•High efficiency thermal vaporiser designed and used for on-line reaction monitoring.•Concentration profiles of all reactants and products obtained from mass spectra.•By-product formed from the presence of an impurity detected by MS but not MIR.•Mass spectrometry can detect trace and bulk components unlike molecular spectrometry.A specially designed thermal vaporiser was used with a process mass spectrometer designed for gas analysis to monitor the esterification of butan-1-ol and acetic anhydride. The reaction was conducted at two scales: in a 150 mL flask and a 1 L jacketed batch reactor, with liquid delivery flow rates to the vaporiser of 0.1 and 1.0 mL min−1, respectively. Mass spectrometry measurements were made at selected ion masses, and classical least squares multivariate linear regression was used to produce concentration profiles for the reactants, products and catalyst. The extent of reaction was obtained from the butyl acetate profile and found to be 83% and 76% at 40 °C and 20 °C, respectively, at the 1 L scale. Reactions in the 1 L reactor were also monitored by in-line mid-infrared (MIR) spectrometry; off-line gas chromatography (GC) was used as a reference technique when building partial least squares (PLS) multivariate calibration models for prediction of butyl acetate concentrations from the MIR spectra. In validation experiments, good agreement was achieved between the concentration of butyl acetate obtained from in-line MIR spectra and off-line GC. In the initial few minutes of the reaction the profiles for butyl acetate derived from on-line direct liquid sampling mass spectrometry (DLSMS) differed from those of in-line MIR spectrometry owing to the 2 min transfer time between the reactor and mass spectrometer. As the reaction proceeded, however, the difference between the concentration profiles became less noticeable. DLSMS had advantages over in-line MIR spectrometry as it was easier to generate concentration profiles for all the components in the reaction. Also, it was possible to detect the presence of a simulated impurity of ethanol (at levels of 2.6 and 9.1% mol/mol) in butan-1-ol, and the resulting production of ethyl acetate, by DLSMS, but not by in-line MIR spectrometry.

A thermal vaporiser has been designed for analysis of liquid streams by a process mass spectrometer normally used for gas analysis. Concentrations of benzene, toluene and o-xylene at mg kg−1 levels in ethanol were determined from continuous vaporisation of the liquid. Ions with m/z values of 39, 57, 73, 77, 78, 91, 92 and 106 were selected and the optimal regression model (multiple linear regression with mean-centring) was found using an automated design of experiments approach to calibration model selection. It was discovered that the linearity of the response allowed excellent calibration to be performed using only four standards (at 0 and 110 mg kg−1 for each of the three analytes) and that there were minimal inter-analyte interferences. The detection limit of benzene, toluene and o-xylene was 0.5, 0.8 and 0.5 mg kg−1, respectively. Average differences between the actual and predicted concentrations, expressed as a percentage of the actual concentrations, for 27–82 mg kg−1 of benzene, toluene and o-xylene were 0.5–1.4%, 0.0–0.4% and 0.3–1.6%, respectively, while the average relative standard deviations were 1.3–2.6%, 1.0–2.5% and 1.1–2.3%, respectively. Detection of 3 mg kg−1 changes in the concentration of each of the analytes (at the 36 mg kg−1 level) was also demonstrated, indicating the sensitivity of the technique and the potential ability of the procedure to detect minor deviations in the specification of process streams from continuous analysis.

