A comparison of acid hydrolyses for the determination of carbohydrate content in soils

Abstract

Four Italian surface soils were used to compare four different acid hydrolyses for the determination of the total content of carbohydrates in soils. Soil hydrolyses in 0.25M and 1M H₂SO₄ and by mechanical shaking for 16 h released carbohydrates as efficiently as the 8 h soil hydrolysis under reflux. Degradation of released carbohydrates was probably the cause of the low values given by the hydrolysis in 72% H₂SO₄ for 15 min followed by a 16 h shaking in 0.5M H₂SO₄. This study confirms that the carbohydrate determination based on the colorimetric phenol‐sulphuric acid method is more accurate than the colorimetric anthrone‐sulphuric acid method. Moreover, soil characteristics may influence the accuracy and precision of results depending on the hydrolysis procedure as it was shown by the soils rich in organic carbon and clay.     

Sephadex gel fractionation of humic acids

Using Sephadex G 50 gel filtration, three soil humic acids were separated into two to four fractions, which differed more or less in their spectrophotometric properties. The distribution of a humic acid fraction on an RF-Δlog K diagram was classified into two cases; in the first case, the RF increased and Δlog K decreased with the elution order, and in the second case, humic acid fractions distributed clockwise around the original humic acid.

A small amount of B type humic acid was separated by gel filtration from newly formed Rp type humic acid obtained from the mixtures of grass and soil materials incubated for four months under alternate field and air-dry conditions.     

接种单细胞微生物对土壤团聚体形成及其稳定性的影响

将根瘤菌(Rhizobium sp.)G-01、肠杆菌(Enterobacter sp.)San8及粘红酵母(Rhodotorula mucilaginosa)R1等3株产胞外多聚物(Extracellular polymeric substances,EPS)的单细胞微生物接种于供试土壤,进行土培试验和盆栽黄瓜试验,...     

Glucose oxidase activity in soil and its possible interference in assays of cellulase activity

The occurrence of naturally-occurring glucose oxidase activity in a soil collected at a depth of 0–8 cm under tussock has been indicated. This activity was probably responsible for utilization of some of the glucose added to a system of soil, buffer and toluene that was incubated at 30°C; no loss of added glucose was apparent at 50°C.The cellulase activity of this soil was assessed by measuring rates of hydrolysis of added cellulose with Somogyi and anthrone reagents in systems of soil, buffer and toluene at 30 and 50°C. The production of reducing sugars was approximately linear over the first 48 or 72 h of incubation but appeared to decline subsequently at both temperatures. Interference by the activity of the naturally-occurring glucose oxidase at 30°C is suggested. Interference by glucose oxidase appears less likely at 50°C because of the apparent stability of added glucose at this temperature and the instability of added glucose oxidase. An incubation period of 48 h at 30°C appears generally satisfactory for assaying the cellulase activity of this soil.The possible role of glucose oxidase in interfering in assays of other soil enzymes in which the production of glucose is measured is discussed.     

Dichromate Digestion–Spectrophotometric Procedure for Determination of Soil Microbial Biomass Carbon in Association with Fumigation–Extraction

A dichromate digestion and spectrophotometric procedure is proposed for estimating soil microbial biomass carbon (C) in association with fumigation–extraction. The recommended procedure uses a volume (1.6 ml) of 0.5 M potassium sulfate (K₂SO₄) soil extracts and oxidant solution (dichromate–sulfuric acid, 2.4 mL), mixed with a volume (4 mL) for digestion at 140 °C for 30 min. The digested solution is then directly read for absorbance at 350 nm using a spectrophotometer, and the C in the digested soil extracts is measured against glucose standards. The K_EC (indicating the extractable part of microbial biomass C after fumigation) value is estimated as 0.33 for the proposed method. There are good correlations between soil microbial biomass C measured by the proposed method, the dichromate digestion titration, and oven oxidation by total organic C (TOC) analytical method. This method is a simple, rapid, and economical procedure associated with fumigation–extraction for biomass C analysis.     

Attempts to determine available carbon in soils

Summary The size of the C pool that is readily available to microorganisms affects important N transformations that occur in soils, e.g., denitrification and N immobilization. In the present work, the C content of soil extracts, the C in water displaced from soil and biomass C were compared as indicators of available C. A comparison of C measured by the anthrone method and a total organic-C analysis of extracts indicated that only a small portion of C was in carbohydrates. The substrate-induced respiration method of measuring biomass in conjunction with the Wright-Hobbie model was used as an additional determination of available C. Total organic-C analysis of a 1 N H₂SO₄ extract gave the highest C values (500–1700 mg C kg^-1 soil) and the substrate-induced respiration method gave the lowest (1–5 mg glucose equivalents kg^-1 soil). The C values closest to the C turnover measured in long-term incubation studies were obtained by the substrate-induced respiration method using the Wright-Hobbie model.Contribution from the Soil-Microbial Systems Laboratory, NRI, USDA-ARS, Beltsville, MD 20705, USA     

Determination of low concentrations of organic phosphorus in soil solution

Abstract

Phosphorus (P) export from agricultural land is an important source of water‐quality deterioration in many areas of the world. Part of the total phosphorus in the soil solution is represented by dissolved organic P at concentrations that can be as low as 1x10^‐6 M of P. The suitability of four digestion methods for the destruction of organic P and determination of orthophosphate at low concentrations and small volumes using the malachite green method has been evaluated. The acid digestion procedures evaluated were 1) sulfuric and perchloric acid, 2) sulfuric acid and potassium persulphate, 3) nitric acid, and 4) nitric and perchloric acid. As inositol hexaphosphate (IHP) represents one of the more resistant molecules to acid hydrolysis in soils, this compound has been chosen to assess the recovery assay of the recommended procedure. The digestion procedures were adapted for the malachite green spectrophotometric method, in order to obtain lower analytical limits for P determination. The sulfuric‐perchloric acid digestion gave excellent recovery and reproducibility, and can therefore be used for determining organic P in solution at concentrations as low as 6.45x10^‐7 M.     

