Accurate reflectance measurements in the infrared spectral range using an integrating sphere

An integrating sphere is used together with a Fourier transform spectrometer for directional-hemispherical reflectance measurements in the spectral range from 1m to 15m. Comparisons with PTB's fundamental sphere reflectometer around 1m show that the uncertainty of the infrared measurements is ±0.01.     

Infrared regular reflectance and transmittance instrumentation and standards at NIST

Instrumentation is described that has been constructed at the National Institute of Standards and Technology (NIST) for the measurement of regular reflectance and transmittance over the 2–25 μm wavelength region. This includes both specialized accessories used with Fourier-transform infrared (FT-IR) spectrometers and laser-based systems for high optical density transmittance measurements. The FT-IR systems have been used to develop standard reference materials for IR regular transmittance.     

Rapid determination of aluminum by UV-vis diffuse reflectance spectroscopy with application of suitable adsorbents

Diffuse reflectance spectroscopy (DRS) can be used as a rapid and sensitive method for the quantitative determination of low amounts of aluminum. In this analytical technique, the analyte in samples are extracted onto a solid sorbent matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface. Alternatively, colored aluminum complexes formed in solution can also be immobilized onto adsorbent surface and be measured by DRS technique. Octadecyl silica disk, methyltrioctylammonium chloride–naphthalene and MCM-41 were examined as adsorbents. Eriochrome cyanine R and quinalizarin were used as coloring reagents. Optimal sorption conditions were found for each system of analyte–reagent–adsorbent. The concentration of analyte is determined using the appropriate form of the Kubelka–Munk function. We obtained for each of the aluminium–reagent–adsorbent system a calibration curve by plotting the absorbance versus the log 10²[Al³⁺] μg ml⁻¹. The linear dynamic range extends over two orders of magnitude within 0.01–15 μg ml⁻¹ with little differences in the range and in the correlation coefficients among the adsorbents. We consider that for a rapid determination of aluminum a spot-test-DRS combination with a detection limit of 1.0 × 10⁻² μg ml⁻¹ is the more facile and preferred technique.     

Intercomparison of industrial near-infrared diffuse reflectance measurements

An intercomparison of diffuse reflectance measurements in the near-infrared region was carried out. Fourteen participants from industry and academia measured a number of different reflectance standards, calibrated at the NPL, over the wavelength range from 800 to 2500 nm. Measurements were made in the integrating sphere geometries, i.e. specular included and specular excluded and in the 0/45 geometry. The results of the intercomparison are presented. The raw data results showed significant variations in the value of diffuse reflectance measured across industry, in excess of 80% difference from NPL reflectance values in some cases. Renormalisation of the data to the NPL near-infrared diffuse reflectance scale significantly improved the agreement in measured values between participants, most being within 5% of the NPL values. Integrating sphere errors were present in many of the instruments used.     

Investigation of the hydrothermal stability of cross-linked liquid silicone rubber (LSR)

We investigate the hydrothermal stability of cross-linked liquid silicone rubber (LSR) in water at 100 °C up to period of two years. Optical microscopy of cross-sections of the exposed samples reveal that only the outer 100 μm of the surface layer is affected after two years. However, the surface chemistry of the material after prolonged exposure becomes significantly modified, as monitored by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR), which probes depths of 10 nm and 1 μm, respectively. In addition, changes to the bulk physical properties of the rubber samples, prior to and after the exposure, were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Micro-hardness analysis showed that surface roughness of the two year exposed sample increased from 60 (IRHD) to 75 (IRHD). Furthermore, the volume change (%) measurement showed a significant decrease in the course of exposure at prolonged time. The results provide the experimental basis for development of LSR materials suitable for numerous technical applications.     

Establishment of absolute diffuse reflectance scales using the NPL Reference Reflectometer

Absolute scales of radiance factor and diffuse reflectance are being established at the NPL using the Reference Reflectometer. In the basic instrument, a reflecting sample and a detector can be rotated about a common vertical axis to any angular positions relative to an incident light beam. The sample can also be displaced horizontally and vertically, allowing examination of its uniformity and removal for direct measurement of the incident beam. The polarization of the incident light is defined by a Rochon prism, and wavelengths are selected by means of interference filters or a double monochromator. The wavelength range has been extended into the near ultraviolet and the near infrared using UV-enhanced silicon and Peltier-cooled InGaAs photodiodes.

