Rana N.S. Sodhi

Time-of-flight secondary ion mass spectrometry (TOF-SIMS):—versatility in chemical and imaging surface analysis

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has emerged as one of the most important and versatile surface analytical techniques available for advanced materials research. This arises from its excellent mass resolution, sensitivity and high spatial resolution providing both chemical and distributional (laterally and depth) information for a wide variety of materials and applications. Understanding the various modes of operation and the information that each provides is crucial to the analyst in order to optimise the type of data that is obtained. New developments in primary ion sources and the application of multivariate analysis techniques, which can only extend the versatility and applicability of the technique, are also discussed.

Determination of 4-Chloroaniline and Its Derivatives Formed in the Interaction of Sodium Hypochlorite and Chlorhexidine by Using Gas Chromatography

INTRODUCTION The combination of sodium hypochlorite (NaOCl) and chlorhexidine (CHX) results in the formation of a precipitate. In a previous study, we demonstrated the formation of 4-chloroaniline (PCA) in the precipitate by using x-ray photon spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). The TOF-SIMS results showed a peak at 127 amu, which is characteristic of 4-chloroaniline. However, this could also be characteristic of other isomers of 4-chloroaniline such as 2-chloroaniline and 3-chloroaniline. AIMS AND METHODS The aim of this study was to further identify the precipitate by using gas chromatography-mass spectrometry (GC-MS). RESULTS The results showed an absence of other aniline derivatives in the precipitate. Only PCA was found. CONCLUSIONS Further investigations of the precipitate should address the bioavailability of PCA leaching out from dentin and its cytotoxicity. Until the precipitate is studied further, it would appear prudent to minimize its formation by avoiding the use of CHX together with NaOCl.

Application of surface analytical and modification techniques to biomaterial research

Abstract The development of suitable materials for biomedical applications requires a thorough understanding of the structure and chemistry of the solid-liquid interface when such a material is placed in the biological environment. The field is made complex by the diversity of materials used, the different applications one has to consider, and the complexity of the various biological environments the implanted material may find itself in. To understand the interactions which may occur, it is important to have information on the structure and composition of the top few atomic layers. Concepts from surface science, such as surface analysis and modification techniques prove to be valuable aids in the development of suitable biomaterials. These methods are not new or unique but are well established in other technologies. In this paper, several areas of surface modification techniques will be chosen to illustrate how they are being applied in the biomaterial field, stressing the interdisciplinary nature of the work as well as the surface analytical techniques involved.

Application of electron spectroscopy and surface modification techniques in the development of anti-microbial coatings for medical devices

Abstract Various gas plasmas were used to modify biomedical polymers (polyurethane and silicone) to examine the effect changes in hydrophilicity–surface functionality would have on bacterial adhesion and antibiotic retention. X-ray photoelectron spectroscopy (XPS) was used to characterise the modifications. Such treatments could reduce device-related infection on medical devices. While changes in hydrophilicty, as noted by changes in the contact angle, were seen for the various gas plasma (CO 2 , H 2 O and NH 3 ), these had little effect upon bacterial adhesion or antibiotic retention. An improvement was noted for antibiotic retention (ciprofloxacin) on the H 2 O-plasma treated polyurethane, attributable to the presence of –OH groups, however, this was small. These results suggest that other approaches for reducing device-related infection be examined, such as the direct attachment of a drug-delivery system. To accomplish this for the drug-delivery system of choice, which utilises diisocynate chemistry, the introduction of primary amine groups onto the surface is required. Radiofrequency (RF) and remote microwave (MW) systems were used to introduce these groups onto both the biomedical polymer directly, and an intermediate, ethylene-based, plasma deposited film. The use of such a film would allow this technology to be applied to a variety of different substrates as well as provide a solvent barrier and a means of surface stabilisation. The MW system was found to be superior over the RF system in terms of deposition rate of the polymeric film, the effectiveness of its barrier properties and for the introduction of a higher proportion of primary amine functionality onto the surfaces as determined by XPS. Finally, use of a model system, in conjunction with XPS, confirmed the ability of these modified surfaces to be further derivatised using the isocyanate chemistry associated with the drug-delivery system. The results indicate that electron spectroscopy and surface modification techniques play an important and critical role towards the development of antimicrobial coatings for medical devices.