A 785 nm diode laser and probe with a 6 mm spot size were used to obtain spectra of stationary powders and powders mixing at 50 rpm in a high shear convective blender. Two methods of assessing the effect of particle characteristics on the Raman sampling depth for microcrystalline cellulose (Avicel), aspirin or sodium nitrate were compared: (i) the information depth, based on the diminishing Raman signal of TiO2 in a reference plate as the depth of powder prior to the plate was increased, and (ii) the depth at which a sample became infinitely thick, based on the depth of powder at which the Raman signal of the compound became constant. The particle size, shape, density and/or light absorption capability of the compounds were shown to affect the “information” and “infinitely thick” depths of individual compounds. However, when different sized fractions of aspirin were added to Avicel as the main component, the depth values of aspirin were the same and matched that of the Avicel: 1.7 mm for the “information” depth and 3.5 mm for the “infinitely thick” depth. This latter value was considered to be the minimum Raman sampling depth when monitoring the addition of aspirin to Avicel in the blender. Mixing profiles for aspirin were obtained non-invasively through the glass wall of the vessel and could be used to assess how the aspirin blended into the main component, identify the end point of the mixing process (which varied with the particle size of the aspirin), and determine the concentration of aspirin in real time. The Raman procedure was compared to two other non-invasive monitoring techniques, near infrared (NIR) spectrometry and broadband acoustic emission spectrometry. The features of the mixing profiles generated by the three techniques were similar for addition of aspirin to Avicel. Although Raman was less sensitive than NIR spectrometry, Raman allowed compound specific mixing profiles to be generated by studying the mixing behaviour of an aspirin–aspartame–Avicel mixture.Graphical abstractHighlights► Powder blending monitored non-invasively by wide area Raman spectrometry. ► Effect of particle size on sampling depth and Raman signal investigated for wide area illumination. ► Raman measurements used to monitor mixing dynamics, determine end-point and perform quantitative analysis. ► Higher chemical specificity of Raman compared to near infrared spectrometry offers advantages for multi-component mixtures.

Cellulose acetate artefacts from various museums have been analysed by micro-FTIR spectrometry and ion chromatography in an attempt to identify whether there are any common factors associated with their degradation. There was good correlation between the IR spectra, the concentration of ions extracted from an artefact and the visual degree of degradation. Deacetylation, which produced acetate, was found to be the primary process with chain scission (indicated by the appearance of oxalate ion) occurring after degradation is well advanced. Oxidative degradation (indicated by formate) was not a major factor for most artefacts studied, however the loss of formate by volatilization cannot be excluded. Changes to the polymer matrix as a consequence of degradation were indicated in some artefacts by the presence of plasticiser on the surface and increased levels of extractable chloride and/or sulphate.A simple test of the onset of degradation was developed that involved analysis of an aqueous swab of the surface of an artefact by ion chromatography. Analysis by X-ray fluorescence spectrometry allowed identification of selenium as a potential stabilizing element in certain areas of a doll which were less degraded than other parts that had no selenium.

Transmission Raman measurements of a 1 mm thick sulfur-containing disk were made at different positions as it was moved through 4 mm of aspirin (150–212 μm) or microcrystalline cellulose (Avicel) of different size ranges (<38, 53–106, and 150–212 μm). The transmission Raman intensity of the sulfur interlayer at 218 cm–1 was lower when the disk was placed at the top or bottom of the powder bed, compared to positions within the bed and the difference between the sulfur intensity at the outer and inner positions increased with Avicel particle size. Also, the positional intensity difference was smaller for needle-shaped aspirin than for granular Avicel of the same size. The attenuation coefficients for the propagation of the exciting laser and transmitted Raman photons through the individual powders were the same but decreased as the particle size of Avicel increased; also, the attenuation coefficients for propagation through 150–212 μm aspirin were almost half of those through similar sized Avicel particles. The study has demonstrated that particulate size and type affect transmitted Raman intensities and, consequently, such factors need to be considered in the analysis of powders, especially if particle properties vary between the samples.