For absolute measurement of radiance factor, the light reaching the detector passes through a circular aperture whose diameter and distance from the reflecting surface are determined. The flux distribution is made closely similar when observing the incident beam and the reflected beam. Diffuse reflectance is then derived by numerical integration of results over a full hemisphere, avoiding errors due to nonuniformity of an integrating sphere and giving a direct link between radiance factor and diffuse reflectance scales.     

Spectrophotometric simultaneous determination of nitroaniline isomers by orthogonal signal correction-partial least squares

The simultaneous determination of nitroaniline isomer mixtures by using spectrophotometric methods is a difficult problem in analytical chemistry, due to spectral interferences. By multivariate calibration methods, such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removes the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for partial least squares calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 200–500 nm range for 21 different mixtures of nitroaniline isomers. Calibration matrices were containing 1–21, 1–15 and 1–18 μg ml⁻¹ of m-nitroaniline, o-nitroaniline and p-nitroaniline, respectively. The RMSEP for m-nitroaniline, o-nitroaniline and p-nitroaniline with OSC and without OSC were 0.6567, 0.2692, and 0.3134, and 1.3818, 1.2181, and 0.3953, respectively. This procedure allows the simultaneous determination of nitroaniline isomers in real matrix samples and good reliability of the determination was proved.     

Fast sample preparation involving MASE and coupled column normal phase liquid chromatography for the rapid trace analysis of dioxins in air-dust samples from fire catastrophe emissions

A new approach has been developed and tested for the urgent analysis of dioxins in samples of air-dust filters originating from catastrophe emissions. The procedure consists of a fast extraction of the sample with microwave solvent extraction (MASE) and acetone as solvent followed by a fast cleanup of the extract with normal phase coupled column liquid chromatography (LC/LC).

The multi-dimensional LC/LC system employs a 50 mm×4.6 mm i.d. column packed with 3 μm silica and a 150 mm×4.6 mm i.d. column packed with 5 μm PYE as the first and second analytical column, respectively. Iso-hexane is used on both columns to perform cleanup and dichloromethane to perform efficient back-flush elution of the compounds from the second column. The obtained polarity-based separation in the first dimension and molecular-structure based separation in the second dimension provides a fast and powerful cleanup.

Validation was done by analysing samples of homemade RIVM air-dust with aged residues (n=8, spiking level about 15 pg mg⁻¹ per compound) of dioxins/furans and samples of reference Urban Dust SRM 1649a (n=4) with both the new approach and the existing conventional procedure and were instrumentally analyzed with capillary gas chromatography and high resolution mass spectrometric detection (GC/HRMS).

In comparison to the existing conventional procedure, the new approach reduces sample processing from several days to several hours per sample.

As regards the aged-residue air-dust samples, the new method shows a good accuracy, precision and high selectivity providing a performance in good agreement with the existing procedure. In SRM air-dust, the concentration of a few compounds obtained by the new method was below (10–50%) the certified value.     

Instrumentation, standards, and procedures used at the National Research Council of Canada for high-accuracy fluorescence measurements

This paper describes the two-monochromator reference spectrofluorimeter, calibration standards, and procedures used at the National Research Council of Canada for performing high-accuracy fluorescence measurements over the spectral range 250–1050 nm. The basic measurement principles of the two-monochromator method and the calibration procedures used to determine the instrument spectral characteristics are described in detail. The instrumental set-ups, data acquisition procedures, and representative results for the measurement of reflected and bispectral luminescent radiance factors and calculation of total radiance factors are graphically illustrated in a step-by-step fashion for a typical red fluorescent material. The measurement performance of this instrument is demonstrated for several applications, including customer-supplied source data, paper, paint and textile samples.     

