Micro- and nanostructures and their application in gas chromatography.

This mini-review focuses on the latest developments in the field of micro- and nanostructures in gas chromatography (GC). Significant progress has been made in recent years in designing miniaturized structures, for example, structures based on cyclodextrins. These are now commercially available and thus not the topic of this short review. Rather, we concentrate here on on-going research activities on nanoparticles, micro-electromechanical systems (MEMS) and metal-organic framework (MOF) supports as well as state-of-the-art column geometries, with particular emphasis on lab-on-a-chip columns, which undoubtedly will find their way into regular GC developments in the future.

Perspectives for Metabolomics in Human Nutrition: An Overview.

Metabolomics describes the measurement of the full complement of the products of metabolism in a single biological sample and correlating these metabolomic profiles with known physiological or pathological states. The metabolome offers the possibility of finding unique fingerprints responsible for different phenotypes. Analytical techniques such as nuclear magnetic resonance or mass spectrometry measure thousands of compounds within the metabolome simultaneously and appropriate data mining and database tools allow the finding of significant correlations between the measured metabolomes. The first direct outcome of nutritional metabolomics will be the discovery of biomarkers, which can reveal changes in health and disease but also indicate short term and long-term dietary intake. The concerted actions of nutrigenomics and metabolomics will play a crucial role in understanding how specific interactions of single nucleotide polymorphisms (SNP) influence a person's response to a diet. Finally, systems biology approaches to human nutrition combine transcriptomics, proteomics and metabolomics with the aim of understanding how diets interact within the human being.

An experimental comparison of electrospray ion-trap and matrix-assisted laser desorption/ionization post-source decay mass spectra for the characterization of small drug molecules.

An experimental comparison of product ion spectra produced by matrix-assisted laser desorption/ionization (MALDI) and electrospray ion-trap MS( n) for a group of small drug molecules is presented in this paper. The goal of the study was to demonstrate the usefulness of MALDI-MS with post-source decay (PSD) and collision-induced dissociation (CID) for the structural analysis of small drug molecules in the drug discovery process, where traditionally electrospray LC/MS methods are used. PSD and PSD/CID gave diverse product ions that were highly indicative of the structure of the drugs investigated (a group of 4-quinolone antibiotics and oleandomycin). In addition, the number of different product ions generated with MALDI-MS was always higher than with electrospray ion-trap MS( n) (with n < or =4) for the drug molecules studied. This investigation also showed that the choice of a suitable MALDI matrix for the analysis of low molecular weight compounds is quite important. It was found that of the three matrices examined, alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA) produced the most intense fragmentation levels while TiO2, with its advantage of virtually no low mass background signals, did not generate quite the same amount of information.

Rapid analysis of tetracycline antibiotics by combined solid phase microextraction/high performance liquid chromatography/mass spectrometry.

The technique of solid phase microextraction (SPME) combined on-line with high performance liquid chromatography/mass spectrometry (HPLC/MS) has been applied to the analysis of seven tetracycline analogues. Rapid baseline separation was achieved in under 5 min using a short 3 microm RP-18e cartridge column. Optimisation of the SPME procedure is described including choice of extracting fibre and modification of the sample by heating or salting out of the analytes. Detection limits of 4-40 ng/mL were obtained for the various analogues from extracted aqueous samples and absolute amounts of analyte extracted by the method determined using external calibration. To demonstrate the applicability of the technique for real samples the extraction of tetracycline from milk is described.

Rapid SPME/LC/MS/MS analysis of N-methylcarbamate pesticides in water.

Solid-phase microextraction combined with fast short-column liquid chromatography/electrospray ionization tandem mass spectrometry (SPME/LC/MS/MS) was used for isolating and analyzing nine N-methylcarbamate pesticides from water samples. Several SPME parameters, such as polarity of fibers, extraction time, and effect of ionic strength, were investigated and their impact on the SPME/LC/MS/MS technique was studied. The method was shown to be sensitive with detection limits between 0.3 and 1.9 microg/L and reproducible with precision between 4.5 and 12.7% RSD. The versatility of the method was exhibited by its excellent linearity in the concentration range of 2-2,000 microg/L in drinking water. A comparison of the SPME/LC/MS/MS method with LC/MS/MS methods utilizing traditional sample preparation techniques shows that the former offers similar performance in terms of precision and linearity, but is clearly easier to use and faster to perform.

Electrospray ionization and collision-induced dissociation of antibiotic polyether ionophores.

