Grinding the Sample

Some fine-powder solid samples are ready to be dissolved without grinding for them, mere passage through a fine-mesh sieve (mesh is typically 0.1-0.2 mm ) is enough. 

Some fine-powder solid samples are ready to be dissolved without grinding for them, mere passage through a fine-mesh sieve (mesh is typically 0.1-0.2 mm ) is enough. Other types of coarser solid samples, such as soils, need to be passed through a coarse-mesh sieve (typically 2 mm mesh) to make it ready for dissolution. However, 

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Several factors affect the bandshapes observed ia drifts of bulk materials, and hence the magnitude of the diffuse reflectance response. Particle size is extremely important, siace as particle size decreases, spectral bandwidths generally decrease. Therefore, it is desirable to uniformly grind the samples to particle sizes of <50 fim. Sample homogeneity is also important as is the need for dilute concentrations ia the aoaabsorbiag matrix. 

For fruits and vegetables, mince and homogenize 1 kg of the sample with a mixer together with an appropriate amount of water, if necessary, and weigh 50 g of the sample. For small fruit samples such as citron, kabosu lime and rind, weigh 20-25 g of the sample. For beans, after grinding the sample, weigh 20 g of the sample and add 40 mL of distilled water to swell the sample for 2h. 

To obtain representative samples from nonhomoge-neous sample materials, such as polymer compounds, particle-size reduction techniques need often to be applied (not for film) [50]. Also, for destructive inpolymer additive analysis it is advantageous to change the physical state of solid samples to provide a larger surface area per unit mass. Complete extraction is sometimes achieved only after grinding the sample. Typically, Perlstein [51] has reported recoveries of only 59 % for extraction of Tinuvin 320 from unground PVC after 16 h of Soxhlet extraction with diethyl ether while recoveries rise to 97 % for ground polymer. 

We use gel content analysis to determine the weight fraction of a crosslinked polymer that is bound into an insoluble network. We immerse a stainless steel mesh basket containing a known weight of the crosslinked polymer in a suitable solvent (which may be heated to facilitate dissolution). If necessary, we can slice or grind the sample to increase its surface area. After 24 hours or more, we remove the basket from the solvent and dry it to constant weight. We calculate the gel content from Eq. 5.6. 

Note that mosaic artifacts can also occur physically in real spectra when a real powder sample of a model compound exhibits microcrystallinity and thus contains too few different molecular orientations. This phenomenon is rare in X-band EPR and is usually easily solved by grinding the sample in a mortar it is, however, not at all uncommon even for extensively ground samples in high-frequency EPR with single-mode resonators where the sample size is orders of magnitude less than that of an X-band sample. 

Drying and grinding the samples are two important steps prior to extraction, because many fruits and vegetables contain 80-95% moisture and grinding to achieve small particle size will favor the high contact surface area necessary for efficient extraction. 

There are two major problems associated with the x-ray method. The first problem is encountered during sample preparation. At this step, preferred orientation of the particles must be minimized [1], Reduction of particle size is one of the most effective ways of minimizing preferred orientation, and this is usually achieved by grinding the sample. Grinding, however, can also disorder the crystal lattice. Moreover, decreased particle size can cause a broadening of x-ray lines, which in mm affects the values of /c and /a. The relationship between the crystallite size, t, and its x-ray line breadth, /3, (assuming no lattice strain) is given by the Scherrer equation [2] ... 

Preferred orientation of the particles must be minimized. One of the most effective ways to achieve this is to reduce the particle size by grinding the sample [1], As already discussed in Section III.A, however, grinding can disorder the crystal lattice. Grinding can also induce other undesirable transitions, such as polymorphic transformations [59]. In order to obtain reproducible intensities, there is an optimum crystallite size. The crystallites have to be sufficiently small so that the diffracted intensities are reproducible. Careful studies have been carried out to determine the desired crystallite size of quartz, but no such studies have been reported for pharmaceutical solids [60]. Care should be taken to ensure that the crystallites are not very small, since decreased particle size can cause a broadening of x-ray lines. This effect, discussed earlier (Eq. 9), usually becomes apparent when the particle size is below 0.1 jum. 

The composition and amount of pigments in marine environments have also been vigorously investigated. Thus, on RP-HPLC method has been developed for the study of the effect of variable irradiance on the xanthophyll cycle of the seagrass Zostera marina. Extraction of pigments from seagrass was carried out by grinding the samples with acid-washed sand in the presence of 1 ml of 90 per cent acetone and the liquid phase was... 

Slurry nebulization has also proved very popular. In this technique, sample (typically 0.25 g) is placed in a 30 ml plastic bottle and 10 g of expanded zirconia beads are added. A dispersant is added and the bottle is sealed and then placed on a mechanical shaker for several hours. During the shaking, the zirconia beads grind the sample into very fine particles. After dilution to a known volume, the slurry may be aspirated directly into an atomic spectrometric instrument. Other methods of slurry preparation also exist, e.g. using a micronizer, but the bottle and bead method is the most common. 

Liquid samples such as milk do not normally require application of any pretreatment procedure. Semisolid samples such as muscle, liver, and fat tissues usually require more intensive sample pretreatment for tissue break-up. The most popular approach is grinding the sample in a food chopper or homogenization in a Waring blender to expose residues to the extraction solvent. Fatty tissue samples are usually warmed at 35 C until fat melts (491-493), or sometimes blended with immersion blender (494). A fat sample that has been blended with immersion blender melts to produce yellow oil, whereas oil does not separate... 

An explosion-proof motor-driven grinder or steel or glass balls can also be used to grind the sample (see Critical Parameters). 

Grind the sample evenly (the sorbent acts as an abrasive material)... 

Weigh out 3 g of lauric acid and place it in a 25-mL beaker. Weigh out 0.6 g of benzoic acid. Heat the lauric acid gently on a hot plate until it melts (50°C). Add the benzoic acid to the beaker. Mix it thoroughly until a uniform solution is obtained. Cool the beaker in cold water to obtain a solid sample. Grind the sample to a fine powder in a mortar with a pestle. 

Stuart and Wills (2000b) reported a decrease, from 60 to 15%, in alkamide content of extracts prepared from Echinacea root with increasing particle size, from 300 to 4000 xm. Particle size is also important in SF extractions as noted by Sun et al. (2002). These authors noted a 10-fold increase in alkamide extraction simply due to grinding the sample. 

Material - shall consist of the beta polymorph only as determined by the examination of a 5% muli of the sample in hexachlorobutadiene or tetrachloro-ethylene by means of a Perkin Elmer Double Beam Infrared Spectrophotometer, Model 21. The mull is prepd by grinding the sample one min in dry state and then adding hexachlorobutadiene and again grinding for another min. The spectrophotometer has a drum setting for th e slit of 980. This gives a slit of about 460 microns ac 13.5 microns and a... 

Treated Sample Place 20 to 25 g of the starch sample in a 250-mL beaker, add 200 mL of a 7 3 methanokwater mixture, disperse the sample, and agitate mechanically for 15 min. Recover the starch by vacuum filtration in a 150-mL medium-porosity fritted-glass or Biichner funnel, and wash the wet cake with 200 mL of the methanokwater mixture. Reslurry the wet cake in the solvent, and wash it a second time in the same manner. Dry the filter cake in an air oven at a temperature below 50°, then grind the sample to 20-mesh or finer, and blend thoroughly. Determine the amount of dry substance by drying a 5-g portion in a vacuum oven, not exceeding 100 mm Hg, at 120° for 5 h. 

Dried vegetables. Grind the sample to pass a ca. 0.5 mm mesh sieve and store in an air-tight container. 

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