A total of 383 tablets of a pharmaceutical product were analyzed by backscatter and transmission Raman spectrometry to determine the concentration of an active pharmaceutical ingredient (API), chlorpheniramine maleate, at the 2% m/m (4 mg) level. As the exact composition of the tablets was unknown, external calibration samples were prepared from chlorpheniramine maleate and microcrystalline cellulose (Avicel) of different particle size. The API peak at 1594 cm–1 in the second derivative Raman spectra was used to generate linear calibration models. The API concentration predicted using backscatter Raman measurements was relatively insensitive to the particle size of Avicel. With transmission, however, particle size effects were greater and accurate prediction of the API content was only possible when the photon propagation properties of the calibration and sample tablets were matched. Good agreement was obtained with HPLC analysis when matched calibration tablets were used for both modes. When the calibration and sample tablets are not chemically matched, spectral normalization based on calculation of relative intensities cannot be used to reduce the effects of differences in physical properties. The main conclusion is that although better for whole tablet analysis, transmission Raman is more sensitive to differences in the photon propagation properties of the calibration and sample tablets.

Analysis of needle-shaped particles of cellobiose octaacetate (COA) obtained from vacuum agitated drying experiments was performed using three particle size analysis techniques: laser diffraction (LD), focused beam reflectance measurements (FBRM) and dynamic image analysis. Comparative measurements were also made for various size fractions of granular particles of microcrystalline cellulose. The study demonstrated that the light scattering particle size methods (LD and FBRM) can be used qualitatively to study the attrition that occurs during drying of needle-shaped particles, however, for full quantitative analysis, image analysis is required. The algorithm used in analysis of LD data assumes the scattering particles are spherical regardless of the actual shape of the particles under evaluation. FBRM measures a chord length distribution (CLD) rather than the particle size distribution (PSD), which in the case of needles is weighted towards the needle width rather than their length. Dynamic image analysis allowed evaluation of the particles based on attributes of the needles such as length (e.g. the maximum Feret diameter) or width (e.g. the minimum Feret diameter) and as such, was the most informative of the techniques for the analysis of attrition that occurred during drying.

A novel method has been devised to derive kinetic information about reactions in microfluidic systems. Advantages have been demonstrated over conventional procedures for a Knoevenagel condensation reaction in terms of the time required to obtain the data (fivefold reduction) and the efficient use of reagents (tenfold reduction). The procedure is based on a step change from a low (e.g., 0.6 μL min−1) to a high (e.g., 14 μL min−1) flow rate and real-time noninvasive Raman measurements at the end of the flow line, which allows location-specific information to be obtained without the need to move the measurement probe along the microreactor channel. To validate the method, values of the effective reaction order n were obtained employing two different experimental methodologies. Using these values of n, rate constants k were calculated and compared. The values of k derived from the proposed method at 10 and 40 °C were 0.0356 ± 0.0008 mol−0.3 dm0.9 s−1 (n = 1.3) and 0.24 ± 0.018 mol−0.1 dm0.3 s−1 (n = 1.1), respectively, whereas the values obtained using a more laborious conventional methodology were 0.0335 ± 0.0032 mol−0.4 dm1.2 s−1 (n = 1.4) at 10 °C and 0.244 ± 0.032 mol−0.3 dm0.9 s−1 (n = 1.3) at 40 °C. The new approach is not limited to analysis by Raman spectrometry and can be used with different techniques that can be incorporated into the end of the flow path to provide rapid measurements.

The evaporation of methanol from needle-shaped particles of cellobiose octaacetate (COA) has been studied directly in a jacketed vacuum drier using in situ measurements by Raman spectrometry. A design of experiments (DoE) approach was used to investigate the effects of three parameters (method of agitation, % solvent loss on drying and jacket temperature), with the intention of minimising the drying time and extent of particle attrition. Drying curves based on Raman signals for methanol and COA in the spectra of the wet particles indicated the end of drying and revealed three stages in the drying process that could be used to monitor the progress of solvent removal in real time. Off-line particle size measurements based on laser diffraction were made to obtain information on the extent of attrition, to compare with the trends revealed by the Raman drying curves. The study demonstrated that non-invasive Raman spectrometry can be used to study the progress of drying during agitation of particles in a vacuum drier, allowing optimisation of operating conditions to minimise attrition and reduce drying times. Although a correlation between particle size and off-line Raman measurements of COA was demonstrated, it was not possible to derive equivalent information from the in situRaman spectra owing to the greater effects of particle motion or bulk density variations of the particles in the drier.

