCPs) in environmental and food samples coupled to a multi dimensional gas chromatograph-mass spectrometer system. The SPE parameters, including sample acidity (pH), sample loading rate, the eluent and elution volume, were optimized in detail to achieve a good extraction efficiency. In water, rice and tea leaf samples spiked with nine OCPs, the OCPs were simultaneously determined with suitable recoveries from 65.65% to 129.61% and a good relative standard deviation (n = 3) of 0.91%–11.47%, indicating the satisfied accuracy and precision of the developed method.

Characteristics and Chemical Composition of Maleo-Pimaric and Fumaro-Pimaric Rosins Made of Indonesian Pinus merkusii Rosin

This study was directed to look at the chemical composition of maleo-pimaric and fumaro-pimaric rosins made of unmodified rosin with maleic anhydride (MA) or fumaric acid (FA). The results showed that one peak of a maleopimaric acid (MPA) adduct on the chromatogram was obtained when a sample of this reaction product was injected into a Gas liquid chromatography (GLC) or Gas chromatograph-Mass spectrometer (GC-MS) system. Identification of this adduct using a GC-MS showed that a reaction product of rosin and MA produced endo-maleopimaric acid methyl ester. This peak of the adduct had a similar profile as in a previous study with a base peak at m/z =146 and prominent ions at m/z = 386, m/z = 187 and at m/z = 121. In the making of MPA and fumaropimaric acid (FPA) adducts, the increase in molar ratio for both reaction temperatures of 125 and 2000C and all rosin samples used in the reaction process gave a higher yield of endo maleopimaric acid. The largest amount of this product was obtained at a molar ratio of 1:10 with the reaction at 200 degrees C. Among the origin of the rosin used in this experiment, rosin from Central Java produced the highest MPA, while the highest FPA was achieved by using rosin from North Sumatra. The relationship between the molar ratio and the concentration of MPA or FPA could be expressed as a quadratic equation. From the equation, one could predict the best molar ratio to produce the highest MPA or FPA adducts at a suitable molar ratio. Using the equation Y = -0.8475 X2 + 10.448X - 9.7125, at the reaction temperature 200 degrees C, the highest MPA (around 22.50%) could be achieved by using a molar ratio of rosin and MA of 1:6.2.

Determination of volatile characteristics of Greek and Turkish pine honey samples and their classification by using Kohonen self organising maps

Forty-four samples of pine honey were analysed, 22 from Greece and 22 from Turkey. A purge & trap–gas chromatograph–mass spectrometer system was used for the extraction, separation and identification of volatile and semi-volatile compounds. In all, 77 compounds were extracted and identified. Two of them, the 3-carene, and one unidentified compound ( m/z 55, 79, 91, 107, 123, 165) were found to be specific to Turkish honeys and may be considered as markers characterising the Turkish origin of samples. Beyond this result, and by using the Kohonen self-organizing map (KSOM), a clear differentiation was obtained between the Turkish and Greek pine honey samples from a global consideration of all the analysed volatile constituents.

Fullerenes as sorbent materials for benzene, toluene, ethylbenzene, and xylene isomers preconcentration

A simple and novel SPE system for benzene, toluene, ethylbenzene, and xylene isomers (BTEX) compounds in water is proposed in which samples are directly propelled from a 15 mL glass vial through a sorbent column by means of a needle, thereby avoiding evaporative losses and the sorption of BTEX on the manifold materials. Following elution with 150 microL of ethyl acetate, 1 microL of extract is injected into a gas chromatograph-mass spectrometer system. A comparative study of various sorbent materials (C60 fullerene, Tenax TA, and RP-C18) revealed C60 fullerene to be the best choice in terms of sensitivity (a likely result of its increased sample breakthrough volume), precision (the surfactant medium used to prepare samples minimizes evaporative losses), selectivity (C60 fullerene only interacts with nonpolar aromatic compounds), and reusability (columns containing 60 mg of C60 fullerene remain serviceable for at least 6 months). This C60 fullerene-based method exhibits a linear range of 0.1-100 microg/L, a detection limit of 0.04 microg/L, and an RSD of ca. 3%. It was applied to the determination of BTEX in various types of water including sea and waste water with good precision.

Measurement of Volatile Organic Compounds in the Urban Atmosphere of Harris County, Texas

Volatile organic compounds (VOCs) are a major component of urban air pollution. It is well documented that exposure to certain types of VOCs can cause adverse health effects such as cancer, immune and neurological damage, and reproductive and endocrine disorders. Urban air samples were collected at five locations in Harris County, Texas to determine the measurement of VOCs in the ambient air of residential areas in close proximity to industrial facilities that emit toxic air pollutants into the air. Three locations used in this study were located along the Houston Ship Channel (HSC), in the heart of one of the largest petrochemical complexes in the nation. Two other sampling locations were located many miles away from the ship channel and any industrial facilities that are required to report toxic air emissions. Air samples were collected daily over an 8-h period from December 2002 to March 2003. The samples were collected in 6-L stainless steel Silonite-coated canisters and analyzed using a modified version of EPA Method TO-15. A total of 53 compounds was quantitated using a gas chromatograph mass spectrometer system coupled to a cryogenic preconcentrator. Eighteen alkanes and oxygenated compounds were identified, along with 7 alkenes and 5 aromatic compounds. Several alkanes such as butane, isobutane, 2-methyl butane, and pentane were detected at all five sites. The total VOC concentrations determined were highest at two of the industrial sites and lowest at the site farthest away from the ship channel and any industrial facilities. This study concluded that the atmosphere near Harris County's industrial complex had higher concentrations of VOCs than the atmosphere in areas farther away from the HSC. The atmosphere of areas downwind from emission sources were found to be directly affected by toxic air emissions from industrial process but not at the levels seen in areas closer to the HSC.

