Freeze drying materials

Flavonoids may be extracted from fresh or frozen plant tissues or from herbarium material, although freeze-dried material may also be utilized [34]. It is very important to ensure that the matoial to be extracted is finely divided, whether by cutting or emshing, to ensure proper extraction. Extraction can be carried out successively with methanol containing some 10% of wate and thm with a 1 1 mixture of methanol and water. Each extraction should be carried out for a period of about 2 h, shaking or stirring to facilitate the process. The extracts are then combined for chromatographic separation. 

Frozen reference materials have been produced by NIST (Wise et al. 1993). These materials do not have the disadvantages of the oils or freeze-dried materials, but are more difficult to transport. Obviously they have to be kept deep-frozen during transport, which makes their use rather expensive. Since the early 1990 s a new approach in this field has been introduced. This concerned the use of wet, sterilized fish and shellfish samples. These samples, packed in glass jars or in tins, were firstly used in the QUASIMEME program as reference materials for inter-laboratory studies (de Boer 1997). Later, when it appeared that the stability was maintained for longer periods, tests for organic contaminants based on this principle were also prepared. 

The acetylation of amylopectin with pyridine and acetic anhydride presents more difficulty, even when using freeze-dried material,26 and the most satisfactory method is that involving prior dispersion in formamide, after which esterification occurs readily at room temperature. 

The starting material (batch) after appropriate homogenization should be stored in appropriate containers. Later these containers would be distributed to the interested scientists in order to support their measurements. Of course, first, the appropriate containers, in terms of size (large, small), shape (bottle, vial), properties (hard, soft, coloured), material (glass, plastic) have to be selected. Some other important items at this stage are the preparation of the units imder the appropriate conditions (e.g. freeze-dried material tmder low humidity), each unit should contain an appropriate amount of material (depending on the amoimt needed for each measurement and the availability of the material) and the appropriate number of units has to be decided (taking into account the needs for this specific certified reference material). 

Extraction of flavonoids from grapes is classically carried out with organic solvents, starting from fresh, frozen, or freeze-dried material. The most commonly used solvents are methanol, ethanol, and acetone, which can be used pure or mixed with water. Extraction of anthocyanins is commonly achieved at low temperatures with acidified methanol. The use of acid maintains the anthocyanins in the most stable flavylium forms but may cause degradation of... 

Remove freeze-dried material from the sides of the flasks using a spatula. Gently scrape off any other material that is adhering. Weigh and analyze (unitfj.2 and units... 

After the samples have been freeze dried, record weights. Dry a portion over desiccant and record weights (i.e., use the freeze dried material without further drying for analyses). 

Frozen materials should be stored at —20°C, fruits and salad vegetables at around 4°C, and canned foods at room temperature. Powdered and freeze-dried materials should be stored in the dark in their original containers. Storage of fresh materials should preferably not exceed 3 days. After the initial preparation (see below), fresh or cooked materials can be conveniently stored at -20°C for a short time prior to extraction. 

Dissolve freeze dried material in a minimum of double-distilled water, filter through a 0.45-pm HA-Millipore filter and chromatograph by preparatory LC—i.e., place ten... 

Vegetables, fruits Extract freeze dried material with THF/MeOH (1 1) + MgC03 + internal standard (/3-apo-8 -carotenoate) at 0°C. Homogenize, centrifuge. Saponify if /3-cryptoxanthin needs to be determined. Add 10% NaCl (w/v) to either saponified or unsaponified solution and extract with petroleum ether. Vydac 201 TP C,g 5 /zm (Hastalloy frits replaced with PAT (Peek alloyed with Teflon frits) 250 X 4.6 mm... 

A total 6.5 g (1 1.55 mmol) of7-[D-a-t-butoxycarbonylamino-a-(p-hydroxyphenyl)acetamido]-3-(l,2,3-triazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid was dissolved in 175 ml (98 to 100% formic acid under anhydrous conditions. The mixture was stirred at room temperature for 2.5 hours. Part of the solution, 125 ml, was evaporated under reduced pressure to an amber oil. The oil was then azeotroped 3 times with 70 ml of toluene under reduced pressure. The residue was suspended in an 80 20 H20-CH30H solution (700 ml) and stirred for 0.5 hour until most of the solid dissolved, then filtered. The filtration was treated with 1.59 of (Darko) charcoal for about 20 minutes. The charcoal was filtered off through a Celite pad. The solution was then freeze-dried in 9 separate 100 ml round bottom flasks. The freeze-dried material weighed 2.415 g. It was recrystallized in batches of 0.200 g as described above to yield a total of 0.923 g 7-[D-a-amino-a-(p-hydroxyphenyl) acetamidol-3-(l,2,3-triazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid. NMR was consistent, indicating the presence of 0.33 mol of CH3OH. 

Sublimation is the reason your ice cubes disappear if left for long periods in the freezer and forms the basis for freeze drying materials. 

Collapse in freeze-drying occurs above a critical temperature, which allows viscous flow of freeze-concentrated amorphous solutes (Bellows and King 1973) as they are plasticized by unfrozen water (Roos 2004). The onset temperature of ice melting, T, can be used as a critical reference temperature for production of properly freeze-dried materials. 

As a result of a detailed collaborative investigation between the Chemistry Department of the University of Nottingham (Crombie, Whiting) and the U.N. Narcotics Laboratory (Szendrei), at least 14 cathedulin alkaloids have been isolated and formulated (46,47). Plant material collected in Kenya, Ethiopia, and the Yemen Arab Republic was extracted as fresh material, as freeze-dried material, and as sun-dried material. A number of extraction procedures were also employed, with methods directed toward the isolation of weak bases. In one procedure fresh material was extracted with ethanol in the presence of sodium bicarbonate, and the diluted extract was adjusted to pH 5.5 and extracted with... 

