Non-destructive analysis of pigments and other organic compounds in lichens using Fourier-transform Raman spectroscopy: a study of Antarctic epilithic lichens

Lichens in Antarctic habitats are subjected to environmental extremes, including UVB radiation, desiccation and low temperatures, as well as to rapid fluctuations in these. Lichens synthesise a variety of chemical compounds in response to their environmental conditions which contribute towards their colour, and which act as protectants against physiological stresses. The fluorescence generated by the lichens at 532 nm can be used in epifluorescence microscopy to identify their presence on substrata but this can severely affect the Raman spectra using visible excitation. The advantage of the near infrared excitation used in FT-Raman spectroscopy in minimising fluorescence emission facilitates the molecular characterisation of lichen encrustations without having to remove the thallus from its substrate or remove or otherwise damage any part of the thallus. Spectroscopic biomarkers are proposed which allow the lichens to be characterised by the identification of characteristic lichen substances; the use of these biomarkers for the preliminary taxonomic identification of Antarctic lichens is examined and some potential pitfalls are described.     

Identification and quantitative determination of some inorganic lanthanide compounds by diffuse reflectance spectroscopy

Diffuse reflectance spectroscopy in the UV, visible, and near-IR regions is found to allow the detection and identification of lanthanide oxides, fluorides, sulfides, and sulfofluorides without decomposing and dissolving samples. A nondestructive method for the detection and quantitative determination of more than 1 wt % of Eu(II) in the corresponding fluorides is proposed.     

Raman optical activity: a powerful technique to investigate essential oil components

The theory and some applications of Raman Optical Activity (ROA) towards terpene analysis are presented. With this technique, vibrational optical activity from chiral molecules can be measured providing their absolute configuration. This short review provides data obtained for pinene, verbenone, menthol, camphor, carenes and related molecules. The ROA technique seems to be a powerful tool which permits correlation between the properties of biocompounds and their structure.     

High-energy collisional spectroscopy in qualitative and quantitative analysis of diesel particulates

High-energy collisional spectroscopy provides a powerful analytical method for the characterization of polynuclear aromatic hydrocarbons present in diesel particulates. The absence of any need for extraction procedures and the large amount of information available from collisional spectra makes this technique of great interest. In particular, 3-methylcholanthrene can be determined from the daughter spectra of its molecular ion, with methylene iodide as internal standard.     

Colorimetric diffusion-reflection imaging high-throughput analysis of organic or inorganic compounds

A colorimetric diffusion-reflection imaging (CDRI) high-throughput analytical technology was developed for library analysis. In the investigation, quartz sands were employed as light diffusion-reflection media. Inorganic and organic compounds with characteristic absorption bands in visible light could be quantified by this method. In the current investigation, compounds such as CrCl3, KMnO4, methylene blue, and acrolein were employed as substrates, and the UV spectrometer and traditional GC (with thermal conductivity detector) were employed to check the reliability of our CDRI technology. The current technology is capable of analyzing more then 100 samples simultaneously. Relative errors below 10% were achieved.     

Local covariance order diffusion-ordered spectroscopy: a powerful tool for mixture analysis

Diffusion-ordered spectroscopy (DOSY) is an important tool in NMR mixture analysis that has found use in most areas of chemistry, including organic synthesis, drug discovery, and supramolecular chemistry. Typically the aim is to disentangle the overlaid, and often overlapped, NMR spectra of individual mixture components and/or to obtain size and interaction information from their respective diffusion coefficients. The most common processing method, high-resolution DOSY, breaks down where component spectra overlap; here multivariate methods can be very effective, but only for small numbers (2-5) of components. In this study, we present a hybrid method, local covariance order DOSY (LOCODOSY), that breaks a spectral data set into suitable windows and analyzes each individually before combining the results. This approach uses a multivariate algorithm (e.g., SCORE or DECRA) to resolve only a small number of components in any given window. Because a small spectral region should contain signals from only a few components, even when the spectrum as a whole contains many more, the total number of resolvable chemical components rises dramatically. It is demonstrated here that complete resolution of component spectra can be achieved for mixtures that are much more complex than could previously be analyzed with DOSY. Thus, LOCODOSY is a powerful, flexible tool for processing NMR diffusion data of complex mixtures.     

