The influence of mixed solvents volatility on charge state distribution of peptides during positive electrospray ionization mass spectrometry

Understanding the mechanisms that control and concentrate the observed electrospray ionisation (ESI) response from peptides is important. Controlling these mechanisms can improve signal-to-noise ratio in the mass spectrum, and enhances the generation of intact ions, and thus, improves the detection of peptides when analysing mixtures. The effects of different mixtures of aqueous: organic solvents (25, 50, 75%; v/v): formic acid solution (at pH 3.26) compositions on the ESI response and chargestate distribution (CSD) during mass spectrometry (MS) were determined in a group of biologically active peptides (molecular wt range 1.3 - 3.3 kDa). The ESI response is dependent on type of organic solvent in the mobile phase mixture and therefore, solvent choice affects optimal ion intensities. As expected, intact peptide ions gave a more intense ESI signal in polar protic solvent mixtures than in the low polarity solvent. However, for four out of the five analysed peptides, neither the ESI response nor the CSD were affected by the volatility of the solvent mixture. Therefore, in solvent mixtures, as the composition changes during the evaporation processes, the pKb of the amino acid composition is a better predictor of multiple charging of the peptides

Levels of Polychlorinated Biphenyls in Plastic Resin Pellets from Six Beaches on the Accra-Tema Coastline, Ghana

Background. Polychlorinated biphenyls (PCBs) are organic compounds, known to be carcinogenic and banned by the Stockholm Convention. PCBs are hydrophobic substances able to accumulate in organic materials, including plastic pellets. Plastic resin pellets are industrial raw materials that are remolded finished products for industrial and domestic use, commonly used for packaging. Plastic resin pellets were chosen as the medium for monitoring hydrophobic contaminants because they are able to adsorb PCB contaminants. Pellets can be unintentionally washed into the ocean where hydrophobic contaminants such as PCBs are also deposited. Objectives. We aimed to identify PCB congeners and quantify PCB pollution levels in the marine environment using resin plastic pellets collected from six beaches along the Accra-Tema coastline in Ghana. Methods. Plastic resin pellets (5 g) were extracted with 200 mL of n-hexane for 16 hours by Soxhlet extraction. Concentrations of PCBs from the extracts were determined using gas chromatography with an electron capture detector. Results. The individual PCB congeners detected were PCB 28, 52, 101, 105, 138, 153, 156 and 180. PCB 28 was detected at all six beaches, with a total concentration of 43.5 ng/g pellet (mean/beach 7.25 +/− 2.47 ng/g pellet; CV = 34%), while PCB 138 was only detected on one beach (Castle Beach) at a total concentration of 0.8 ng/g pellet. The concentration of PCBs ranged from 7.4 ng/g (Sunset Beach) to 47.5 ng/g (Castle Beach) (mean 16.4±15.4 ng/g per beach; CV=94%). Discussion. PCB concentrations at Castle Beach have been studied previously, showing an increase from 39 ng/g to 47.5 ng/g, whereas levels decreased significantly from 28 ng/g to 14.2 ng/g in Sakumono Beach over the span of three years. Conclusions. The concentrations of four detected PCB congeners (28, 52, 101 and 156) were significantly higher than the World Health Organization (WHO) allowable daily intake of 6 ng/g food per day for PCBs. A more efficient industrial and domestic waste disposal system is advocated for Ghana. Competing Interests. The authors declare no competing financial interests

Influence of electrolytes and a supercharging reagent on charge state distribution and response of neuropeptide ions generated during positive electrospray ionisation mass spectrometry

