Wide Area Illumination Scheme Research Articles

Dual-wavelength wide area illumination Raman difference spectroscopy for remote detection of chemicals.

Remote Raman instruments have become powerful analytical tools in some special environments. However, ambient daylight is the main limitation in the data acquisition process. To suppress daylight background interference and obtain a high signal-to-background ratio (SBR), we develop a dual-wavelength wide area illumination Raman difference spectroscopy (WAIRDS) system for daytime remote detection. In the WAIRDS system, a wide area illumination scheme and shifted-excitation Raman difference spectroscopy method are used to improve the reliability of collected Raman spectra. Measurements of polystyrene indicate that the WAIRDS system can be operated to obtain background-free Raman spectra under different levels of daylight background interference. The remote results show that the improvement in SBR is about three- to fivefold, and the system can work at distances of up to 9.2 m on a sunny afternoon. Moreover, to be close to the actual detection, the system is used for mineral and explosive raw material detection during daytime measurement. Measurements show that the WAIRDS system will be a useful tool for many remote applications in the future.

At‐Line Raman Spectroscopy Determination of Tablet Mass Gains during the Tablet Coating Process

The coating process in the manufacturing of solid dosage forms is important for optimizing therapeutic efficacy because the coating is vital for controlling the drug release rate. The coating is most commonly applied by spraying a solution containing the coating material to form a film. In this study, core tablet samples were collected at regular intervals from four batches made using a scale‐up manufacturing coating process, and the Raman spectra were obtained to determine the mass increase of the coated tablets. To acquire the spectra, a wide area illumination scheme was used to sample a large area (28.3 mm2) with a 785‐nm laser. Additionally, we established a calibration model using the Raman spectra of three tablet batches and verified the accuracy of the model by predicting the tablet weights of a fourth batch. All spectra were preprocessed with baseline correction and normalization. The spectral range was 1700 to 300 cm−1, and partial least squares analysis was performed to establish a model with full cross‐validation. The accuracy was assessed by comparing the difference between the predicted weights using the model and that measured on an analytical balance, which was the reference test method. Standard error of cross‐validation (SECV) values and standard error of prediction (SEP) values for the fourth batch were 0.0023 and 0.0020 g, respectively, showing high accuracy. We established four optimal models that encompassed all combinations of different batches in a workplace environment and verified them by predicting each of the remaining batches.

Wide area coverage Raman spectroscopy for reliable quantitative analysis and its applications

This review summarizes recent studies to improve sample representation in Raman measurement by covering a large area of a sample in spectral collection. Three different schemes have been mainly investigated to fulfill the goal: (1) averaging of Raman spectra collected at many different locations on a sample, (2) rotation of a sample during spectral collection and (3) simultaneous wide area illumination (WAI) for spectral collection. The use of a wide area illumination scheme, simultaneously illuminating a laser over a large area for spectral acquisition without any further assistance such as sample rotation, has increased in diverse fields. Applications employing the WAI scheme in pharmaceutical, polymer/chemical/petrochemical and other areas are described in this review.

Non-destructive determination of TiO 2 concentration in cream formulation using Raman spectroscopy

The concentration of TiO 2 in a cream formulation has been non-destructively measured using Raman spectroscopy without further sample pretreatments. The distribution of TiO 2 particles in a highly viscous cream may not be homogeneous on a microscopic scale and local aggregation of the particles is possible; therefore, acquisition of Raman spectra capable of representing the whole sample identity rather than the localized chemical information was critically necessary to ensure reliable quantitative analysis. A wide area illumination (WAI) scheme, applying 6-mm diameter laser illumination area (total coverage: 28.3 mm 2) on a sample, was used to achieve representative sample presentation and improved accuracy. When Raman spectra were collected for the same sample using a conventional scheme with a much smaller laser spot (∼100 μm), the spectral reproducibility was degraded, as expected. The local aggregation of TiO 2 particles was confirmed by analyzing both SEM (scanning electron microscopy) and Raman images of a cream sample. When the WAI scheme was used, the resulting error in the determination of TiO 2 concentration was 0.03 wt%, while 0.17 wt% in the case of using the conventional scheme. The proposed Raman scheme would be advantageous over the conventional titration method that requires destructive incineration of the organic cream matrix, as well as a large consumption of chemical reagents.

