An LC-MS/MS-based platform for the quantification of multiple amyloid beta peptides in surrogate cerebrospinal fluid.

Introduction: The accurate quantification of amyloid beta (Aß) peptides in cerebrospinal fluid (CSF) is crucial for Alzheimer's disease (AD) research, particularly in terms of preclinical and biomarker studies. Traditional methods, such as the enzyme-linked immunosorbent assay (ELISA), have limitations. These include high costs, labor intensity, lengthy processes, and the possibility of cross-reactivity. Objectives: The primary objectives of this research were twofold: to comprehensively characterize Aß peptides and to develop a reliable and accurate method for the simultaneous quantification of Aß 1-40 and Aß 1-42 peptides in surrogate CSF that is traceable to the International System of Units (SI). Methods: We developed a novel method that combined solid phase extraction (SPE) with isotope dilution liquid chromatography/tandem mass spectrometry (ID-LC/MSMS). SPE was employed to efficiently eliminate matrix interferences, while [15N] Aß1-40 and [15N] Aß1-42 served as internal standards to improve accuracy. In addition, we introduced Peptide Impurity Corrected Amino Acid Analysis (PICAA) to ensure traceability to the SI and reliable quantification of Aß peptides. Results: The developed platform demonstrated a linear calibration range of 300-20000 pg/ml for both Aß1-42 and Aß1-40 peptides, accompanied by strong correlation coefficients greater than 0.995. Quality Control (QC) samples demonstrated an accuracy of at least 90.0 %. Conclusion: The enhanced specificity and flexibility of the developed platform potentially have implications for Alzheimer's disease diagnosis and future investigations of novel Aß peptide biomarkers.

Bioaccessibility and bioavailability of selenium species in Se-enriched leeks (Allium Porrum) cultivated by hydroponically.

The Allium genus vegetables are of special interest since being potentially sources for selenium. In this study, the metabolization of selenite and selenate fortification at low and high levels in hydroponically cultivated Allium porrum (Leek) was investigated. The total Se analysis of nutritional solutions which was used in cultivation medium revealed that leeks had potential to accumulate Se above over 1000 mg/kg without any growth disturbance which was proved by comparing dry masses of control group with the ones fortified by Se species. Speciation analyses performed in edible parts which are leaves and stems showed that approximately 90% of total selenium was biotransformed into organo-selenium species in which MeSeCys and SeMet were found to be the most dominant in Se(IV) fortified leeks. However, selenate was found to be the most abundant species in edible parts of selenate fortified leeks especially at high levels. Although bioavailability rate of total selenium in selenate fortified leeks was found to be higher, lower amount of inorganic selenium and higher amount of MeSeCys were found to be bioavailable in Se(IV) fortified.

Quantification of tributyltin in seawater using triple isotope dilution gas chromatography-inductively coupled plasma mass spectrometry achieving high accuracy and complying with European Water Framework Directive limits.

A triple isotope dilution GC-ICPMS method for the determination of tributyltin (TBT) was developed and validated to meet the European Water Framework Directive (WFD) requirements. The validation procedure involved the evaluation of trueness, precision (repeatability, intermediate precision), limit of detection (LOD) and limit of quantification (LOQ), stability, measurement uncertainty and traceability studies. The method is one of the most sensitive methods published to date with good accuracy, 103% average recovery in the range with %RSDs of 2.8-6.7%. A LOD value of 0.015 ng L-1 for the TBT cation was achieved with a sample volume of 12 mL seawater. TBT was derivatized using 20 µL sodium tetraethylborate solution (0.05% NaBEt4) to make volatile for GC-ICPMS. Measurement uncertainty was in the range of 4.8-13% which was achieved through dissolution of tributyltinchloride (TBTCl) in 1-propanol, a low-volatility solvent combined with the use of a triple isotope dilution (ID) calibration technique. Isotope dilution calibration was performed by adding 117Sn isotopically enriched TBT to the seawater samples. The stability test results showed that TBT concentration was stable for three months in seawater samples after passing through a 0.2 µm filter and stored in amber glass bottles at 4°C. The response surface methodology (RSM) approach was successfully implemented to provide optimal conditions for large volume injection (LVI) to obtain the maximum analytical signal. The key variables selected in the experimental design were evaporation time, evaporation temperature, carrier flow, and injection speed. This method was applied to seawater samples collected from the Bay of Izmit, Kocaeli, Turkey, where TBT pollution has not been measured yet.

