Citric acid effectiveness

Acid cleaning agents such as hydrochloric, phosphoric, or citric acids effectively remove common scaling compounds. With cellulose acetate membranes the pH of the solution should not go below 2.0 or else hydrolysis of the membrane will occur. Oxalic acid is particularly effective for removing iron deposits. Acids such as citric acid are not very effective with calcium, magnesium, or barium sulfate scale in this case a chelatant such as ethylene diamine tetraacetic acid (EDTA) may be used. 

Common stabilizers for organic cellulose molding compounds include epoxides, especially epoxidized soybean oil, alkaline and alkaline-earth salts of acetic and carbonic acid as well as tartaric acid, oxalic acid and citric acid. Effective antioxidants include substituted phenols, such as t-butylphenol, or preferably sterically hindered phenols, such as 2,6-di-tert-butyl-p-cresol. Diphenylamine or esters of thiopropionic acid exhibit an effect similar to that of antioxidants [501]. 

Bizek V, Hov46ek J, Kousova M (1993) Amine extraction of citric acid effect of diluent. Chem Eng Sci 48 1447-1457... 

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

In appHcations as hard surface cleaners of stainless steel boilers and process equipment, glycoHc acid and formic acid mixtures are particularly advantageous because of effective removal of operational and preoperational deposits, absence of chlorides, low corrosion, freedom from organic Hon precipitations, economy, and volatile decomposition products. Ammoniated glycoHc acid Hi mixture with citric acid shows exceUent dissolution of the oxides and salts and the corrosion rates are low. 

Activators. Activators are often added to removers to make them more efficient. Acids such as phenol [108-95-2] phosphoric acid [7664-38-2] acetic acid [64-19-7] formic acid [64-18-6]., and citric acid [5949-29-1] are used to increase the cutting abiHty on epoxide-type paints and other modem finishes. Strongly alkaline activators are effective on enamel andlatex paints. Other activators include ammonia [7664-41-7] monoethyl amine [75-04-7], and /V-phenyIdiethan ol amines. Acid and base activators shorten the shelf life of some removers. 

Ascorbic acid also forms soluble chelate complexes with iron (142—145). It seems ascorbic acid has no effect on high iron levels found in people with iron overload (146). It is well known, in fact, that ascorbic acid in the presence of iron can exhibit either prooxidant or antioxidant effects, depending on the concentration used (147). The combination of citric acid and ascorbic acid may enhance the iron load in aging populations. Iron overload may be the most important common etiologic factor in the development of heart disease, cancer, diabetes, osteoporosis, arthritis, and possibly other disorders. The synergistic combination of citric acid and ascorbic acid needs further study, particularly because the iron overload produced may be correctable (147). 

Meat Products. Citric acid is used in cured meat products to increase the effectiveness of the antioxidant preservatives, as a processing aid, and a texture modifier. It is often encapsulated and released at a specific temperature from a controlled release matrix. 

Medical Uses. Citric acid and citrate salts are used to buffer a wide range of pharmaceuticals at their optimum pH for stabiUty and effectiveness (65—74). Effervescent formulations use citric acid and bicarbonate to provide rapid dissolution of active ingredients and improve palatabiUty. Citrates are used to chelate trace metal ions, preventing degradation of ingredients. Citrates are used to prevent the coagulation of both human and animal blood in plasma and blood fractionation. Calcium and ferric ammonium citrates are used in mineral supplements. 

Tobacco. Citric acid is a natural constituent of the tobacco leaf and during tobacco processing additional citric acid is added to enhance the flavor and to effect more complete combustion of tobaccos (212). 

D. D. Brooks and co-workers, "The Synergistic Effect of Neutral Bleaching Clay and Citric Acid Chlorophyll Removal," paper presented at the... 

Another important piece of the puzzle came from the work of Carl Martius and Franz Knoop, who showed that citric acid could be converted to isocitrate and then to a-ketoglutarate. This finding was significant because it was already known that a-ketoglutarate could be enzymatically oxidized to succinate. At this juncture, the pathway from citrate to oxaloacetate seemed to be as shown in Figure 20.3. Whereas the pathway made sense, the catalytic effect of succinate and the other dicarboxylic acids from Szent-Gyorgyi s studies remained a puzzle. 

There is an accelerating trend away from the use of lead-containing solders in contact with potable water. The effects of galvanic corrosion of one of the substitute alloys (Sn3%Ag) in contact with a number of other metals including copper have therefore been studied . The corrosion of tin/Iead alloys in different electrolytes including nitrates, nitric and acetic acids, and citric acid over the pH range 2-6 were reported. The specific alloy Pb/15%Sn was studied in contact with aqueous solutions in the pH range... 

Fig. 12.1. Effect of iron concentration on yield of citric acid by A. niger.

Sodium a-sulfomethylmyristate is used together with the sodium salt of hardened beef tallow fatty acid to produce a soap with little skin irritation [88]. Shampoos for application to hair as well as skin comprise a-sulfo fatty acid ester salts, fatty acid dialkanolamides, and citric acid. For example, a shampoo that consists of 15% sodium a-sulfoethylmyristate, 3% lauric acid diethanolamide, 0.5% citric acid, and 81.5% water is very effective even in hard water and only slightly irritating to the skin [89]. 

Ishizaki T, Saito N, Takai O, Asakura S, Goto K, Euwa A (2005) An investigation into the effect of ionic species on the formation of ZnTe from a citric acid electrolyte. Electrochim Acta 50 3509-3516... 

No other additive has the same effect although many alternatives were examined by Wilson, Crisp Femer (1976) and Prosser, Jerome Wilson (1982). Other multifunctional carboxylic acids, including citric acid, had little effect, apart from a slight tendency to shorten working time and increase the setting rate. That the effect is a subtle one is shown by the fact... 

Figure 5.20 The effect of a citric acid solution on tooth structure (a) enamel surface before application, (b) enamel surface after application showing etching, (c) dentine surface before application, (d) dentine surface after application showing the opening-up of the dental tubules (Powis et al, 1982).

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