[Improved Indophenol Titration Method for Ascorbic Acid Using a Dropper and Electronic Balance: Enhanced Convenience and Efficiency]

The analysis of ascorbic acid using the 2,6-dichloroindophenol (DCIP) titration method is a well-established technique, but requires the skilled handling of a burette for accurate measurements. In the present study, we propose a modified DCIP titrimetric method that replaces the burette with a dropper and employs an electronic balance to measure the titrated amount by weight. The dropper used can be flexibly selected, allowing for a wide range of drop sizes, from large to very small. This modification offers several advantages, including lower skill requirements, a 43% reduction in the analysis time, a 50% decrease in sample/reagent consumption, and the ability to prepare DCIP standard solutions tailored to the concentration of ascorbic acid in the sample being analyzed. Our analysis of several food samples using this improved method showed that inherent issues of the DCIP method, such as determining the titration end point, could not be resolved. Nevertheless, the improved titration method remains more convenient and adaptable than the original approach using a burette, enabling quick and accurate analysis, especially for unskilled analysts.

Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core-shell nanostructures by pulsed laser technique

The biochemical reduction of nitrite (NO₂^-) ions to ammonia (NH₃) requires six electrons and is catalyzed by the cytochrome c NO₂^- reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO₃^-) and NO₂^- in wastewater, to produce the more valuable NH₃ product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO₃^- reduction reaction (NO₃^-RR), but the NO₂^-RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO₂^- to NH₃ using Cu@Cu₂O core-shell NPs to simultaneously treat wastewater by removing NO₂^- and producing valuable NH₃. The Cu@Cu₂O core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO₂^- and the ammonium (NH₄⁺)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu₂O core-shell NPs exhibited outstanding NO₂^-RR activity, demonstrating a maximum NO₂^- removal efficiency of approximately 94% and a high NH₄⁺-N yield rate of approximately 0.03 mmol h^-1.cm^-2 at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO₂^-RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO₂^- to NH₃ via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO₂^- to NH₄⁺.

EVALUATION OF INDOPHENOL DERIVATIVES AS REAGENTS FOR DEMONSTRATING CYTOCHROME OXIDASE IN TISSUE SECTIONS

Seven redox dyes were investigated as possible histochemical indicators of cytochrome oxidase activity. All failed to meet one prime requisite, namely, that the oxidized product remain at the site of enzymatic action.

The "color fading" phenomenon was studied. This effect was one in which sections and homogenates became colored as a result of oxidase activity and then faded during further incubation. Evidence was provided that this reaction occurred as a result of endogenous dehydrogenase activity, mainly succinic dehydrogenase. The decoloration in solution could be prevented by N-ethyl maleimide, without inhibiting cytochrome oxidase.

INDOPHENOL OXIDASE AND PEROXIDASE ACTIVITIES IN MAMMALIAN ERYTHROCYTES

Cytochrome oxidase and peroxidase activities in mammalian red cells are suggested by G- and M-Nadi reactions in rabbit, mouse, and human erythrocytes. Peroxidase activity was present in both the hemoglobin and the nonhemoglobin constituents of the red cells. Removal of oxygen stopped the G-Nadi reaction but not the M-Nadi reaction. Potassium cyanide and sodium azide at a concentration of 10–3-10–4 M partially inhibited G- and M-Nadi reactions. Microscopic examination of reacting cells revealed accumulation of reaction products at the cell periphery. This was not evident when the cells were incubated in a suspension of indophenol blue.

Mammalian erythrocytes reduced the tetrazolium salt nitro-BT. Reduction was augmented by removal of oxygen and by cytochrome oxidase inhibitors. Accumulation of formazan at the surface of reacting cells was evident upon microscopic examination.

The Nadi reactions were similar whether Ehrlich ascites tumor cells or stroma of hemolyzed erythrocytes were used. Reactions of stroma or whole erythrocytes with nitro-BT were essentially similar. Fixation or heating slowed or abolished all the reactions described.