Pulsed fast/thermal neutron analysis: a technique for explosives detection

Explosives, narcotics and other contraband material contain various chemical elements, such as hydrogen, carbon, nitrogen and oxygen, etc. in quantities and ratios that differentiate them from each other and from other innocuous substances. Neutrons and gamma-rays have the ability to penetrate through various materials to large depths. They are able to interrogate, in a non-intrusive manner, volumes ranging from suitcases to Sea-Land containers. Pulsed fast/thermal neutron analysis (PFTNA) is a neutron-based technique which utilizes the (n,n'gamma), (n,pgamma), and (n,gamma) reactions to identify and quantify a large number of elements. The elements emit characteristic gamma-rays that are the 'fingerprints' of each isotope. This technique is being employed in a variety of applications: bulk coal analysis, contraband detection and detection of explosives.     

Analysis of zone-melted ultra-pure organic compounds: a new quantitative differential thermal analysis method

A method for the rapid quantitative determination of impurities in ultra-pure organic compounds is described. It is based on the difference in slopes of the curves obtained when the difference in temperature between the sample and a reference shield is plotted against time. The results are compared with those obtained by thermal analysis.     

Detection of volatile organic compounds using surface enhanced Raman spectroscopy substrates mounted on a thermoelectric cooler

Preliminary results for a volatile organic compound (VOC) sensor based on surface enhanced Raman spectroscopy (SERS) are described. The sensor is comprised of a SERS substrate mounted on a thermoelectric cooler (TEC). The SERS substrate is chemically modified with a thiol coating that prevents oxidation of the roughened silver surface and attracts the analyte of interest to the SERS surface. Using this sensor, detection of chlorinated solvents, aromatic compounds, and methyl t-butyl ether (MTBE) is demonstrated.     

A quantitative chemiluminescent assay for analysis of peroxide-based explosives

A quantitative chemiluminescent method, enabling indirect identification of the peroxide-based explosives TATP (triacetone triperoxide) and HMTD (hexamethylene triperoxide diamine) has been developed. Treatment of these compounds with acidic solutions produced peroxides, which were transformed into radical derivatives by horseradish peroxidase (HRP) and then quantified by measuring the light emitted during their oxidation of luminol. The method was first developed in the microplate format and later optimized for a portable luminometer, to enable rapid application of the assay directly on site. When the portable luminometer was used each analysis took only 5–10 min. The method had good selectivity, sensitivity, and reproducibility; in the microplate format the limits of detection (LOD) and quantification (LOQ) were 40 and 50 ng mL⁻¹, respectively, for both TATP and HMTD. When the portable luminometer was used the LOD and LOQ were 50 and 100 ng mL⁻¹, respectively, for both compounds. Introduction of light emission-enhancing compounds did not improve the analytical performance of the assay. Imprecision (CV values) was always below 10%. Recovery varied rapidly with time, with an average value of 78% after 5 min. No false-positive result was detected on measurement of a variety of samples; this is an important feature for analysis on site. The method was applied both to contaminated materials and to fortified soil samples, simulating operational conditions.     

Coupled reversed-phase and ion chromatographic system for the simultaneous identification of inorganic and organic explosives

There are many methods available to detect and positively identify either organic or inorganic explosives separately, however no one method has been developed which can detect both types of explosive species simultaneously from a single sample. In this work, a unique coupled-chromatographic system is reported for the simultaneous determination of both organic and inorganic explosive species and is used for pre-blast analysis/identification purposes. This novel approach is based on the combination of reversed-phase high performance liquid chromatography and ion chromatography which allows trace levels of organic and inorganic explosives to be determined simultaneously from a single sample. Using this procedure, a 20 min reversed-phase separation of organic explosives is coupled to a 16 min ion-exchange separation of anions present in inorganic explosives, providing a complete pre-blast analysis/identification system for the separation and detection of a complex mixture containing organic and/or inorganic explosive species. The total analysis time, including sufficient column re-equilibration between runs, was <25 min using the coupled system. By this method, the minimum resolution for the organic separation was 1.16 between nitroglycerin and tetryl and the detection limits ranged from 0.31 mg L(-1) for cyclotetramethylene tetranitramine (HMX) and 1.54 mg L(-1) for pentaerythrite tetranitrate (PETN), while the minimum resolution for the inorganic separation was 0.99 between azide and nitrate, and the detection limits ranged from 7.70 μg L(-1) for fluoride and 159.50 μg L(-1) for benzoate.     

