Use Of Gas Chromatography Research Articles

High-speed gas chromatographic separations with diaphragm valve-based injection and chemometric analysis as a gas chromatographic “sensor”

A high-speed gas chromatography system, the gas chromatographic sensor (GCS), is developed and evaluated. The GCS combines fast separations and chemometric analysis to produce an instrument capable of high-speed, high-throughput screening and quantitative analysis of complex chemical mixtures on a similar time scale as typical chemical sensors. The GCS was evaluated with 28 test mixtures consisting of 15 compounds from four chemical classes: alkanes, ketones, alkyl benzenes, and alcohols. The chromatograms are on the order of one second in duration, which is considerably faster than the traditional use of gas chromatography. While complete chromatographic separation of each analyte peak is not aimed for, chemical information is readily extracted through chemometric data analysis and quantification of the samples is achieved in considerably less time than conventional gas chromatography. Calibration models to predict percent volume content of either alkanes or ketones were constructed using partial least squares (PLS) regression on calibration sets consisting of the five replicate GCS runs of six different samples. The percent volume content of the alkane and ketone chemical classes were predicted on five replicate runs of the 22 remaining samples ranging from 0 to 50 or 60% depending on the class. Root mean square errors of prediction were 2–3% relative to the mean percent volume values for either alkane or ketone prediction models, depending on the samples chosen for the calibration set of that model. The alkyl benzenes and alcohols present in the calibration sets or samples were treated as variable background interference. It is anticipated that the GCS will eventually be used to rapidly sample and directly analyze industrial processes or for the high throughput analysis of batches of samples.

Accurate enzymatic measurement of fecal bile acids in patients with malabsorption

Quantitation of fecal bile acid excretion can help elucidate the cause of diarrhea or steatorrhea. Fecal bile acids can be measured with gas chromatography–mass spectrometry, but this is time-consuming, expensive, and not available for clinical use. Relatively simple enzymatic methods have been described for the measurement of fecal 3α-hydroxy bile acids, but these have not been validated in patients with gastrointestinal disease. We found that an enzymatic method yielded falsely low results in patients with malabsorption syndromes for two reasons: First, the preliminary hydrolysis step did not completely deconjugate bile acids, precluding their extraction into diethyl ether for enzymatic assay. Second, long-chain fatty acids inhibited 3α-hydroxysteroid dehydrogenase activity. By increasing the duration of hydrolysis and the concentration of enzyme, we developed a simple, accurate, and reproducible method for measuring fecal 3α-hydroxy bile acids that agreed well with values obtained with the use of gas chromatography–mass spectrometry ( R = .95), both in normal subjects and in patients with malabsorption syndromes.

Identification of plant odours activating receptor neurones in the weevil Pissodes notatus F. (Coleoptera, Curculionidae).

Plants release complex mixtures of volatiles important in the interaction with insects and other organisms. In the search for compounds that contribute to the perception of odour quality in the weevil Pissodes notatus, single olfactory receptor neurones on the antennae were screened for sensitivity to naturally produced plant volatiles by the use of gas chromatography linked to single cell recordings. We here present 60 olfactory neurones responding to 25 of the numerous compounds released by host and non-host plants. All the neurones show high selectivity and are classified into 12 distinct types. The two most abundant types respond to alpha-pinene, beta-pinene, and 3-carene ( n=17), and to isopinocamphone and pinocamphone ( n=17), respectively. Other neurone types respond to limonene ( n=9), beta-phellandrene ( n=3), and fenchone ( n=4). Responses to beta-caryophyllene ( n=1) and to ethanol ( n=4) are also shown. Except for two pairs, the neurone types do not show overlap of the molecular receptive range. The active compounds are present in the host, Pinus pinaster, as well as in non-hosts, supporting the idea that plant odour quality is mediated by the ratio of the compounds rather than specific odorants.

Dissecting Pelias: The use of gas chromatography in the identification of traditional binding media

Existing gas chromatographic techniques were applied to the analysis of binding media present in a case studya large 16th-century Italian painting on canvas. This period in art history is known for its mixed use of media, a transitional phase between tempera and oil paint. The painting had also undergone various restoration treatments in the past, resulting in the presence of an interesting variety of binders, including oils, resins, proteins and waxes. Samples were taken from the various strata of the painting, and identification was achieved by comparison against standards. Experiments were carried out using gas chromatography/mass spectrometry (GC/MS), and a recently developed methylation process using Meth-Prep®reagent. The main challenge of the project was the practical application of analytical theory to an actual painting. Ultimately, this project gave positive identification of the binding media present, evaluated existing GC techniques, and established clear, reproducible experiment protocols.