Tests of an omnipresent standard for absolute spectral radiance measurements

Correlated pairs of photons can be used to access what is effectively an omnipresent absolute standard of spectral radiance. The process of spontaneous parametric downconversion, in which pump photons are converted into pairs of photons, can be thought of as being stimulated by an omnipresent and omnidirectional one photon per mode vacuum background. This background has units of spectral radiance and can be expressed in terms of fundamental constants. An unknown radiance can be determined by comparison to this background radiance. The comparison is made by adding the unknown radiance into downconversion process so as to stimulate the downconversion process over that level produced by the vacuum background only. This is done by inputting the unknown radiance into the system so as to overlap spatially and spectrally a portion of the output light. The process is monitored, not by observing the input light beam, but by observing only the light correlated to that unknown radiance. (This makes possible an additional advantage of this measurement technique; it allows IR radiance to be measured by monitoring a visible beam.) The ratio of the increase in the correlated signal is the absolute spectral radiance of the unknown source expressed in units of photons per mode. Initial studies of feasibility and accuracy have been performed. IR radiance has been measured to wavelengths of 5 μm with better than 3% uncertainty. We present the status of work to further improve the uncertainty of this method.     

Preparation and properties of inhalable nanocomposite particles: effects of the temperature at a spray-dryer inlet upon the properties of particles

To overcome the disadvantages both of microparticles and nanoparticles for inhalation, we have prepared nanocomposite particles as drug carriers targeting lungs. The nanocomposite particles having sizes about 2.5 μm composed of sugar and drug-loaded PLGA nanoparticles can reach deep in the lungs, and they are decomposed into drug-loaded PLGA nanoparticles in the alveoli. Sugar was used as a binder of PLGA nanoparticles to be nanocomposite particles and is soluble in alveolar lining fluid. The primary nanoparticles containing bioactive materials were prepared by using a probe sonicator. And then they were spray dried with carrier materials, such as trehalose and lactose. The effects of inlet temperature of spray dryer were studied between 60 and 120 °C and the kind of sugars upon properties of nanocomposite particles. When the inlet temperatures were 80 and 90 °C, nanocomposite particles with average diameters of about 2.5 μm are obtained and they are decomposed into primary nanoparticles in water, in both sugars are used as a binder. But, those prepared above 100 °C are not decomposed into nanoparticles in water, while the average diameter was almost 2.5 μm. On the other hand, nanocomposite particles prepared at lower inlet temperatures have larger sizes but better redispersion efficiency in water. By the measurements of aerodynamic diameters of the nanocomposite particles prepared with trehalose at 70, 80, and 90 °C, it was shown that the particles prepared at 80 °C have the highest fine particle fraction (FPF) value and the particles are suitable for pulmonary delivery of bioactive materials deep in the lungs. Meanwhile the case with lactose, the particles prepared at 90 °C have near the best FPF value but they have many particles larger than 11 μm.     

Serial filter method for fluorescence evaluation

A method has been developed to obtain the reflective spectral data, β_R(λ), for a fluorescent sample by making a simple modification to a conventional poly-chromatically illuminated spectrophotometer. To use this procedure, a series of sharp cut-off filters are inserted successively into the illumination beam of the instrument to obtain a number of spectral curves from which the complete reflectance curve is constructed piece-wise. The calculation of the complete reflectance curve is done wavelength-by-wavelength, starting at about 30 nm above the peak emission of the sample and proceeding toward the shortest wavelength cut-off filter, selecting the spectral data that are the lowest value. When the data from each filter are assembled, the long wavelength portion above the peak emission is made equal to the unmodified spectrum. Examples are given of the method of computation and comparison with bi-spectral data. The serial filter technique is equally applicable to instruments having either 45/0 or d/8 integrating sphere optical geometry.     

Solvent-induced swelling of membranes — Measurements and influence in nanofiltration

This paper describes improvements to an apparatus for in-situ determinations of swelling where a linear inductive probe and electronic column gauge with an overall resolution of 0.1 μm was used for measurements of seven variants of polyacrylonitrile (PAN)/polydimethylsiloxane (PDMS) composite nanofiltration membranes in a range of alkane, aromatic and alcohol solvents. The unswollen membranes incorporated PDMS layers between 1 and 10 μm nominal thickness and were manufactured with a radiation and/or thermal crosslinking step.

The tested membranes exhibited a range of swelling dependent on the degree of crosslinking, the initial PDMS layer thickness and the type of solvent. With no applied pressure the PDMS layer on some radiation cross-linked membranes swelled as much as 170% of the initial thickness whilst other membranes were restricted to a maximum swelling of 80%. When a pressure up to 2000 kPa was applied to a membrane then swelling could be reduced to 20% of the value obtained at zero applied pressure. By vertically stacking up to three membrane samples it was possible to determine the swelling of PDMS layers as thin as 1 μm, although higher imposed pressures rendered some results unreliable as the measurement resolution of the apparatus was approached. The results of the swelling experiments are contrasted with crossflow nanofiltration performance in terms of solvent flux and solute rejection.     

