Polymorphs of Aspirin – Solid-state IR-LD spectroscopic and quantitative determination in solid mixtures

Solid-state linear-dichroic infrared (IR-LD) spectroscopy, using an orientation technique as a suspension in nematic liquid crystal, has been carried out of Aspirin polymorphs (forms I and II). Reducing-difference procedure for polarized IR-spectra interpretation has been applied for structural analysis of both modifications and the data have been compared with known crystallographic ones. A vibration assignment of forms I and II has been included and on this basis, a quantitative determination by FT-IR spectra for form I in mixtures with second one has been presented, using intensity ratio of 1606 cm⁻¹ peak (characteristic for both forms) to 599 cm⁻¹ one (attributed to form I). The obtained reliability is 99.78%.     

Raman spectroscopic identification of single bacterial cells at different stages of their lifecycle

Early, rapid, and reliable bacterial identification is of great importance in natural environments and in medical situations. Numerous studies have shown that Raman spectroscopy can be used to differentiate between different bacteria under controlled laboratory conditions. However, individual bacteria within a population exhibit macromolecular and metabolic heterogeneity over their lifetime. Therefore it is important to be able to identify and classify specific bacteria at different time points of the growth cycle. In this study, four species of bacteria were used to explore the capability of confocal Raman spectroscopy as a tool for the identification of (and discrimination between) diverse bacterial species at various growth time points. The results show that bacterial cells from different growth time points (as well as from a random growth phase) can be discriminated among the four species using principal component analysis (PCA). The results also show that bacteria selected from different growth phases can be classified with the help of a prediction model based on principal component and linear discriminant analysis (PC-LDA). These findings demonstrate that Raman spectroscopy with the application of a PC-LDA model rooted in chemotaxonomic analysis has potential for rapid sensing of microbial cells in environmental and clinical studies.     

Chemical ionization mass spectrometric determination of the configuration of decahydroquinolin-4-ols

Chemical ionization mass spectrometry (isobutane or methane as a reagent gas) was proposed for the determination of the configuration of the C(4) chiral center in 1,4-disubstituted decahydroquinolin-4-ols.     

Aurichalcite – An SEM and Raman spectroscopic study

Raman spectroscopy complimented with supplementary infrared spectroscopy has been used to characterise the vibrational spectrum of aurichalcite a zinc/copper hydroxy carbonate (Zn,Cu²⁺)₅(CO₃)₂(OH)₆. XRD patterns of all specimens show high orientation and indicate the presence of some impurities such as rosasite and hydrozincite. However, the diffraction patterns for all samples are well correlated to the standard reference patterns. SEM images show highly crystalline and ordered structures in the form of micron long fibres and plates. EDAX analyses indicate variations in chemical composition of Cu/Zn ratios ranging from 1/1.06 to 1/2.87. The symmetry of the carbonate anion in aurichalcite is C_s and is composition dependent. This symmetry reduction results in multiple bands in both the symmetric stretching and bending regions. The intense band at 1072 cm⁻¹ is assigned to the ν₁(CO₃)²⁻ symmetric stretching mode. Three Raman bands assigned to the ν₃(CO₃)²⁻ antisymmetric stretching modes are observed for aurichalcite at 1506, 1485 and 1337 cm⁻¹. Multiple Raman bands are observed in 800–850 cm⁻¹ and 720–750 cm⁻¹ regions and are attributed to ν₂ and ν₄ bending modes confirming the reduction of the carbonate anion symmetry in the aurichalcite structure. An intense Raman band at 1060 cm⁻¹ is attributed to the δ OH deformation mode.     

Application of complementary mass spectrometric techniques to the identification of ketoprofen phototransformation products

Ketoprofen (KP) is a nonsteroidal anti-inflammatory drug, which during UV irradiation rapidly transforms into benzophenone derivatives. Such transformation products may occur after topical application of KP, which is then exposed to sunlight resulting in a photo-allergic reaction. These reactions are mediated by the benzophenone moiety independently of the amount of allergen. The same reactions will also occur during wastewater or drinking water treatment albeit their effect in the aqueous environment is yet to be ascertained. In addition, only a few such transformation products have been recognised. To enable the detection and structural elucidation of the widest range of KP transformation products, this study applies complementary chromatographic and mass spectrometric techniques including gas chromatography coupled to single quadrupole or ion trap mass spectrometry and liquid chromatography hyphenated with quadrupole-time-of-flight mass spectrometry. Based on structural information gained in tandem and multiple MS experiments, and on highly accurate molecular mass measurements, chemical structures of 22 transformation products are proposed and used to construct an overall breakdown pathway. Among the identified transformation products all but two compounds retained the benzophenone moiety--a result, which raises important issues concerning the possible toxic synergistic effects of KP and its transformation products. These findings trigger further research into water treatment technologies that would limit their entrance into environmental or drinking waters.     