Uptake and effects of the cypermethrin-containing sea lice treatment Excis® in the marine mussel, Mytilus edulis

Wild and farmed mussels, Mytilus edulis, coexist with salmon farms in Scottish sea lochs. A synthetic pyrethroid, cypermethrin, is licensed for use on fish farms to control sea lice infestations as a formulation called Excis®. In this study, uptake of cypermethrin from Excis® exposure is investigated through the use of gas chromatography with mass-spectrometry. The effects of Excis® on mussels are also examined by measuring the neutral red retention time of lysosomes, aerial survival and shell closure. The isomeric ratios of cis:trans cypermethrin measured in mussels are around 80:20; a marked increase from 40:60 to which the mussels were exposed. This is most likely due to preferential metabolism of trans-isomers, as the same response is seen in vertebrates. There is a pronounced behavioural effect of shell closure, where mussels exposed to 1000 μg/l cypermethrin shut their shells within an hour of exposure. Arguments are presented for this effect being either a voluntary response on recognition of cypermethrin, or an effect arising from an involuntary action of cypermethrin on the adductor muscle. Even at 1000 μg/l cypermethrin, neutral red retention time and aerial survival are not affected. The data suggest that the responses of mussels shown here are unlikely to occur in the field, even at the concentrations of cypermethrin used in fish cages, for the treatment of sea lice.

Use of gas chromatography-olfactometry to identify key odorant compounds in dark chocolate. Comparison of samples before and after conching.

After vacuum distillation and liquid-liquid extraction, the volatile fractions of dark chocolates were analyzed by gas chromatography-olfactometry and gas chromatography-mass spectrometry. Aroma extract dilution analysis revealed the presence of 33 potent odorants in the neutral/basic fraction. Three of these had a strong chocolate flavor: 2-methylpropanal, 2-methylbutanal, and 3-methylbutanal. Many others were characterized by cocoa/praline-flavored/nutty/coffee notes: 2,3-dimethylpyrazine, trimethylpyrazine, tetramethylpyrazine, 3(or 2),5-dimethyl-2(or 3)-ethylpyrazine, 3,5(or 6)-diethyl-2-methylpyrazine, and furfurylpyrrole. Comparisons carried out before and after conching indicate that although no new key odorant is synthesized during the heating process, levels of 2-phenyl-5-methyl-2-hexenal, Furaneol, and branched pyrazines are significantly increased while most Strecker aldehydes are lost by evaporation.

The Maternal Lifestyle Study: Drug exposure during pregnancy and short-term maternal outcomes

OBJECTIVE: Reports of maternal effects resulting from drug exposure during pregnancy are inconsistent. The Maternal Lifestyle Study (MLS) is a multicenter, prospective, observational study that was initiated to better define the effects of exposure to illicit drugs during pregnancy on the mother, fetus, and infant. METHODS: Between May 1993 and May 1995, of 19,079 mother-infant dyads that were screened after delivery for cocaine and opiate exposure at four clinical centers (Brown University, University of Miami, University of Tennessee, Memphis, and Wayne State University), 16,988 (89%) met eligibility criteria and 11,811 (70%) of those eligible agreed to participate in the study. Exposure was defined as an admission of use of cocaine or opiates or both or the presence of cocaine or opiate metabolites in meconium as determined by use of gas chromatography–mass spectroscopy assay. Nonexposure was defined as a negative drug use history by interview and a negative immunoassay screen. When exposure could not be confirmed, such as when meconium was not obtained or was inadequate for confirmatory analysis, the mother-infant dyad was excluded (n = 3184). RESULTS: Of the mothers who consented to participate, 50% were African American, 38% were married, 64% were Medicaid recipients, and 95% had at least one prenatal care visit (median, 10 visits). Significant differences (P <.01) between cocaine-opiate exposed (n = 1185) and nonexposed (n = 7442) mothers included race (African American: 74.6% and 47.0%, respectively), mean age (29.6 and 26.1 years, respectively), and polydrug use including any combination of alcohol, tobacco, and/or marijuana (93% and 42%, respectively). Odds ratios (99% CI) indicate that exposed mothers had a significantly higher risk(P <.001) of medical complications including syphilis 6.7 (4.8-9.6), gonorrhea 1.9 (1.3-3.0), and hepatitis 4.8 (2.6-8.91); psychiatric, nervous, and emotional disorders 4.0 (2.2-7.4); and abruptio placenta 2.3 (1.4-3.9). The odds of a positive test for human immunodeficiency virus were higher (available on 28% of the cohort) in the exposed group 8.2 (14.3-15.4). Seventeen cases of maternal acquired immunodeficiency syndrome (AIDS) were identified. Opiate exposure with its attendant needle use significantly increased the risk of hepatitis and AIDS. The number of hospitalizations during pregnancy did not differ between the exposure groups because 11% of patients in each group were hospitalized at least once. However, violence as a cause of hospitalization was more common in the cocaine-exposed group, 19.6 (2.7-144.7). CONCLUSION: This observational study confirmed many of the reported adverse social and serious medical perinatal complications of mothers exposed to cocaine or opiates during pregnancy. The overall prevalence of these risk outcomes was lower than has been reported previously. (Am J Obstet Gynecol 2002;186:487-95.)