Cellulose nitrate was one of the first semi-synthetic plastics to be commercially exploited and as such many museums contain a large number of artefacts illustrating the versatility of this plastic for the creation of a wide variety of functional and aesthetic artefacts. Conservators find themselves faced with the challenge of preserving these ageing artefacts which are showing evidence of significant degradation. The challenge is enhanced by artefacts of similar age and type exhibiting different degrees of degradation. This paper reports the analytical study of selected historical artefacts to explore the origins of these differences. A connection between the durability of the artefacts and the quality of the original synthetic process is identified, indicating the influence of inherent chemical factors on stability. The major contributory factors determining degradation appear to be the sulphate content remaining from the stabilization process and the rate of loss of the camphor plasticizer. A simple swab test is proposed to aid the identification of artefacts which are potentially susceptible to degradation. The test involves analysis of swab extracts by ion chromatography to reveal the presence of oxalate, which is indicative of cellulose nitrate chain scission.

Cellulose nitrate is susceptible to hydrolysis as well as loss of plasticiser when left in a humid atmosphere. A comparison of the ageing behaviour of cellulose nitrate samples prepared from cotton linters was used to simulate the artefacts studied in a previous study. Certain artefacts were also subjected to accelerated ageing at 12%, 55% and 75% relative humidity at 70 °C. The rate of degradation was observed to vary with the RH, indicating the connection between the absorption of moisture and the hydrolysis process. The effect of varying the sulphate level on the rate of hydrolysis was studied using concentrations similar to those detected in artefacts. The study was carried out using <0.1 mg g−1, 2 mg g−1 and 5 mg g−1 of sulphate and distinct differences were observed which is consistent with the conclusions drawn for a study of a number of artefacts. The observed rates of degradation are consistent with previous studies on cellulose nitrate. The degradation was studied using a combination of infrared spectroscopy, ion chromatography and gel permeation chromatography. The analysis was complemented by a study of the weight changes which occur during ageing.

An optical interface has been designed to maximise the sensitivity and spatial resolution required when Raman spectrometry is used to monitor a reaction in a micro-reactor, revealing advantages over a conventional commercial probe. A miniature aspheric lens was shown to be better than microscope objectives to focus the probing laser beam onto the sample. The diameters of the exciting and collection optical fibres were also shown to have a significant influence on sensitivity and the signal-to-background ratio, with 62.5 µm diameter 0.28 numerical aperture (NA) fibres found to be best for analysis of liquids in the 150 µm deep channel in the micro-reactor used. With a spectral measurement time of 2 s, it was shown that the probe could monitor the progress of an esterification reaction in real time and quickly optimise the reagent flow rates. The fast response time revealed features related to short-term pump instabilities and micro-reactor rheology effects that would not have been identified without rapid real-time measurements.

Broadband acoustic transducers, including an intrinsically safe device, were assessed for non-invasive monitoring of aspirin, citric acid or Avicel mixing in a bench scale convective blender. The frequency information content of the acoustic emission (AE) spectra depends on the response characteristics of the transducers, which vary depending on the design. As acoustic waves generated from the impact of particles propagated through and around the glass mixing vessel, comparable spectra were obtained from different locations on the glass. The intensity of AE increased as the impeller speed, mass of powder or density of the particles was increased. AE also increased with particle size, with a relatively greater increase in intensity at lower frequencies. Mixing profiles were generated in real time from the change in the integrated intensity over selected frequency ranges on addition of aspirin to Avicel; the AE signal initially increased and then came to a plateau as the mixture became homogeneous. The average plateau signal was plotted against concentration for three different particle size ranges of aspirin in Avicel; for aspirin concentrations <21% m/m the increase in the AE was relatively small with no discernable effects of the aspirin particle size; however, for >21% m/m aspirin, there was a proportionally greater increase in AE, and particle size effects were more obvious. The study has shown that AE is relatively easy to measure non-invasively during powder mixing, but has poorer sensitivity than NIR spectrometry for detection of effects caused by addition of secondary compounds, especially at smaller particle sizes.

Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 μg L−1), the limit of detection (3σ), and the characteristic mass of beryllium were 2.50%, 0.009 μg L−1 and 0.42 pg, respectively.

A convective blender based on a scaled down version of a high shear mixer-granulator was used to produce binary mixtures of microcrystalline cellulose (Avicel) and aspirin, citric acid, aspartame or povidone. Spectra of stationary Avicel or aspirin powder provided an indication of the information depth achieved with the NIR spectrometer used in the study, and confirmed previously reported effects of particle size and wavenumber. However, it was demonstrated that for 10% w/w aspirin in Avicel, the information depth at the C–H second overtone of aspirin (about 2.4 mm) was unaffected by changes in the particle size of aspirin and was determined by the major component. By making non-invasive NIR measurements as powders were mixed, it was possible to illustrate differences in the mixing characteristics of aspirin, citric acid, aspartame or povidone with Avicel, which were related to differences in the cohesive properties of the particles. Mixing profiles based on second overtone signals were better for quantitative analysis than those derived from first overtone measurements. It was also demonstrated that the peak-to-peak noise of the mixing profile obtained from the second overtone of aspirin changed linearly with the particle size of aspirin added to Avicel. Hence, measurement of the mixing profile in real time with NIR spectrometry provided simultaneously the opportunity to study the dynamics of powder mixing, make quantitative measurements and monitor possible changes in particle size during blending.

The chemical and morphological transformations of condensed phase species of a thorium-based modifier were studied over the temperature range 200–2500 °C, without and with the presence of aluminium and silicon as matrix components, and in some instances, arsenic as an analyte element. A similar study was also conducted with palladium as the modifier, for comparison. Results were derived using scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry, Raman microanalysis and attenuated total reflectance (ATR) Fourier transform-infrared (FT-IR) spectrometry. Comparable results were found using pyrolytic and non-pyrolytic graphite platforms, with processes occurring at slightly higher temperatures on the pyrolytic graphite platform. With thorium as the modifier, metal oxides were the predominant species on the platform surface at relatively low temperatures (<1500 °C), whereas metal phases became prevalent at high temperatures, when thorium and aluminium tended to behave independently from one other. Some spatial variations in the composition of the salt residues on different regions of the platform were observed (from the region closest to the slot in the tube, to the region furthest from the slot). Nonetheless, thorium metal remained on the graphite platform to higher temperatures than did aluminium metal. In the presence of arsenic, the existence of mixtures of thorium and arsenic oxides, just before the appearance temperature of gas phase arsenic atoms, was confirmed by SEM studies, ED X-ray spectra and Raman microanalysis. This suggests that any modifying effect of thorium on arsenic occurs while the modifier is in the oxide phase rather than in the metal phase. The presence of silicon added as silica, did not influence significantly the thermochemical behaviour of mixtures of thorium and aluminium. However, coexistence of silicon and arsenic oxides at the appearance temperature of the atomic absorption signal of arsenic was obtained, confirming that silicon can act as an internal modifier for arsenic. In the presence of palladium, aluminium exhibited greater interaction with the modifier; consequently, aluminium metal was retained on the platform surface to higher temperatures than thorium, which could explain how interference effects of aluminium on e.g. arsenic are avoided or reduced. Similarly, there was evidence for interaction of palladium and arsenic in the reduced state. However, when aluminium and silicon were present, the transformation of the palladium oxide to the metallic state was affected, which could diminish the modifying benefits of palladium for arsenic in the presence of aluminium.