Fourier-transform Raman spectroscopic study of unsaturated and saturated waxes

The application of Fourier-transform (FT)-Raman spectroscopy to the non-destructive analysis of plant biomaterials, comprising ten different waxes, is illustrated in this work. All the wax specimens studied are multicomponent systems and comparison of the individual spectra was effected. This leads to a means of distinguishing the individual wax specimen using FT-Raman spectroscopy. The samples were not pre-treated before analysis and were used directly from their respective storage collections.     

Improved liquid chromatographic tandem mass spectrometric determination and pharmacokinetic study of glimepiride in human plasma

An improved liquid chromatographic tandem mass spectrometric method for the determination of glimepiride in human plasma has been developed and fully validated. The article describes in detail the bioanalytical procedure and summarizes the validation results obtained. The samples were extracted using liquid--liquid extraction with a mixture of 1-chlorobutane-isopropanol-ethyl acetate (88:2:10, v/v/v). The chromatographic separation was performed on a reversed-phase Hypersil ODScolumn (250 x 4.6 mm i.d.; 5 microm particle size) using a mobile phase consisting of formic acid 0.05 M-acetonitrile (28:72, v/v), pumped at a flow rate of 0.3 ml min(-1) heated to 25 degrees C. The analytes were detected using an API 3000 triple quadrupole mass spectrometer with positive electrospray ionization in multiple reaction monitoring mode. Tandem mass spectrometric detection enabled the quantitation of glimepiride down to 0.50 ng mL(-1). Calibration graphs were linear (r better than 0.998, n=1), in concentration range 0.50--1000 ng mL(-1), and the intra- and inter- day RSD values were less than 10.37 and 11.55% for glimepiride. The method was successfully applied to a kinetic study in order to assess the main pharmacokinetic parameters of glimepiride.     

Multidimensional Raman spectroscopic signature of sweat and its potential application to forensic body fluid identification

This proof-of-concept study demonstrated the potential of Raman microspectroscopy for nondestructive identification of traces of sweat for forensic purposes. Advanced statistical analysis of Raman spectra revealed that dry sweat was intrinsically heterogeneous, and its biochemical composition varies significantly with the donor. As a result, no single Raman spectrum could adequately represent sweat traces. Instead, a multidimensional spectroscopic signature of sweat was built that allowed for the presentation of any single experimental spectrum as a linear combination of two fluorescent backgrounds and three Raman spectral components dominated by the contribution from lactate, lactic acid, urea and single amino acids.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Separation and determination of alkylglycosides by liquid chromatography with electrospray mass spectrometric detection

The separation of alkylpolyglycosides by liquid chromatography with electrospray mass spectrometric detection, using either an alkylamide or a cyanopropyl column, and acetonitrile/water mixtures as mobile phases, was developed. Using the alkylamide column and isocratic elution, the α- and β-epimers and ring isomers (pyranosides and furanosides) of the alkylmonoglycosides were resolved. The ring isomers were also resolved in a much shorter time using the cyanopropyl column with gradient elution. Using these columns, the isomers of the alkyldiglycosides and alkyltriglycosides were also partially resolved. The equilibration time was much shorter with the cyanopropyl column, which was selected to perform quantitation studies. The response factors increased more than an order of magnitude with the length of the alkyl chain, from the methyl to the decylmonoglycoside, and decrease largely for the dodecyl and tetradecylmonoglycoside. The limits of detection were of ca. 25 μM from the hexyl up to the dodecylmonoglycoside. The procedures were applied to the characterisation and determination of alkylmonoglycosides in toiletries.     

