On-line additions of aqueous standards for calibration of Laser Ablation Inductively Coupled Plasma Mass Spectrometry: theory and comparison of wet and dry plasma conditions

This paper describes the theory of on-line additions of aqueous standards for calibration of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Establishment of a calibration curve enabled investigation of: fractionation, matrix effects, mass flow ratios, and the relative merits of wet and dry plasma conditions for laser ablation sampling. It was found that a wet plasma was much more tolerant of increased sample loading without reducing plasma robustness, leading to less severe and more constant mutual matrix effects. These findings indicate that the on-line addition of water is the preferred mode of operation for quantification by LA-ICP-MS. The analytical performance of the method was validated by the analysis of three certified reference materials: National Institute of Standards and Technology (NIST) 612 Trace Elements in Glass, European Reference Material (ERM) 681 Trace Elements in Polyethylene and British Chemical Standards (BCS) No. 387 Nimonic 901 Alloy. Analysis of NIST 612 was performed under both wet and dry plasma conditions, and the correlation with certified elemental concentrations was much better when a wet plasma was employed. Analyses of ERM 681 and BCS No. 387 were performed under wet plasma conditions, due to its proven advantages. The differences between the found and certified elemental concentrations varied between 1 – 10 % for the majority of elements, for all three certified reference materials

Liquid chromatography–flame ionisation detection using a nebuliser/spray chamber interface. Part 1. Design and testing

AbstractA nebuliser and spray chamber have been used to link a flow injection analyser to a flame ionisation detector, with the potential for the combination to be used as a universal detector for liquid chromatography. The hydrogen and air flows were adjusted to achieve a stable system. The detector responded to both volatile and involatile analytes and to compounds with and without chromophores, including alkanes, alkanols, aromatic amides and acids, phenols, amino-acids and carbohydrates and gave a linear response for many analytes. However, for involatile polar analytes it was necessary to add traces of acid or salt to the carrier stream to obtain a linear response

Applications of a novel flame ionisation detector for liquid chromatography

Over the last twenty years liquid chromatography has come to dominate analytical chemistry because of its ability to analyse a wide range of products from pharmaceuticals to environmental and forensic samples but some groups of analytes still cause practical difficulties in detection. The most common detector for HPLC is the UV-Visible spectroscopic detector, which is both sensitive and linear. However, detection is limited to analytes containing chromophores. For other analytes the analyst has to either rely on derivatisation or employ a “universal detector”, such as the less sensitive refractive index detector or the evaporative light scattering detector, which cannot easily detect small, volatile compounds. The universal flame ionisation detector when interfaced to LC has had problems in the past because of the signal from the organic component of the mobile phase, however, the use of superheated water as the eluent overcomes this problem and enables reversed-phase separations with the ability to detect analytes with and without chromophores. A revised design of interface (patent pending) enables a wide range of columns to be employed with differing flow rates

An ICP-MS, ESI-MS and molecular modelling investigation of homogeneous gallium affinity tagging (HMAT) of phosphopeptides

Protein phosphorylation and de-phosphorylation, provide one of the most common signalling pathways within cells, being involved in regulating cellular processes, mediating enzyme inhibition, protein-protein recognition and protein degradation. Compared with normal proteomics, phosphoproteomics poses some additional challenges requiring more initial separation and additional sensitivity to detect and quantify potentially ultra-low abundance species. In this work, the selective detection of phosphopeptides is described based on the incorporation of a metal tag, gallium-N,N-biscarboxymethyl lysine (Ga-LysNTA), in solution before separation and detection by liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP-MS). Experimental and theoretical characterisation of the resulting Ga-phosphopeptide complex is presented based on linear ion trap electrospray ionisation mass spectrometry (ESI-MS), Fourier transform mass spectrometry (FT-MS) and molecular modelling data. Linear ion trap electrospray ionisation mass spectrometry (ESI-MS) was employed to study the interaction of the gallium tag with platelet derived growth factor beta receptor (β-PDGF), a small phosphopeptide. In addition high resolution Fourier transform mass spectrometry (FT-MS) was used for accurate mass determination and multistage tandem mass spectrometry of the gallium-β-PDGF complex identified the fragmentation pathway. Finally, molecular modelling was used to investigate the energetically favoured structures of both the Ga-LysNTA material and the β-PDGF-Ga-LysNTA complex

Analysis of mono-phosphate nucleotides as a potential method for quantification of DNA using high performance liquid chromatography-inductively coupled plasma-mass spectrometry

The determination of total deoxyribonucleic acid (DNA) concentration is of great importance in many biological and bio-medical analyses. The quantification of DNA is traditionally performed by UV spectroscopy; however the results can be affected greatly by the sample matrix. The proposed method quantifies phosphorus in digested calf thymus DNA and human DNA by high performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS). The method presented showed excellent baseline separation between all 4 DNA mono-nucleotides and 5’UMP. Column recoveries ranging from 95% to 99% for phosphorus resulted in a mass balance of 95% ± 0.5% for standard nucleotides, determined by LC-ICP-MS, compared to total DNA determined by flow injection coupled to ICP-MS (FI-ICP-MS). The ability of LC-ICPMS to act as an internal check that only DNA derived phosphorus was counted in the assay was demonstrated by establishing a mass balance between the total phosphorous signal from undigested DNA and that from the speciated DNA. The method for quantification was evaluated by analysis of NIST SRM 2372; a total speciated DNA recovery of 52.1 ng/μL, compared with an expected value of 53.6 ng/μL, was determined by external calibration. From repeat measurements a mass balance of 97% ± 0.5% for NIST DNA was achieved. The method limits of detection for individual nucleotides were determined between 0.8 to 1.7 μg L-1 (31P) for individual nucleotides by LC-ICP-MS, and 360 ng L-1 for 5’AMP by direct nebulisation