The inorganic and organic components of 100-fold diluted serum enhance the signal of 79Br+ in ICP-MS by about 13%. Sodium and albumin are the main causes of the effect. Different calibration procedures were investigated to compensate for the enhancement interference. The effect of albumin could not be mimicked sufficiently by use of low molecular weight sources of carbon such as sucrose. Plasma substitute proved a convenient material and can be used, in most circumstances, to matrix match for serum. Plasma substitute also has the advantage of containing no endogenous bromine. The proposed ICP-MS method produced results for Br in serum in agreement with those of an ICP-OES method. The detection limits of the ICP-MS and ICP-OES methods were 0.09 and 0.8 mg L−1, respectively.

Thermal treatment of alkaline and alkaline earth metal sulphates on a graphite platform was performed over the temperature range 200–2000 °C. The solid residues produced at each temperature were located by scanning electron microscopy (SEM) and then identified by energy-dispersive (ED) X-ray spectroscopy and Raman microanalysis. Additional experiments involved the dissolution of the residues from the platform and analysis by ion chromatography to determine the concentration of sulphate and other ions. A decomposition pattern was derived for the alkaline and alkaline earth metal sulphates. The transformation of the metal sulphates was dependent on temperature and the cation present. In general, the metal sulphates do not undergo significant decomposition to other species at temperatures less than 900 °C, with the exception of magnesium and beryllium sulphates, which are transformed into metal oxides to some extent. Above 900 °C, major transformations occur mainly for sodium, magnesium, and beryllium sulphates. For all the salts studied, there is evidence of the formation of species such as metal sulphides and elemental sulphur.

The identification and distribution of condensed phase species produced on a graphite platform at temperatures between 200 and 2000 °C was studied using data obtained by scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry and Raman microanalysis. The first general conclusion is that there is no unique path in the thermal transformation of the metal chlorides tested, even for a particular metal chloride. Sodium, potassium and calcium chlorides showed similar vaporization characteristics, evolving mainly as monochlorides, while magnesium, beryllium and aluminium mainly vaporized as free atoms, following transformation caused by hydrolysis. The replacement of chlorine atoms by oxygen occurred at lower temperatures for beryllium and aluminium chlorides than for magnesium chloride. There were some particular areas on the platform surface where other mechanisms, such as hydrolysis of calcium chloride and dissociation of sodium chloride in the condensed phase, seemed occasionally to occur to a minor extent.

Methods have been developed and compared for the analysis of a glycerol-based polyether polyol using a low-field, medium-resolution NMR spectrometer, with an operating frequency of 29 MHz for . Signal areas in the time and frequency domains were used to calculate the ethylene oxide (EO) content of individual samples. The time domain signals (free induction decay) were analysed using a new version of the direct exponential curve resolution algorithm (FID-DECRA). Direct analysis of the NMR FT spectra gave percentage EO concentrations of reasonable accuracy (average percentage error of 1.3%) and precision (average RSD of 1.8%) when compared with results derived from high-field NMR spectrometry. The direct FID-DECRA method showed a negative bias (−0.8±0.12% w/w) in the estimation of percentage EO concentration, but the precision (average RSD of 0.9%) was twice as good as that of direct spectral analysis. When the NMR analysis was used as a reference method for univariate calibration of the NMR procedures, the best accuracy (average percentage error of 0.5%) and precision (average RSD of 0.6%) were obtained using FID-DECRA, for EO concentrations in the range 14.8–15.5% w/w. An additional advantage of FID-DECRA is that the analytical procedure could be automated, which is particularly desirable for process analysis.

In-line Raman, near infrared and UV-visible spectometries, and at-line low-field NMR spectrometry have been used to monitor the acid-catalysed esterification of crotonic acid and butan-2-ol. Repeat reactions were carried out in a 1 L batch reactor. Spectra taken during the reactions, along with reference ester concentrations determined by gas chromatography (GC), were used to determine the concentration of 2-butyl crotonate as the reaction proceeded. Ester concentrations were determined from 1st derivative Raman and UV-visible spectra by employing univariate calibration models, whereas the low-field NMR and NIR data required multivariate analysis by partial least squares regression. The techniques have been compared on the basis of the accuracy and between-run precision of the 2-butyl crotonate concentrations, and the ability to determine the rate constant of the reaction in the shortest possible time after the start of the reaction. The ester concentrations determined by all of the techniques were similar to those obtained by the GC reference method. In-line UV-visible spectrometry gave the poorest between-run precision. Raman and NIR spectrometries provided an estimate of the rate constant of the reaction after 90 min when the ester concentration had reached 0.09 mol dm−3, meaning that if the rate constant at this time was not as expected then corrective action could be taken to salvage the batch.