Rapid quantitation of cyanide in whole blood by automated headspace gas chromatography

Cyanide (CN), a chemical asphyxiant, is a rapidly acting and powerful poison. We have developed a sensitive, rapid, simple, and fully automated method for measuring CN in whole blood. The assay is based on the use of gas chromatography (GC) with nitrogen–phosphorus detection and acetonitrile as an internal reference. Following the automated addition of phosphoric acid to the blood sample, the released hydrogen cyanide is analyzed using a fully automated headspace GC system. The assay, validated on human blood samples spiked with potassium cyanide and on clinical samples from fire victims who had smoke inhalation injury, can detect CN at a wide range of concentrations (30–6000 μg/l) in about 17 min (including incubation and GC run time, and <2 min for manual sample preparation). This automated, high-throughput, simple, and sensitive method is suitable for the rapid diagnosis of CN in clinical and forensic specimens.

Tissue solubility of four volatile anesthetics in fresh and frozen tissue specimens from swine

To determine tissue solubilities of desflurane, sevoflurane, enflurane, and halothane in swine and to evaluate the effects of freezing specimens on tissue solubility, Arterial blood samples and specimens of brain, heart, liver, kidney, muscle, and subcutaneous fat from 5 healthy female adult Chinese Meishan pigs. Each tissue specimen was divided into 2 parts. One part was used to measure tissue-gas partition coefficients immediately after collection. The other part was frozen at -20 C for 6 days prior to determination of tissue-gas partition coefficients. Tissue-gas and blood-gas partition coefficients were measured by use of gas chromatography, and tissue-blood partition coefficients were calculated. Regression analysis was performed to determine whether fat-gas partition coefficients were correlated with lean tissue-gas partition coefficients. Tissue-gas and blood-gas partition coefficients of halothane were greater than those of enflurane followed by coefficients of sevoflurane and desflurane. However, the order of anesthetic agents with the greatest to smallest tissue-blood partition coefficients was sevoflurane, halothane, enflurane, and desflurane. Muscle-gas partition coefficients of sevoflurane and enflurane, liver-gas partition coefficients of desflurane and halothane, and the kidney-gas partition coefficient of enflurane were significantly greater in frozen specimens, compared with fresh specimens. Lean tissue-gas partition coefficients of all 4 volatile anesthetics correlated directly with fat-gas partition coefficients. The fat content of lean tissue is an important factor in determining the tissue solubility of volatile anesthetics. Freezing specimens before determination of tissue-gas partition coefficients may result in a false increase in tissue solubility.

Semiochemicals and social signaling in the wild European rabbit in Australia: II. Variations in chemical composition of chin gland secretion across sampling sites.

The volatile components of the chin gland secretion of the wild European rabbit, Oryctolagus cuniculus (L.), were investigated with the use of gas chromatography. Studies of the chemical nature of this secretion by previous workers demonstrated that it was important in the maintenance of social structure in this species. This study identified 34 different volatile components that consist primarily of aromatic and aliphatic hydrocarbons. Especially common are a series of alkyl-substituted benzene derivatives that provide most of the compound diversity in the secretion. Samples of chin gland secretion collected from animals at three different geographical locations, separated by more than 100 km, showed significant differences in composition. This work suggests that variation among populations needs to be considered when undertaking semiochemical research. Alternate nonparametric methods are also used for the analysis of chromatographic data.