Helicobacter pylori and ammonia concentrations of whole, parotid and submandibular/sublingual saliva

The aim of this study was to determine the ammonia concentration in whole, parotid and submandibular/sublingual saliva of healthy volunteers using the indophenol direct method. It also investigated the hypothesis that higher saliva ammonia concentrations are associated with the presence of Helicobacter pylori (H. pylori) in the oral cavity. In healthy volunteers, the mean ammonia concentration of whole saliva (2574 mumol/l) was significantly higher (P < 0.0001) than the mean ammonia concentration of both parotid (238 mumol/l) and submandibular/sublingual (355 mumol/l) saliva. In whole saliva, no difference in ammonia concentration was found between healthy controls and dyspeptic patients (mean ammonia values 2574 and 2489 mumol/l respectively, P = 0.7). In addition, no significant differences were observed in the salivary ammonia concentration between dyspeptic patients with and without H. pylori carriage. It is concluded that the ammonia concentration in parotid and submandibular/sublingual saliva does not differ, but is significantly lower than the ammonia concentration of whole saliva. This difference is not due to carriage of H. pylori with its strong urease activity. Therefore, the determination of ammonia in whole saliva is an inappropriate screening test for patients being at risk for (chronic) gastritis and peptic ulcer disease.

Indophenol blue as a chromogenic agent for identification of halogenated aromatic hydrocarbons

The metachromatic dye indophenol blue [N-(p-dimethylaminophenyl)-1,4-naphthoquinoneimine] is adaptable for qualitative and quantitative measurements of halogenated aromatic hydrocarbons in paper chromatographic procedures and spot tests.

Determination of ammonia in cerebrospinal fluid using the indophenol direct method

We have determined ammonia in cerebrospinal fluid (CSF) with the indophenol direct method. The results were compared with an enzymatic method. The method is very simple, and precision (coefficient of variation 1.6%) and linearity (r = 0.9999, p < 0.001) of the method are excellent. The recoveries of the method are very good (within-sample recovery: range 88-93, median 93%; between-sample recovery: 88-93, median 91%). In a population of 23 neurological patients not suffering from liver disease, the reference values ranged from 8 to 26, median 18 microM. Males and females did not differ (p = 0.5). The values obtained with the indophenol method were equal to the enzymatic method (range 9-28, median 18 microM, p = 0.6). On storage in the deep freeze (-20 degrees C), there was no change in CSF ammonia concentration for at least 1 mo. When stored at 4 degrees C (refrigerator), ammonia determinations have to be performed within 2 d. CSF storage at room temperature results in artificially elevated ammonia levels and should be avoided.

Quantitative colorimetric determination of urinary p-aminophenol with an automated analyzer

We developed an automated colorimetric method for the quantitative determination of p-aminophenol with a Cobas Mira analyzer. The procedure can be used for the biological monitoring of human exposure to aniline. An absorbed aniline dose is extensively oxidized to p-aminophenol, which is excreted in urine mainly as glucurono- and sulfo- conjugates. After enzymatic hydrolysis, we reacted the free compound with resorcinol in the presence of manganese ions to form an indophenol dye, which is measured at 550 nm. Excellent accuracy (102.8%, 103.9%, and 96.8% at 2.5, 50, and 90 mg/L, respectively) and precision (7.7%, 2.1%, and 0.8% CV for within-run and 11.1%, 4.7%, and 4.6% for total reproducibility at 2.5, 50, and 90 mg/L, respectively) were achieved over a linear concentration range of 2.0 to 100 mg/L. The detection limit was 0.9 mg/L and no significant interference (except for o-aminophenol) was found for several investigated drugs and related compounds. The proposed method was used for a stability study and to analyze several samples from an occupational health screen.