Feasibility of using solid sampling graphite furnace atomic absorption spectrometry for speciation analysis of volatile and non-volatile compounds of nickel and vanadium in crude oil

A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L⁻¹ Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g⁻¹, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test.     

Hydrogen peroxide in basic media for whole blood sample dissolution for determination of its lead content by electrothermal atomization atomic absorption spectrometry

Hydrogen peroxide in basic media is proposed as a means for dissolving whole blood samples to be analyzed by electrothermal atomization atomic absorption spectrometry, ET AAS. Approximately 2 g of the whole blood sample were directly weighed in a 150 mL volumetric flask; 3 mL of a NaOH 0.2 mol L⁻¹ solution, two drops of 1-octanol, as an antifoaming agent, and 1 mL of 30% volume hydrogen peroxide were added to the flask to promote oxidation. The solution was then manually shaken and after approximately three minutes of shaking, a clear solution, with no apparent suspended solids or greasy layers, was obtained. Distilled-deionized water was used to complete the volume. Ten μL of the resulting solution along with 10 μL of a solution containing 5000 mg L⁻¹ of NH₄H₂PO₄ and 300 mg L⁻¹ of Mg(NO₃)₂ as a modifier, were injected into transversely heated graphite tubes for lead determination. Both aqueous standards and standard addition calibration curves produced results not significantly different at a 95% confidence limit level. Accuracy of the measurements was assessed by analysis of the IAEA A-13 (concentration of trace and minor elements in freeze dried animal blood) standard reference material containing 0.18 mg L⁻¹ lead on a dry basis and by means of recovery tests. Analysis of the IAEA A-13 standard produced 0.17 ± 0.02 mg L⁻¹ lead on a dry basis; recovery tests afforded values from 95 to 105%. Ten consecutive measurements of a 5 ppb lead solution gave a characteristic mass of 47.2 pg and a (3S) detection limit of 1.77 μg L⁻¹ Pb. Results obtained from analysis of whole blood samples of volunteer donors covered a lead concentration range between 8 and 21 μg L⁻¹ with a mean value of 11.9 ± 4.7 μg L⁻¹.     

A new immune resonance scattering spectral assay for trace fibrinogen with gold nanoparticle label

An on-line stacking method based on moving reaction boundary (MRB) was developed for the sensitive determination of barbital and phenobarbital in human urine via capillary electrophoresis (CE). The optimized conditions for the method are: 60 mmol L⁻¹ pH 11.0 Gly–NaOH as the background electrolyte, 10 mmol L⁻¹ pH 5.5 Gly–HCl as sample buffer, secobarbital as the internal standard (IS), 12.5 kV, 1.4 psi 10 s sample injection, 75 μm ID 60.2 cm total length (50 cm effective length) capillary and 214 nm detect wavelength. Under the optimized conditions, the method can well stack and separate barbital and phenobarbital in urine samples and result in 20.5-fold and 22.6-fold improvement in concentration sensitivity for barbital and phenobarbital, respectively. Furthermore, the method holds: (1) good linear calibration functions for the two target compounds (correlation coefficients r > 0.999), (2) low limits of detection (0.27 μg mL⁻¹ for barbital and 0.26 μg mL⁻¹ for phenobarbital), (3) low limits of quantification (0.92 μg mL⁻¹ for barbital and 0.87 μg mL⁻¹ for phenobarbital), (4) good precision (R.S.D. of intra-day and inter-day less than 5.38% for barbital and 1.67% for phenobarbital, respectively) and (5) high recoveries at three concentration levels (90.27–106.36% for barbital and 93.05–113.60% for phenobarbital in urine). The method is simple, sensitive and efficient, and can fit to the need of clinical and forensic toxicology.     