Wide area illumination Raman scheme for simple and nondestructive discrimination of seawater cultured pearls

AbstractRaman spectroscopy, along with discriminant partial least squares (PLS), was successfully used to discriminate among three different groups of cultured pearls (fresh water, Akoya and South seawater). The discrimination between Akoya and South seawater pearls using XRF (X‐ray fluorescence), one of the most frequently adopted analytical methods in pearl analysis, has been especially difficult owing to their similar mineral compositions. The selective Raman features helped in effectively discriminating between these two pearl groups. The difference in the intensities of the CaCO3 bands of Akoya and South seawater pearls provided a valuable clue. Along with the selective Raman feature, a reproducible Raman spectral collection achieved using a wide area illumination (WAI) scheme played an important role in the determination of the pearl groups, although the pearls were hard‐surfaced, round, solid samples of different sizes and surface shapes. Unwanted spectral variation originating from sensitivity to sample placement relative to the focal plane and from unsuccessful sample representation due to the probing of a localized area, factors that could possibly deteriorate Raman reproducibility, were substantially lessened using the WAI scheme. ATR (attenuated total reflection) IR spectroscopy requiring direct contact with the pearl could be inadequate for discrimination or classification where large numbers of repeating and reproducible measurements are required. Copyright © 2009 John Wiley & Sons, Ltd.

Comparison of near-infrared and Raman spectroscopy for the determination of the density of polyethylene pellets

In this study, we compare near-infrared (NIR) and Raman spectroscopy for the determination of the density of linear low density polyethylene (PE) (in a pellet form). As generally known, Raman spectral features are more selective than those of NIR for most chemical samples. NIR spectroscopy has been more extensively used for the quantitative analysis of polymers, but Raman spectroscopy is the better choice as long as the problem of reproducibility of Raman measurements (especially for solid samples), mostly resulting from insufficient sample representation due to probing only localized chemical information and the sensitivity of sample placement with regard to the focal plane, can be overcome. To improve sample representation and reproducibility of Raman measurements, we have employed the wide area illumination (WAI) Raman scheme, capable of illuminating a laser onto a large sample area (28.3 mm 2) for Raman spectral collection (a 6-mm laser spot with a focal length of 248 mm). Diffuse reflectance NIR spectra of PE pellets were collected using a sample moving system which allowed for the scanning of large areas. The prediction error was 0.0008 g cm −3 for Raman spectroscopy and 0.0011 g cm −3 for NIR spectroscopy. The harmonization of inherently selective Raman features and a reproducible spectral collection with correct sample representations using the WAI scheme led to an accurate determination of the density of the PE pellets.

Improving Raman spectroscopic differentiation of the geographical origin of rice by simultaneous illumination over a wide sample area

AbstractThis research substantially improved the differentiation of rice of two geographical origins utilizing a wide area illumination (WAI) scheme capable of collecting Raman spectra of a large sample area (28.3 mm2) synchronously without sample rotation. For the purposes of comparison, we also employed a conventional scheme in which the laser illuminated only small areas. Principal component analysis (PCA) was used to differentiate the two geographical origins using the Raman spectra collected through both the conventional and the WAI schemes. The WAI scheme exhibited improved differentiation, primarily due to the fact that the WAI scheme could efficiently produce Raman spectra with a more reliable sample representation, as well as better reproducibility. The spectral feature obtained using the conventional scheme appeared to be more variable; however, this variation resulted more from unsuccessful sample representation than from an actual change in the sample composition. We conclude that the WAI scheme has a good potential for the analysis of diverse agricultural samples that consist of solid granules. Copyright © 2008 John Wiley & Sons, Ltd.