GLYCOLIC ACID OXIDATION BY ESCHERICHIA COLI ADAPTED TO GLYCOLATE

Furuya, Akira (University of Illinois College of Medicine, Chicago) and James A. Hayashi. Glycolic acid oxidation by Escherichia coli adapted to glycolate. J. Bacteriol. 85:1124-1131. 1963.-A procedure is described for extraction and partial purification of glycolic acid oxidase from Escherichia coli adapted to grow on glycolate as the sole carbon source. Enzyme activity was assayed by oxygen uptake and by reduction of 2,6-dichlorophenol-indophenol. Glyoxylic acid was the product of glycolate oxidation by the enzyme. Enzyme activity, which diminishes rapidly on storage, shows a maximum at pH 6 to 7. We were unable to show any cofactor requirement. Compounds which inhibited glycolate oxidation and their order of inhibitory activity were: p-hydroxymercuribenzoate > sodium azide > iodoacetate and o-phenanthroline > ethylenediaminetetraacetic acid. Tests of enzyme specificity showed that the following compounds were oxidized, but at different rates: glycolate, d-lactate, l-lactate, dl-alpha-hydroxybutyrate, dl-malate, and dl-glycerate. Citrate, tartrate, and dl-beta-hydroxybutyrate were not oxidized. Potassium cyanide stimulated oxygen uptake when glycolate and lactate were oxidized. Whether the oxidations were due to different oxidases or to a single oxidase with a wide range of specificities was tested by observing the oxidation of glycolate, d-lactate, and l-lactate under various conditions. Ammonium sulfate fractionation of a crude extract did not change the relative ability to oxidize the three acids. However, the three oxidative capacities diminished at different rates during storage at 0 C for 6 days. The partially purified glycolic oxidase preparations were probably mixtures of several different oxidases.

Arterial ammonia with Blood Ammonia Checker II and with indophenol reaction to assess presence of hepatic encephalopathy

Hepatic encephalopathy (HE) is associated with elevated arterial ammonia levels. The relationship is variable, in part due to ammonia methodology. One method, based on the indophenol reaction (IPh), is interfered with a number of amino acids including all aromatic amino acids. We have determined arterial ammonia simultaneously with the Blood Ammonia Checker II (BAC) as reference method and with the IPh method. The difference BAC-IPh, mumol/l, was assumed to express the interference in the indophenol method (IFI) by amino acids. It may be positive or negative. The aim was to establish the value of BAC in comparison with IPh in the diagnosis of liver disease and overt HE and to assess any added value of IFI. Of two reference groups without disturbances, A (n = 39) had not and B (n = 13) had encephalopathy. Group C consisted of 125 liver patients (34 no cirrhosis, 91 cirrhosis) of which 55 had no manifest HE (C:HE-) and 70 had HE (C:HE+). Median BAC ammonia nitrogen (NH3-N), mumol/l: A 21, B 35, C 80, C:HE - 57 and C:HE+ 98 (A < B < C and A < B < C:HE - < C:HE +, P < 0.001). Median IPh NH3-N, mumol/l: A 27, B 30, C 30, C:HE - 25 and C:HE + 35 mumol/l (A = B = C and C:HE - < C:HE+, P < 0.01). IFI medians: A -6, B 3, C 40, C:HE - 29 and C:HE + 58 mumol/l (A < B (P < 0.05) < C (P < 0.0001); A, B < C:HE - and C:HE+; C:HE- < C:HE + (all P < 0.0001)). While BAC correlated weakly with IPh in the (sub)groups C, C:HE-, C:HE+ (r = 0.3, 0.3, 0.4, P < 0.05), it correlated strongly with IFI (r = 0.9, 0.9, 0.8, P < 0.0001). There was no correlation between IPh and IFI. BAC, as well as IFI, could discriminate all liver patients (C) from both reference groups A and B with 100% positive likelihoods. BAC, IPh and IFI could discriminate between HE- and HE+. To differentiate cirrhosis from non-cirrhosis the specificity of IPh was uniformly high and the sensitivity satisfactory, whereas BAC had a high sensitivity but an insufficient specificity. In conclusion, in blood, BAC is the ammonia determination of choice. It differentiates between reference groups (encephalopathic or not) and liver disease and the more so HE. The combination of BAC and IPh (indicating IFI) may eventually be shown useful to rapidly assess the severity of underlying liver disease in HE patients. In other biological fluids, IPh is excellent when the inhibiting influence of non-protein nitrogen substances is absent or can be eliminated.

