Ignacio López García

A Review of the Application of Near-Infrared Spectroscopy for the Analysis of Potatoes

Potato (Solanum tuberosum L.) is one of the most important crops in the world being considered as a staple food in many developing countries. The potato industry like other vegetable and fruit industries is subject to the current demand of quality products. In order to meet this challenge, the food industry is relying on the adoption of nondestructive and environmentally friendly techniques to determine quality of products. Near-infrared spectroscopy (NIRS) is currently one of the most advanced nondestructive technologies regarding instrumentation and application, and it also complies with the environment requirements as it does not generate emissions or waste. This paper reviews research progress on the analysis of potatoes by NIRS both in terms of determination of constituents and classification according to the different constituents of the tubers. A brief description of the fundamentals of NIRS technology and its advantages over other quality assessment techniques is included. Finally, future prospects of the development of NIRS technology at the industrial level are explored.

Calibration in flame atomic absorption spectrometry using a single standard and a gradient technique

To obtain calibration graphs, a standard solution of the analyte was pumped using an increasing flow rate while pure water was aspirated, for compensation, through a T-piece. In this way an on-line concentration gradient was obtained and a constant flow was supplied to the nebulizer. The absorbance was monitored via a computer which facilitated data acquisition and handling. In spite of the problems posed at low flow rates by the pulsations caused by the rollers of the peristaltic pump, this calibration strategy gave graphs comparable to those obtained by means of the separate measurement of several standard solutions. A calibration graph could be obtained in only 50 s with errors of less than ±3%. The mode of operation also permits the on-line dilution of moderately concentrated solutions, which cannot be measured by direct aspiration, and simplifies the standard additions method.

Slurry–electrothermal atomic absorption spectrometric methods for the determination of copper, lead, zinc, iron and chromium in sweets and chewing gum after partial dry ashing

Slurry–electrothermal atomic absorption spectrometric procedures for the rapid determination of the copper, lead, zinc, iron and chromium contents of sweets and chewing gum samples are discussed. The samples were first subjected to a process of mild calcination; suspensions were then prepared in a medium containing 8% ethanol as stabilizing agent, 0.1% ammonium dihydrogenphosphate as chemical modifier and 4% hydrogen peroxide to prevent the build-up of carbonaceous residues inside the atomizer. Fast-programme methodology was used for the heating programmes. Calibration was carried out using aqueous standards, and the reliability of the procedures was verified by analysing several standard reference materials.

Flow injection atomic absorption spectrometry with air compensation

Flow injection atomic absorption spectrometry (FI-AAS) with air compensation was studied and compared with Fl-AAS using solvent compensation and with conventional AAS. It seems clear that air compensation offers important advantages, as the great increase in nebulisation efficiency improves the sensitivity and selectivity. The reproducibility obtained for both peak height and peak area is similar to or better than that obtained using other FI-AAS systems and comparable to that given by conventional AAS. The problem of using a pumping flow-rate lower than that of the nebuliser aspiration (necessary for chromatographic and solvent extraction procedures coupled with FI-AAS) is solved using the air compensation method with advantages over other procedures.

Rapid furnace programmes for the slurry-electrothermal atomic absorption spectrometric determination of chromium, lead and copper in diatomaceous earth

The samples are suspended in water containing hydrofluoric acid and then injected into the electrothermal atomizer. To decrease the heating programme time, the drying step is performed at higher than usual temperatures, and ashing and clean-up steps are omitted. Simple aqueous standards are used for calibration. The results reveal no significant differences at the 95% confidence level (Wilcoxon T-test and use of regression lines) from those obtained using acid digestion of the samples. The analysis of certified reference materials shows the reliability of the approach. The use of hydrofluoric acid solutions as the suspending media is confirmed to be a reliable way of prolonging the lifetime of platforms and tubes when slurries prepared from samples with a high silica content are used.

Slurry-electrothermal atomic absorption spectrometry of samples with large amounts of silica. Determination of cadmium, zinc and manganese using fast temperature programmes

Abstract The determination of cadmium, zinc and manganese in diatomaceous earth, as well as in other materials with high silica content, is carried out by first suspending the ground samples in dilute hydrofluoric acid. Following this, aliquots of the slurries are directly injected into the electrothermal atomizer. Using the the fast-temperature methodology, the drying and ashing steps are replaced by a modified drying stage in which temperature and hold time are experimentally optimized by studying the temperature changes inside the atomizer with a thermocouple. Zinc and cadmium are atomized from a platform using ammonium phosphate as a matrix modifier. Wall atomization and no modifier other than hydrofluoric acid is used for manganese determination. Calibration is performed using aqueous standards. The optimized conditions for diatomaceous earth samples are applicable to other materials with high silica content, as is shown by the analysis of five standard reference materials.

A fast method for the determination of lead in paprika by electrothermal atomic-absorption spectrometry with slurry sample introduction.

A rapid procedure for the determination of lead in commercial paprika samples is described. The samples are first calcined at 350 degrees , then suspensions are prepared in water containing 0.1% v/v Triton X-100 and 0.1% w/v ammonium phosphate and injected into the electrothermal atomiser. The use of platform atomisation with a preatomisation cooling step allows for simple calibration with aqueous standards. When using 0.4% suspensions the detection limit is 0.2 ug/g. The results for seven paprika samples agree with those obtained by an alternative method involving calcination and dissolution in acid.

Use of flow injection flame atomic absorption spectrometry for slurry atomization. Determination of copper, manganese, chromium and zinc in iron oxide pigments

A procedure for the determination of copper, manganese, chromium and zinc in slurries of commercial iron oxide pigments using flame atomic absorption spectrometry is described. The samples are suspended in water and introduced directly into the spectrometer using a flow injection manifold with air-compensation of the difference between the peristaltic pump flow-rate and the nebulizer uptake rate. In order to avoid matrix effects, calibration is achieved by using slurries prepared from previously analysed iron oxide samples. Excellent agreement was found between the results of the slurry procedure and those obtained by conventional acid-dissolution.

Sensitive method for the spectrophotometric determination of boron in plants and waters using crystal violet

A sensitive and rapid spectrophotometric method for the determination of boron is described, which is based on the formation of a blue complex at pH 1–2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet; the colour is stabilised with poly(vinyl alcohol). At 600 nm the calibration graph is linear in the range 0.3–4.5 µg of boron per 25 ml of final solution with a relative standard deviation of ±2.6% for 0.069 µg ml–1 of boron. The molar absorptivity is 3.75 × 104 l mol–1 cm–1. The method has been applied to the determination of boron in plants and natural waters.

Flow injection dilution system for the analysis of highly concentrated samples using flame atomic absorption spectrometry

A versatile computer-controlled flow injection manifold which extends the determination range of flame atomic absorption spectrometry is discussed. The system uses a peristaltic pump equipped with a small bore pump tube. While the pump is working at a low rate, a small volume of sample is metered into the system. Next, the pump rate is increased linearly with time. The inclusion of a T-piece before the nebulizer permits this device to be fed at a constant flow rate and an efficient dilution of the sample plug. Dilution of about 2000-fold can be obtained. Sampling frequencies are in the 40–120 samples h–1 range. By choosing appropriate pump rates and injection times, the problems posed by the pulsations due to the rollers of the peristaltic pump are overcome. Calibration can be performed by using peak height or integrated absorbance. Repeatability of the integrated absorbance measurements is in the 0.6–2.3% range.