Boron curcumin method

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

The very sensitive curcumin method is often used for determining trace amounts of boron. The carmine-acid method is much less sensitive. Extraction-spectrophotometric methods based on ion-associates of BF4 with Methylene Blue and other basic dyes are of importance in the determination of boron. 

In a modification of the curcumin method, a ternary complex is formed between curcumin, boron, and oxalic acid [26]. The method is more rapid, but it is only about half as sensitive. The ternary complex formed (rubrocurcumin) contains curcumin, boron, and oxalate in the ratio 1 1 1. 

The curcumin method (in either the rosocyanin or rubrocurcumin version) has been applied for determining traee amounts of boron in biologieal materials [10], soils and plants [17], waters [51], silicon [52], chlorosilanes [20], uranium [1,53], zirconium and its alloys [53,54], nickel [55,56], copper alloys [56], cast iron and steel [12,57-59], beryllium and magnesium [53], and phosphates [2]. This method was also used for determining boric acid admixtures (about 0.05%) in powdered boron [11]. Some synthetic compounds having the structure similar to that of curcumin, were used in determining boron in water [60]. 

In a highly sensitive indirect method (e > 3.0-10 ) Ni is separated as the precipitate formed with H2Dm and diphenylboric acid, Ni(HDm)2.2(C6H5)2BOH. After mineralization of the organic moiety, boron is determined by the curcumin method (see Section 11.2.1) [59]. 

For determination of the total boron content, the spectrophotometric curcumin method is described, which was first applied to seawater by Greenhalgh and Riley (1962) but was modified and simplified by Uppstrdm (1968). An outline of the mannitol-boric acid method is presented in Section 11.2.7.7. 

With curcumin (l,7-bis(4-hydroxy-3-methoxyphenyl)-l,6-heptadiene-3,5-dione) boron forms two different complexes both procedures are known in the literature as the curcumin method . Rubrocurcumin is formed from boric acid, curcumin and oxalic acid in a 1 1 1 complex rosocyanin forms in the presence of strong sulphuric add by the reaction between boric acid and curcumin, probably in a ratio of 1 2. An extensive study of the chemistry has been given by Dyrssenetal (1972). Rosocyanin is the preferred complex for boron determi-... 

A simplified variant of the curcumine method is described in reference (15) a 1 g sample is dissolved under reflux in 15 ml concentrated sulphuric acid and 5 g ammonium sulphate, after which the solution is diluted to 50 ml with a mixture of glacial acetic acid and concentrated sulphuric acid (1+1). From this solution 10 ml is mixed with the curcumine reagent (see above), and after 30 min the reagent in excess is shaken out with ether. Hereby the boron compound rosocyanine collects at the phase boundary surface. The main amount of water and ether is removed, the rosocyanine is dissolved with methanol to 15 ml and the absorbance is measured at 555 nm. It is claimed that using this method boron concentrations as small as 0.1 (iq/q can be determined. 

Emission spectrometry with plasma excitation is based on chemical separation of boron by wet chemistry and is matrix and form independent. The sensitivity is good (0.01 to 0.02 Mg/g) but the method requires several difficult manipulations, thus highly skilled operators. The latter also applies to photometry which was used under different forms the methylene blue method, with varying BF formation times and with and without reextraction of fluorine, and the curcumine method. Under optimal conditions, these methods allow precisions and accuracies of + 10 % at the 0.5 to 1 /ig/g level. 

Aznarez et al. [2] have described a Spectrophotometric method using curcumin as chromopore for the determination of boron in soil. Boron is extracted from the soil into methyl isobutyl ketone with 2-methylpentane-2,4-diol. In this method 0.2-lg of finely ground soil is digested with 5ml concentrated nitric-perchloric acid (3 + 1) in a polytetrafluoroethylene lined pressure pump for 2h at 150°C. The filtrate is neutralized with 6M sodium hydroxide and diluted to 100ml with hydrochloric acid 1+l.This solution is triple extracted with 10ml of methyl isobutyl ketone to remove iron interference. This solution is then extracted with 10ml 2-methyl pentane-2,4 diol and this extract dried over anhydrous sodium sulphate. 

Also, boron can be analyzed by colorimetry techniques (APHA, AWWA, and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington DC American Public Health Association). Boron in acidified aqueous phase reacts with curcumin to form a red-colored product, roso-cyanine. Presence of calcium and magnesium at high concentrations can interfere in the test. Another colorimetric measurement involves the reaction of boron with carmine or carminic acid in concentrated sulfuric acid. The color of the solution changes from bright red to bluish red or blue, depending on boron concentration. 

Saito M., Hirose F. and Okochi H. (1995) Comparative study of the determination of micro-amounts of boron in high-purity molybdenum by a spectrophotometric method using curcumin, spark source mass spectrometry and glow discharge mass spectrometry, Anal Sci 11 695-697. 

The aluminon (24) procedure for the determination of beryllium produced the best precision and the curcumin (4) procedure for boron, the poorest. In general, all of the methods (3, 15, 20) were found to be acceptable. 

A new photometric method for the determination of boron using curcumin has been developed. ... 

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