C. H. Petter

Near-infrared reflection spectroscopy (NIRS) as a successful tool for simultaneous identification and particle size determination of amoxicillin trihydrate

A successful application of NIR spectroscopy (NIRS) in combination with multivariate data analysis (MVA) for the simultaneous identification and particle size determination of amoxicillin trihydrate particles was developed. Particle size analysis was ascertained by NIRS in diffuse reflection mode on different particle size fractions of amoxicillin trihydrate with D90 particle diameters ranging from 6.9 to 21.7 μm. The present problem of fractionating the powder into good enough size fractions to achieve a stable calibration model was solved. By probing dried suspensions measurement parameters were optimized and further combined with the best suitable chemometric operations. Thereby the quality of established regression models could be improved considerably. A linear coherence between particle size and absorbance signal was found at specific wavenumbers. Satisfactory clustering by particle size was achieved by principal component analysis (PCA) whereas partial least squares regression (PLSR) and principal component regression (PCR) was compared for quantitatively calibrating the NIRS data. PLSR turned out to predict unknown test samples slightly better than PCR.

Near Infrared Spectroscopy for Polymer Research, Quality Control and Reaction Monitoring:

This review covers recent applications of near infrared (NIR) spectroscopy in the determination of physico-chemical and morphological parameters of polymeric materials. Near infrared measurements in the diffuse reflection mode are highlighted, which analyse the structural parameters such as porosity, surface area and particle size. Fundamentals and applications of the technique are discussed and examples of quantitative and qualitative analysis are explained. Various approaches like on- and in-line techniques, bulk measurements and kinetic studies for recording spectra are discussed. Furthermore, this review addresses the development of calibrations, which allow for the differentiation and quantification of materials with varying physical and morphological properties. Parameters like constitution, composition and crystallinity have a strong affect on the material characteristics. Therefore, chemical, physical and mechanical properties of synthetic as well as natural substances, such as polymeric composites and cotton or wool, need to be studied in-depth. To sum up, NIR spectroscopy has been developed as a flexible, robust and high-throughput analytical method that can be combined with chemometric and multivariate data analysis for fast and reliable screening in material science.

Simultaneous determination of the micro-, meso-, and macropore size fractions of porous polymers by a combined use of Fourier transform near-infrared diffuse reflection spectroscopy and multivariate techniques.

Fourier transform near-infrared (FT-NIR) diffuse reflection spectroscopy was used in combination with principal component analysis and partial least-squares regression to simultaneously determine the physical and the chemical parameters of a porous poly(p-methylstyrene-co-1,2-bis(p-vinylphenyl)ethane) (MS/BVPE) monolithic polymer. Chemical variations during the synthesis of the polymer material can alter the pore volume and pore area distributions within the polymer scaffold. Furthermore, mid-infrared and near-infrared (NIR) spectroscopic chemical imaging was implemented as a tool to assess the uniformity of the samples. The presented study summarizes the comparative results derived from the spectral FT-NIR data combined with chemometric techniques. The relevance of the interrelation of physical and chemical parameters is highlighted whereas the amount of MS/BVPE (%, v/v) and the quantity (%) of micropores (diameter, d < 6 nm), mesopores (6 nm < d < 50 nm), and macropores (50 nm < d < 200 nm) could be determined with one measurement. For comparison of the quantitative data, the standard error of prediction (SEP) was used. The SEP for determining the MS/BVPE amount in the samples showed 0.35%, for pore volume quantiles 1.42-8.44%, and for pore area quantiles 0.38-1.45%, respectively. The implication of these results is that FT-NIR spectroscopy is a suitable technique for the screening of samples with varying physicochemical properties and to quantitatively determine the parameters simultaneously within a few seconds.

Quantification of Low-Density and High-Density Lipoproteins in Human Serum by Material Enhanced Infrared Spectroscopy (MEIRS)

