Absorption of fluoride

In humans, the predominant route of absorption of fluoride is via the gastrointestinal tract. Airborne fluoride may also be inhaled. Dermal absorption is negligible except in cases of hydrofluoric acid burns [42]. 

Treatment. Aluminum sulfate, aluminum chloride, calcium aluminate, calcfum catboiv ate, and defluoridated phosphate are recommended to reduce absorption of fluoride. Treatment is ineffective once dental aixi skeletal lesions have developed. 

Toxicity. Fluoroborates are excreted mostly in the urine (22). Sodium fluoroborate is absorbed almost completely into the human bloodstream and over a 14-d experiment all of the NaBF ingested was found in the urine. Although the fluoride ion is covalently bound to boron, the rate of absorption of the physiologically inert BF from the gastrointestinal tract of rats exceeds that of the physiologically active simple fluorides (23). 

The proposed mechanism includes the production of HCl from the pyro-hydrolysis of the metal chlorides. Similar reactions are likely for bromides and iodides. Fluorides however are relatively stable and would not be expected to hydrolyse. It was considered that this might account for the inability of fluorides to cause cracking. Hydrogen absorption by titanium alloys exposed to chloride salts at elevated temperatures has been detected and found to be proportional to the amount of moisture participating in the reaction. 

Vibration spectra of fluoride and oxyfuoride compounds correspond to X Me ratios, especially in the case of island-type structure compounds. Analysis of IR absorption spectra provides additional indication of the coordination number of the central atom. Fig. 45 shows the dependence on the X Me ratio of the most intensive IR bands, which correspond to asymmetric Me-F modes in fluoride complexes, as well as v(Me=0) and v(Me-F) in oxyfluoride complexes. Wave numbers of TaF5, NbF5 and NbOF3 IR spectra were taken from [283-286]. 

As the cement ages, absorption of water and loss of aluminium ions ceases (after 7 days). Other species - sodium and fluoride ions and silicic acid - continue to be eluted. The release of fluoride is important, for the glass polyalkenoate cement can be seen as a device for its sustained release. 

Decrease absorption of iron, telracydine, quinolones, bisphosphonates, phenyloin, and fluoride when given concomitantiy... 

Based on limited epidemiologic evidence, fluoride supplements, with or without calcium, estrogen and vitamin D, are used by clinicians for the treatment of osteoporosis. However, knowledge of the effects of fluoride on calcium and phosphorus metabolism in normal animals is limited although Spencer et al. (32) reported that ingestion of fluoride by three osteoporotic men did not affect calcium absorption but caused a decrease in urinary excretion. Moreover, there is a need to determine the long-term effects of fluoride treatment on bone strength and on soft tissues ( ). 

These studies have shown that phosphorus, magnesium and fluoride In the doses used had no effect on the bloavailablllty of calcium, while large doses of zinc given during a low calcium Intake Inhibited the Intestinal absorption of calcium The effect of protein and of certain drugs on calcium metabolism Is also described ... 

In extensive studies of the effect of fluoride In patients with osteoporosis carried out In this Research Unit, a therapeutic dally dose of 45 mg fluoride per day was used as sodium fluoride. The main effect of fluoride on calcium metabolism was a decrease of the urinary calcium, while the fecal calcium did not change and the calcium balance also remained unchanged. Also, the Intestinal absorption of calcium remained unchanged during the high fluoride Intake (Table I), The decrease In urinary calcium, Induced by sodium fluoride, may be due to decreased bone resorption, a very desirable effect for patients with osteoporosis. 

Prescribed Limit The colour of the resulting solution is greater than that obtained by repeating the operation with no substance enclosed in the successive portions of filter paper burnt in the method for oxygen flask combustion, but adding 3.0 ml of fluoride standard solution (10 ppm F) to the combined absorption liquids before adding the acid zirconyl alizarin solution. ... 

When substances adsorbed on aerosol particles are to be determined, the gas is passed through a membrane or other filter and the filter is dissolved in or extracted with a suitable solution. An interesting method is used for determination of fluoride adsorbed on atmospheric aerosols [87]. The particles are trapped on a filter impregnated with citric acid and heated to 80 °C, while the fluorides pass through and are absorbed in a thin layer of sodium carbonate in a spiral absorber. The sodium carbonate is periodically washed with a sodium citrate solution, in which solution the fluoride is then determined, and the absorption layer regenerated. 

Toxicology. Fluoride causes irritation of the eyes and respiratory tract and gastrointestinal effects absorption of excessive amounts of fluoride over a long period of time results in skeletal fluorosis. 

Fluoride taken in the form of sodium fluoride as a tablet or solution is absorbed rapidly. Only a few minutes after intake, there is a rise in plasma fluoride. The fluctuation in plasma fluoride concentration is dependent on the fluoride dose ingested, the dose frequency and the plasma half-life of fluoride. The half time for absorption is --30 min, so peak plasma concentration usually occurs within 30-60 min [64-69]. Absorbed fluoride is rapidly distributed by the circulation to the intracellular and extracellular fluids and is retained only in calcified tissues. The sensitivity of the serum fluoride concentrations to previous intake, glomerular filtration and the intensity of bone resorption suggests that the human organism exerts no direct homeostatic control and that fluoride concentrations reflect the recent intake [73]. Plasma fluoride levels increase with age, with increasing fluoride content of bone and as a consequence of renal insufficiency [2]. 

Methods for determining gaseous fluorides are generally based on the absorption of gaseous fluorides into a train of absorbing solutions, or collection on a filter with a treated pad and subsequent determination of fluoride. 

G. Cobo, M. Gomez, C. Camara, M.A. Palacios, Determination of fluoride in complex liquid matrices by electrothermal atomic absorption spectrometry with in-furnace oxygen-assisted ashing, Mikrochim. Acta 110 (1993) 103-110. 

Providing no other acidic species are present and water has been used as the absorption medium in either the 02 flask or pyrohydrolytic tube decomposition, the acidimetric titration of hydrogen fluoride is the simplest. Unfortunately this is often not the case, so one of the other finishes such as colorimetry and titrimetry has to be used. One of the best colorimetric procedures employs Ce-Alizarin complexone reagent5 which changes from wine red to dark blue in the presence of fluoride ion. The color takes a while to develop fully, but it is very reliable. 

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