X-ray photoelectron spectroscopy of lignocellulosic materials treated with maleated polypropylenes

Abstract The esterification reaction between lignocellulosic materials (ALCELL lignin and Bleached kraft cellulose) and maleated polypropylenes (graft copolymerization of maleic anhydride into polypropylene chains) was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as a catalyst. The reaction between lignocellulosic materials and pure maleic anhydride was also conducted to determine the effect of the long polypropylene chains on the formation of ester bonds. The XPS studies of maleated bleached kraft cellulose showed the emergence of C4 carbon type on high resolution spectra, which was related to ester carbonyl functionality formed by esterification reaction. No evidence of esterification was observed between ALCELL lignin and maleated polypropylenes. The XPS studies demonstrated that both ALCELL lignin and bleached kraft cellulose chemically react with maleic anhydride with the formation of ester bonds.

Enhancing drug delivery for boron neutron capture therapy of brain tumors with focused ultrasound

BACKGROUND Glioblastoma is a notoriously difficult tumor to treat because of its relative sanctuary in the brain and infiltrative behavior. Therapies need to penetrate the CNS but avoid collateral tissue injury. Boron neutron capture therapy (BNCT) is a treatment whereby a (10)B-containing drug preferentially accumulates in malignant cells and causes highly localized damage when exposed to epithermal neutron irradiation. Studies have suggested that (10)B-enriched L-4-boronophenylalanine-fructose (BPA-f) complex uptake can be improved by enhancing the permeability of the cerebrovasculature with osmotic agents. We investigated the use of MRI-guided focused ultrasound, in combination with injectable microbubbles, to noninvasively and focally augment the uptake of BPA-f. METHODS With the use of a 9L gliosarcoma tumor model in Fisher 344 rats, the blood-brain and blood-tumor barriers were disrupted with pulsed ultrasound using a 558 kHz transducer and Definity microbubbles, and BPA-f (250 mg/kg) was delivered intravenously over 2 h. (10)B concentrations were estimated with imaging mass spectrometry and inductively coupled plasma atomic emission spectroscopy. RESULTS The tumor to brain ratio of (10)B was 6.7 ± 0.5 with focused ultrasound and only 4.1 ± 0.4 in the control group (P < .01), corresponding to a mean tumor [(10)B] of 123 ± 25 ppm and 85 ± 29 ppm, respectively. (10)B uptake in infiltrating clusters treated with ultrasound was 0.86 ± 0.10 times the main tumor concentration, compared with only 0.29 ± 0.08 in controls. CONCLUSIONS Ultrasound increases the accumulation of (10)B in the main tumor and infiltrating cells. These findings, in combination with the expanding clinical use of focused ultrasound, may offer improvements in BNCT and the treatment of glioblastoma.

Differentiation of human kidney stones induced by melamine and uric acid using surface desorption atmospheric pressure chemical ionization mass spectrometry

Clinically obtained human kidney stones of different pathogenesis were dissolved in acetic acid/methanol solutions and then rapidly analyzed by surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS) without any desalination treatment. The mass spectral fingerprints of six groups of kidney stone samples were rapidly recorded in the mass range of m/z 50-400. A set of ten melamine-induced kidney stone samples and nine uric acid derived kidney stone samples were successfully differentiated from other groups by principal component analysis of SDAPCI-MS fingerprints upon positive-ion detection mode. In contrast, the mass spectra recorded using negative-ion detection mode did not give enough information to differentiate those stone samples. The results showed that in addition to the melamine, the chemical compounds enwrapped in the melamine-induced kidney stone samples differed from other kidney stone samples, providing useful hints for studying on the formation mechanisms of melamine-induced kidney stones. This study also provides useful information on establishing a MS-based platform for rapid analysis of the melamine-induced human kidney stones at molecular levels.