Investigation of laser-induced breakdown spectroscopy and multivariate analysis for differentiating inorganic and organic C in a variety of soils

Laser-induced breakdown spectroscopy (LIBS) along with multivariate analysis was used to differentiate between the total carbon (C), inorganic C, and organic C in a set of 58 different soils from 5 soil orders. A 532 nm laser with 45 mJ of laser power was used to excite the 58 samples of soil and the emission of all the elements present in the soil samples was recorded in a single spectrum with a wide wavelength range of 200–800 nm. The results were compared to the laboratory standard technique, e.g., combustion on a LECO-CN analyzer, to determine the true values for total C, inorganic C, and organic C concentrations. Our objectives were: 1) to determine the characteristic spectra of soils containing different amounts of organic and inorganic C, and 2) to examine the viability of this technique for differentiating between soils that contain predominantly organic and/or inorganic C content for a range of diverse soils. Previous work has shown that LIBS is an accurate and reliable approach to measuring total carbon content of soils, but it remains uncertain whether inorganic and organic forms of carbon can be separated using this approach. Total C and inorganic C exhibited correlation with rock-forming elements such as Al, Si, Fe, Ti, Ca, and Sr, while organic C exhibited minor correlation with these elements and a major correlation with Mg. We calculated a figure of merit (Mg/Ca) based on our results to enable differentiation between inorganic versus organic C. We obtained the LIBS validation prediction for total, inorganic, and organic C to have a coefficient of regression, r² = 0.91, 0.87, and 0.91 respectively. These examples demonstrate an advance in LIBS-based techniques to distinguish between organic and inorganic C using the full wavelength spectra.     

Capillary gas chromatography-ICP mass spectrometry: a powerful hyphenated technique for the determination of organometallic compounds

The development and improvement of a gas chromatography inductively coupled plasma mass spectrometry system, GC-ICP-MS, is described. The GC and ICP-MS are coupled with a heated stainless steel transfer line. Xe, present in the GC carrier gas, is used to facilitate the nebuliser gas flow rate setting and the positioning of the torch. Alkyltin compounds are separated by GC using a 30 m capillary column within 9 min. The necessity of applying double internal standardisation (use of Bu₃PeSn and Xe gas as internal standards) is shown. The repeatabilities at 50 g/l concentration for both retention time and peak are better than 0.25% and 5%, respectively. The detection limits for alkyltin compounds are better than those of existing methods and range between 15 and 35 fg Sn. Finally, GC-ICP-MS is applied to the determination of mono-, di- and tributyltin in some harbour waters, after extraction and Grignard derivation with PrMgCl. Concentrations between 1 and 20 ng/l are found.     

Raman, surface enhanced Raman spectroscopy, and DFT calculations: a powerful approach for the identification and characterization of 5-fluorouracil anticarcinogenic drug species

The normal Raman and SERS spectra of 5-fluorouracil (5-FU) in water solution and attached to a biological artificial model (a silver colloid) at different pH values were recorded and discussed. The DFT calculation results helped us to establish for the first time the most stable resonance structure for each of the tautomeric forms (i.e., two enol and two enolate forms) and to interpret the Raman and SERS spectra. At alkaline pH, both deprotonated forms of 5-FU were found to be present in solution and to adsorb on the Ag surface in a perpendicular orientation or an orientation not significantly tilted from the surface normal. The N3-deprotonated form seems to be the dominant tautomer in the adsorbed state, more probably attached through the O7 atom. At acid pH values, the N3-deprotonated form was again found to be the mainly chemisorbed species adopting a similar orientation. The combination of these two approaches (i.e., the theoretical and experimental one) proved to be a viable candidate for inclusion in a rapid, sensitive biological method of detecting and studying such essential anticarcinogenic species or biological threats in different conditions.     

Vibrational spectroscopy of solids under high pressures. Part I. Raman spectra of inorganic hexafluorometallate compounds

Raman spectra of a series of isomorphous hexafluorometallates (TlSbF₆; BaMF₆, M = Si, Ge, Sn, and Ti, space group $\text{R}\text{3}\text{m-D}{}^5{}_{\mathrm{3d}}\text{, Z = 1}$) have been measured under high pressures up to 25 kbar with a new opposed sapphire anvil cell. Pressure calibration has been achieved by means of the R₁ fluorescence band of ruby. The frequency of the only Raman active lattice mode (libration of the octahedral anion) of each compound shows a higher pressure dependence than do the internal vibrations of the anions. The E_g components of the ν₅ modes of the MF₆ octahedra which are coupled to the E_g lattice modes because of their same symmetries and small frequency differences exhibit higher pressure sensitivities than do the uncoupled internal modes. These findings may be used as a further means for symmetry assignment. BaGeF₆ undergoes a reversible phase transition at 9.6 kbar; the split librational modes of the high-pressure phase show the highest pressure dependences of up to about 3 cm^?1 · kbar^?1 found in this investigation.     