Determination of arsenic, lead, selenium and tin in sediments by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry using Ru as permanent modifier and NaCl as a carrier

A procedure for the determination of As, Pb, Se and Sn in sediment slurries by electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The slurry, 1 mg ml⁻¹, is prepared by mixing the sample ground to a particle size 50 μm with 5% v/v nitric and 1% v/v hydrofluoric acids in an ultrasonic bath. The slurry was homogenized with a constant flow of argon in the autosampler cup, just before transferring an aliquot to the graphite furnace. The tube was treated with Ru as a permanent modifier, and an optimized mass of 1 μg of NaCl was added as a physical carrier. The pyrolysis temperature was optimized through pyrolysis curves, and a compromised temperature of 800 °C was used; the vaporization temperature was 2300 °C. The effect of different acid concentrations in the slurry on the analyte signal intensities was also evaluated. The accuracy of the method was assured by the analysis of certified reference sediments MESS-2, PACS-2 and HISS-1 from the National Research Council Canada, SRM 2704 and SRM 1646a from the National Institute of Standards and Technology and RS-4 from a round robin test, using external calibration with aqueous standards prepared in the same medium as the slurries. The obtained concentrations were in agreement with the certified values according to the Student's t-test for a confidence level of 95%. The detection limits in the samples were: 0.17 μg g⁻¹ for As; 0.3 μg g⁻¹ for Pb; 0.05 μg g⁻¹ for Se and 0.28 μg g⁻¹ for Sn. The precision found for the different sediment samples, expressed as R.S.D. was 1–8% for As, 2–9% for Pb, 6–12% for Se and 3–8% for Sn (n=5).     

Biosorption of heavy metals on Aspergillus fumigatus immobilized Diaion HP-2MG resin for their atomic absorption spectrometric determinations

A solid phase extraction procedure based on biosorption of copper(II), lead(II), zinc(II), iron(III), nickel(II) and cobalt(II) ions on Aspergillus fumigatus immobilized Diaion HP-2MG has been investigated. The analytical conditions including amounts of A. fumigatus, eluent type, flow rates of sample and eluent solutions were examined. Good recoveries were obtained to the spiked natural waters. The influences of the concomitant ions on the retentions of the analytes were also examined. The detection limits (3sigma, N = 11) were 0.30 μg l⁻¹ for copper, 0.32 μg l⁻¹ for iron, 0.41 μg l⁻¹ for zinc, 0.52 μg l⁻¹ for lead, 0.59 μg l⁻¹ for nickel and 0.72 μg l⁻¹ for cobalt. The relative standard deviations of the procedure were below 7%. The validation of the presented procedure is performed by the analysis of three standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 1515 Apple leaves and GBW 07605 Tea). The procedure was successfully applied for the determination of analyte ions in natural waters microwave digested samples including street dust, tomato paste, black tea, etc.     

Measurement of diffuse reflectance from combinatorial samples

Using a luminescence spectrometer as a platform, a system of fibre-optic probes was created that allows full colour characterisation, fluorescence and phosphorescence spectra to be recorded in diffuse reflectance and in transmission from thick or thin film arrays of combinatorial samples of diameter down to 2 mm and from liquids. An integrating sphere is not required and the method is more versatile than the instrument's fibre-optic plate reader which has conjoined fibre bundles set at a fixed angle. Incident and detected light is routed via separate optical fibre bundles which remain stationary above or below a two-axis table. The validation and calibration are described. A library of 25 members was scanned for both diffuse reflectance (colour) and fluorescence in less than an hour. The method thus combines techniques that conventionally rely on different instruments and makes them amenable for high throughput libraries.     

Sequential injection spectrophotometric determination of trace amounts of iodide by its catalytic effect on the 4,4'-methylenebis(N,N-dimethylaniline)-chloramine-T reaction

A simple and sensitive sequential injection spectrophotometric procedure is proposed for the determination of trace amounts of iodide in pharmaceutical preparations. The method is based on the catalytic effect of iodide on the (tetra base) 4,4′-methylenebis(N,N-dimethylaniline)-chloramine-T reaction in acidic solution. The method involves a sequential aspiration of 255 μl sample/standard followed by 170 μl tetra base and then 128 μl chloramine-T solutions into a carrier stream to be stacked inside a holding coil and flow reversed through a reaction coil towards a detector. The resulting colored compound is measured at 600 nm using an UV/Vis-spectrophotometer. All the parameters that affect the reaction were evaluated and the calibration curve is linear over a range of 0.1–6.0 μg l⁻¹ of iodide concentration with detection limit of 0.05 μg l⁻¹. A sample throughput of 80 samples per hour and relative standard deviation of less than 2.0% was achieved. The method is successfully applied for the determination of iodide in three different samples (tablets).