Detection of fruit- and flower-emitted volatiles by olfactory receptor neurons in the polyphagous fruit chafer Pachnoda marginata (Coleoptera: Cetoniinae).

Olfactory receptor neurons on the antennae of the African fruit chafer species Pachnoda marginata (Coleoptera: Scarabaeidae) were examined through extensive use of gas chromatography linked with electrophysiological recordings from single olfactory receptor neurons. Contacted neurons were stimulated with a large number of extracted volatiles from 22 different fruits and with 64 synthetic plant compounds. Extracted fruit volatiles were identified using linked gas chromatography-mass spectrometry. In total, 48 different odor compounds were found to elicit responses. Analysis of the response spectra of the contacted neurons (n = 232) revealed the presence of 28 classes of receptor neurons. The neurons exhibited strong selectivity as well as high sensitivity. Eleven of the identified classes were selectively activated by single compounds, while the remaining were activated by 2-6 compounds. Several receptor neurons that were activated by more than one compound responded to compounds sharing basic structural similarities. The results support the growing hypothesis that a significant proportion of plant-odor receptor neurons in insects are highly sensitive and selective for single odors.

Development of perfluorocarbon (PFC) primary standards for monitoring of emissions from aluminum production.

An EPA Voluntary Aluminum Industrial Partnership (VAIP) program has been formed to help US primary producers focus on reducing the emissions of two perfluorocarbons (PFCs), tetrafluoromethane (CF4) and hexafluoroethane (C2F6), during the production of aluminum. To ensure comparability of measurements over space and time, traceability to national sources was desirable. Hence, the EPA approached the NIST to develop a suite of primary standards to cover a mole fraction (concentration) range of 0.1 to 1400 micromol mol(-1) for CF4 and 0.01 to 150 micromol mol(-1) of C2F6. A total of eight gravimetric PFC gas standards were prepared with relative expanded uncertainties of < or = 0.52% (approximately 95% confidence level). These primary standards were ultimately used to assign values to a series of secondary gas standards at three mole-fraction levels with relative expanded uncertainties ranging from +/- 0.7% to 5.3% (approximately 95% confidence level). This series of secondary standards was used within the aluminum industry to calibrate instruments used to make emission measurements. Assignment of values to the secondary standards was performed by use of gas chromatography with flame-ionization detection (GC-FID) and Fourier transform infrared spectrometry (FTIR). Real time pot-line and stack samples from a local aluminum plant were also obtained and sub-samples sent to each participating facility for analysis. The data generated from each facility were sent to NIST for analysis. The maximum difference between the NIST and individual facilities' values for the same sub-sample was +/- 26%.

Analysis of Chemical Markers as a Means of Characterising Airborne Micro-Organisms in Indoor Environments: A Case Study

Analysis of chemical markers can be done to character ise the microbiological composition of indoor environ ments. Here we describe the use of gas chromatography- tandem mass spectrometry methods to determine mu ramic acid, 3-hydroxy fatty acids and ergosterol, which are, respectively, markers of bacterial biomass, endotox in, and fungal biomass. We also report how these meth ods were applied to determine airborne micro-organ isms in a water-damaged building.

Characteristics of patients complaining of halitosis and the usefulness of gas chromatography for diagnosing halitosis

Objective: The purpose of this study was to examine the characteristics of patients complaining of halitosis and to evaluate the diagnostic accuracy of 3 methods of measuring halitosis. Study Design: The actual degree of halitosis was determined through use of an organoleptic test in 155 patients aged 46 ± 17 years (mean ± SD). The volatile sulfur compounds (VSCs) were determined with gas chromatography and with sulfide monitoring. Results: The organoleptic test revealed that 55% of the subjects had either no mouth odor or slight mouth odor. There was a significant correlation between the organoleptic score and the total VSC level as determined through use of other methods. The critical discrimination value of the total VSC level was calculated to be 0.057 ppm for gas chromatography and 0.117 ppm for sulfide monitoring; high sensitivity and specificity were obtained when the gas chromatography value was used. The amount of tongue coating was significantly greater in the halitosis-positive group than in the halitosis-negative group, whereas there was no difference in salivary flow rate between the 2 groups. Conclusion: These results indicate that determining VSCs with gas chromatography is a useful means of diagnosing halitosis.(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:531-4)

Assessing the effect of fatty acids on prostate carcinogenesis in humans: does self-reported dietary intake rank prostatic exposure correctly?