Characterizing the formation of organic layers on the surface of inorganic/aqueous aerosols by Raman spectroscopy

We demonstrate that nonlinear Raman spectroscopy coupled with aerosol optical tweezers can be used to probe the evolving phase partitioning in mixed organic/inorganic/aqueous aerosol droplets that adopt a core-shell structure in which the aqueous phase is coated in an organic layer. Specifically, we demonstrate that the characteristic fingerprint of wavelengths at which stimulated Raman scattering is observed can be used to assess the phase behavior of multiphase decane/aqueous sodium chloride droplets. Decane is observed to form a layer on the surface of the core aqueous droplet, and from the spectroscopic signature the aqueous core size can be determined with nanometer accuracy and the thickness of the decane layer with an accuracy of +/-8 nm. Further, the presence of the organic layer is observed to reduce the rate at which water evaporates from the core of the droplet with an increasing rate of evaporation observed with diminishing layer thickness.     

Capillary electrophoretic separation of inorganic and organic arsenic compounds

Capillary zone electrophoresis was used to separate arsenite, arsenate, dimethylarsinic and diphenylarsinic acid, methanearsonic acid, phenyl- and p-aminophenyl arsonic acid, phenylarsineoxide and phenarsazinic acid. Anionic and uncharged species were separated in a fused silica capillary with on-column UV detection at 200 nm. A 15 mM phosphate solution adjusted to pH 6.5 containing 10 mM sodium dodecylsulfonate served as background electrolyte. The influence of pH and applied voltage on separation efficiency, as well as the feasibility of identification of arsenic compounds in spiked urine, were investigated. Received: 18 March 1998 / Revised: 25 May 1998 / Accepted: 30 May 1998     

Raman spectroscopy for the analysis of biomolecules

Spurred on by technological advances, Raman spectroscopy is becoming an important tool in the analysis of biological materials. It can provide unique information on composition and molecular structure. For biological chromophores resonance Raman effectively transforms absorption spectroscopy into a high information technique.     

Transformation of organic and inorganic compounds in trifluoroacetic acid

It is established that the effectiveness of fluorine-containing acids in the transformation of organic and inorganic substrates is due to the ability of the acid to perform several functions: to accumulate relatively high concentrations of molecular oxygen, to activate it, and to serve as a hydrogen-containing medium.     

Bead injection for surface enhanced Raman spectroscopy: automated on-line monitoring of substrate generation and application in quantitative analysis

The technique of bead injection has been adapted for surface enhanced Raman scattering (SERS) to substantially improve precision, long term stability and sensitivity of SERS detection in analytical chemistry. For this purpose a fully automated flow system comprising a dedicated flow-cell has been developed and tested. With the developed flow-cell, which contains two inlet and two outlet channels, it is possible to retain, perfuse and discharge minute amounts of polymer beads while monitoring all steps by Raman spectroscopy. First, beads carrying cation exchanger moieties were retained in the flow-cell and subsequently perfused with a silver nitrate and a hydroxylamine solution using one inlet of the flow cell. By this sequence homogeneous SERS active silver layers were formed on the beads. The uniformity of the achieved silver layer was studied by secondary electron microscopy. For measurement, the analyte was then introduced from the second inlet channel such that the interaction between the activated SERS beads and analyte occurred in close proximity and within the focus of the laser excitation beam. Due to the complete computer control of all experimental steps, including bead entrapment, SERS layer generation, sample introduction and final bead removal, highly reproducible conditions for SERS were achieved. The method was developed using 9-aminoacridine as a test molecule. Quantitative studies were carried out for 9-aminoacridine and acridine showing linear calibrations from 1-100 nmol l(-1) and 50-1,000 nmol l(-1), respectively, using a sample volume of 200 microl each. Typical relative standard deviations were 4.7% for 9-aminoacrine and 5.8% for acridine.