Compositional mapping of mixed gels using FTIR microspectroscopy

Durrani, C. Matin; Donald, Athene M.

doi:10.1016/0144-8617(95)00107-7

Cited by 20 publications

(6 citation statements)

References 7 publications

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“…While the technique presented here is capable of studying polymer concentration profiles in macroscopically large objects (on the millimeter scale), other techniques such as confocal Raman spectroscopy [13][14][15] or Fourier transform infrared (FT-IR) microscopy 31 allow the study of structures on the micrometer level with improved spatial resolution. However, for macroscopically large structures such as the inhomogeneity of 4 mm alginate beads investigated here, a microscopic technique would not have been adequate.…”

Section: Resultsmentioning

confidence: 99%

Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

Heinemann¹,

Meinberg

Büchs

et al. 2005

Appl Spectrosc

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A new method based on Raman spectroscopy is presented for non-invasive, quantitative determination of the spatial polymer distribution in alginate beads of approximately 4 mm diameter. With the experimental setup, a two-dimensional image is created along a thin measuring line through the bead comprising one spatial and one spectral dimension. For quantitative analysis of the Raman spectra, the method of indirect hard modeling was applied to make use of the information contained in the entire recorded spectra. For quantification of the alginate signals from within the beads, a calibration curve acquired from sodium alginate solutions was used after it was shown that only negligible differences occur between signals from alginate solutions and alginate gels. The distribution of alginate over the bead gel matrix was acquired with high spatial (51 microm) and time (12 s) resolution. The inhomogeneous distribution obtained using the new measuring technique is qualitatively in excellent agreement with data from the literature. In contrast to known measuring techniques, correct quantitative information about the spatial polymer distribution within the matrix was derived. It gave an alginate mass fraction of approximately 0.045 g/g at the edges and 0.02 g/g in the center of the beads. Next to the determination of mere polymer concentrations, the excellent time resolution of the presented method will enable investigation of the dynamic process of gel formation and it will also serve as a basis for investigation of mass transfer of small diffusing molecules in alginate matrices.

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Section: Resultsmentioning

confidence: 99%

Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

Heinemann¹,

Meinberg

Büchs

et al. 2005

Appl Spectrosc

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“…Effective concentration measurement is, however, quite difficult and has not been widely reported or used in testing gel models. The most direct way would be spectroscopic determination applied microscopically to the individual composite phases, either in pregelling solutions or in gels, and some progress has been made in this direction using infrared 11 and Raman microscopes and confocal microscopy. 12 Where this is unavailable, however, methods have to rely on some concentration-dependent feature of the gelling process in a phase, which can be monitored during the gelling of the composite as a whole and attributed to the segregated component in that phase without ambiguity.…”

Section: Resultsmentioning

confidence: 99%

Interpenetrating Network Formation in Gellan−Maltodextrin Gel Composites

et al. 1999

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Formation of cold-set gels from mixtures of the bacterial polysaccharide gellan and the modified potato starch Paselli SA2 has been studied by mechanical spectroscopy, turbidity measurements, and confocal and transmission electron microscopy. The hot solutions gave no indication of a tendency to liquid-liquid demix over normal concentration ranges. A microphase-separated gel structure arose after a substantial period at 4 °C, but electron microscope evidence suggested aggregation of the starch polymers in a fine-pored homogeneous preformed gellan network, not simple separation of the two components into distinct gel phases. A novel method based on assessing local effective polymer concentrations during gelling, from mechanical cure curves and turbidity data, also suggested that a simple phase-separated microstructure was inappropriate, and an interpenetrating network model was able to describe shear modulus-composition data for the final gels.

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“…Thus if concentrations are required then it is necessary for the sample volume to be larger than this to get an accurate valve. The actual volume will depend on the accuracy required, but as previously estimated for infrared spectroscopy [12] it will be 2/3 times the spatial resolution. Thus as the z-resolution is limiting in this case, a particle will need to be approximately 10 µm, given no other influences.…”

Section: Spatial Resolutionmentioning

confidence: 99%

The use of confocal Raman spectroscopy to characterise the microstructure of complex biomaterials: foods

Pudney

Hancewicz²,

Cunningham

2002

Journal of Spectroscopy

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The properties and behaviour of many biomaterials often depends crucially on their microstructure. This is especially true of the largest class of biomaterials in use, foods. They include general properties, e.g., food texture, and others, such as spreadability of margarine/butter, pourablity of ketchup, scoopablity of ice cream, and also flavour release (a problem that has much in common with drug delivery), to name but a few. Thus, most food laboratories do a large amount of work in rheology and microscopy to relate structure and properties. However, a knowledge gap exists, i.e., what is the location and quantity of ingredients/molecules within a structure? Both of these questions need to be answered if a complete understanding is to be obtained. The "what is where" question can sometimes be answered by using various microscopic labelling techniques, although there can be many problems with these methods. Bulk separation is often attempted, followed by some kind of more classical analysis, but this is often either not possible or may cause some kind of uncontrolled perturbation. Thus, the ability to obtain quantitative information in situ within a microstructure has been an unobtained goal in much of food science research. These types of questions are, of course, also asked in many related fields of research. This paper will illustrate how the advances in confocal Raman spectroscopy have allowed this problem to be tackled, in a noninvasive way. It will show how careful development of experimental procedures and advances in data analysis methods, allow even quantitative maps of microstructures to be obtained. The details of this approach will be described including a discussion of the limitations of current methods, especially depth resolution, and how these were overcome. The use of these methods will be illustrated with a gelled mixture of two carbohydrate polymers, κ-carageenan and gellan. Despite being similar polymers, and hence having highly overlapping spectra, the pure spectral components can be separated using a chemometrics based method, multivariate curve resolution (MCR). The principles of this method will be described. Under certain concentration regimes these two biopolymers phase separate. This property can be used to produce different microstructures. Two different microstructures were produced and mapped using Raman spectroscopy. This data was analysed using the MCR method to show the relative locations of the two polymers within the microstructure. Furthermore, by augmenting the data from these maps with calibration data for the two bioploymers, quantitative maps were produced. The resultant concentrations can then be used to produce tie lines for the κ-carageenan/gellan phase diagram, which is essential for understanding and manipulating the structure and properties in a systematic way. This methodology can be readily extended to much more complex multicomponent systems, such as complete food products. This paper shows that the combination of the confocal Raman spectroscopy and MCR data analys...

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Compositional mapping of mixed gels using FTIR microspectroscopy

Cited by 20 publications

References 7 publications

Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

Method for Quantitative Determination of Spatial Polymer Distribution in Alginate Beads Using Raman Spectroscopy

Interpenetrating Network Formation in Gellan−Maltodextrin Gel Composites

The use of confocal Raman spectroscopy to characterise the microstructure of complex biomaterials: foods

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