Qualitative Analysis of Precipitate Formation on the Surface and in the Tubules of Dentin Irrigated with Sodium Hypochlorite and a Final Rinse of Chlorhexidine or QMiX

INTRODUCTION Interaction of sodium hypochlorite (NaOCl) mixed with chlorhexidine (CHX) produces a brown precipitate containing para-chloroaniline (PCA). When QMiX is mixed with NaOCl, no precipitate forms, but color change occurs. The aim of this study was to qualitatively assess the formation of precipitate and PCA on the surface and in the tubules of dentin irrigated with NaOCl, followed either by EDTA, NaOCl, and CHX or by saline and QMiX by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). METHODS Dentin blocks were obtained from human maxillary molars, embedded in resin, and cross-sectioned to expose dentin. Specimens in group 1 were immersed in 2.5% NaOCl, followed by 17% EDTA, 2.5% NaOCl, and 2% CHX. Specimens in group 2 were immersed in 2.5% NaOCl, followed by saline and QMiX. The dentin surfaces were subjected to TOF-SIMS spectra analysis. Longitudinal sections of dentin blocks were then exposed and subjected to TOF-SIMS analysis. All samples and analysis were performed in triplicate for confirmation. RESULTS TOF-SIMS analysis of group 1 revealed an irregular precipitate, containing PCA and CHX breakdown products, on the dentin surfaces, occluding and extending into the tubules. In TOF-SIMS analysis of group 2, no precipitates, including PCA, were detected on the dentin surface or in the tubules. CONCLUSIONS Within the limitations of this study, precipitate containing PCA was formed in the tubules of dentin irrigated with NaOCl followed by CHX. No precipitates or PCA were detected in the tubules of dentin irrigated with NaOCl followed by saline and QMiX.

Speciation of surface gold in pressure oxidized carbonaceous gold ores by TOF-SIMS and TOF-LIMS

Abstract To the best of our knowledge, this is the first attempt ever to speciate gold preg-robbed by carbonaceous matter using a surface sensitive microbeam technique. This approach enables the direct determination of gold species sorbed on carbonaceous particulates thus providing a new tool in understanding the chemistry of gold sorption on carbon. The reasoning behind this effort was to study the detrimental effect chloride ions have on gold recovery by pressure oxidation of carbonaceous sulfide ores, a technology largely used by the mining industry. The characterization of the sorbed gold species involved three surface sensitive microbeam analytical techniques (TOF-SIMS, TOF-LIMS and XPS) providing confirmatory results for better accuracy. Optimum conditions for detection of gold compounds with minimum fragmentation by TOF-SIMS and TOF-LIMS mass spectrometers have been determined. A reference library of 16 major gold complexes with halogen, thiosulfate, cyanide and thiocyanate groups relevant to the gold recovery processes has been established. The most suitable of the microbeam techniques tested was found to be negative (−ve) ion TOF-LIMS, offering best sensitivity and a small analytical spot size.

Oxidation of Wood Components During Chromated Copper Arsenate (CCA-C) Fixation

Abstract Pre-extracted radial sections of southern yellow pine sapwood were treated with CCA-C and analyzed by x-ray photoelectron spectroscopy (xps). The ratio of CI (carbon bonded only to carbon and/or hydrogen) to C2 (carbon bonded to one oxygen with a single bond) was used to determine the progress of oxidation of wood components during CCA fixation. This ratio increased after treating times of 10 minutes and 60 minutes and decreased after 180 minutes soaking suggesting that oxidation of C2 predominates on initial contact with CCA solution but oxidation of CI (lignin) becomes more important with extended exposure to the treating solution. Oxidation of C2 to C3 (carbon bonded to two oxygens or a carbonyl group) was demonstrated by in situ trapping of C3 with ethylene glycol as it was formed. Further oxidation of C3 to C4 (carboxylic carbon) was not observed in the xps spectra, consistent with the findings of others. The hypothesis that rapid decarboxylation results in loss of C4 as evolved CO2 is suppo...