A series of polyether ionophores (lasalocid, monensin-A, narasin-A and salinomycin) was investigated by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). A fast short-column liquid chromatographic (LC) method, using a ternary gradient sequence, was developed to separate the ionophores in less than 4 minutes. Several mobile phase parameters such as pH and solvent additives were investigated, and their impact on both chromatographic and mass spectrometric behavior was studied. The ionophores readily formed stable complexes with various metal cations present as impurities in the solvents. Therefore, a method was developed to convert the ionophores into only sodium adduct species prior to ESI analysis. This procedure maximized both sensitivity and specificity in the subsequent MS/MS step. Low energy collision-induced dissociation (CID) of the sodium adduct ions resulted in a number of structure-diagnostic product ions for all ionophores. The proposed interpretation of these fragment ions is presented in this work. Additionally, the fragmentation of a series of monovalent carboxylic alkali-metal ion complexes of lasalocid was investigated under CID conditions. A comparison of the CID spectra revealed a decreasing degree of fragmentation in the order [M + H]+ approximately [M + NH4]+ > [M + Li]+ > [M-H + 2Li]+ > [M + Na]+ >> [M + Cs]+. To demonstrate the analytical potential of the LC/MS/MS method, its application to the determination of salinomycin in catfood samples was investigated. Salinomycin was recovered from catfood by a microwave solvent extraction procedure, and subsequently analyzed using LC/MS/MS of the sodium adduct ions.

Investigation of photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography-electrospray ionization tandem mass spectrometry system. Application to trace and confirmatory analyses in food samples.

The photochemical behavior of pesticides in a photolysis reactor coupled on-line with a liquid chromatography-electrospray ionization mass spectrometer (LC-hv-MS) was investigated. This paper describes the application of LC-hv-MS, in combination with tandem mass spectrometry (MS-MS), to identification of phototransformation products and to the establishment of possible photolytic pathways of pesticides. In addition, the applicability of LC-hv-MS as an alternative to LC-MS-MS, for trace and confirmatory multiresidue analysis in food samples was investigated. To demonstrate the potential of this technique, a series of N-heterocyclic compounds, phenylureas and carbamates, was studied. Several parameters, such as irradiation time and nature of photosensitizers, were investigated, and their impact on the photolytic transformation is presented here. The technique's versatility is also exhibited by using it for identification of triazine isomers, and for detection of pesticide residues in food sample extracts. Illustrative applications for analysis in lettuce and blueberry extracts are described.

Study of erythromycin A decomposition products in aqueous solution by solid-phase microextraction/liquid chromatography/tandem mass spectrometry.

The decomposition of erythromycin A (EA) in aqueous solution was examined in the pH range 2-13 by means of combined solid-phase microextraction (SPME) and liquid chromatography/electrospray ionization tandem mass spectrometry. Degradation of EA, especially at lower pH values (pH < or = 3), was very rapid and yielded a wide variety of decomposition products. Identification of these degradation products was achieved by means of tandem mass spectrometry in the product ion and precursor ion scan modes. Anhydroerythromycin A was shown to be the major reaction product in both acidic and basic solutions. Among the different SPME fibers investigated for extraction from aqueous solutions, polydimethylsiloxane/divinylbenzene exhibited the best performance for EA and its degradation products.

Study of 4-quinolone antibiotics in biological samples by short-column liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

Simultaneous detection and confirmation of 15 quinolone antibiotics was accomplished by fast short-column liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC/MS/MS). Several physiochemical parameters such as hydrophobicity and aqueous dissociation constants were calculated from the structural formulas of the quinolone drugs, and their impact on both chromatographic and mass spectrometric behavior was studied. Additionally, a possible influence of bulk solution pH on electrospray detection sensitivity of 4-quinolones was investigated and compared to predictions based on solution-phase equilibria. A signal intensity comparison of the MH+ ions at different pH values for all 15 compounds did not reveal any pH effect, despite variations by several orders of magnitude in equilibrium concentrations in bulk solution. To demonstrate the potential of the LC/MS/MS method, its application to trace analysis in several biological matrices such as milk, salmon, and human urine was investigated. The method was shown to be sensitive with detection limits down to 1 ppb in both milk and salmon tissue. The versatility of the method was also exhibited by utilizing it for rapid identification of urinary metabolites of ciprofloxacin. Finally, a new complementary approach is described for confirmatory analyses of 4-quinolones by means of a quasi-MS/MS/MS technique involving in-source collision-induced dissociation. It is shown that LC/quasi-MS/MS/MS can significantly enhance structural information and, thus, the specificity of analysis for the investigated 4-quinolones.

Rapid determination of corticosteroids in urine by combined solid phase microextraction/liquid chromatography/mass spectrometry.

