Prussian blue method

Total phenolic compounds content was assayed spectrophotometri-cally using a modified Prussian blue method as described by Graham (28) employing an LKB Biochrom Ultrospec II spectrophotometer (Cambridge, England). Tannic acid was used as calibration standard. 

Today, the most widely used method for the estimation of total phenolics in plant extracts as well as in foods and beverages is the Folin-Ciocalteu method. Some authors prefer the Prussian blue method, because... 

Price-Butler method = Prussian blue method Reduction of ferric to ferrous ions followed by formation of the hexacyanoferrate-(l 1 )-chelate (Prussian blue). detection wavelength 720 nm complexes are unstable (precipitates), cuvettes become stained, timed addition of FeClj (instability ), sensitivity toward flavanols < I0 4 M, use of Prussian blue standard, number of reduced moles of ferric ions can be calculated 58,109... 

Budini, R., Tonelli, D., and Girotti, S. (1980) Analysis of total phenols using the Prussian blue method J Agric Food Chem. 28, 1236-1238. 

These disadvantages of the otherwise excellent nitroprusside reaction are not present in the case of the Prussian blue method which has been applied to the same problems by Chevremont and Frederic (25). However, the Prussian blue methodjs not specific for —SH groups, but... 

Ferric ions (demonstrated histochemically by the Prussian blue method) in the dentate gyrus of Swiss-Webster mice chronically implanted with either stainless steel or Pt-Ir wire probes correlated with significant P <0.05) performance deficits tested in a one-trial inhibitory avoidance task (Boast et al. 1975). 

The Prussian blue method is based on the reduction of Fe(III) to Fe(II) and the subsequent detection of Fe(II) by formation of the hexacyanoferrate(II) chelate (Prussian blue). 

More recently, a new method of assembling multilayers of PB on surfaces has been described.110 In contrast to the familiar process of self-assembly, which is spontaneous and leads to single monolayers, directed assembly is driven by the experimenter and leads to extended multilayers. In a proof-of-concept experiment, the generation of multilayers of Prussian blue (and the mixed Fein/Run analog ruthenium purple) on gold surfaces by exposing them alternately to positively charged ferric cations and [Fe(CN)6]4- or [Ru(CN)f,]4 anions has been demonstrated.110... 

Tabun may be detected by the air-flow method, by aspirating into ferrous sulphate solution to which a few drops of 10 per cent sodium hydroxide has been added. The mixture is then boiled and acidified with dilute sulphuric acid and filtered to observe the blue specks of Prussian blue on the filter paper. 

A GCE coated with a film of Prussian Blue (Fe4[Fe(CN)6]3) mimics HRP as catalyst for selective electrochemical reduction of H2O2 in the presence of O2. A careful deposition method has to be followed to prevent leakage of the oxidized form of the pigment from the coating into the solution. Amperometric determinations in phosphate buffer at pH 6.0, with an apphed potential of —50 mV vs. SCSE, shows Unearity in the 0.1 to 100 p,M range. ... 

Prussian blue is regarded as a compound of three equivalents of ferroeyanogen with two of iron, and its composition is therefore expressed by the formula 8 Cfy -j- 2 Fea, or Fe, Cys, It is formed whenever a salt of sesquioxide of iron is added to a soluble metallio ferrocyanide. The usual method is to precipitate a solution of sesquiehloride or sesquinitrate of iron by ferrocyanide of potassium and In point qf fact a very important part of its manufacture consists in the preparation of this latter salt, which will now be described. 

Potassium ferrocyanide has long been used to remove excess copper and iron from wines. When not used in excess it appears effective and harmless, but if any ferrocyanide residue remains, cyanide may form. While the amounts produced by a slight excess would pose little danger, the blue precipitate and distinctive odor would be undesirable. Special equipment has been devised to detect free cyanide and ferrocyanide (4, 5, 6) as Prussian blue. The suggested limit is 1 mg/liter as cyanide. Hoppe and Romminger (72) devised a rapid procedure for free and bound cyanide, and Bates (73) gives a qualitative screening method sensitive to 0.05 mg/liter. 

Another candidate for the first coordination compound is Prussian Blue, potassium iron(III) hexacyanoferrate(II), a complex of empirical formula KCN-Fe(CN)2- Fe(CN)3. It was first obtained accidentally in 1704 by Diesbach, a manufacturer of artist s colors from Berlin. Initially it was described9 as a nontoxic pigment suitable for oil colors, but its method of preparation was kept secret, probably because Diesbach wished to benefit monetarily from his discovery. 

X-ray diffraction (XRD) is a routine method for determining crystal lattice parameters and molecular structure. The application of XRD to modified electrodes has been limited, particularly for actual molecular structure determination. First, such experiments presuppose a single-crystal electrode substrate. Second, the small amount of sample present in a thin film on an electrode surface means that the scattered intensities will be restrictively low, at least for commonly available x-ray sources [67]. However, if one is fortunate enough to have access to a synchrotron, such experiments are quite feasible. For details, the reader is directed to an excellent review by Toney and Melroy [68]. On the other hand, powder diffraction experiments with Cu or Mo Ka anode sources are straightforward, and can yield lattice-constant data in situ. For example, Ikeshoji and Iwasaki measured lattice constants for Prussian blue films (discussed earlier) on gold electrode surfaces [69]. 