Indophenol method for acetaminophen in serum examined

We show that an indophenol-based colorimetric method for acetaminophen (Clin Toxicol 15: 67-73, 1979) has less than maximal sensitivity because of (a) incomplete hydrolysis, related to suboptimal acid concentration; (b) suboptimal hydrolysis time; and (c) possible deterioration of the ammonium hydroxide reagent after 2.5 months. We have modified the method by optimizing duration of hydrolysis and color development. Results by the method correlate linearly with acetaminophen concentrations to 250 mg/L (1.66 mmol/L). Moreover, the modified method is free from interference by compounds in serum from uremic patients.

Salivary urea nitrogen as an index to renal function: a test-strip method

To investigate the feasibility of using salivary urea nitrogen as an index of renal glomerular filtration rate, we developed and applied a new analytical system consisting of a urease-containing test strip and an automatic reflectance spectrometer. The concentrations of urea nitrogen so determined correlate well (r = 0.93) with concentrations in serum. These preliminary data suggest that our method can be used routinely as a simple and reliable means of detecting abnormalities of renal function.

Determination of ammonia in saliva using indophenol, an ammonium electrode and an enzymatic method: a comparative investigation

Three methods for determination of ammonia in saliva are reported. The indophenol method on diluted saliva has the best precision (coefficient of variation 0.8%) and the lowest reagent cost. The ammonium electrode method is the quickest, but it requires simultaneous determination of the potassium content of the specimen. The enzymatic method give the same result as the electrode method, but is more expensive. Deproteinisation proved not to be necessary. In one hour 10, 20 or 40 determinations can be performed with the enzymatic, indophenol- or the electrode method, respectively.

Optimal conditions for the estimation of ammonium by the Berthelot reaction

A technique for optimising reagent concentrations on the AutoAnalyzer has been applied to the estimation of ammonia by the Berthelot reaction in the determination of urea and organic nitrogen. Comparison of the use of phenol and salicylate revealed that the optimum concentration of the latter is about four times that of the former. The optimum concentration of hypochlorite is five times greater with salicylate than with phenol, and for the catalyst, sodium nitroprusside, the factor is two. The precision obtained with the different methods is similar.

Rapid heterolysis of indophenyl acetate by a constituent of a preparation of horse serum cholinesterase

A transient phase for the hydrolysis of indophenyl acetate by the commercial preparation of horse serum cholinesterase was observed on a stopped-flow spectrophotometer. It was found that the transient process is a reaction of the ester with a major component of the preparation and is not caused by the serum cholinesterase enzyme. This noncholinesterase component was isolated and the dependence of its concentration and that of the ester upon the transient liberation of the indophenolate ion were determined. Studies with the isolated component and subsequent analyses have led to the tentative identification of the burst active component as serum alpha1-acid glycoprotein.

Indophenyl acetate and acetylcholinesterase: binding of a non-specific substrate on the margin of the active center

1. Indophenyl acetate is a very poor substrate of eel or bovine acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7), with a V less than 5% of that of phenyl acetate, but it is a labile ester and in imidazole buffer is hydrolyzed, non-enzymically, even faster than phenyl acetate. 2. Indophenyl acetate completely protects the enzymes against inhibition by diisopropylphosphorofluoridate but promotes inhibition by methanesulfonyl fluoride. 3. With either of these inhibitors the measured rate of inactivation of eel acetylcholinesterase is the same whether activity is determined with this poor substrate or with a good substrate, acetylthiocholine. With bovine enzyme the inactivation rate is 25% lower when assayed with the former substrate. However this preparation contains a minor enzyme component which is involved in hydrolysis of indophenyl acetate but not good substrates, and which is not readily inhibited. When this is taken into account the inactivation rates for bovine acetylcholinesterase, too, are found to be the same in either assay. These and other observations in the literature can be explained if indophenyl acetate, because of its size, cannot fully penetrate into the active center and is bound in adjoining non-polar regions of the protein. From this external position it makes only intermittent contact with the esteratic site. Hence it is slowly hydrolyzed and fails to protect the enzyme against methanesulfonyl fluoride, though it does protect, possibly sterically, against the larger inhibitor diisopropylphosphorofluoridate.