Robust Raman measurement of hydrogen peroxide directly through plastic containers under the change of bottle position and its long-term prediction reproducibility

Hydrogen peroxide concentration in antiseptic solutions has been non-destructively measured with the use of wide area illumination (WAI) scheme by applying a laser beam directly through a plastic container. The prediction accuracy was comparable to that from the use of quartz cell instead of a plastic bottle as well as near-infrared (NIR) prediction result in the previous study. Although the position of a plastic bottle was artificially changed in three-dimensional directions up to ±10 mm to simulate real situation of practical measurement, the prediction accuracy was not degraded within ±5 mm positional variation. This robust prediction performance was powered by the merits of WAI scheme that could provide improved reproducibility by illuminating large sample areas as well as less sensitivity of sample placement by the design of long focal length. Moreover, the prediction accuracy was successfully maintained over a long period of time. Finally, the prediction was also reproducible under the situation of laser power variation. The overall results demonstrate that WAI Raman scheme can provide robust and non-destructive quantitative analysis for not only hydrogen peroxide in antiseptic solution, but also other active pharmaceutical ingredients in diverse containers.

Direct, non-destructive quantitative measurement of an active pharmaceutical ingredient in an intact capsule formulation using Raman spectroscopy

The active pharmaceutical ingredient (ambroxol) in an intact capsule formulation has been non-destructively quantified using Raman spectroscopy. To improve the problem of insufficient representive sampling inherent in Raman measurements, we have employed a wide area illumination (WAI) scheme that enables much improved sample coverage through a circular excitation laser spot with a 6 mm diameter. One of the anticipated sources of variation for this measurement was variation in the capsule shells. However, the WAI scheme significantly decreased the spectral variation among empty capsules compared to a measurement with a traditional small-spot excitation. Therefore, measurement variations emanating from the capsule shell did not significantly influence the accuracy of the determination of ambroxol concentrations. The resulting standard error of prediction (SEP) using the WAI scheme was comparable to that from previous Raman measurements which used a conventional small-spot excitation and employed a sampling scheme that involved rotation of an ambroxol pellet. It is further noteworthy that the SEP was also similar to that obtained from the use of transmission NIR spectroscopy, which was achieved by collection of spectra of the powdered capsule contents removed from the shell. The proposed Raman measurement using the WAI scheme in this case was sufficient to achieve the quantitative measurement of the active pharmaceutical ingredient (API) content of capsules non-destructively.

Feasibility of a Wide Area Illumination Scheme for Reliable Raman Measurement of Petroleum Products

A newly developed Raman collection scheme, a wide area illumination (WAI) scheme, was employed to demonstrate its utility for the analysis of petroleum products. For this purpose, the compositional analysis of simulated naphtha samples was attempted. The WAI scheme utilized a laser beam that illuminated a sample in a circular fashion with a diameter of 6 mm and a focal length of 250 mm. The reproducibility of the Raman measurement can be improved due to decreased sensitivity of the sample position as well as orientation with regard to the focal plane, as shown in a previous study. Near-infrared (NIR) spectroscopy, widely adopted in the field of petroleum refining, was also employed to compare with the prediction results obtained using the WAI scheme. Since the Raman spectral feature is more distinct and selective, the resulting calibration accuracy could be improved as long as reproducible Raman spectra could be collected. Overall prediction results using Raman spectroscopy were superior to those from NIR spectroscopy. The feasibility of the WAI scheme for reliable Raman analysis of petroleum products such as naphtha was demonstrated in this paper.

Reliable and fast quantitative analysis of active ingredient in pharmaceutical suspension using Raman spectroscopy

The concentration of acetaminophen in a turbid pharmaceutical suspension has been measured successfully using Raman spectroscopy. The spectrometer was equipped with a large spot probe which enabled the coverage of a representative area during sampling. This wide area illumination (WAI) scheme (coverage area 28.3 mm 2) for Raman data collection proved to be more reliable for the compositional determination of these pharmaceutical suspensions, especially when the samples were turbid. The reproducibility of measurement using the WAI scheme was compared to that of using a conventional small-spot scheme which employed a much smaller illumination area (about 100 μm spot size). A layer of isobutyric anhydride was placed in front of the sample vials to correct the variation in the Raman intensity due to the fluctuation of laser power. Corrections were accomplished using the isolated carbonyl band of isobutyric anhydride. The acetaminophen concentrations of prediction samples were accurately estimated using a partial least squares (PLS) calibration model. The prediction accuracy was maintained even with changes in laser power. It was noted that the prediction performance was somewhat degraded for turbid suspensions with high acetaminophen contents. When comparing the results of reproducibility obtained with the WAI scheme and those obtained using the conventional scheme, it was concluded that the quantitative determination of the active pharmaceutical ingredient (API) in turbid suspensions is much improved when employing a larger laser coverage area. This is presumably due to the improvement in representative sampling.

