Selective Gas Chromatography Mass Spectrometry Method for Ultratrace Detection of Selenocyanate

Single Molecule-Level Detection via Liposome-Based Signal Amplification Mass Spectrometry Counting Assay

Because of the low atomization and/or ionization efficiencies of many biological macromolecules, the application of mass spectrometry to the direct quantitative detection of low-abundance proteins and nucleic acids remains a significant challenge. Herein, we report mass spectrum tags (MS-tags) based upon gold nanoparticle (AuNP)-templated phosphatidylcholine phospholipid (DSPC) liposomes, which exhibit high and reliable signals via electrospray ionization (ESI). Using these MS-tags, we constructed a liposome signal amplification-based mass spectrometric (LSAMS) "digital" counting assay to enable ultrasensitive detection of target nucleic acids. The LSAMS system consists of liposomes modified with a gold nanoparticle core and surface-anchored photocleavable DNA. In the presence of target nucleic acids, the modified liposome and a magnetic bead simultaneously hybridize with the target nucleic acid. After magnetic separation and photolysis, the MS-tag is released and can be analyzed by ESI-MS. At very low target concentrations, one liposome particle corresponds to one target molecule; thus, the concentration of the target can be estimated by counting the number of liposomes. With this assay, hepatitis C (HCV) virus RNA was successfully analyzed in clinical samples.

Comparison of quantification of selenocyanate and thiocyanate in cultured mammalian cells between HPLC-fluorescence detector and HPLC-inductively coupled plasma mass spectrometer

The simultaneous detection of cyanide (CN), thiocyanate (SCN), and selenocyanate (SeCN) by a HPLC-fluorescence detector (FLD) with the post-column König reaction was recently reported. SCN and SeCN are also detectable by HPLC-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) because sulfur and selenium can be detected, respectively, without any pre- or post-treatment. ICP-MS has high sensitivity for selenium and sulfur detection and is robust to sample matrices. In this study, we compared HPLC-FLD with the post-column König reaction and HPLC-ICP-MS in terms of SCN and SeCN detection sensitivity and linearity. The limit of detection (LOD) for SCN indicated that HPLC-FLD with the post-column König reaction was 354 times more sensitive than HPLC-ICP-MS. Likewise, the LOD for SeCN indicated that HPLC-FLD was 51 times more sensitive than HPLC-ICP-MS. These results demonstrated that HPLC-FLD was a more suitable technique for SeCN and SCN detection than HPLC-ICP-MS. We previously reported that SeCN was generated in selenite-exposed mammalian cells to detoxify excess selenite. HPLC-FLD with the post-column König reaction enabled good separation and detection for quantifying SCN and SeCN in mammalian cell lines exposed to selenite. The intracellular SCN and SeCN concentrations determined by this technique suggested differences in the metabolic capacity for selenite to form SeCN among the cell lines. In addition, since the amount of intracellular SCN and SeCN were significantly decreased by pretreatment of myeloperoxidase (MPO) inhibitors, SCN and SeCN were resulted from the interaction of sulfur and selenium with endogenous CN, respectively, generated with MPO.

Determination of selenocyanate, selenate, and selenite in mining wastewater by GC-MS using sequential derivatization and extraction

Selenium speciation analysis is usually carried out using complex hyphenated analytical systems such as LC-ICP-MS. Here we present a novel selenium speciation approach based on a sequential derivatization and extraction combined with gas chromatography mass spectrometry for the simultaneous determination of selenite, selenate, and selenocyanate in aqueous mine wastewater samples. Selenocyanate was derivatized with triethyloxonium tetrafluoroborate to ethylselenocyanate, which was extracted into chloroform, following which the sample was split into two aliquots. One aliquot was acidified and 3,5-bis(trifluoromethyl)-o-phenylenediamine was used for the novel derivatization of selenite to 4,6-bis(trifluoromethyl)-2,1,3-benzoselenadiazole, for the determination of selenite. For the second aliquot, concentrated hydrochloric acid was added along with 4-nitro-o-phenylenediamine to simultaneously reduce selenate to selenite and derivatize the combined "selenite + selenate" fraction to 5-nitro-2,1,3-benzoselenadiazole. The benzoselenadiazoles were extracted with chloroform and all extracts were combined for GC-MS analysis. Low ng g^-1 detection limits were reported for all three species. The method is unhindered by concentrations of chloride and sulphate up to 3%, as well as nitrate concentrations up to 3% for selenocyanate and selenite analysis, with minor losses in sensitivity for selenate up to 100 ppm nitrate, making the method particularly suitable for aqueous mine waste characterization. Quantitative trace selenium speciation was achieved using cost-effective materials and apparatus on a simple-to-operate benchtop instrument. The novel methodology was tested on gold mine wastewater samples; comparing to total selenium, a 63-149% recovery as the sum of species was observed. Additionally, this novel speciation approach was compared to LC-ICP-MS based selenium speciation and a reasonable agreement was found in the species distribution.

Versatile derivatization for GC-MS and LC-MS: alkylation with trialkyloxonium tetrafluoroborates for inorganic anions, chemical warfare agent degradation products, organic acids, and proteomic analysis

Analytical chemists resort to derivatization for improving the detection performance of certain categories of analytes. Within this context, alkylation reactions are regarded as an important asset for many methods based on GC-MS and LC-MS. Trialkyloxonium tetrafluoroborates (R[Formula: see text][BF₄]^-) are powerful alkylating agents with ionic liquid properties: they are nonvolatile salts soluble in water which are easier and safer to handle with respect to common alkylating agents like diazomethane. R[Formula: see text][BF₄]^- can perform the alkylation in both organic and aqueous media at pH conditions ranging from acidic to alkaline. Recent analytical applications of trialkyloxonium derivatizations include the high-precision determination of inorganic anions in complex matrices, the qualitative confirmation of chemical warfare agent degradation products in soils, the profiling of carboxylic acids in urine, and the detection of protein post-translational modifications induced by carbon dioxide. The common denominator for all methods presented can be found in the simplicity of the alkylation protocol which, in most of the cases, requires a single step addition of the reagent directly to the sample. Graphical Abstract Alkylation with trialkyloxonium salts for GC-MS and LC-MS analysis.