A key risk factor in the development of atherosclerosis is a high concentration of serum low density lipoprotein (LDL)-cholesterol. The main purpose of this study was to assess the LDL and high density lipoprotein (HDL) content in human serum by employing near-infrared (NIR) spectroscopy and multivariate calibration techniques. Initially a qualitative principal component analysis (PCA) based cluster model was generated to evaluate the feasibility of NIRS for classifying and identifying the LDL and HDL-cholesterol. Therefore TiO(2) beads were used as an adsorbent for selectively immobilizing LDL and HDL-cholesterol and further analysing the incubated and washed samples via NIR diffuse reflection spectroscopy. A principle component regression (PCR) model of 24 LDL standards in a range from 500 - 3000 ppm (clinical value is 1500 ppm) and a partial least squares regression (PLSR) model of 25 HDL standards in a range from 100 - 1000 ppm (clinical value is 400 ppm) were computed. Furthermore, the wavenumber region between 4000 cm(-1) and 7240 cm(-1) was found comprising the main spectral information regarding the TiO(2)-LDL and TiO(2)-HDL composites. The regression coefficients (r) for LDL and HDL were > 0.99 (calibration curve) and > 0.97 (validation curve), respectively. The PCR model of TiO(2)-LDL showed a standard error of estimation (SEE) of 122.80 ppm and a standard error of prediction (SEP) of 121.15 ppm while the PLSR model of TiO(2)-HDL showed 47.70 and 47.14 ppm, respectively. In order to determine the concentration of HDL in real serum samples, LDL was removed by adding a precipitation reagent containing 10 mg/mL magnesium dextran-sulfate, followed by incubation and centrifugation. The pretreated serum samples were predicted by the PLSR model while the standard deviation (SD) from the reference to the NIR predicted values of six test samples in a concentration range from 500 - 2500 ppm showed < 10 %. These results indicate the usefulness of the NIR spectroscopy (NIRS) as a potential alternative or even supplementary clinical method for the quick determination of LDL and HDL in human serum.

Near infrared spectroscopy compared to liquid chromatography coupled to mass spectrometry and capillary electrophoresis as a detection tool for peptide reaction monitoring

Peptide interaction is normally monitored by liquid chromatography (LC), liquid chromatography coupled to mass spectrometry (LC-MS), mass spectrometric (MS) methods such as MALDI-TOF/MS or capillary electrophoresis (CE). These analytical techniques need to apply either high pressure or high voltages, which can cause cleavage of newly formed bondages. Therefore, near infrared reflectance spectroscopy (NIRS) is presented as a rapid alternative to monitor the interaction of glutathione and oxytocin, simulating physiological conditions. Thereby, glutathione can act as a nucleophile with oxytocin forming four new conjugates via a disulphide bondage. Liquid chromatography coupled to UV (LC-UV) and mass spectrometry via an electrospray ionisation interface (LC-ESI-MS) resulted in a 82% and a 78% degradation of oxytocin at pH 3 and a 5% and a 7% degradation at pH 6.5. Capillary electrophoresis employing UV-detection (CE-UV) showed a 44% degradation of oxytocin. LC and CE in addition to the NIRS are found to be authentic tools for quantitative analysis. Nevertheless, NIRS proved to be highly suitable for the detection of newly formed conjugates after separating them on a thin layer chromatography (TLC) plate. The recorded fingerprint in the near infrared region allows for a selective distinct qualitative identification of conjugates without the need for expensive instrumentation such as quadrupole or MALDI-TOF mass spectrometers. The performance of the established NIRS method is compared to LC and CE; its advantages are discussed in detail.

Near-infrared spectroscopic study on guest-host interactions among G0-G7 amine-terminated poly(amidoamine) dendrimers and porous silica materials for simultaneously determining the molecular weight and particle diameter by multivariate calibration techniques.

The guest-host interactions of poly(amidoamine) (PAMAM) dendrimers and porous silica surfaces were investigated by near-infrared (NIR) diffuse reflection spectroscopy. G0-G7 of amine-terminated PAMAM (PAMAM-NH2) dendrimers were analyzed comprising early, mid, and late generations. For early stages, the adsorption process of the partly protonated dendrimers to the negatively charged silica surface strongly depends on the size/shape characteristics of the guest (PAMAM-NH2 dendrimers) and host (porous silica) materials. G0-G4 (15-45 A) show smaller particle sizes than the pore diameter of the silica (60 A) and thus have access to the interior surface of the host material. For mid and later stages (G5-G7; 54-81 A) only low amounts of the dendrimers adsorb to the silica surface due to the inaccessibility to the interior surface. The loading capacity of the silica material with adsorbed PAMAM-NH(2) was evaluated by means of capillary zone electrophoresis (CZE), whereas deviations from the theoretical to the effective particle size and molecular weight (MW) was determined by gas-phase electrophoretic mobility molecular analysis (GEMMA) and matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometry (MALDI-lin TOF-MS). Deviations from the theoretical to the actual values showed a maximum of 13.8% and 28.0% for the particle size and MW, respectively. The NIR absorption spectra show a distinct band at 4932 cm(-1) (nu(sym) (NH) + amide II) due to the adsorbed dendrimers. It was found that the absorbance tends to increase with decreasing generation number. On this basis multivariate calibration was performed with the theoretical data and the data obtained by GEMMA and MALDI-lin TOF-MS. All in all, the calculated partial least-squares regression (PLSR) model containing the GEMMA/MALDI-lin TOF-MS reference values showed better results than the models exclusively calculated from the theoretical values. This indicates that the theoretical values do not imply the structural imperfections arising during the synthesis that may be present in the PAMAM-NH2 dendrimers.

