ABB Analytical

FT-NIR spectroscopy for the quantitative determination of key physical parameters in bulk polymers and products, including density and melt index (MI). These measurements can often be made with little or no sample preparation.

Fourier transform (mid) infrared spectroscopy is an established technique for the fast and nondestructive analysis of plastic films, where it can typically provide critical compositional information, such as additive content and co-polymer concentration. However, in the manufacturing processes for bulk polymers of polyethylene (PE), physical property determination (for example, density and melt index) can be important quality control parameters. Due to the simplicity of sampling when using near infrared spectroscopy, FT-NIR has proved to be a very adaptable and useful method in these circumstances. 

For the PE samples, 65 different bulk polymer samples were provided, each sample in both pellet and powder form, so a total of 130 sample measurements were made. Both pellet and polymer samples were presented in glass scintillation vials approximately 2 cm in diameter and 6 cm in height, and were loaded into the FT-NIR spectrometer rotating powder sampler device without further sample preparation and measured in diffuse reflectance. 

Figure 1: PE pellet samples - variation in FT-NIR spectra as MI and density change. 

Spectral acquisitions were performed using an ABB MB3600 FT-NIR spectrometer, fitted with a TE-cooled InGaAs detector at 16 cm

  resolution and with 128 co-added scans. The background reference measurement was made using a PTFE standard. 

Calibration models were developed using PLS/IQ (Grams/AI version 7.0 software). Calibration model uncertainty is estimated by the standard error of cross validation (SECV). The static repeatability of the calibration is given by the standard deviation of ten consecutive measurements of the same sample without moving it from the sampling accessory. 

The variations of properties in this study are presented in Figure 1. 

Figure 2 displays the vibration regions of -CH

 function groups and spectra variation as to the change of properties in PE pellets samples.

Figure 2: Experimental design - variation of MI and density in PE sample set. 

The calibration results are summarized in Table I for PE samples. It has been demonstrated that ABB MB3600 with a Powder SamplIR accessory could successfully determine MI and density in pellet and powder PE samples with: 1) SECV< lab reproducibility, 2) FT-NIR repeatability < lab repeatability. 

FT-NIR technology could provide the solutions for the realization of at-line or on-line determination of these properties and provide quick feedback to the plant operator for the quality control. 

585 Blvd. Charest E., Ste 300, Quebec, QC Canada G1K9H4 

Articles

Fast Quality Evaluation of Bulk Polymers and Products Using FT-NIR Spectroscopy

A drug-eluting stent (DES) is an expandable metal alloy framework placed into narrowed coronary arteries that slowly releases a drug coating to treat atherosclerosis. Production of DES is a labor-intensive batch process that requires very tight control. Fourier Transform Near-InfraRed spectroscopy (FT-NIR) is an efficient technique to perform accurate quantification of the different components in DES coating solutions.

Coronary artery disease is the leading cause of death in the developed world. It is caused by the gradual deposition of lipid and cholesterol plaques on the inner layer of the coronary arteries, leading to their hardening. Since the 1980s interventional cardiologists have developed DES using elaborate metal mesh-like design with a coating made of biostable polymer matrix that holds and releases an encapsulated active ingredient by diffusion into arterial walls.  

Quantification of coating solution components using liquid chromatography (HPLC) is a time-consuming approach that requires preparation of column, sample and standards, and is using costly solvents. We present an application of FT-NIR as a fast and non-destructive alternative technology that can be operated by an operator without analytical background.  

Components of two coating solutions including biostable polymers (BP1, BP2), solvents (S1, S2, S3, S4) and the immunosuppressant everolimus (API) were analysed. Synthetic sets comprising samples with varying component concentrations were gravimetrically prepared for calibration of the FT-NIR spectrometer. Solution 1: BP1/S1/S2 (15 samples). Solution 2: API /BP2/S3/S4 (17 samples). 

The %weight for each component was used as a reference value. For everolimus, the actual content was measured with HPLC and those values were used to calibrate the spectrometer equipped with a vial sampling accessory. A reference spectrum was first recorded in open beam condition. Each sample was then transferred with a pipette to a 1 mL disposable glass vial placed in the holder. Near-infrared transmission spectra were recorded at 20 °C over the range 5000-10000 cm

Calibration models were developed for the different components using the Partial Least Squares algorithm that calculates a set of factors from the calibration spectra and corresponding reference values. Linear combinations of these factors are generated to reconstruct the calibration spectra and regressed against the components concentrations. Predicted concentrations of unknown samples are given by the scalar product of the regression vector and the sample spectra.       

The performance of the calibrations for the different components is reported in Figure 1, including the coefficient of determination (r

 ). The uncertainty of each calibration is expressed by the standard deviation of the differences between reference concentrations and calibration model predictions (SECV).   

Figures 1a and 1b show the excellent agreement between FT-NIR predictions and actual concentration values for BP1 and everolimus. 

FT-NIR spectroscopy is a powerful tool for the analysis of stent coating solutions. Its accuracy make it a very reliable technique for fast quality checks in laboratory. Furthermore, flexibility of the instrumentation also allows to streamline the batch production process and increase production throughput by performing real time monitoring of the components mixing, using in-situ probes connected to the FT-NIR spectrometer with fiber optics.  

ABB Analytical

Articles

Fast Quality Evaluation of Bulk Polymers and Products Using FT-NIR Spectroscopy

Analysis of Drug Eluting Stent Coating Solutions Using FT-NIR Spectroscopy