Liquid chromatographic tandem mass spectrometric determination of trandolapril in human plasma

A liquid chromatographic tandem mass spectrometric method for the determination of trandolapril in human plasma has been developed and fully validated. The article describes, in detail, the bioanalytical procedure and summarizes the validation results obtained. The samples were extracted using HLB Oasis solid-phase extraction cartridges. The chromatographic separation was performed on X-Terra C8 MS column (150 mm × 4.6 mm i.d., 5 μm particle size) using a mobile phase consisting of acetic acid 20 mM and triethylamine 4.3 mM/acetonitrile (40:60 (v/v)), pumped isocratically at 0.35 ml/min.

The analytes were detected using a micromass quattro micro triple quadrupole mass spectrometer with positive electrospray ionization in multiple reaction-monitoring (MRM) mode. Tandem mass spectrometric detection enabled the quantitation of trandolapril down to 2.0 ng/ml. Calibration graphs were linear (r better than 0.996, n = 9) in the concentration ranges 2.0–750 ng/ml and the intra- and inter-day R.S.D. values were less than 3.83 and 3.86% for trandolapril.     

Seven-minute synthesis of pure C(s)-C60Cl6 from [60]fullerene and iodine monochloride: first IR, Raman, and mass spectra of 99 mol % C60Cl6

Three previously reported procedures for the synthesis of pure C(s)-C60Cl6 from C60 and ICl dissolved in benzene or 1,2-dichlorobenzene were shown to actually yield complex mixtures of products that contain, at best, 54-80% C(s)-C60Cl6 based on HPLC integrated intensities. MALDI mass spectrometry was used for the first time to identify other components of the reaction mixtures. An improved synthetic procedure was developed for the synthesis of about 150 mg batches of chlorofullerenes containing 90% C(s)-C60Cl6 based on HPLC intensities. The optimum reaction time was decreased from several days to seven minutes. Small amounts of the product were purified by HPLC (toluene eluent) to 99% purity. The pure compound C(s)-C60Cl6 is stable for at least three months as a solvent-free powder at 25 degrees C. The Raman, far-IR, and MALDI mass spectra of pure C(s)-C60Cl6 are reported for the first time. The Raman and far-IR spectra, the first reported for any C60Cl(n) chlorofullerene, were used to carry out a vibrational analysis of C(s)-C60Cl6 at the DFT level of theory.     

Multiresidue determination of sulfonamides in a variety of biological matrices by supported liquid membrane with high pressure liquid chromatography-electrospray mass spectrometry detection

A high performance liquid chromatography (HPLC) coupled to a mass spectrometer (MS) was used for a simultaneous determination of 16 sulfonamide compounds spiked in water, urine, milk, and bovine liver and kidney tissues. Supported liquid membrane (SLM) made up of 5% tri-n-octylphosphine oxide (TOPO) dissolved in hexyl amine was used as a sample clean-up and/or enrichment technique. The sulfonamides mixture was made up of 5-sulfaminouracil, sulfaguanidine, sulfamethoxazole, sulfamerazine, sulfamethizole, sulfamethazine (sulfadimidine), sulfacetamide, sulfapyridine, sulfabenzamide, sulfamethoxypyridazine, sulfamonomethoxine, sulfadimethoxine sulfasalazine, sulfaquinoxaline, sulfadiazine, and sulfathiazole. Some of these compounds, such as, sulfaquinoxaline, sulfadiazine, sulfabenzamide, sulfathiazole and sulfapyridine failed to be trapped efficiently by the same liquid membrane (5% TOPO in hexylamine). The detection limits (DL) obtained were 1.8 ppb for sulfaguanidine and sulfamerazine and between 3.3 and 10 ppb in bovine liver and kidney tissues for the other sulfonamides that were successfully enriched with SLM; 2.1 ppb for sulfaguanidine and sulfamerazine and between 7.5 and 15 ppb in cow’s urine, whereas the DL values in milk were 12.4 ppb for sulfaguanidine and sulfamerazine and between 16.8 and 24.3 for the other compounds that were successfully enriched by the membrane. Several factors affecting the extraction efficiency during SLM enrichment, such as donor pH, acceptor pH, enrichment time and the membrane solvent were studied.     