When size matters—near infrared reflection spectroscopy of nanostructured materials

This article evaluates the applicability of near infrared (NIR) reflection spectroscopy for the physico-chemical and morphological characterisation of matter on a scale smaller than 1 micrometre (normally between 1 and 100 nanometres). The investigated materials comprise porous and non-porous silica particles, carbon based materials such as C60 fullerenes, nano-crystalline diamond (NCD) and dendrimers, all of them having diameters and/or pore sizes in the nanometre range, respectively. In case of the silica packings and differently derivatised C60 fullerenes, absorbance signals could be clearly assigned to corresponding surface modifications. Identification or classification of the material can be achieved successfully by principal component analysis. Nano crystalline diamond surfaces, whether H- or O-terminated, could be differentiated by a computed partial least squares (PLS) regression model with around 80% precision. Generations 0–7 of poly(amidoamine) (PAMAM) dendrimers with functionalised surface amine groups are characterised in respect of particle diameter and molecular weight. The established PLS models showed a standard error of prediction of only 0.43 nm and 12.30 kDa, respectively. NIR spectroscopy has developed as a flexible analytical method that can be utilized for fast, reliable and highly reproducible screening of matter even in the nanometer range.

Fast, noninvasive and simultaneous near-infrared spectroscopic characterisation of physicochemical stationary phases' properties: from silica particles towards monoliths.

The design of novel stationary phases is a permanent demanding challenge in chromatographic separation science to enable analysis with enhanced selectivity, specificity and speed. Therefore, the characterisation of chemical and physical properties is next to calculation of chromatographic parameters essential. Conventionally, chemical parameters including surface coverage are determined by burning combustion or frontal analysis, physical parameters including particle size, pore size, pore volume and surface area are determined by SEM, mercury intrusion porosimetry (MIP) and Brunauer-Emmett-Teller (BET). All these methods are time consuming, invasive and require besides special equipment some special trained laboratory staff. Therefore, we introduced near-infrared spectroscopy (NIRS) as a noninvasive, easy-to-handle technology with wavenumber ranging from 4000 to 10,000 cm(-1) enabling analysis within only a few seconds at higher precision than the conventional methods. Investigated materials comprise porous and nonporous silica gel, carbon-based nanomaterials (fullerenes), polymer beads and monoliths. Different carriers themselves and their kind of derivatisations (RP, normal-phase, ion-exchanger, IMAC (immobilised metal affinity chromatography), affinity) can be determined by applying principal component analysis (PCA) of recorded spectra. Partial least square regression (PLSR) enables the determination of particle size, pore size, pore volume, porosity, total porosity and surface area with one single measurement. For the optimised design of well-defined polymer beads and monoliths, real-time in situ monitoring to control, e. g. particle and pore sizes as well as monomer content during the polymerisation process, can be extremely helpful. In this article, the advantages of this fast, noninvasive high-throughput NIRS methods are summarised, discussed in detail and different applications of the individual characterised materials are shown.

Near infrared spectroscopy hyphenated to thin-layer chromatography for the analysis of amino acids

napproachforacombineduse� ofthin-layerchromatography� (TLC)� andnearinfrared� (NIR)� spectroscopy,� botheconomical,� rapidandsimpletechniques,�isdescribedin� thisfeasibilitystudy. 1 �Spectroscopicstudies� ofaminoacids,�di-,�tri-� tetrapeptidesand� proteinshavealreadybeencarriedoutwith� Raman,�mid-�andNIRtechniques. 2,3 �Advan- tagesofNIRspectroscopyoverRamanand� mid-IRspectroscopyarethelackofoften� lavishsamplepreparation,�theimplementa- tionofdiffusereflectionprobesthatprovide� intenselightscatteringsignalsofthesam- plesandtheavoidanceoffluorescenceand� laser-inducedsampledamage.�Forthatrea- sondevelopmentoffastandnon-invasive� analysistechniquesarerequiredinorder� toshortenturn-aroundtimeinthelaband� toreduceanalysiscosts.�Today,� NIRspec- trometersareveryuser-friendlyandhighly� sophisticatedsystems,�equippedwithsen- sitivedetectorsandpowerfulchemometric� softwarepackages.� Also,�reliablein-� and� onlinemonitoringcanbeperformedwith� adequateinstrumentation,�thatiswhy� theuseofNIRspectroscopyisverypopular� inchemical,�synthetic,�polymerandbioana- lyticalstudies. Aminoacidspossessatleasttwoor� moreC-H,� o-HandN-Hgroups,�soNIR� spectroscopyisusefulforstudyinghydra- tionandhydrogenbondsaswellaspep- tidesandproteins. 4,5