Acquisition of fast transient signals in ICP-MS with enhanced time resolution

In recent years, the field of ICP-MS has seen an increasing trend towards sampling systems and methods that produce short transient signals, rather than a continuous signal response. Fast data acquisition, readout and storage are crucial to take advantage of the wealth of information available from these approaches. However, many of the current generation mass spectrometers, in particular sector-field instruments, were not designed to cope with such short duration signals. This article reports the use of a commercially available multi-channel scaler board, which facilitates capture of TTL pulses from an ICP-MS detector at a user defined time resolution down to 100 ns. The board was used to profile 400–600 μs wide signals with 10 μs resolution, derived from the nebulisation of a 50 nm gold nanoparticle suspension. Furthermore, the benefit of a 100% duty cycle was demonstrated for ∼10 ms wide signals, following ablation of individual macrophage cells with a fast response LA-ICP-MS interface

‘Blind time’ – current limitations on laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for ultra-transient signal isotope ratio analysis and application to individual sub-micron sized uranium particles

The application of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to the isotope ratio analysis of UOx particles has the potential to improve the isotopic determination of these particles when compared to currently utilised ICP-MS techniques. To investigate this a high-speed, integrated ablation cell and dual concentric injector design was tested in the expectation that the resulting increase in signal to noise ratio and sample ion yield would improve the determination of 234U/238U, 235U/238U and 236U/238U for such materials. However, when compared to a slower washout, more established low-volume cell design, the highly transient signals of the new design proved challenging for the mixed detector array of the multi-collector mass spectrometer, introducing a new bias. We describe a major component of this bias, referred to as ‘blind time’, and model its impact on UOx particle analysis. After accounting for blind time, average precisions for the uranium isotopic composition of sub-micron sized UOx particles using LA-MC-ICP-MS were 3% 1RSD for 235U/238U and 8% 1RSD for 234U/238U. When ablating a glass rather than a UOx particle, uncertainties of 1.3% 1RSD for 235U/238U were achieved for 150 nm equivalent particle sizes using LA-MC-ICP-MS

Oxaliplatin complexes with carnosine and its derivatives: in vitro cytotoxicity, mass spectrometric and computational studies with a focus on complex fragmentation

The complexation of the Pt-based anti-cancer drug oxaliplatin (OxPt) with biological ligands other than DNA is believed to be a major cellular sink for the drug reducing its therapeutic potential and acting as a potential cause of toxicity. In this paper, an in vitro study on hepatocellular carcinoma HepG2 cells suggests that the naturally abundant cytoplasmic dipeptide ligand β-alanyl-L-histidine dipeptide (carnosine) may inhibit the cytotoxic action of OxPt most likely through the formation of complexes that are less cytotoxic than OxPt alone. Evidence is provided to suggest that pre-exposure of HepG2 cells to elevated levels of carnosine appears to have a lasting effect on reducing the cytotoxicity of OxPt even after the removal of the carnosine. This effect, however, is shown to be under kinetic control as its magnitude was shown not to vary significantly with the level of carnosine exposure within the concentration range used in this study. Various mass spectrometry techniques employing electrospray ionization and chip nanospray were employed to study the interaction of oxaliplatin with carnosine as well as two of its derivatives being β-alanyl-N-methylhistidine (anserine) and N-Acetylcarnosine (NAC). Evidence of complexation between OxPt and each of the three ligands examined is presented. Most species observed were unambiguously assigned and compared to their theoretical isotopic patterns. Common fragmentation products due to the collisionally-activated protonated complexes of each of the ligands examined with OxPt, [M + OxPt + H]+ where M= carnosine, anserine or NAC were reported. Density functional calculations at B3LYP/LANL2DZ were used to obtain structural information and relative free energies of different isomers of the observed precursor [Carnosine + OxPt + H]+ both in the gas phase and in solution as well as to probe its fragmentation, highlighting plausible fragmentation mechanisms that account for all the experimental results.Data are presented to show several binding modes between electron rich sites such as N and O centers of carnosine and the Pt metal of OxPt. Calculations were also employed to obtain proton affinities and free energies of key reactions. The proton affinities of carnosine, Anserine and NAC at 298 K were calculated to be 254.4, 255.9 and 250.2 kcal mol-1 respectively. To the best of our knowledge the proton affinities of anserine and N-acetyl-carnosine are the first reported values in the literature

Determination of Pt-DNA adducts and the sub-cellular distribution of Pt in human cancer cell lines and the leukocytes of cancer patients, following mono- or combination treatments, by inductively-coupled plasma mass spectrometry

Determination of Pt-DNA adducts and the sub-cellular distribution of Pt in human cancer cell lines and the leukocytes of cancer patients, following mono- or combination treatments, by inductively-coupled plasma mass spectrometr