Hydrated double carbonates – A Raman and infrared spectroscopic study

The Raman spectra of selected double carbonates including pirssonite, gaylussite, shortite and quintinite complemented with infrared spectra have been used to characterise the structure of these carbonate minerals. By using a Libowitzky type function hydrogen bond distances for these minerals of 2.669–2.766 Å are estimated. The variation in the hydrogen bond distances contributed to the stability of the mineral. The Raman spectrum of pirssonite shows a single band at 1080 cm⁻¹ attributed to the (CO₃)²⁻ symmetric stretching mode, in contrast to shortite and quintinite where two bands are observed. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of pirssonite and gaylussite.     

An infrared and Raman spectroscopic study of polyanilines co-doped with metal ions and H+

Polyanilines doped with (HCl+KCl) and (HCl+CoCl2) were prepared by co-doping method, respectively. For comparison, polyaniline emeraldine salt (ES) by doping with HCl and its emeraldine base (EB) form were also synthesized. The co-doped polyanilines, ES and EB samples were all characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy aiming to understand the transformations in the different doping status. The results show that the doping degree of K+ ions is considerably higher than that of Co2+ ions under the same co-doping conditions possibly due to different pseudoprotonation constants of EB with K+ ions and Co2+ ions. Moreover, morphology difference of polyaniline co-doped with alkaline metal ions or transition meal ions may arise from different coordination geometry of metal ions. Nevertheless, there are similar chemical transformations of quinoid units to benzenoid ones on polyaniline backbones for the ES and both co-doped samples. And the polyaniline backbones co-doped with H+ and metal cations are found to attain weaker charge delocalization than the ES which is doped solely with H+.     

Raman spectroscopic study of a post-medieval wall painting in need of conservation

Raman spectroscopic studies of four specimens from an important angel wall painting in need of conservation work in a medieval church have provided some information about the pigments and pigment compositions which will influence possible future preservation and restoration strategies. Excitation of the Raman spectra at 1,064 nm in macroscopic mode and at 785 nm in microscopic mode revealed that the white pigment on the angel's wings was a mixture of barytes with calcite and lead white in minor composition. Although the specimens provided were not directly associated with coloured regions of the painting, yellow and blue microcrystals were found and they were identified as chrome yellow and lazurite, respectively. Red and brown particles were identified as cinnabar/vermilion and haematite. Several green particles were also found but could not be identified. The green and blue crystals could be related to neighbouring coloured regions of the artwork and the yellow colour could be identified as a background to the angel figure. Particles of carbon were found to be dispersed throughout the specimens and can be ascribed to soot from candles, heating stoves or oil lamps providing lighting in the church. No evidence for biological deterioration was found from the spectra. The unusual pigment palette is strongly suggestive of a later date of painting than was originally believed but there is a possibility that an earlier rendition exists underneath. Following a review of the spectroscopic data, a more extensive sampling protocol is recommended, from which some stratigraphic evidence could identify the underlying plaster and possible artwork.     

Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical study

The ion-molecule reactions occurring in GeH(4)/NF(3), GeH(4)/SF(6), and GeH(4)/SiF(4) gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NF(x)(+) (x=1-3) react with GeH(4) mainly by the exothermic charge transfer, the open-shell Ge(+) and GeH(2)(+) undergo the efficient F-atom abstraction from NF(3) and form GeF(+) and F-GeH(2)(+) as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes Ge-F-NF(2)(+) and H(2)Ge-F-NF(2)(+), their subsequent crossing to the significantly more stable isomers FGe-NF(2)(+) and F-GeH(2)-NF(2)(+), and the eventual dissociation of these ions into GeF(+) (or F-GeH(2)(+)) and NF(2). The closed-shell GeH(+) and GeH(3)(+) are instead much less reactive towards NF(3), and the only observed process is the less efficient formation of GeF(+) from GeH(+). The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH(+). Passing from NF(3) to SF(6) and SiF(4), the average strength of the M-F bond increases from 70 to 79 and 142 kcal mol(-1), and in fact the only process observed by reacting GeH(n)(+) (n=0-3) with SF(6) and SiF(4) is the little efficient F-atom abstraction from SF(6) by Ge(+). Irrespective of the experimental conditions, we did not observe any ionic product of Ge-N, Ge-S, or Ge-Si connectivity. This is in line with the previously observed exclusive formation of GeF(+) from the reaction between Ge(+) and C-F compounds such as CH(3)F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF(+) and GeH(4).     