Dietary fatty acids may influence prostate carcinogenesis. Although the standard for assessing dietary effects in humans is the semiquantitative food-frequency questionnaire, the extent to which self-reported intake correctly ranks prostatic exposure is unknown. The objective was to examine the correlation between reported intakes of different fatty acids and their concentrations in prostate tissue. This was a cross-sectional study of 52 men undergoing surgical resection of the prostate gland. Usual dietary intake of saturated, total unsaturated, oleic, and linoleic fatty acids over the previous year was estimated with use of a 122-item version of the Health Habits and History Questionnaire. Concentrations in prostate tissue were measured directly by use of gas chromatography in healthy tissue collected at the time of surgery and were expressed as a percentage of total fatty acids. Correlations with 4 measures of dietary intake [g/d, g/d adjusted for total daily energy intake, % of total fat (as g/d), and % of total energy] were evaluated by Spearman's rank-order correlation coefficients. Linoleic acid concentrations in prostate tissue were significantly correlated with dietary intake expressed as g/d adjusted for total energy [r = 0.29 (95% CI: 0.03, 0.49), P = 0.04], % of total fat [r = 0.36 (0.14, 0.550), P = 0.008], and % of total energy [r = 0.28 (0.04, 0.49), P = 0.042], but not as g/d. Although mean concentrations of saturated, total unsaturated, and oleic fatty acids in prostate tissue resembled mean intakes for the group, prostatic concentrations did not correlate with individual intakes. Self-reported intake of fatty acids is a satisfactory marker of prostatic exposure at the group level, but, with the exception of linoleic acid, does not correctly rank individuals with respect to intensity of exposure.

A technical and economic comparison of biofiltration and wet chemical oxidation (scrubbing) for odor control at wastewater treatment plants

An economic and technical comparison of two odor control systems, a biofilter and a chemical wet scrubber, was conducted over a 1-year time period at a large municipal wastewater treatment plant. The biofilter system was designed to remove hydrogen sulfide gas and other oxidizable sewage odors from four covered gravity sludge thickeners, a gravity sludge thickener effluent channel and an influent splitter box for the gravity sludge thickeners. The sodium hypochlorite/sodium hydroxide wet scrubber was designed to control hydrogen sulfide gas and other oxidizable sewage odors from the covered primary settling tanks, influent distribution channels and effluent channel, and the mixing tank effluent channel. The technical comparison comprised their overall removal rates and efficiencies based on inlet HZS concentrations and other operating variables. The economic comparison was designed to provide the cost per cubic meter of H2S removed for each system. Influent and effluent gas samples were collected on a weekly basis. H2S concentration levels were determined through the use of gas chromatography with a flame photometric detector. The results showed that the H2S inlet gas concentration has a seasonal change with a maximum value occurring in August and September. The effluent H2S concentration was lower than 2 ppmv for both systems for most of the samples. The efficiency for both the biofilter and wet scrubber was above 95%, and was related to the operating and ambient conditions. The economic comparison revealed that the actual unit cost for the biofilter was higher than for the wet scrubber (U.S.$160/m3 H2S removed versus U.S.$131/m3 H2S removed). For both the biofilter and the wet scrubber, the investment costs are affected by the size/scale of the system, the design flow and other factors. For these systems, the mulch change costs, chemical usage costs, maintenance costs and power usage costs were mainly dependent on the actual odor gas loadings which showed substantial seasonal fluctuations as a function of the seasonal temperature. The worst case conditions reported here indicate that the H2S concentrations generated during the summer months should be used to determine the design load.