The investigation of these pigments includes, besides technical tests, also tests for the detection of extraneous substances, these being carried out by the ordinary methods (see Chrome yellow and Prussian blue). Sometimes the lead chromate and Prussian blue are determined, the following methods giving sufficiently exact results. 

Stability of Prussian blue modified screen-printed electrodes The operational stability of all the PB-modified sensors is a critical point, especially at neutral and alkaline pH. A possible explanation for reduced stability could be the presence of hydroxyl ions at the electrode surface as a product of the H202 reduction. Hydroxyl ions are known to be able to break the Fe-CN-Fe bond, hence solubilising the PB [21]. An increased stability of PB at alkaline pH was first observed by our group after adopting a chemical deposition method for the modification of graphite particles with PB for the assembling of carbon paste electrodes [48]. 

K. Itaya, H. Akahoshi and S. Toshima, Electrochemistry of Prussian blue modified electrodes an electrochemical preparation method, J. Electroc-hem. Soc., 129(7) (1982) 1498-1500. 

The uptake if iron often requires Fe(II) as the bioavailable form, and uptake from soils containing insoluble Fe(III) is accomplished by phenolic compounds which are exuded by certain plants (Chaney and Bell, 1987). A particular use of staining has been in the study of the sites if iron reduction in plants, using Prussian blue stain (PB) (Ambler et al., 1971 Brown and Ambler, 1974). The method consists of placing the roots in a nutrient solution containing Fe(III) and ferricyanide. Since PB can be produced both from Fe(III) and Fe(CN)64 and from Fe(II) and Fe(CN)63, reduction of either source of iron in the presence of the roots will produce PB at the sites of... 

Prussian blue — iron(III) hexacyanoferrate(II) is the archetype of sparingly soluble mixed valence polymeric metal hexacyanometalates with the formula Me Me(N) [Me c (CN)6] with (i), (N), and (C) indicating the position in the crystal lattice, where (i) means interstitial sites, (N) means metal coordinated to the nitrogen of the cyanides, and (C) means metal ions coordinated to the carbon of the cyanides. It is one of the oldest synthetically produced coordination compounds and was widely used as pigment in paints because of the intensive blue color. The compound has been studied extensively by electrochemical and other methods. The importance of Prussian blue in electrochemistry is related to the fact that it has two redox-active metal centers and that it has an open structure that allows small cations to... 

The widespread occurrence of iron ores, coupled with the relative ease of extraction of the metal, has led to its extensive use as a constructional material with the result that the analysis of steels by both classic wet and instrumental methods has been pursued with vigour over many years.3 Iron complexes are themselves widely used as the basis of convenient analytical methods for the detection and estimation of iron down to parts per million. Familiar tests for iron(III) in aqueous solution include the formation of Prussian blue as a result of reaction with [Fe(CN)6]4, and the formation of the intensely red-coloured [Fe(H20)5SCN]2+ on reaction with thiocyanate ion.4 Iron(II) forms particularly stable red tris chelates with a,a -diimines such as 1,10-phenanthroline or 2,2 -bipyridine that have been used extensively in spectrophotometric determinations of iron and in the estimation of various anions.5 In gravimetric estimations, iron(III) can be precipitated as the insoluble 8-hydroxyquinoline or a-nitroso-jS-naphthol complex which is then ignited to Fe203.6 In many situations the levels of free [Fe(H20)6]3+ may be controlled through complex formation by addition of edta. 

Commercial Preparation and Uses of Prussian Blue.—Prussian blue was discovered accidentally in 1704 by Diesbach,4 and is highly valued as a pigment on account of its remarkable intensity of colour. It was manufactured in Great Britain in 1770, and sold at 2 guineas per lb. One pound of Prussian blue will perceptibly tinge some 600 lbs. of white lead. The pigment is sometimes prepared commercially by the direct method of adding a ferric salt to a solution of potassium ferrocyanide but it is more usual to adopt an indirect method, namely to add a ferrous salt to potassium ferrocyanide and subsequently to oxidise the white precipitated mass of ferrous potassium ferrocyanide.5 Chemically it consists of a variable mixture of some or all of the Prussian blues already described. 

Addition of ferric chloride to certain liquors produced in the manufacture of Prussian blue in a French factory by the methylamine method (see p. 213) resulted in the precipitation of a violet compound.1 Several hundred grams of this were isolated by Muller, warmed with potassium carbonate and hydroxide successively, and the filtered solution allowed to crystallise. The product thus isolated crystallised in thin scales and rectangular prisms, and proved to be the potassium salt of an entirely new acid, namely hydrogen carbonyl ferrocyanide, H3Fe(CN)5.CO. Following up this discovery, Muller succeeded in preparing a series of well-defined salts. 

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