Anthony M. C. Davies

A Preliminary Study on the Characterisation of Honey by near Infrared Spectroscopy

Near infrared (NIR) spectra were measured, at five temperatures, for 48 samples of honey, from a variety of geographical and botanical sources, and the data was used to explore the possibility of using NIR spectroscopy for testing label claims concerning the geographical and botanical source of honey being offered for sale to the public. Three spectra were obtained at each temperature and a blank spectrum was also recorded to check on the state of the system. Thus a total of 16 spectra were collected for each sample, and the complete experiment amounted to 768 spectra each containing 700 data points. These data were compressed by selection and principal component analysis so that they could be used in a canonical variates analysis (CVA) program. There were sufficient numbers of honeys from four botanical sources, acacia, chestnut, heather and rapeseed, to make use of CVA. Acacia and rapeseed formed clusters that were well separated from chestnut and heather clusters, which were partially overlapped. Mahalanobis distance (MD) calculations were used to test group membership in a cross-validation experiment in which each of the 28 members of groups was left out of the calibration calculations, one at a time. When using 10 principal components (PCs) as the input variables, 19 of the honeys were assigned to the correct group while two honeys were incorrectly assigned to another group. When using 15 PCs, the number of correct assignments reduced to 13 but there were no incorrect assignments. There were 20 honeys which did not belong to the four test groups. When these were tested for group membership at 10 PCs, 10 were incorrectly assigned to a group. This reduced to two errors at 15 PCs. Tests on the country of origin were inconclusive. These results demonstrate that the successful characterisation of the botanical source of a honey may be obtained by NIR spectroscopy. Further work with larger numbers of samples and groups will be required to realise this potential.

The application of fourier-transformed near-infrared spectra to quantitative analysis by comparison of similarity indices (CARNAC)

A new technique for utilising near-infrared spectroscopic data for quantitative analysis is proposed. The method uses a database of spectra stored in the form of the Fourier transform together with the associated chemical analysis. The spectrum of an unknown sample is compared to each member of the database and a small subset of very similar samples is isolated. The analyte value for the unknown is calculated from the analytical values of the subset. Results are given for the application of the method to the analysis of nicotine in tobacco.

Cell wall glycoproteins and polysaccharides of mature runner beans

Abstract A novel use of chlorite-HOAc treatment (delignification procedure) for the isolation of hydroxyproline (HP) rich “glycoproteins” from the depectinated cell wall material of mature runner beans is described. This procedure can be used for the isolation of wall proteins even from heavily lignified tissues. Its main disadvantage is that some of the constituent amino acids are either destroyed or modified; the nature of these changes was studied using gelatine, lysozyme and “cytoplasmic proteins” of mature beans. The main amino acids to be affected were tyrosine, cystine, methionine and lysine. The chlorite-HOAc solubilized proteins were separated by PhOH-H 2 O fractionation into two distinct “glycoprotein fractions”. The major fraction (isolated from the aqueous layer) contained most of the HP of the solubilized proteins. The sugars obtained on hydrolysis of both “glycoproteins” were galactose, arabinose, glucose, xylose, rhamnose and uronic acid. Most of the proteins remaining in the holocellulose could readily be extracted with cold alkali and were relatively poor in HP.

Locally-biased regression

After a brief review of local calibration methods, a new and relatively simple method is proposed. Given a database of calibration samples, a global calibration based on all these samples and an unknown for which we wish to make a prediction, the method selects a subset of the calibration samples judged to be spectrally similar to the unknown and uses these to determine either a skew and bias or a simple bias correction to the global calibration. Spectral similarity is defined in a two-dimensional space, with one axis focussing on similarity with respect to the analyte value to be predicted, and the other on more general spectral similarity. The computations required to make a prediction are simple by the standards of local methods.

Agropine, a new amino acid derivative from crown gall tumours

Abstract Agropine, an unusual compound produced in plant tumours was shown by mass spectrometry and proton and carbon-13 nmr spectroscopy to be a bicyclic derivative of glutamic acid and a hexitol sugar.

Simultaneous determination of sodium hydroxide, sodium carbonate and sodium chloride concentrations in aqueous solutions by near-infrared spectrometry

The quantitative analysis of solutions containing various concentrations of sodium hydroxide, sodium chloride and sodium carbonate, over the range 0–15%m/m, has been carried out by near-infrared (NIR) spectrometry. Errors, caused by a high concentration of one salt when determining small amounts of another, have been investigated. The standard errors of the computed results from NIR measurements of each ion were: hydroxide, 0.12; carbonate, 0.34; and chloride, 0.52%. The measurements were made using a liquid sample cup in a fixed-filter NIR instrument and it was concluded that this was a practical system for continuous monitoring of the sodium hydroxide concentration in a process line even when contamination from hydrochloric acid and carbon dioxide occurred.

Quantitative analysis via near infrared databases: comparison analysis using restructured near infrared and constituent data-deux (CARNAC-D)

The method originally proposed in 1988 as “CARNAC” has been re-developed to incorporate the use of wavelet compression, modern programming techniques that make it potentially more transportable and some refinements of the technique. The idea is demonstrated on the small database that was used for program testing as it gives surprisingly acceptable results.

Rapid analysis of packaging laminates by near-infrared spectroscopy

Qualitative and quantitative analyses of three components of a packaging laminate have been obtained by the application of near-infrared spectroscopy. The absence of any of the components (cast polypropylene, linear low density polyethylene and nylon) could be detected with ease. A semi-quantitative analysis of the components, using a simple linear regression calibration, gave good estimates of the number of layers of a given type when multiple layers of components were presented to the spectrometer. This was improved to a quantitative method by calibration using layers of components of known thickness. The precision of the method was calculated to be 10% for a single determination.

A comparison of Fourier and wavelet transforms in the processing of near infrared spectroscopic data: Part 1. Data compression

The advent of spectral imaging and recent trends towards the compilation of large spectral databases have caused renewed interest in the compression of near infrared spectra for purposes of storage. A comparison of approaches using Fourier and wavelet transforms shows that wavelets are generally, though not always, more efficient than Fourier at compressing near infrared spectra. The Daubechies extremal phase wavelet of order 4 is a good choice for this purpose.

Fourier self-deconvolution in the analysis of near infrared spectra of chemically complex samples

A demonstrated analytical tool for band enhancements in the mid-IR, Fourier self-deconvolution can serve similarly in the analysis of NIR spectra even when the spectra, obtained with dispersion instruments in the diffuse reflectance mode, have broad, overlapping bands not easily resolved. Unlike derivative enhancement methods, Fourier self-deconvolution preserves peak areas so that the deconvolted results may prove advantageous in using multilinear calibration techniques. Band enhancements of both synthetic and real spectra are discussed.