Calcium solubility procedure

The in vitro procedure was tested in "critical" experiments designed to make direct comparisons of in vivo and in vitro estimates of exchangeability and potential bioavailability and to test the use of in vitro exchangeability values in in vivo experiments. (8). Three foods which were expected to show different levels of calcium solubility and exchangeability, collards, soybeans and spinach, were intrinsically labeled with 45Ca in nutrient solution culture. They were used together with 47 Ca as an extrinsic label in both in vitro and in vivo experiments. 

Experiments were conducted to determine if varying the conditions in the in vitro digestion procedure would affect post-digestion calcium solubility and in some cases, exchangeability. This was done with two purposes to test the use of the in vitro digestion procedure for studying factors which might influence calcium bioavailability and to use the results to modify the standard procedure. 

Choice of Potential Bioavailability Criterion. It is usually assumed that calcium must be soluble and probably ionized in order to be available for absorption ( ). For the in vitro procedure, as a first approximation we chose calcium solubility after centrifugation at 18,000 x g as the measure of potential bioavailability (Figure 1). We assumed that this would probably overestimate the available calcium and later work based on fractionation might define the bioavailable calcium more precisely. The data in Table IV illustrate how the choice of criterion for "solubility" could affect the in vitro estimate of potential availability, even if in vitro conditions closely resembled in vivo conditions. Since our in vitro criterion unexpectedly underestimated calcium bioavailability for two of the three foods in the direct in vivo - in vitro comparison (8), it was necessary to determine the in vitro digestion conditions which might be limiting solubility before addressing the choice of appropriate criterion. 

The term "standard" is not meant to denote a digestion procedure which should be routinely used to determine potentially available calcium. Since the number of foods tested so far is limited, it will be more useful to think of the "standard" procedure as a set of conditions to be used to see how well we understand food chemistry and calcium solubility in the gastrointestinal environment. It should be used for measuring the relative solubility of calcium from foods and meals, but mostly in the context of comparisons with in vivo results to define factors which require further study. 

Verduch analyzed the W spacing of the primary diffraction line of cristobalite to determine the extent of calcium solubility. Since the procedure was not the usual lattice parameter determination, his results may be questionable. It is noted that Verduch confirmed the work of Jander and Hoffman with respect to the order in appearance of products. 

Soluble sulfides such as sodium sulfide, potassium sulfide, and calcium polysulfides have been used to precipitate mercury salts from alkaline solutions. When this procedure is used, exercise of caution is requked to maintain the pH within a given alkaline range so as to prevent evolution of H2S. Because the solubiUty of mercuric sulfide in water is 12.5 flg/L at 18°C or 10.7 ppb of mercury, use of this method for removal of mercury is adequate for most purposes. However, the presence of excess alkah, such as sodium hydroxide or sodium sulfide, increases the solubiUty of mercuric sulfide as shown ... 

Two asymmetric carbon atoms, the or carbon in the glutamic acid portion of the molecule and the C6 carbon in the tetrahydropteridine ring, allow four possible isomers. Since synthetic procedures would undoubtedly start with L-glutamic acid, the isomeric possibilities are reduced to the dL and 1L diastereomers. Of these, the biologically more active form is the 1L separation of the diastereomers is effected by solubility differences of the calcium salts.2... 

Part of this objection to the calcium pectate as a means of following the hydrolysis of pectic materials can be met by using the simple procedure developed by Fellers and Rice" for the estimation of pectic substances as pectic acid. This approximate method measures the volume of the pectic acid which can be produced from a sample of soluble pectic material and will therefore show the loss of colloidality by the rapidly decreasing volume even if the weight of the precipitate remains the same. Unfortunately the Fellers-Rice method is not sufficiently accurate for exact kinetic studies. 

