Analysis Of Labile Compounds Research Articles

Gas chromatography with dual cold electron ionization mass spectrometry and vacuum ultraviolet detection for the analysis of phenylethylamine analogues

Identification of phenethylamine (PEA) analogues is of great importance and requires analytical methods of high specificity. Forensic drug analysis is often performed by gas chromatography (GC) most commonly coupled with mass spectrometric (MS) detection. However, analysis of labile compounds is problematic with classical electron ionization (EI)-MS, and positional isomers may be difficult to differentiate by MS. Cold electron ionization (cold EI) improves molecular ion relative intensity by reducing the analyte vibrational energy prior to ionization. Vacuum ultraviolet (VUV) is a gas phase technique that can provide complementary selectivity to MS for identification. In this study, cold EI-MS was used in parallel with VUV detection for the analysis of select PEA analogues and positional isomers. Molecular ion relative intensity was increased for nearly all compounds included in this study. Principal component analysis demonstrated that VUV is more successful at distinguishing between positional isomers than MS. A library database of VUV spectra was set up to identify compounds, which was later used to deconvolute spectra of coeluting compounds. Detection limits for VUV are lower than those of MS with cold-EI, where VUV is capable of reaching sub-microgram per milliliter levels. Linearity tests on VUV showed high correlation coefficients (R2 > 0.999) for close to or over and order-of-magnitude dynamic range.

Improving quantification using curtain flow chromatography columns in the analysis of labile compounds: A study on amino acids

The performance of curtain flow chromatography column technology with MS detection was evaluated for the analysis of labile compounds. The curtain flow column design allows for separations that are faster and/or more sensitive than conventional columns, depending on how exactly the curtain flow column is configured. For example, when mass spectral detection is employed, the curtain flow column can yield separations that are 5-times faster than conventional columns when the curtain flow and the conventional columns have the same internal diameter. Or when the internal diameter of the conventional column is reduced in order to yield the same analytical through-put as the curtain flow column, the sensitivity on the curtain flow column can be as much as 66-fold higher than the conventional column. As a consequence of the higher analytical through-put less standardization is required in the analysis of labile compounds because less sample degradation is apparent. Consequently the sample integrity is preserved yielding data of a higher quality.

Pressurised hot water extraction in continuous flow mode for thermolabile compounds: extraction of polyphenols in red onions

Extraction and analysis of labile compounds in complex sample matrices, such as plants, is often a big analytical challenge. In this work, the use of a “green and clean” pressurised hot water extraction (PHWE) approach performed in continuous flow mode is explored. Experimental data for extraction and degradation kinetics of selected compounds were utilised to develop a continuous flow extraction (CFE) method targeting thermolabile polyphenols in red onions, with detection by high-performance liquid chromatography (HPLC)–diode array detection (DAD)–mass spectrometry (MS). Water containing ethanol and formic acid was used as extraction solvent. Method performance was focused on extraction yield with minimal analyte degradation. By adjusting the flow rate of the extraction solvent, degradation effects were minimised, and complete extraction could be achieved within 60 min. The CFE extraction yields of the polyphenols investigated were 80–90 % of the theoretically calculated quantitative yields and were significantly higher than the yields obtained by conventional methanol extraction and static batch extraction (70–79 and 58–67 % of the theoretical yields, respectively). The precision of the developed method was lower than 8 % expressed as relative standard deviation. FigureScheme of pressurised hot water extraction of polyphenols in continuous flow mode Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-013-7370-7) contains supplementary material, which is available to authorized users.

Internal energy deposition with silicon nanoparticle-assisted laser desorption/ionization (SPALDI) mass spectrometry

The use of silicon nanoparticles for laser desorption/ionization (LDI) is a new appealing matrix-less approach for the selective and sensitive mass spectrometry of small molecules in MALDI instruments. Chemically modified silicon nanoparticles (30 nm) were previously found to require very low laser fluence in order to induce efficient LDI, which raised the question of internal energy deposition processes in that system. Here we report a comparative study of internal energy deposition from silicon nanoparticles to previously explored benzylpyridinium (BP) model compounds during LDI experiments. The internal energy deposition in silicon nanoparticle-assisted laser desorption/ionization (SPALDI) with different fluorinated linear chain modifiers (decyl, hexyl and propyl) was compared to LDI from untreated silicon nanoparticles and from the organic matrix, α-cyano-4-hydroxycinnamic acid (CHCA). The energy deposition to internal vibrational modes was evaluated by molecular ion survival curves and indicated that the ions produced by SPALDI have an internal energy threshold of 2.8–3.7 eV. This is slightly lower than the internal energy induced using the organic CHCA matrix, with similar molecular survival curves as previously reported for LDI off silicon nanowires. However, the internal energy associated with desorption/ionization from the silicon nanoparticles is significantly lower than that reported for desorption/ionization on silicon (DIOS). The measured survival yields in SPALDI gradually decrease with increasing laser fluence, contrary to reported results for silicon nanowires. The effect of modification of the silicon particle surface with semifluorinated linear chain silanes, including fluorinated decyl (C10), fluorinated hexyl (C6) and fluorinated propyl (C3) was explored too. The internal energy deposited increased with a decrease in the length of the modifier alkyl chain. Unmodified silicon particles exhibited the highest analyte internal energy deposition. These findings may suggest a role of the modifier as a moderator in the energy dissipation and relaxation process. The relatively low internal energy content of SPALDI-produced ions indicates that this is a “soft” desorption technique, with potential advantages in the analysis of labile compounds.

Secondary emission mass spectrometer, application and evaluation

A versatile research mass spectrometer has been developed to study various ionization techniques for applications in analytical mass spectrometry. The secondary emission of electrons and ions under bombardment by ions, neutrals and electrons is being investigated. The instrument will make possible the development of new ion sources for biological research. It has the following features: (1) ultra-high vacuum (UHV) multi-flanged ionization chamber; (ii) single (MS) and tandem (MS/MS) quadrupole mass spectrometers; (iii) ion/ neutral beam (pulsed, rastered and mass filtered) probe with energies up to 10 keV; (iv) sample introduction via an electro-pneumatic probe for up to 8 samples, direct insertion probe or gas inlet system. The instrument's performance is evaluated and its application in the analysis of labile compounds is discussed.