Application of Solid-Phase Microextraction to Antidoping Analysis: Determination of Stimulants, Narcotics, and Other Classes of Substances Excreted Free in Urine

This paper describes the application of solid-phase microextraction (SPME) with subsequent injection in a gas chromatograph-mass spectrometer (GC-MS) (electron impact, full scan) for the screening analysis of stimulants and narcotics in urine. Several different kinds of fibers were preliminarily tested and comparatively evaluated considering the influence on the overall analytical performance of the method; other experimental parameters; and, primarily among them, the volume of urine, the pH value, and the time of adsorbtion. The optimal experimental conditions have been recorded using 0.5 mL of urine with the pH value adjusted to 10 with carbonate buffer, and in which is immersed a polydimethylsiloxane/divinylbenzene fiber, with a sampling time of 30 min; the fiber is then directly desorbed in the injection port of the GC-MS equipment. All the analytes show a good linearity (R2 > 0.99 for most substances) and a good reproducibility at the concentration corresponding to the minimum performance requirement limit or at the cut-off value fixed by the World AntiDoping Agency (CV% < 11). The limit of detection of the method is 50 ng/mL for the majority of the substances investigated. Imidazole-based drugs (e.g., naphazoline) and local anesthetics can also be included in this screening method. Whenever necessary, confirmation analyses may also be performed by following the same pre-chromatographic procedure. Integrating the SPME process and the GC-MS analysis with a dedicated autosampler that combines the microextraction and injection capacities maximizes the overall analytical capacity of a single GC-MS system and reduces the human labor necessary for and the environmental impact of screening for stimulants and narcotics excreted free in urine.

Solid-phase extraction–gas chromatography–mass spectrometry using a fullerene sorbent for the determination of inorganic mercury(II), methylmercury(I) and ethylmercury(I) in surface waters at sub-ng/ml levels

A novel, straightforward solid-phase extraction system for the determination of inorganic mercury and organomercury compounds in water is proposed. The analytes, in a buffer medium at pH 4.5, are sorbed as diethyldithiocarbamate complexes on a C 60 fullerene column an subsequently eluted and derivatized with sodium tetra- n-propylborate in ethyl acetate. Following elution, 1 μl of extract is injected into a gas chromatograph–mass spectrometer system. The proposed gas chromatography–mass spectrometry speciation method exhibits a linear range of 4–1 ng/ml, and a detection limit of 1.5 ng/l (sample volume, 50 ml). Its repeatibility, as relative standard deviation (RSD) (from 11 standards containing 50 ng/l for each analyte), is ca. 7%. No interferences from metals ions, such as Zn 2+, Fe 3+, Sb 3+, As 3+, Pb 2+, Ni 2+, Cu 2+, Sn 2+, Co 2+, Mn 2+and Cd 2+ were encountered at concentrations 1000 times higher than those of the mercury compounds. The method was used for the speciation of inorganic mercury, methylmercury and ethylmercury in various types of water including sea and waste water.

Evaluation of an automatic sampling gas chromatographic–mass spectrometric instrument for continuous monitoring of trace anthropogenic gases

Continuous monitoring of the atmospheric volatile halogenated hydrocarbons is needed in light of the role played by these compounds in global climate change phenomena. The analytical methodology described in the following implies the use of a gas chromatographic–mass spectrometric system equipped with a sampling/pre-concentration unit, for the simultaneous and continuous analysis of a number of halogenated hydrocarbons present in the atmosphere at concentration levels ranging from a few to hundreds of part per trillion by volume. The optimization of the analytical procedure in terms of efficiency, linearity, and reproducibility is reported together with some of the results obtained in the frame of a monitoring activity carried out on a remote mountain station in central Italy.

Application of a simple and sensitive GC-MS method for determination of morphine in the hair of opium abusers.

Thirty hair samples were collected from male opioid abusers for whom the presence of morphine in their urine samples was confirmed by thin layer chromatography (TLC). The hair samples were decontaminated by washing with isopropanol, deionized water, and isopropanol, dried at room temperature, and cut into small pieces. Samples of the latter (30 mg ) were digested by incubation in a mixture of methanol-trifluoroacetic acid (9:1) for 18 h at 45 degrees C and sonicated to improve the extraction process. The methanolic phase was evaporated to dryness under a stream of nitrogen at 50 degrees C. The sample was derivatized by addition of N-methyl- N-trimethylsilyltrifluoroacetamide (MSTFA) and 1% trimethyliodosilane (TMIS) at 70 degrees C for 20 min, with sonication. Derivatized samples (1 microL) were injected into a gas chromatograph-mass spectrometer (GC-MS) system fitted with a capillary column; the Finnigan MS was operated in SIM mode. Naltrexone was used as internal standard (IS). The masses of the ions selected for morphine and naltrexone were 429 and 557, respectively. The limit of quantitation was set at 0.03 ng mg(-1) hair. By using the above procedure we detected morphine in all the samples examined, in the concentration range 0.26-10.31 ng mg(-1 )hair.