Again, there are several choices of extractant, and the preferred one depends mainly on the type of soil under test. One of the most widely used procedures is the Olsen method (Olsen ef al., 1954), which was developed in the USA to correlate crop response to fertilizer on calcareous soils. The amount of P extracted will vary with temperature (increases by 0.43 mg P kg- per degree rise between 20°C and 30°C) and shaking speed, so conditions should be standardized. The extractant is 0.5 M sodium bicarbonate adjusted to pH 8.5. The bicarbonate competes with phosphate on the adsorption sites extracts, and removes most, but not all of it, together with some soluble calcium phosphate. Addition of phosphate-free activated carbon before shaking is necessary if coloured soil extracts are obtained, and then they will require filtration. 

As a check on the degassing procedure, solubilities of carbon dioxide in aqueous calcium chloride solutions prepared in the same manner were determined at 25 °C and 1 atm. The results agreed with the previous results (4), in which the aqueous solutions were prepared by another method. Thus the degassing procedure adopted in this work can be considered satisfactory. 

Tartaric Acid. Quantitative measures of total tartrate are useful in determining the amount of acid reduction required for high acid musts and in predicting the tartrate stability of finished wines. Three procedures may be used. Precipitation as calcium racemate is accurate (85), but the cost and unavailability of L-tartaric acid are prohibitive. Precipitation of tartaric acid as potassium bitartrate is the oldest procedure but is somewhat empirical because of the appreciable solubility of potassium bi-tartrate. Nevertheless, it is still an official AO AC method (3). The colorimetric metavanadate procedure is widely used (4, 6, 86, 87). Tanner and Sandoz (88) reported good correlation between their bitartrate procedure and Rebeleins rapid colorimetric method (87). Potentiometric titration in Me2CO after ion exchange was specific for tartaric acid (89). 

The procedure to be followed is the same as for the calcium salt except that about 180g of barium hydroxide 8-hydrate is employed, instead of the slaked lime. As the former is more soluble, some care should be exercised not to add too great an excess because the quantity of slurry... 

Other preliminary experiments on alkali lignin included oxidations by barium peroxide and alkali (5, 6), alkali fusion, and alkali fusions in the presence of calcium peroxide, sodium borate perhydrate, and monopersulfate compound. Ether extractives and water extractives were examined, but in all cases too many of the oxidation products obtained were new and unidentifiable, and it was impossible to evaluate the experiments adequately with the available techniques. Vanillic acid appeared to be the chief oxidation product under conditions which did not demethylate further or destroy the aromatic nature of the oxidation products. Some oxidation conditions yielded p-hydroxybenzyl moieties as products, and some gave no trace of these products whatever. More detailed studies of the ether-insoluble, water-soluble components of the several oxidation mixtures were postponed until adequate procedures were developed for analytical isolation and identification. 

An official procedure [10,11] describes a method for the determination of chloride in a saturated calcium sulfate extract of soil. The extract is acidified and the concentration of chloride is determined by titration with mercuric nitrate using diphenylcarbazone as indicator. Mercuric ion in the presence of chloride forms mercuric chloride, which, although soluble, provides insufficient mercuric ion to form the mercuric-diphenylcarbazone complex. When all of the chloride has been removed in this way, addition of further mercuric ion produces the violet complex. 

Scale control is complex the particular procedure depends on the composition of the feed water. Fortunately, calcium carbonate scale, by far the most common problem, is easily controlled by acidifying the feed or by using an ion exchange water softener to exchange calcium for sodium. Alternatively, an antisealant chemical such as sodium hexametaphosphate can be added. Antisealants interfere with the precipitation of the insoluble salt and maintain the salt in solution even when the solubility limit is exceeded. Polymeric antisealants may also be used, sometimes in combination with a dispersant to break up any floes that occur. 

Fe3+ can be quantitatively removed from sour wine with [Fe(CN)6]4, a usual procedure to remove iron ions from wine.371 Concentrated alkali carbonate solutions will precipitate the Fe2+ of Iron Blue as FeC03, so that they destroy the entire pigment by precipitating Fe3+ as Fe(OH)3 (due to alkalinity) and the hexacyanoferrate(II) salt [Fe(CN)6]4 372 Calcium carbonate solutions, however, would not be sufficient due to their marginal saturation solubility. Besides that, Kohn examined the supportive effect of most of the organic ligands to disperse Iron Blue.373... 

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