Temporary preservatives

Several methods have received considerable research attention as alternatives to salt curing. These include use of sodium bisulfite as a disinfectant to allow preservation with or without decreased salt in a brine cure use of disinfectants such as quatenary amines for temporary preservation in direct shipping to the taimery from the packing plant (see Disinfectants and antiseptics) preservation of hides by radiation sterilization (see Sterilization techniques) and substitution of materials such as potassium chloride for sodium chloride. These methods have found only limited commercial success. 

Fig. 24 Enantioselective non covalent synthesis of double rosettes exploiting the chiral memory effect. Exchange of chiral barbiturate with the achiral cyanurate occurs faster then racemization by dissociation of the supramolecular structure and allows temporary preservation of the asymmetry instructed in the first diastereoselective step...

Methods commonly used for determining the elemental content of these biota samples include AAS, NAA, DPASV and ICP-AES. A pretreatment step is almost always necessary. The samples of urine should be acidified with a mineral acid or acetic acid for temporary preservation. The samples should, however, be freeze-dried or lyophilised for long term storage. It is possible to determine a number of elements in urine by diluting the samples with deionised water and aspiration into a flame or plasma. 

The urine samples are usually treated with a mineral acid e.g. HCI, HNO3 or acetic acid for temporary preservation. However, for long term storage these human specimens need to be frozen, lyophilised or freeze-dried. Fecal samples should almost always be lyophil-ised or freeze dried before treatment. 

Biodegradable hydrogels have also been developed for use in controlled drug delivery as carriers of biologically active materials such as hormones, enz5mes, antibiotics, antineoplastic agents, and cell suspensions. Temporary preservation of functional properties of a carried species, as well as the controlled release of the species into local tissues or systemic circulation, have been achieved. 

Temporary hair dye products usually are formulated at a neutral or slightly acidic pH. Besides the dyes, the formulations may contain a small amount of a quaternary amine to neutralize the negative charge on the dyes, a fragrance, a small amount of a solvent or surfactant to solubilize the fragrance, and a preservative (Table 6). 

Open-top display can gain considerable heat from air currents and radiant heat from lighting. Temporary covers are frequently used when the building is closed, to reduce these gains and help preserve the foodstuffs. This is of considerable importance where cut meats are displayed, since the radiant heat from lights and loss... 

This method can be regarded as an example of memory of chirality,71 a phenomenon in which the chirality of the starting material is preserved in a reactive intermediate for a limited time. The example in Scheme 2-35 can also be explained by the temporary transfer of chirality from the a-carbon to the t-BuCH moiety so that the newly formed chiral center t-BuCH acts as a memory of the previous chiral center. The original chirality can then be restored upon completion of the reaction. 

Sediment deposition is defined as the temporary emplacement of particles on the seabed while sediment accumulation is defined as the net sum of particle deposition and removal processes over a long period. The term sedimentation refers to integrated particle transport to—and emplacement—on the seabed, as well as removal, and preservation. 

Benzalkonium chloride at concentrations greater than 0.005 mg/ml causes histamine release from mast cells in vitro. At a concentration of 0.03 mg/ml an excess of 90% of the histamine content is released (5). This is in the range of the minimum concentration of benzalkonium chloride recommended as a disinfectant (0.025 mg/ml). Inhalation of benzalkonium chloride nebulizer solution causes concentration-related falls in FEVi in patients with asthma (6). Benzalkonium chloride 0.3 mg also causes a temporary increase in airway reactivity to histamine. This amount of benzalkonium chloride is similar to that in a 2.5 mg dose from a multidose vial of salbutamol (7). Ipratropium containing benzalkonium chloride 0.25 mg/ml causes bronchoconstriction in a proportion of patients with asthma. BronchodUatation is seen when 2 ml (0.5 mg) of preservative-free ipratropium bromide solution is inhaled (8). Benzalkonium chloride 0.1 mg/ml does not alter the bronchodUator effect of salbutamol. The difference between salbutamol and ipratropium may be the lower concentration of benzalkonium chloride in the salbutamol solution (0.1 versus 0.25 mg/ml) and the greater potency and more rapid onset of the bronchodilator response to salbutamol (9). Individual case reports suggest that... 

On the timescale of thousands of years it is clear that changes in the land and ocean reservoirs have led to imbalances in their C02 fluxes with the atmosphere. The best evidence for this comes from ice cores and the record of atmospheric composition preserved in them. Figure 7.10 shows how atmospheric C02 concentrations and earth-surface temperatures have changed over the last 420000 years, as recorded in the Vostok ice core from Antarctica. There have clearly been dramatic changes in atmospheric C02 levels over this period and the most likely explanation for these shifts is that they arise from (temporary) imbalances between the inter-reservoir fluxes. 

With some preservatives the temporary residenee of the solution within the wood ean result in partial fixation and in some eases seleetive absorption of one or more of the ehemieal eomponents in the formulation sueh that the expelled solution ( kick-baek ) is no longer eorreetly balaneed. Imbalanee in the preservative solution needs to be monitored. Another undesirable eharaeteristie of empty cell cycles is the fact the kiek-baek solution can contain dissolved wood sugars. These sugars can react with preservative components leading to the aeeumulation and deposition of insoluble precipitates, commonly referred to as sludge, in the bulk storage tanks. 

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