[Aeromonas punctata subsp. caviae as the causative agent of acute gastroenteritis (author's transl)]

Since in the past, Aeromonas hydrophila had been isolated from all cases of human infection described. A. punctata and the anaerogenic sub-species were considered as apathogenic. From the case described, a close association between acute diarrhea with vomiting and the identification of A. punctata subsp. caviae becomes evident so that a conditional pathogenicity of this sub-species must be assumed. The question is discussed whether a preceding disturbance of the intestinal habitat in the presence of a particular susceptibility of the gastrointestinal tract promoted gastro-enteritis. Infection may have been brought about by the ingestion of surface water contaminated by sewage. Attention is again drawn to the fact that in the case of enteritis occuring during the open-air bathing season, faeces samples should also be examined for their Aeromonas content which may be performed by a simple indophenol or so-called cytochrome oxidase reaction of the aerobic flora in feces by rubbing off colonies into a corresponding test strip.

Quantitative determination of phenol in ointments

A quantitative method for the assay of phenol in ointments is described. The procedure involves the formation of a blue indophenol by reacting phenol with 2,6-dibromoquinone-4-chloroimide which can be measured spectrophotometrically. The method is accurate, and interference from other active ingredients (hydrocortisone and menthol) does not occur.

Determination of serum nucleotidase with cytidine monophosphate as substrate, (I)

This paper deals with a new method for the determination of serum nucleotidase (EC 3.1.3.5). The assay is performed with cytidine-5'-monophosphate as substrate, followed by deamination of the generated cytidine. The principle of the method and the determination of the liberated ammonia by the Berthelot indophenol-reaction are comparable to the Persijn--van der Slik method in which adenosine-5'-monophosphate is used as substrate. The correlation between the results obtained with these two methods was found to be good; the new method has the advantage of higher sensitivity.

The non-light-dependent reduction of 2,6-dichlorophenolindophenol by cells of the blue-green alga Anacystis nidulans

Whole cells of the blue-green alga Anacystis nidulans reduced, in the dark, the oxidation-reduction dye, 2,6-dichlorophenolindophenol at rates severalfold higher than those of the other algae tested. Under anaerobiosis, the endogenous reductant was depleted after up to 80 nmol of dye were reduced per microliter of cells. Cells held in darkness for several hours exhibited lowered dark reduction rates relative to cells held in light. Treatment with lysozyme and ethylenediaminetetraacetic acid yielded cells that would photoreduce the dye, whereas untreated cells would not. Comparisons of photoreduction and dark reduction revealed that the dark reduction proceeded independently of the photoreduction. It was concluded that the dark reduction represents a pool of endogenous reductant of sufficiently low oxidation-reduction potenital to reduce completely 2,6-dichlorophenolindophenol. Additionally, untreated cells were shown to be permeable to the dye although they did not photoreduce it; thus lysozyme/ethylenediaminetetraacetic acid treatment was considered to make the oxidant accessible to the photosynthetic machinery.

Quenching of excited chlorophyll A in vivo by nitrobenzene

Nitrobenzene exerts a dual effect on the excitation of chlorophyll a(Chl a) in vivo. (a) A 3(3,4-dichlorophenyl)-1,1-dimethylurea-inhibited quenching that manifests as a partial inhibition of variable chloroplast fluorescence and of 2,6-dichlorophenol indophenol (DCPIP) photoreduction and saturates at ca. 5-10 muM. Since nitrobenzene is not a Hill oxidant, this effect is attributed to a catalyzed back flow of electrons from intersystem intermediates to pre-photosystem II oxidants. (b) A direct quenching of the excited Chl a in vivo. This effect has a threshold of ca. 100 muM nitrobenzene; at higher concentrations it leads to almost complete suppression of chloroplast fluorescence and DCPIP photoreduction. Tris-washed chloroplast enriched in the photosystem II reaction center species Z+Q- and ZQ- are nearly four times more sensitive to nitrobenzene quenching than those enriched in Z+Q. On the other hand, normal chloroplasts are about 10 to the fourth times more sensitive. Hence, it is argued that the extreme sensitivity of normal chloroplast fluorescence is not due to a preferential association of nitrobenzene with a particular redox species of the reaction center.