Normal Cellulose Powder

Fibrous cellulose is high quality material prepared in the usual way in the cellulose or cotton industry and then reduced under mild conditions to a fibre grade suitable for TLC. The average degree of polymerisation of the native cellulose powder MN 300 (Firm 83) is of the order of 400—600. The fibre length of MN 300 ranges from 2 to 20 [xm. 

Preparation of the Layers. An aquieous siLspension containing about 15% cellulose powder, rendered homogeneous by 30—60 secs in an electric mixer, yields layers with the optimum uniformity, smoothness etc. The layers adhere excellently and can even he wiped in the dried state. Cellulose layers are best air dried. It is unnecessary to activate them at higher temperatures. In fact, the separating properties of cellulose layers improve on long exposure to air. 

The duration of homogenisation is thus of great importance. The data in the following Table 7 illustrate the influence of stirring time. 

With the fibrous cellulose powder MN 300 (Firm 83), the time of homogenisation has an influence only when exceeding 10 min. On the other hand, in contrast to Avicel, a mixture satisfactory for layer preparation cannot be attained by merely mixing with a glass rod. The length of run on a MN 300 layer with the same solvents as that used 

Magnified photographs of cellulose fibres from paper and cellulose powder for TLC are in Fig. 3. Rapid substance transportation along long fibres cannot occur on the short fibres of the cellulose powder as a result, the spots from the same amounts of substance are more compact than on paper. 

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Cellulose consists of a large number of cellobiose units linked via jS-l,4-glycosidic bonds. It possesses hydrophilic properties due to the numerous hydroxyl groups of the units (Fig. 9). Normal cellulose powder is therefore suitable for separating hydrophilic compounds. More detailed information and examples of application are to be found in the review articles of P. Wollenweber [770, 771, 772, 773]. 

For conventional or normal, in contrast with reversed-phase, LLPC, many materials have been used as the solid support for the stationary liquid. In addition to silica gel, which was the first and is still the most popular material, a variety of other adsorbents that adsorb the polar solvent such as cellulose powder, starch, alumina, and silicic acid have been used. The more recent practice of HPLC has greatly simplified the technique in providing column stability for repeated use and for treatment of large volumes. 

Our experimental work started from the following original cellulose samples (a) acetate-grade, bleached cotton linters, DP 1800 (b) hot, refined, spruce, sulphite-dissolving pulp, machine dried, ca. 93% a-cellulose, DP — 750 (c) never-dried, normal, rayon-grade, beech sulphite pulp, ca. 90% a-cellulose, DP = 825 (d) commercial cellulose powders obtained by hydrolytic degradation and/or mechanical disintegration of cotton linters or spruce sulphite pulp. 

These modified cellulose powders can be used to obtain ion exchange separations on thin layers, with similar advantages over column or paper sheet methods. Both normal and modified cellulose powders can be used with or without a binder and fluorescent indicator. 

There are several stationary phases that can be used for separation of various compounds including lipids, natural products, biological compounds, drugs, etc. Examples are Celite (Supelco Inc., PA), cellulose powder, ion-exchange cellulose, starch, polyamides and Sephadex (Supelco Inc., PA), but the most popular ones for lipid separations include silica gel, alumina and kieselguhr. These adsorbents can also be modified by impregnation with other substances so as to achieve the desired separations. Based on their characteristics these phases can be classified as normal or reversed. 

The rate of migration can be influenced or varied through addition of normal, non-ion exchanging cellulose powder. 

FIGURE 4.9 Illustration of standard normal variate (SNV) preprocessing, (a) NIR reflectance spectra of 20 powdered samples of microcrystalline cellulose, (b) Same NIR reflectance spectra after SNV preprocessing, revealing differences in moisture content. 

Observe normal precautions appropriate to the circumstances and quantity of material handled. Powdered cellulose may be irritant to the eyes. Gloves, eye protection, and a dust mask are recommended. In the UK, the occupational exposure limits for cellulose have been set at lOmg/m long-term (8-hour TWA) for total inhalable dust and 4mg/m for respirable dust the short-term limit for total inhalable dust has been set at 20mg/m < ... 

Today, both MCC and PC fiber grades are widely used in tabletting. Depending on the composition of the formulation, one or the other cellulose product results in better hardness, friability, and disintegration values. However, the quantity of MCC required to yield comparable tablet properties is normally at least one-third higher than that of PC fibers. Since, because of a more economical production process, the cost of PC fibers is also lower than that of MCC, monetary advantages can be derived from using powdered cellulose. 

Another novel approach to utilizing affinity surfaces is referred to as the material-enhanced laser desorption/ionization (MELDI) technique [95] (Figure 3.10). This method was developed with the use of specially derivatized chromatographic materials (cellulose, silica, poly [glycidyl methacrylate/divinylbenzene] particles, and diamond powder) for fast and direct protein profiling to evaluate normal and pathological human serum samples. 

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