A new non-invasive, quantitative Raman technique for the determination of an active ingredient in pharmaceutical liquids by direct measurement through a plastic bottle

The concentration of an active pharmaceutical ingredient (povidone) in a commercial eyewash solution has been measured directly through a plastic (low-density polyethylene: LDPE) container using a wide area illumination (WAI) Raman scheme. The WAI scheme allows excitation using a 6 mm laser spot (focal length: 248 mm) that is designed to cover a wide sample area. As a result, it has the potential to improve the reliability Raman measurements by significantly enhancing representative sample interrogation, thus improving the reproducibility of sampling. It also decreases the sensitivity of sample placement with regard to the excitation focal plane. Simultaneously, isobutyric anhydride was placed in front of the bottles to use for a synchronous external standard configuration. This helps to correct the problematic variation of Raman intensity from the inherent fluctuation in laser power. Using the WAI Raman scheme combined with the synchronous standard method, the povidone concentration was successfully measured with spectral collection that was performed through a plastic barrier. The conventional Raman scheme was difficult to employ for the same purpose because of the degraded spectral reproducibility resulting from the smaller laser illumination area and the sensitivity of such an approach to the position of the sample bottle. The result from this study suggests that the WAI scheme exhibits a strong potential for the non-destructive quantitative analysis of pharmaceuticals measured directly in plastic containers. Preliminary work also shows that similar measurements can also be made in glass bottles. If implemented, this technique could be utilized as a simple and rugged method for quality assurance of final products in a manner consistent with Process analytical technology (PAT) requirements.

A new quantitative Raman measurement scheme using Teflon as a novel intensity correction standard as well as the sample container

AbstractA novel and reliable quantitative Raman measurement scheme has been proposed for the analyses of ethanol and isopropanol solutions. Teflon tubing was employed as an effective intensity correction standard as well as the sample cell. This allowed for the synchronous collection of the mixed Raman spectrum from the Teflon standard and the sample without any extra optical configuration. A non‐overlapping Teflon band was used as the standard peak to correct the Raman intensity changes resulting from laser power variations. In addition to the use of Teflon tubing,a wide area illumination (WAI) scheme was employed, which made the laser illumination into a circle of 6 mm diameter (area: 28.7 mm2), to cover a wide sample area. The WAI scheme improved the reliability of the Raman measurement by significantly increasing the reproducibility of the sampling owing to a decreased sensitivity to sample placement with respect to the focal plane as well as a wider sample coverage area. The resulting Raman spectra were more reproducible and more representative of the correct sample composition. Overall, a superior prediction performance was achieved using the WAI scheme compared to the conventional Raman collection method. The proposed system has great potential for use in the quantitative analysis of diverse liquid samples with good reproducibility. Copyright © 2006 John Wiley & Sons, Ltd.

New reliable Raman collection system using the wide area illumination (WAI) scheme combined with the synchronous intensity correction standard for the analysis of pharmaceutical tablets

A novel and reliable Raman collection system for the non-destructive analysis of pharmaceutical tablets has been proposed. The main idea was to develop and utilize the wide area illumination (WAI) scheme for Raman collection to cover a large surface area (coverage area: 28.3 mm 2) of solid tablet to dramatically improve the reliability in sample representation and the reproducibility of sampling due to less sensitivity of sample placement with regard to the focal plane. Simultaneously, the effective and synchronous standard configuration using isobutyric anhydride was harmonized with the WAI scheme to correct the problematic variation of Raman intensity from the change of laser power. To verify the quantitative performance of the proposed scheme, the compositional analysis of active ingredient in naproxen tablet has been performed. The average sample composition was successfully represented by using the WAI scheme compared to the conventional scheme with a much smaller illumination area. After the intensity correction using the non-overlapping peak of isobutyric anhydride standard and area normalization, a partial least squares (PLS) model was developed using an optimized spectral range and the concentrations of naproxen in tablets were accurately predicted. The prediction accuracy was not sensitive to changes in laser power or tablet position within ±2 mm. Additionally, the prediction accuracy was repeatable without systematic drift or need for re-calibration.