Introduzione: La tendenza è quella di avere quantità di campione dalle dimensioni sempre minori e controllate ma comunque rappresentative.
Nell’analisi dei materiali solidi certamente non si applica il detto popolare “più grande è meglio”. L’obiettivo è produrre particelle sufficientemente piccole da soddisfare i requisiti delle analisi, garantendo nel contempo una rappresentazione accurata del materiale originale. Le “particelle” d’interesse per l’analista vanno generalmente da 10 µm a 2 mm, ma in molte applicazioni sono necessarie granulometrie ancora più fini. Un esempio sono i principi attivi, dove è necessario operare nel range dei submicron. Infine, per l’estrazione di DNA ed RNA, la tecnica della lisi cellulare è già ben consolidata.
I produttori alimentari spesso promuovono i propri prodotti come “light” o come, nel caso delle barrette di cereali come “sane”. Se questo è effettivamente vero, non può che essere verificato analizzando i valori nutrizionali, una procedura che costituisce una parte importante nel controllo della qualità alimentare. I valori di grassi, acidi grassi saturi, zuccheri e sale stampati sulle confezioni rappresentano una media del contenuto di ogni sostanza e si riferiscono a 100 ml in 100 g di prodotto. Le barrette di cereali sono costituite da un mix eterogeneo di ingredienti (noci, uvetta, fiocchi d’avena, ecc..) pertanto è necessaria una completa omogeneizzazione del campione per ottenere risultati d’analisi significativi.
La diversità degli alimenti con le spesso differenti proprietà dei prodotti rappresenta una reale competizione per i laboratori di analisi alimentari. Per le attuali analisi, i campioni – che possono essere molto tenaci a seconda della loro durezza o umidità – necessitano di essere ridotti e omogeneizzati in modo sufficientemente fine. I mulini a coltelli GRINDOMIX RETSCH sono lo strumento ideale per venire incontro ai complessi requisiti richiesta dalla preparazione di alimenti. Il modello GM 200 è ormai consolidato per l’omogeneizzazione di piccoli volumi di campione fino a 700 ml. Per volumi maggiori RETSCH adesso offre il nuovo GRINDOMIX GM 300 con una camera di macinazione del volume di 5000 ml.
A solid sample material should always be sufficiently prepared by size
reduction and homogenization before it is subjected to chemical or physical analysis. Care should be taken that the analysis sample fully represents the original material and that the sample preparation process is carried out reproducibly. Only then are meaningful results guaranteed. Most sample materials can be reduced to the required analytical fineness at room temperature by choosing a mill with a suitable size reduction principle (impact, pressure, friction, shearing, cutting).
The diversity of foodstuffs with their often very different product properties represents a real challenge for food testing laboratories. Before the actual analysis, the sample materials – which can vary strongly with regards to hardness and moisture – need to be homogenized and reduced to a sufficiently small particle size. RETSCH’s GRINDOMIX knife mills are the ideal tools to meet the complex requirements of the sample preparation of food. The model GM 200 has proven itself for the homogenization of small sample volumes of up to 700 ml. For larger volumes RETSCH offers the GM 300 model with a grinding chamber volume of 5,000 ml.
Like all foodstuff, confectionery is subjected to strict quality controls. Parameters of interest are, for example, nutritional value, moisture or fat content, or the quantification of particular ingredients, such as vitamins or alkaloids. Typically, chromatographic methods like High Performance Liquid Chromatography (HPLC) are used to analyze food samples. Most analytical methods only require a few milligram or gram of sample; the previous size reduction/homogenization process ensures that the small analysis sample is representative of the entire laboratory sample, thus allowing for reproducible results. Moreover, homogenized samples show a much better extraction behavior.
Genetic engineering opens up new possibilities in areas such as medical research, development of alternative fuels or global food supply. It is used to modify the characteristics of plants in order to increase the crop yield, improve defense against predators, pesticides or draught, but also increase concentrations of essential vitamins. However, with regards to food the use of genetic engineering is a fairly controversial issue. Moreover, food and feed stuff are subject to rigorous quality control processes to prevent humans and animals from potential harm.
Reliable and accurate analysis results can only be guaranteed by reproducible sample preparation. This consists of transforming a laboratory sample into a representative part sample with homogeneous analytical fineness. Retsch offers a comprehensive range of the most modern mills and crushers for coarse, fine and ultra-fine size reduction of almost any material. The product range also comprises a wide choice of grinding tools and accessories which helps to ensure contamination-free preparation of a great variety of sample materials. The selection of the correct grinding tool depends on the sample material and the subsequent method of analysis. Different grinding tools have different characteristics, such as required energy input, hardness or wear-resistance.
Sample preparation of vegetable-based raw materials with laboratory mills
Thanks to the increasing usage of biomass as a source of energy, the analysis of these materials in the context of R&D and quality control gains importance, too. Due to the complex properties of plant materials, adequate sample preparation can be rather a challenge.
The so-called QuEChERS method (“quick, easy, cheap, effective, rugged and safe”) was developed by Michelangelo Anastassiades (Chemical and Veterinary Investigation Office CVUA, Stuttgart, Germany) to make sample preparation to pesticide residue analysis more efficient. It basically consists of three steps: Homogenization – Extraction – Analysis. Test series have proved that the analysis results obtained with the QuEChERS method can easily compare with more common methods, such as DFG S19. Various RETSCH instruments are used for the sample preparation process.
A variety of methods can be used to analyze solid materials. What they all have in common is the necessity to use a representative, homogeneous analysis sample which needs to have a particular fineness, depending on the analytical method used. The size reduction and homogenization of solids is usually carried out with laboratory crushers and grinders.
A faultless and comparable analysis is closely linked to an accurate sample handling. Only a sample representative of the initial material can provide meaningful analysis results. Rotating dividers and rotary tube dividers are an important means to ensure the representativeness of a sample and thus the reproducibility of the analysis. Correct sample handling consequently minimizes the probability of a production stop due to incorrect analysis results. Thus correct sample handling is the key to effective quality control.
The so-called QuEChERS method (“quick, easy, cheap, effective, rugged and safe”) has been developed to make sample preparation to pesticide analysis more efficient. Serial tests have proved that the analysis results obtained with the QuEChERS method can easily bear comparison with more common methods, such as DFG S19. To guarantee reproducible analysis results, it is essential to completely homogenize the sample. To make sure the sample preparation is reproducible, the homogenization process needs to be carried out with a laboratory mill.
The development of high-performance ceramics is determined by a large number of influencing factors. In addition to material-specific aspects, such as the chemical purity of the initial raw materials, particle size reproducibility and uniformity of particle morphology, production-specific factors also determine the final properties of ceramics.
An efficient sample preparation procedure for rapid, reliable and reproducible analytical results is becoming increasingly important today. Ever more stringent requirements are being set both in research and production, e.g. for product monitoring and quality control.