See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/13574801 Optimisation of sample presentation for the near-infrared spectra of pharmaceutical excipients Article in The Analyst · May 1998 DOI: 10.1039/A800358K · Source: PubMed CITATIONS READS 30 105 3 authors , including: Anthony Christopher Moffat University College London 193 PUBLICATIONS 4,994 CITATIONS SEE PROFILE All content following this page was uploaded by Anthony Christopher Moffat on 16 April 2015. The user has requested enhancement of the downloaded file.
� Analyst, May 1998, Vol. 123 (1029–1034) 1029 Optimisation of sample presentation for the near-infrared spectra of pharmaceutical excipients † Weng Li Yoon * , Roger D. Jee and Anthony C. Moffat Centre for Pharmaceutical Analysis, The School of Pharmacy, University of London, 29–39 Brunswick Square, London, UK WC1N 1AX The effects of sample presentation on near-infrared (NIR) the necessity to standardise parameters such as cup size, amount reflectance spectra were examined. Using a Foss of sample, pressure when inserting the probe, etc . NIRSystems Rapid Content Analyzer, which uses sample Experience gained from the food and agricultural industry cups for sample presentation, four important parameters suggests that sample presentation is a variable which must not be overlooked. Williams 11 found that cell loading affected the were identified: cup diameter, sample thickness, cup material and packing method. Below a critical diameter of precision of protein determination more than sample grinding. 20 mm, which is dependent on the detector geometry, the He also reported that variations in bulk density of the sample could lead to errors. Mark and Tunnel 12 reported that variations spectra became increasingly distorted ( i.e. , changes in spectral intensities and spectral shape, shifts in peak in packing affected the calibrations which they developed for positions and occurrence of Wood’s peak). The minimum the measurement of moisture, fat and protein in ground beef, sample thickness not to cause spectral distortion was mixed animal feed and breakfast cereal. It was necessary to dependent on the physical and chemical nature of the make multiple measurements on the same sample to average out substance. A thickness ≥ 10 mm was found to be adequate the variations due to sample presentation. for most pharmaceutical excipients. The method of In this work, the effects of sample presentation when using a packing was also important. Tapping a powdered sample sample cup module on the reflectance spectra of some sometimes caused significant changes ( P < 0.05) in the commonly used pharmaceutical excipients were systematically spectral absorbance values compared with simply pouring examined. By standardising and eliminating factors responsible the sample into the sample cup. Standard sample cups for spectral variations, it is hoped that in the near future it will made from quartz were to be preferred owing to their be possible to establish transferable libraries of spectra. lack of background absorptivity. However, the two commercially available flat based vials examined, which Experimental were made from soda glass and clear neutral glass, proved to be as suitable for all except applications of the Apparatus most exacting nature. The spectral distortions resulting A NIRSystems 6500 spectrophotometer (Foss) fitted with a from variations in cup diameter, sample thickness and Rapid Content Analyzer (RCA) or a Direct Content Analyzer cup material were also shown to alter significantly the (DCA) was used for the measurement of all reflectance spectra values of two commonly used identification algorithms, over the wavelength range 1100–2500 nm. Except where correlation coefficient ( < 0.95) and maximum distance indicated otherwise, the RCA attachment was used for all ( > 3.0 standard deviation distance), sufficiently to cause investigations. Each recorded spectrum was the average of 32 misidentifications. scans. Keywords: Near-infrared spectroscopy; pharmaceutical Samples were measured in flat based cups : excipients; sample presentation; optimisation (a) quartz (standard sample cup, 52 mm diameter, Foss catalogue number NR7072); (b) Pyrex glass (reflectance vessel, 40 mm diameter, Foss catalogue number NR6544); The application of near-infrared (NIR) spectroscopy in the (c) clear neutral glass (Fbg-Anchor glass vials, 21 mm pharmaceutical industry is facing continued growth because of diameter, catalogue number BDH/Merck/215/0074/23); its ease of use, speed of measurement and minimum of sample (d) soda glass (Philip Harris specimen tubes, 23 mm diameter, preparation. Common applications include the identification of catalogue number PHI3 T82-528). raw materials, quality control and quantitative analysis. 1–6 Establishing such procedures involves the expenditure of considerable time and effort to create the necessary calibration Materials sets and libraries of compounds. Nevertheless, it is generally All excipients were of pharmaceutical grade: microcrystalline recognised that calibrations for quantification purposes are not cellulose (Avicel PH101 and Avicel PH102, FMC, Phil- always transferable between different instruments, even of the adelphia, PA, USA), sodium starch glycollate (Explotab, same type and from the same manufacturer. 7–9 It is still to be Edward Mendells), anhydrous dibasic calcium phosphate (A- established if libraries of reflectance spectra for identification TAB, Edward Mendells), dibasic calcium phosphate dihydrate purposes are transferable. Factors affecting transferability (Emcompress, Edward Mendells), lactose monohydrate regular include instrument variability (ceramic reflectance reference, (Broculo Whey Products UK), hydroxypropylmethylcellulose wavelength accuracy, detector linearity, stray light, radiation (Methocel E5 Premium, Colorcon), purified talc (Luzenac source) and possibly sample presentation. 10,11 Europe), propyl and butyl p -hydroxybenzoate (Nipa Laborato- The most commonly used sample presentation methods in ries) and Kollidon 25 and 30 (Povidone, BASF). reflectance NIR use either a fibre optic probe or sample cups. Despite their wide use, there is still little information concerning Data treatment NSAS Version 3 software 13 was used for the calculation of first- † Presented at the British Pharmaceutical Conference 1997, 134th meeting, and second-derivative spectra using a segment size of 20 data Scarborough, UK, September 15–18, 1997.
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