Calcium masking

The cardiac effects of the calcium antagonists, ie, slowed rate (negative chronotropy) and decreased contractile force (negative inotropy), are prominent in isolated cardiac preparations. However, in the intact circulation, these effects may be masked by reflex compensatory adjustments to the hypotension that these agents produce. The negative inotropic activity of the calcium antagonists may be a problem in patients having heart failure, where contractility is already depressed, or in patients on concomitant -adrenoceptor blockers where reflex compensatory mechanisms are reduced. 

Traces of many metals interfere in the determination of calcium and magnesium using solochrome black indicator, e.g. Co, Ni, Cu, Zn, Hg, and Mn. Their interference can be overcome by the addition of a little hydroxylammonium chloride (which reduces some of the metals to their lower oxidation states), or also of sodium cyanide or potassium cyanide which form very stable cyanide complexes ( masking ). Iron may be rendered harmless by the addition of a little sodium sulphide. 

The magnesium will be liberated quantitatively and may then be titrated with a standard EDTA solution. Where mixtures of metal ions are analysed, the masking procedures already discussed can be utilized or the pH effect exploited. A mixture containing bismuth, cadmium and calcium might be analysed by first titrating the bismuth at pH = 1-2 followed by the titration of cadmium at an adjusted pH = 4 and finally calcium at pH = 8. Titrations of this complexity would be most conveniently carried out potentiometrically using the mercury pool electrode. 

Scarlet Calcium compounds (masked by barium), appear greenish when viewed through cobalt glass and green through green glass. 

The exact mechanism by which HIER works is unknown. It is thought to reverse the masking effects of formaldehyde fixation and routine tissue processing. Hydrolytic-proteolytic cleavage of formaldehyde-related crosslinks, unfolding of inner epitopes, as well as the extraction of calcium ions from coordination complexes with proteins are among the hypothesized mechanisms (13-15). 

Experience at Barringer Research Laboratory demonstrated that the most effective method to reduce stray light is to combine several reduction procedures. The lead/calcium selectivity of the instrumentation as received was 160, but this has been increased to greater than 1,000,000 with the manufacturer s modifications. The actual steps included replacement of the calcium 393.3 nm line with the 315.9 nm line, replacement of the lead 405.8 nm line with the 220.3 nm line, installation of an interference filter mask over the lead photomultiplier, and computer correction of the residual calcium interference. The stray light reduction obtained by installation of interference filters is presented for three common concomitants in Table II. In many cases the stray light levels were less than or equivalent to the detection limit. The interference filters and the photomultiplier masks (which reduce the entrance angle to the photomultiplier to include only the receiver mirror) improved the detection limits for many elements in the array by decreasing the system band pass. 

Calcium carbonate (70%) and sorbitol (30%) Formaxx CaC03 70 Merck KGaA, Darmstadt, Germany High compressibility, excellent taste masking, free flow, superior content uniformity, controlled particle size distribution... 

Perform all work with gaseous hydrogen fluoride, and also with hydrofluoric acid in a fume cupboardl When pouring hydrofluoric acid into a vessel, wear rubber gloves and eye protection or a mask. See that no drops of the acid get onto your skin. Thoroughly wash an affected area with water and put cotton wool wetted with a 10% calcium chloride solution on it. 

Preparation of Chromium. Perform the experiment in the presence of your instructor, in a fume cupboard Wear eye protection or a mask ) Roast chromium(III) oxide in an iron crucible. Triturate potassium dichromate crystals in a mortar, melt the powder in a porcelain crucible with the flame of a gas burner, pour the substance onto a glazed tile plate, and after it solidifies again triturate it into a powder. Weigh 12 g of roasted chromium(III) oxide, 12 g of the fused potassium dichromate, and 10 g of an aluminium powder, and thoroughly mix all the substances in a mortar. Spill 10 g of a calcium fluoride powder onto the bottom of a chamotte crucible, and then the prepared mixture. (If there is no chamotte crucible in your laboratory, make a box from asbestos paper in the form of a crucible and fasten it with wire.) Tamp the substance with a pestle and make a hollow in the middle using a test tube (see Fig. 120). 

A widely applicable masking agent is sodium triphosphate, Na5P3Oi0-6H2O, which readily complexes with a very wide variety of cations in all groups of the Periodic Table, preventing their precipitation by alkali hydroxide, ammonia, phosphate, carbonate or borate. It is used commercially as Calgon to mask calcium which cannot then form precipitates with citrate, fluoride or oxalate ions and in many other instances (see Table 3). 

The term demasking is used rather broadly to describe any process which reverses the process of masking. Control of the pH can be used to mask calcium ions in admixture with copper(II) whereby, in sufficiently acid solution, the latter is precipitated by oxine whereas the concentration of Ox- is reduced sufficiently by protonation to prevent the precipitation of calcium oxinate. Raising the pH will increase [Ox-] and both metals can now be precipitated. A more obvious example is the addition of fluoride ions to form the very stable complex anion SnF62- and so to mask tin(IV) against its precipitation as SnS2- Addition of boric acid will give BF4- and so demask the tin. 

To prevent waste, the receiver should be followed by a flask containing methyl alcohol, and fitted with a calcium chloride tube. The apparatus should be placed in a hood behind a screen of thick plate-glass because anhydrous hydrazoic acid is very liable to explode violently at room temp. The hands should be protected by heavy gloves, and the face by a mask with plate-glass goggles. For phosphorus pentoxide as a desiccating agent, vide infra. 

Cadmium compounds are very toxic and a suitable face mask should be worn to prevent inhalation of dust. Anhydrous cadmium chloride can be obtained from the commercially available hydrated compound in the following way dry the hydrate to constant weight at 110°C grind finely, dry again for 2-3 hours at 110°C and then place in a screw-capped bottle and keep in a desiccator over calcium chloride. The use of anhydrous cadmium chloride in synthesis is described in Expts 5.94 and 6.126. 

The preparation of pure symmetrical secondary amines (e.g. dibutylamine, Expt 5.199) is conveniently achieved by the hydrolysis of dialkylcyanamides with dilute sulphuric acid. The appropriate dialkyl cyanamide is prepared by treating sodium cyanamide (itself obtained from calcium cyanamide and aqueous sodium hydroxide solution) with an alkyl halide. In this case the reagent [ —C=N]20 may be regarded as a masked NH group. 

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