Acidity determination methods

S Blackburn. Sample preparation and hydrolytic methods. In S Blackburn, ed. Amino Acid Determination Methods and Techniques. 2nd ed. New York Marcel Dekker, 1978, pp 7-34. 

Blackburn, S. "Amino Acid Determination, Method and Techniques" Marcel Dekker, Inc. New York, 1968. 

Blackburn, M., 1978. Amino Acid Determination — Methods and Techniques. Marcel Dekker, New York, N.Y., 367 pp. 

Blackburn, S. (1968). Amino Acid Determination. Methods and Techniques, pp. 127-132. Dekker, New York. 

It is beyond the scope of this chapter to discuss all available technologies, just one example of each of three detection principles will be mentioned here, viz., a growth based method, a non-growth based method and a nucleic acid determination method. For an encyclopaedic overview the reader is referred to the literature [71]. 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

Eluorspar assay may be completed by fluoride determination alone, because the mineralogical grouping rarely iacludes fluorine minerals other than fluorite. Calcium can be determined as oxalate or by ion-selective electrodes (67). SiUca can be determined ia the residue from solution ia perchloric acid—boric acid mixture by measuriag the loss ia weight on Aiming off with hydrofluoric acid. Another method for determining siUca ia fluorspar is the ASTM Standard Test Method E463-72. 

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

Nitrometer Method. The nitrometer method also is used to determine nitric acid or nitrates in mixed acid or oleum. It involves the measurement of the volume of NO gas that is Hberated when mercury is oxidized by nitric acid. The method is based on the following reaction ... 

Analytical and Laboratory Operations. Sulfamic acid has been recommended as a reference standard in acidimetry (55). It can be purified by recrystaUization to give a stable product that is 99.95 wt % pure. The reaction with nitrite as used in the sulfamic acid analytical method has also been adapted for determination of nitrites with the acid as the reagent. This reaction is used commercially in other systems for removal of nitrous acid impurities, eg, in sulfuric and hydrochloric acid purification operations. 

The spectra of these ion pairs are largely different, which forms the basis of the determination method for the spectrophotometric determination of acidic impurities. 

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphomolybdenum blue method. Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method. Ion Chromatographic Methods for the Determination of Phosphorus Compound, Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of Molybdate Reactive Silicon-1 -amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid reduction method. Pretreatment Methods to Convert Other Eorms of Silicon to Soluble Molybdate Reactive Silicon, Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992... 

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

Table VIII. Amino Acids Determined by Decarboxylase Methods...

Gravimetric and volumetric methods are practicable for the quantitative determination of the a-sulfo fatty acid esters. Using gravimetric methods the surfactant is precipitated with p-toluidine or barium chloride [105]. The volumetric determination method is two-phase titration. In this technique different titrants and indicators are used. For the analysis of a-sulfo fatty acid esters the quaternary ammonium surfactant hyamine 1622 (p,f-octylphenoxyethyldimethyl-ammonium chloride) is used as the titrant [106]. The indicator depends on the pH value of the titration solution. Titration with a phenol red indicator is carried out at a pH of 9, methylene blue is used in acid medium [106], and a mixed indicator of a cationic (dimidium bromide) and an anionic (disulfine blue VN150) dye can be used in an acid and basic medium [105]. 

Three classes of polyethers, okadaic acid derivatives, pectenotoxins, and yessotoxin were isolated from bivalves in connection with diarrhetic shellfish poisoning. The etiology of the toxins, toxicological properties, and determination methods are described. 

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

Portions (50 mU MCA-hydrolsing activity) of purified CinnAE were incubated at 37°C with SBP (10 mg), both in the presence and absence of other carbohydrases, in 100 mM MOPS (pH 6.0) in a final volume of 1 mL. Incubations containing boiled enzyme were performed as controls. Reactions were terminated by boiling (3 min) and the amount of free ferulic acid determined using a method described previously for de-starched wheat bran [18]. The total amount of alkali-extractable ferulic acid present in the SBP was 0.87% [5]. 

Vitamin Bg and related compoimds (Figure 10.2) were quantitatively separated by preparative TLC on silica gel H. After elution, the pyridoxic acid lactone method was employed for fluorimetric determination of the concentration of the vitamin forms involved [8]. Table 10.2 shows Revalues obtained for various forms of vitamin Bg, using several solvent systems. The solvent selected, ethyl acetate/pyridine/water (2 1 2, v/v), gave excellent separation of pyridoxamine, pyridoxic acid, and pyri-doxine together with pyridoxal. 

As a more sensitive detection method, MS can be very useful in amino acid determinations. For example, S-carboxymethyl-(R) cysteine or SCMC, is a mucolytic agent used in the treatment of respiratory diseases. The development of a method utilizing high performance IEC and atmospheric pressure ionization (API) mass spectrometry to quantify SCMC in plasma has been described.66 This method is simple (no derivatization needed), rapid (inn time 16 min.), sensitive (limit of quantification 200 ng/mL in human plasma), and has an overall throughput of more than 60 analyses per day. API-MS was used successfully with IEC to determine other sulfur-containing amino acids and their cyclic compounds in human urine.67 IEC has also been used as a cleanup step for amino acids prior to their derivatization and analysis by gas chromatography (GC), either alone or in conjunction with MS.68 69... 

LC- H NMR has been used as a purity determination method for phthalic acid esters, as illustrated for DBP [659]. 

ESCHER, B. I., SCHWARZENBACH, R. P., Westall, J. C., Evaluation of liposome-water partitioning of organic acids and bases. 2. Comparison of experimental determination methods, Environ. Sci. Technol. 2000, 34, 3962-3968. 

Dissolve 0.35 g of miconazole nitrate in 75 mL of anhydrous acetic acid R, with slight heating, if necessary. Titrate with 0.1 M perchloric acid determining the end point potentiometrically, according the general method (2.2.20). Carry out a blank titration. One milliliter of 0.1 M perchloric acid is equivalent to 47.91 mg of Ci8H15Cl4N304. 

Dwivedi et al. used a thin-layer chromatographic densitometric and ultraviolet spectrophotometric methods for the simultaneous determination of primaquine and a new antimalarial agent, CDRI compound number 80/53 [68]. The new antimalari-al agent, compound 80/53 is unstable in acidic conditions where it is converted into primaquine. To conduct stability studies of this compound, thin-layer chromatography densitometric and ultraviolet spectrophotometric determination methods were developed. These methods are also suitable of the determination of compound 80/53 or primaquine in bulk and pharmaceutical dosage forms. 

Hannaker and Buchanan [82] used a method based on wet oxidation with potassium persulfate [83] for the determination of dissolved organic content in concentrated brines following the removal of inorganic carbonates with phosphoric acid. The method involves wet oxidation with potassium persulfate at 130 °C followed by a hot copper oxidation and gravimetric measurement of the carbon dioxide produced. The technique overcomes difficulties of calibration curvature, catalytic clogging, and instrument fouling often encountered with instrumental methods. 

Stannane can be prepared and conserved at low temperatures. Its behaviour in the presence of various reagents is summarized in Scheme 1. It should be noted that reagents such as isopropylamine and acetic acid bring about decomposition of stannane, without themselves being apparently affected268. Some of these reactions can be developed into detection or determination methods for this compound. 

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