Traceable and accurate quantification of iron in seawater using isotope dilution calibration strategies by triple quadrupole ICP-MS/MS: Characterization measurements of iron in a candidate seawater CRM.

Accurate quantification of iron is crucial for the characterization of a candidate seawater certified reference material. Isotope dilution mass spectrometry as a primary method is one of the option for this purpose. In this study, triethylamine (TEA) assisted Mg(OH)2 co-precipitation is developed and combined with isotope dilution mass spectrometry for the characterization of candidate certified reference material, UME CRM 1206. The analytical protocol of co-precipitation was optimized to achieve reproducible yields of ~100% Fe with high salt rejection (residual salinity ~0.003%). Three calibration strategies, single, double and triple isotope dilution mass spectrometry (IDMS) coupled with co-precipitation were investigated in terms of metrological aspects. The determination of Fe was carried out by ICP-MS with tandem configuration (ICP-MS/MS) using NH3/He cell gas which was optimized for the minimum background equivalence concentration to be able to measure highly accurate 56Fe/57Fe ratio with the highest possible sensitivity. The background corrected typical procedural blank levels and limit of detection calculated based on three times the standard deviation of blanks were found as 9 ng/kg (0.16 nM) and 11 ng/kg (0.20 nM) for single IDMS, respectively. Trueness of the developed analytical methods has been demonstrated using CASS-6 and NMIA MX014 with complete and very precise recoveries. SI-traceable values with combined uncertainty (k = 2) were obtained for single, double and triple IDMS as (12.70 ±â€¯0.16) ng/g, (12.728 ±â€¯0.084) ng/g and (12.732 ±â€¯0.062) ng/g, respectively. The relative combined uncertainty for each approach was calculated as 0.64%, 0.33% and 0.24%, respectively.

Spontaneous formation of DPPC monolayers at aqueous/vapor interfaces and the impact of charged surfactants.

Surface tensiometry and vibrational sum-frequency spectroscopy were used to examine the structure and organization in phospholipid monolayers at the aqueous/vapor interface in the absence and in the presence of simple, charged surfactants. 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was the phospholipid employed in these studies and surfactants included sodium dodecyl sulfate (SDS) and dodecyl trimethyl ammonium bromide (DTAB). DPPC spontaneously spreads on a pure water (pH=5.5) surface to form monolayers as evidenced by an equilibrium spreading pressure (ESP) of 7.9+/-2.3 mN/m and a clearly resolved vibrational spectrum. Low concentrations of surfactants inhibit the spreading of DPPC and result in significantly lower ESP values. Anionic and cationic surfactants at higher concentrations have opposite effects on monolayer organization; SDS creates well-organized monolayers while DTAB leads to poor organization of lipid molecules. Surface-specific vibrational spectra showed that high concentrations of charged surfactants (>or=100 microM) lead to accumulation of net surface charges as evidenced by destructive and constructive interferences. Selectively deuterating surfactants results in changes in vibrational band intensities and phases enabling assignment of relative orientations of equivalent functional groups belonging to the lipid and surfactant.

Structure and organization of hexadecanol isomers adsorbed to the air/water interface.

The structure and 2D phase behavior of hexadecanol isomers adsorbed to the air/water interface have been studied using surface tension methods and vibrational sum frequency spectroscopy. Isomers include the linear 1-hexadecanol as well isomers with the alcohol functional group in the 2, 3, and 4 positions. Surface-pressure isotherms highlight how the 2D phase behavior of these monolayers depends sensitively on registry and packing efficiency between the alkyl chains whereas vibrational sum frequency spectroscopy, which is vibrational spectroscopy with surface specificity, reveals details about the molecular structure and orientation of molecules within the monolayer films at their equilibrium spreading pressures. At their equilibrium spreading pressures, both 1- and 2-hexadecanol form compact films having a high degree of conformational order and molecular areas of 18.9 and 21.5 A(2)/molecule, respectively. This result for 2-hexadecanol implies that the isomer remains primarily in an all-trans conformation with the methyl group in the C(1) position buried in the water subphase. This conformation leads to significantly reduced intensity in specific vibrational transitions due to partial destructive interference. In contrast, 3-hexadecanol and 4-hexadecanol form more expanded monolayers at their equilibrium spreading pressures, having areas of 28.7 and 40.3 A(2)/molecule, respectively. In these monolayers, the intensities of selected vibrational bands show less evidence of destructive interference, implying that methyl groups on opposite ends of the adsorbates do not adopt strongly correlated orientations.