A thermal vaporiser has been designed for analysis of liquid streams by a process mass spectrometer normally used for gas analysis. Concentrations of benzene, toluene and o-xylene at mg kg−1 levels in ethanol were determined from continuous vaporisation of the liquid. Ions with m/z values of 39, 57, 73, 77, 78, 91, 92 and 106 were selected and the optimal regression model (multiple linear regression with mean-centring) was found using an automated design of experiments approach to calibration model selection. It was discovered that the linearity of the response allowed excellent calibration to be performed using only four standards (at 0 and 110 mg kg−1 for each of the three analytes) and that there were minimal inter-analyte interferences. The detection limit of benzene, toluene and o-xylene was 0.5, 0.8 and 0.5 mg kg−1, respectively. Average differences between the actual and predicted concentrations, expressed as a percentage of the actual concentrations, for 27–82 mg kg−1 of benzene, toluene and o-xylene were 0.5–1.4%, 0.0–0.4% and 0.3–1.6%, respectively, while the average relative standard deviations were 1.3–2.6%, 1.0–2.5% and 1.1–2.3%, respectively. Detection of 3 mg kg−1 changes in the concentration of each of the analytes (at the 36 mg kg−1 level) was also demonstrated, indicating the sensitivity of the technique and the potential ability of the procedure to detect minor deviations in the specification of process streams from continuous analysis.

The chemical and morphological transformations of condensed phase species of a thorium-based modifier were studied over the temperature range 200–2500 °C, without and with the presence of aluminium and silicon as matrix components, and in some instances, arsenic as an analyte element. A similar study was also conducted with palladium as the modifier, for comparison. Results were derived using scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry, Raman microanalysis and attenuated total reflectance (ATR) Fourier transform-infrared (FT-IR) spectrometry. Comparable results were found using pyrolytic and non-pyrolytic graphite platforms, with processes occurring at slightly higher temperatures on the pyrolytic graphite platform. With thorium as the modifier, metal oxides were the predominant species on the platform surface at relatively low temperatures (<1500 °C), whereas metal phases became prevalent at high temperatures, when thorium and aluminium tended to behave independently from one other. Some spatial variations in the composition of the salt residues on different regions of the platform were observed (from the region closest to the slot in the tube, to the region furthest from the slot). Nonetheless, thorium metal remained on the graphite platform to higher temperatures than did aluminium metal. In the presence of arsenic, the existence of mixtures of thorium and arsenic oxides, just before the appearance temperature of gas phase arsenic atoms, was confirmed by SEM studies, ED X-ray spectra and Raman microanalysis. This suggests that any modifying effect of thorium on arsenic occurs while the modifier is in the oxide phase rather than in the metal phase. The presence of silicon added as silica, did not influence significantly the thermochemical behaviour of mixtures of thorium and aluminium. However, coexistence of silicon and arsenic oxides at the appearance temperature of the atomic absorption signal of arsenic was obtained, confirming that silicon can act as an internal modifier for arsenic. In the presence of palladium, aluminium exhibited greater interaction with the modifier; consequently, aluminium metal was retained on the platform surface to higher temperatures than thorium, which could explain how interference effects of aluminium on e.g. arsenic are avoided or reduced. Similarly, there was evidence for interaction of palladium and arsenic in the reduced state. However, when aluminium and silicon were present, the transformation of the palladium oxide to the metallic state was affected, which could diminish the modifying benefits of palladium for arsenic in the presence of aluminium.