High pressure Raman spectroscopic study of phase transformation in TaO2F

High pressure Raman spectroscopic measurements on nearly zero thermal expansion material TaO₂F are carried out up to 19 GPa. Earlier report of high pressure X-ray diffraction studies shows two phase transitions, one at 0.7 and the other at 4 GPa with rhombohedral (R-3c) structure above 4 GPa, but the structure between 0.7 GPa and 4 GPa remained unclear. In high pressure Raman measurements, a reversible, cubic to rhombohedral phase transformation onsets around 0.8 GPa and gets completed at 4.4 GPa with all four predicted normal modes corresponding to R-3c phase and retaining the structure up to 19 GPa. A mixture of cubic and rhombohedral phases is observed between 0.8 and 4.4 GPa. Optically silent modes in the ambient cubic structure exhibit strong, broad Raman bands due to anionic (O/F) disorder in TaO₂F altering the local symmetry and allowing for first order Raman scattering. On compression, these disorder induced first order Raman bands gradually decrease in intensity and disappear around 4.4 GPa due to inhibition of local distortion caused by anions, and the modes corresponding to the rhombohedral phase appear. This is a clear evidence of disorder-free rhombohedral single phase exists above 4.4 GPa in agreement with the reported HPXRD results. Temperature dependent Raman measurements reveal that the intensities of Raman bands remain almost unchanged with rise in temperature indicating static disorder in TaO₂F. Disorder-induced first order Raman modes at 176, 212, 381 and 485 cm⁻¹ soften with increase in pressure whereas the other modes show low positive Gruneisen parameter. The thermal expansion coefficient calculated using these Gruneisen parameters (−2.91 ppm K⁻¹) is in fair agreement with the reported values (−1 to +1 ppm K⁻¹). On the other hand, all four modes of disorder-free rhombohedral phase show the usual hardening behavior with increase in pressure contributing to positive thermal expansion.     

Raman spectroscopic study of hydrogen bonding in benzenesulfonic acid/acrylonitrile solutions

Solutions of benzenesulfonic acid (BSA) in acrylonitrile in the range 1.02-6.53 mol dm(-3) were studied by FT-Raman spectroscopy. Spectra in the region of the acid SOH and benzenesulfonate anion SO3 stretching bands were analysed by band-fitting procedures in order to ascertain the degree of acid dissociation. This parameter changes from 0.42 (1.02 M solution) to 0.185 (6.53 M solution) despite the strong character of the acid. Interaction of acrylonitrile with undissociated BSA produces a new band in the nu(C[triple bond]N) Raman spectral region, displaced +21.4 cm(-1) and assigned to acrylonitrile molecules H-bonded to BSA. This displacement is in accord with the strong H-donor character of the acid. From the concentration of H-bonded acrylonitrile, the mean number of H-bonds in which each solvent molecule participates can be calculated. This number changes from ca. 0.2 in the less concentrated solution up to ca. 2.4 in the most concentrated solution. These results suggest that BSA-acrylonitrile complexes of fixed stoichiometry do not occur in the range of concentrations studied here.     

Metabolite profile of sibutramine in human urine: a liquid chromatography-electrospray ionization mass spectrometric study

We present a detailed experimental approach to detection and subsequent structural characterization of unknown metabolites of sibutramine, using liquid chromatography-mass spectrometric techniques. The full-, precursor ion, and constant neutral loss scan modes of a triple quadrupole mass spectrometer were used for screening sibutramine metabolites in human urine. The structural assessment of unknown metabolites was based on MSn ion trap mass spectrometric analysis and comparison of MSn spectra between the standards and compounds detected. Two phase-I (M1 and M2) and eight phase-II (M3-M6) metabolites of sibutramine were found in human urine. Metabolites M1 and M2, which were found as minor metabolites, originated from N-demethylation of sibutramine. Carbamoyl glucuronides formed from metabolites M1, M2, and their hydroxylated analogs were the main metabolites of sibutramine and were characterized by tandem mass spectrometric analysis and by the chemical modification of their structure. We demonstrate the usefulness of the chemical derivatization approach for estimation of the site of glucuronidation and propose the formation of hydroxylated regioisomers of metabolites M4 and M6.