Other than the absorption at 1718 cm", the freeze-dried material from equilibrated solutions of D-mannose, D-glucose, and L-rhamnose shows only the absorptions characteristic of the respective, crystalline a- and 8-pyranose forms. The lyophilizate of D-galactose solution showed similar behavior, except for an absorption band at 921 cm". The lyophilizates of equilibrated solutions of D-lyxose and D-talose show a number of absorption bands not found in the spectra for the crystalline anomeric pairs. ... 

Moisture in freeze-dried materials Identification of mixes... 

As shown in Figs. 8 and 9, the moisture content in freeze dried material was not constant after freeze drying. 

Certain process steps may be easier to model than others and duplicating the freeze dry/dry heat step at small scale is very difficult. The conclusions drawn from virus clearance studies are reliable only when the appropriateness of the small-scale models can be demonstrated. During the freeze dry/dry heat step of Koate -DVI, virus reduction was dependent on moisture levels so even the formulation of stoppers, which could impact the absorption of water during autoclaving and its release to freeze dried material, must be considered and tested. 

Fig. 15 The XRD patterns of (a) as is sodium nafcillin, (b) frozen solution of sodium nafcillin (40wt%) annealed at —4°C for 1 h, and (c) after freeze-drying the annealed system. The as is sodium nafcillin was a monohydrate. Annealing is believed to result in the crystallization of a higher hydrate of sodium nafcillin (unknown stoichiometry). The freeze-dried material was partially crystalline sodium nafcillin hemi-hydrate. (From Ref. l)...

The freeze-drying technique is also used in the analytical laboratory. Two additional benefits make it attractive to analysts, namely (a) because the removal of water allows samples to be subsequently reconstituted in a minimal volume of liquid, a preconcentration effect is achieved and (b), even more important, because of their texture, freeze-dried materials are very easily attacked by solvents. The process can be optimized for a specific purpose by using an appropriate temperature, pH, reagent addition sequence and time. One major disadvantage of freeze-drying, however, is that some volatile compounds may be removed from the sample matrix during the process. 

The sublimation step separates the ice crystals formed during the freezing step. When an ice crystal forms, that which remains is the concentrated solute phase called the dry layer . This will become the freeze-dried material at the end of the process. Immediately following passage through the interface, however, the solids in the dry layer still contain a substantial amount of water (about 25-30 g per 100 g of solids), which continues to be strongly bound to the solids. Most sample materials will not be structurally or chemically stable unless most of this water (called sorbed water ) is removed. The process... 

The stability of freeze-dried materials is dictated by various factors two of the most important of which are moisture and oxygen. 

By nature, freeze-dried produets are hygroscopic, so exposure to moisture during storage can destabilize them. Packaging used for freeze-dried materials must be impermeable... 

Freeze-dried materials for urine samples are nearly as commonplace as serum samples. These materials possess long-term stability and are used for the determination of pentachlorophenol [25] and metals such as Pb [26] and Cd [27], among others. In most cases, the results for the freeze-dried reference material are indistinguishable from those for fresh urine. 

Moisture, and Ash Content. For Skeletonema, the wet basis moisture content In batches one through four were 88.9%, 87.5%, 90.3%, and 87.6%, respectively. The average wet basis moisture content of the freeze dried material was 5%. The average ash content of all batches was 30% dry weight basis. The high ash level Is due to the silica skeleton of Skeletonema costatum. 

NMR. Quantitative liquid-state carbon-13 nuclear magnetic resonance ( 3c NMR) spectra were recorded for humic and fulvic acid from Como Creek foam and for stream and foam fulvic- and humic- acid samples from the Suwannee River at the U.S. Geological Survey, laboratory in Arvada, CO. C NMR could not be performed on other humic substances due to insufficient sample or instrument availability. The acquisition parameters used were as follows C NMR spectra were recorded on a Varian XL-300 NMR spectrometer at 75 MHz. Each sample (200 mg of freeze-dried material) was dissolved in deuterated water and deuterated sodium hydroxide was added to ensure solution a total solution volume of approximately 6 to 7 mL. Spectra were recorded using a 30,000 Hz spectral window, a 45 pulse width, a 0.199 second acquisition time, and a pulse delay of 10 seconds for quantitative spectra. The number of transients was 10,000, and line broadening was 50 Hz. 

Rehydrate the freeze-dried material, with 0.1 ml H O at 20°C (see Note 18), by vigorous mixing. Let the suspension at peace for 30 min above the lipid Tc. 

Basically, all products which contain water can be dried in this manner. After freezing, the ice crystals remain at first at their original location in the structure. If vacuum is applied, the ice sublimates directly without melting. This results in a porous, dry product which has retained its original form. The volume has hardly changed, the cell walls have been little affected, flavour and other main constituents have been treated gently. If the product is to be restored to its former condition - to be reconstituted -only water has to be added. Water sorption in freeze dried materials proceeds faster than in conventionally dried products. For detailed studies on the fundamentals of freeze drying see the literature [1-10]. 

Analysis of Sediment-Trap Material. The freeze-dried material from the sediment traps was digested with HCl-HN03 in a microwave digestion device (MLS-1200). Teflon beakers, cleaned with NH03, were used. Fe, Mn, Ca, Zn, Cu, and Cr were determined by inductively coupled plasma emission spectrometry, P by the molybdate spectrophotometric method (25) and organic C and N on a C, H, N analyzer (Heraeus). 

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