Solid-phase microextraction combined with fast short-column liquid chromatography/mass spectrometry (SPME/LC/MS) was used for isolating and analysing 11 corticosteroids and 2 steroid conjugates from urine samples. Several SPME parameters such as polarity of fibres, extraction time and effect of ionic strength, were investigated, and their impact on the SPME/LC/MS technique was studied. To demonstrate the potential of the SPME/LC/MS method, its application to the determination of steroids in human urine was investigated. The method was shown to be sensitive with detection limits between 4 and 30 ng/mL and precision between 4.9 and 11.1% RSD through the use of an internal standard technique. The versatility of the method was also exhibited by its excellent linearity in the concentration range of 20 to 20,000 ng/mL in urine for all investigated compounds. A comparison of the SPME/LC/MS method with LC/MS methods utilizing traditional sample preparation techniques, shows that the former offers similar performance in terms of precision, linearity and detection limits, but is clearly easier to use and faster to perform.

Characterization of nitrosation products in cosmetics raw materials by liquid chromatography/mass spectrometry techniques.

Characterization of nitrosation products in cosmetics raw material samples has been accomplished by three liquid chromatography/mass spectrometry (LC/MS) techniques. Two of the techniques involved conventional methodologies of LC/MS and LC/tandem mass spectrometry, both of which can be used to detect and identify products formed under extreme-nitrosation conditions. The third technique utilized an on-line coupling of a photolysis reactor with the LC/MS, and it may be used as a rapid and specific means of screening for the presence of known and unknown N-nitrosamines, which may be carcinogenic.

Determination of underivatized fumonisin B1 and related compounds by HPLC.

A method is presented for determining the purity of the mycotoxin fumonisin B1 (FB1) by high performance liquid chromatography (HPLC) with evaporative light scattering detection (ELSD). The ELSD is a universal HPLC detector that exhibits a non-linear relationship between analyte amount and the resulting response. A log-log plot of ELSD response with the mass of FB1 injected was used as a calibration curve for determining the quantities of both FB1 and also individual impurities present in samples. Assumptions related to the uniformity of ELSD response for different but related compounds and other issues implied in this use of ELSD data were examined. One potential error produced by use of this method for purity analysis comes from the ELSD's decreased sensitivity for low-concentration analytes. Because analytes become more dilute the longer they remain on a chromatographic column, this sensitivity discrimination can be related to the retention times at which they appear. The ELSD response for FB1 at retention time 15.5 minutes was used to construct a general purpose calibration curve. Whenever a peak appeared at any time other than 15.5 minutes, the discrimination effect was corrected using a an empirically determined weighting factor and a proportion calculated from the retention time difference compared to 15.5 minutes. Purities for two fumonisin samples were calculated using both the ELSD method described above and an electrospray/mass spectrometric method. The quantitative assumptions underlying each method were discussed in order to understand and reconcile differences between the two sets of purity values obtained.

Multiresidue determination of sulfonamide antibiotics in milk by short-column liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

Liquid chromatography coupled to electrospray mass spectrometry and tandem mass spectrometry has been used for the determination and quantification of 21 sulfonamides and two potentiators (ormethoprim, trimethoprim) in milk. Separation using high-performance liquid chromatography was achieved in less than 6 min for all compounds on a short (4.0 x 50 mm, 3 micron) reversed-phase column. After sample clean-up, time-scheduled single-ion monitoring (SIM) yielded detection of sulfonamides in milk from low ppb level to the ppt level. The strategy used to detect, confirm and quantify sulfonamides in milk samples was as follows: (a) pre-screening (and cp3firmation) of target and non-target sulfonamides by precursor ion scan and/or multiple reaction monitoring experiments using generic product ions; (b) quantification of identified target compounds by monitoring their protonated molecule ions in a time-scheduled SIM experiment; (c) further confirmation, if necessary, by selected reaction monitoring using characteristic product ions.

Detection and confirmation of N-nitrosodialkylamines using liquid chromatography-electrospray ionization coupled on-line with a photolysis reactor.

Simultaneous detection and confirmation of several N-nitrosodialkylamines are accomplished by on-line coupling of a photolysis reactor with an HPLC-electrospray ionization mass spectrometer. Several parameters such as irradiation wavelength, irradiation time, mobile-phase composition, and pH, as well as different organic acid modifiers are investigated, and their impact on the detection of the N-nitrosodialkylamine-acid complex and its dissociative photolysis products is presented here. Additionally, the type of structural information obtained from the photolytic processes of N-nitrosodialkylamines is compared to that obtained by using in-source collision-induced dissociation. To demonstrate the potential of this technique, six N-nitrosodialkylamines are studied to determine the linearity of the response, the limits of detection and confirmation, and the reproducibility. The technique's versatility is also exhibited by utilizing negative-ion mode as a complementary means for analysis of the compounds. Finally, an illustrative application for N-nitrosodimethylamine analysis in beer is described.