To aid in the detection of trace quantities of neuropeptides in a biological matrix (as saliva), the influence of different electrolytes and a supercharging reagent on the positive electrospray ionisation mass spectrometry (ESI-MS) response was investigated. Ammonium acetate, sodium chloride and sodium bicarbonate (10–7 M to 10–3 M) and the supercharging reagent m-nitrobenzyl alcohol (m-NBA) was added to the mobile phase and the effect on the ESI response and charge-states distribution (CSD) was studied in a group of peptides (molecular weight range 2.2 kDa to 3.5 kDa; CGRP, VIP, GLP1, CRF and PrRP). As expected, the result indicates that the ESI response is affected by the presence of additives: ammonium acetate shifted the observed charge states ratio whereas the addition of m-NBA resulted in the appearance of higher maximum charge state ions. This increase in higher charge state for all the peptide ions, [M + nH]n+ to [M + (n +?1)H]n + 1, was atttributed to protonation of the C-terminal. However, when the composition of MeCN in a mobile phase �containing m-NBA was increased, an enhancement of the total ion signal was observed for non-polar peptide samples. This is a very interesting observation as this is not observed in samples without m-NBA and could be a result of how these peptide ions are solubilised and �positioned relative to the droplet surface/air interface

Determination of homocysteine in human saliva by liquid chromatography and electrospray ionization quadrupole time-of-flight mass spectrometry: profiles in healthy adults

Homocysteine (Hcys) is a non-essential amino acid associated with a range of diseased and abnormal metabolic conditions. Hcys concentration in saliva is routinely determined by enzyme assays, which are broadly specific, but can be expensive and suffer from cross-reactivity. Total Hcys (tHcys) concentrations in eight healthy adults were determined to establish the inter-day variation during resting, normal and intensive physical activity, using the more sensitive analytical techniques of liquid chromatography and tandem mass spectrometry without prior derivatization. Saliva (~ 1.5 mL) was collected over four days; early morning (EA), normal activity (NA) and during physical activity (PA). Samples were processed by disulphide reduction, acetonitrile precipitation and then centrifugation-filtration. Extracts were chromatographically resolved and analysed on a quadrupole time- of-flight (QToF) mass spectrometer. The protonated [M+H]+, m/z 136.101 and product ([M+H]+- HCOOH) m/z 90.103 ions were then monitored against an internal standard (13CHcys) and external set of calibration standards. Mean tHcys concentration for the whole group, including exercise was 6.6 ± 8.0 (range 0.2 – 29.6 nmol/mL). Overall, concentration of tHcys was greater in males than the females but not significantly (p > 0.05). The mean EA concentration was significantly < 0.05) greater than NA for both males (p = 0340) and females (p = 0.0045). There were large within-subject variations (coefficient of variation; CV%; 24% to 103%). The limits of detection (LOD) and quantification (LOQ) were 0.07 and 0.22 nmol/mL, respectively. The procedure potentially provides a convenient means of analyzing salivary Hcys as a diagnostic disease marker

Additional file 1: of Markov chain analysis of the rainfall patterns of five geographical locations in the south eastern coast of Ghana

Supplementary material: Appendix A, B, C, D, E. (DOCX 135 kb

UHAS-MIDA software package: mass isotopomer distribution analysis-applying the inverse matrix for the determination of stable isotopes of chromium distribution during red blood cell labelling.

Clinical assessment of fluid volume status in children during malaria can be taxing and often inaccurate. During malaria, changes in fluid volume are rather multifarious and estimating this parameter, especially in sick children is very challenging for clinicians who frequently rely on indices such as long capillary refill times, tachycardia, central venous pressure and decreased urine volume as guides. Here, we present the UHAS-MIDA, an open-source software tool that calculates the red blood cell (RBC) concentration and blood volume during malaria in children determined using a stable isotope of chromium (53Cr as the label) by gas chromatography-mass spectrometry in selective ion monitoring (GC/MS-SIM) analysis. A key component involves the determination of the compositions of the most abundant naturally occurring isotopes of Cr (50Cr, 52Cr, 53Cr), and converting the proportions into a 3 × 3 matrix. To estimate unknown proportions of chromium isotopic mixtures from the measured abundances of three ions, an inverse matrix was calculated. The inverse together with several inputs is then used to calculate the corrected MS ion abundances. Thus, we constructed the software tool UHAS- MIDA using HTML, CSS/Bootstrap, JavaScript, and PHP scripting languages. The tool enables the user to efficiently determine RBC concentration and fluid volume. The source code, binary packages and associated materials for UHAS-MIDA are freely available at https://github.com/bentil078/Abaye-et-al_UHASmida