Method for determination of methyl tert-butyl ether in gasoline by gas chromatography

A simple method for the determination of methyl tert-butyl ether (MTBE) in gasoline has been developed. The separation of MTBE from other analytes was controlled by the use of gas chromatography–mass spectrometry in the full scan mode using the characteristic primary, secondary and tertiary ions m/ z 73, 57 and 43. The sample mass spectrum did not show any superimposition of other analytes. The separation from the common gasoline component 2-methylpentane was sufficient for reliable quantitation. An application of the developed conditions using gas chromatography with flame ionization detection was performed by the analysis of regular, euro super, super premium unleaded and ‘Optimax’ gasoline from petrol stations in the area of Frankfurt/Main, Germany. Regular unleaded gasoline shows an average MTBE content of 0.4% (w/w), whereas the MTBE content in euro super gasoline varies between 0.4 and 4.2% (w/w). The blending of MTBE to super premium has increased from 8.2% (w/w) in 1998 to 9.8% (w/w) on average in 1999. The recently introduced gasoline ‘Optimax’ shows an average MTBE content of 11.9% (w/w). The presented method might also be used for the analysis of other ethers, such as ethyl tert-butyl ether, which requires the use of another internal standard.

Application of Chromatography and Spectrometry to the Authentication of Alcoholic Beverages

The use of gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and UV–VIS spectrophotometry for identifying the falsification of strong alcoholic beverages (vodka, gin, cognac, and whiskey) was considered. In the GC analysis of ethyl alcohol and vodkas based on it, the test alcohol was assigned to synthetic alcohol or to biochemically produced alcohol using a set of typical impurities, markers of the alcohol nature, which present in the test alcohol in a certain ratio and can be determined by GC or GC–MS analysis. The multicomponent analysis of cognacs and related liquors can reveal the replacement of cognac spirit with alcohol produced from nongrape raw materials, to determine whether the cognac spirit was in contact with oak wood and how long was the duration of its aging, and to detect the falsification of the age by adding certain ingredients. The limitations of chromatographic and spectrometric analytical techniques in the identification of adulterated alcoholic beverages was demonstrated. The validation criteria for testing the identification of alcoholic beverage components by chromatographic techniques received special attention.

Phenolic and volatile composition of wines made from Vitis vinifera cv. Muscat lefko grapes from the island of Samos.

A study of the phenolic and volatile composition of wines produced from the white cultivar Muscat lefko from the island of Samos was conducted. Dry, fortified, naturally sweet wines and mistelles (aged and nonaged) have been studied. The phenolic components (flavan-3-ols, hydroxycinnamates, and flavonols) were measured by high-performance liquid chromatography after solid phase extraction (SPE). The terpenes (free and glycosidically linked) were determined by the use of gas chromatography-mass spectrometry (GC-MS) after SPE. The fermentation aroma components were analyzed by GC-MS after liquid-liquid extraction. It was found that the dry wines contained lower amounts of most of the phenolics and higher quantities of terpenes and fermentation aroma compounds than the sweet wines. The aged mistelle wines contained lower levels of coutaric and caftaric acids, higher concentrations of the free acids, and markedly fewer free and bound terpenes and fermentation aroma components compared to the other sweet wines. The naturally sweet wine contained relatively increased amounts of phenolics, 2,3-butanediol, and glycosidically linked terpenes.

Selective receptor neurone responses to E-beta-ocimene, beta-myrcene, E,E-alpha-farnesene and homo-farnesene in the moth Heliothis virescens, identified by gas chromatography linked to electrophysiology.

An important question in olfaction is for which odorants receptor neurones have evolved. In the present study, olfactory receptor neurones on the antennae of the tobacco budworm moth Heliothis virescens were screened for sensitivity to naturally occurring plant-produced volatiles by the use of gas chromatography linked to electrophysiology. Volatiles of host as well as non-host plants collected by headspace techniques were used for stimulating the neurones, sequentially via two columns, one polar and one nonpolar installed in parallel in the gas chromatograph. Three types of neurones presented in this paper responded to one, two or three compounds for which the retention times were determined in both column types. The chemical structures of the active components were determined on the basis of mass spectrometry linked to gas chromatography, indicating E-beta-ocimene and beta-myrcene as stimulants for neurone type 1, E,E-alpha-farnesene for neurone type 2 and homo-farnesene for neurone type 3. Re-testing authentic materials verified the identifications for the type 1 neurones. The results demonstrate a high specificity for the three types of neurones by strong responses to one or two structurally similar compounds out of hundreds present in a large variety of plants. The study exemplifies plant odour detection by narrowly tuned receptor neurones in a polyphagous moth species.