Boron Estimation in Soil,Plant, and Water Samples using Spectrophotometric Methods

Four spectrophotometric methods of boron (B) determination using azomethine-H, carmine, curcumin, and quinalizarin were compared to screen the most suitable one in estimating B concentration in diverse soils, plants and irrigation water samples. The azomethine-H method was the most sensitive in determining extractable B content of soils. All four methods, however, performed with equal efficiency for estimating B concentration in plant tissues. In the case of irrigation water, both carmine and azomethine-H were equally efficient in B determination. Natural concentration of interfering elements for the methods in all the tested soil, plant, and water samples were less than the tolerance limits. Because of sensitivity, ease of adaptation without using strong sulfuric acid, and rapidity, the azomethine-H method may be used for regular B determination in soil, plant, and irrigation water samples.     

THE HYDROLYTIC EXTRACTION OF CARBOHYDRATES FROM SOIL BY SULPHURIC ACID

The parameters of the extraction and hydrolysis of soil carbohydrates by methods involving 24N H₂SO₄ and N H₂SO₄ were studied for a sandy granitic loam. Sugars were measured by alkaline ferricyanide, orcinol, anthrone (hexoses), orcinol-ferric chloride (pentoses), cysteine-sulphuric acid (methyl pentoses), glucose oxidase (glucose), and also by analysis of the individual sugars by paper chromatography. After shaking the soil with 24N H₂SO₄ at 20° C a further period of treatment with N H₂SO₄ at 100° C was required to obtain maximum hydrolysis of the soil carbohydrates. This period decreased from 17 h to 5 h as the time with 24N H₂SO₄ increased from 2 to 16 h. NH₂SO₄ at 100° C alone was less efficient. The extraction of pentoses by 24N H₂SO₄ reached a maximum within 8 h, and methyl pentoses within 4 h, both declining thereafter. The release of hexoses was continuing after 40 h. The best compromise involved extraction with 24N H₂SO₄ for 16 h followed by hydrolysis with N H₂SO₄ for 5 h. By this treatment yields of pentoses and methyl pentoses were respectively 99 and 92 per cent of the maximum obtainable.     

Enzymatic determination of urea in milk by sequential injection with spectrophotometric and conductometric detection

In this work, an analytical system based on the coupling of gas diffusion separation and sequential injection analysis for urea determination in milk is presented. A versatile manifold that could simultaneously be used for either spectrophotometric or conductometric detection was constructed. The sample and urease solution are sequentially aspirated into the holding coil and sent to a thermoreactor, where urea is enzymatically hydrolyzed by urease and converted into ammonium. This stream merges an alkaline solution at a confluence point where ammonia is formed. Ammonia diffuses through a hydrophobic membrane and modifies the bromothymol blue indicator color, when spectrophotometric detection is used, or changes the conductance of a boric acid solution acceptor stream, when conductometric detection is used.This methodology was applied to the determination of urea in 18 milk samples and the results were statistically comparable with those furnished by the enzymatic recommended procedure. The detection limits were 2.6 x 10(-4) and 2.8 x 10(-5) mol L(-1) for conductometric and spectrophotometric detection, respectively. Repeatability (relative standard deviation, RSD) was better than 3.7% and 2.6% for conductometric and spectrophotometric detection, respectively.     

A Sensitive Spectrophotometric Method for Determination of Trace Quantities of Indium in Soil

A simple and very sensitive method determining microgram quantities of indium in soil has been developed. The spectrophotometric method (??=?1.74?×?10⁵ l mol^-1 cm^-1) based on the mixed complex In (III) with Chrome Azurol S and benzyldodecyldimethylammonium bromide was used for the analysis. A preliminary separation is made by extracting indium into butyl acetate from 5 M HBr solution. The selectivity of indium extraction and determination in the presence of macro- and micro components of soil was studied. Prior reduction of Fe (III) to Fe (II) with ascorbic acid prevents its co-extraction with indium. Indium was determined in synthetic mixtures corresponding to soil compositions and real samples of soil from different agricultural and industrial regions of Poland. The content of indium was found from the calibration graph (in the range, 0.12–0.48 μg/ml; r?=?0.9991) obtained after extraction. The precision was satisfactory: % RSD (n?=?6) ranged from 2.7 to 8.2. The average indium standard recovery ranged from 95 to 101%. Analysis using an ICP-OES method gave comparable results.     

A Modified Walkley-Black Method Based on Spectrophotometric Procedure

The Walkley-Black (WB) method, because of its simplicity and rapidity, has been widely used during the past 50 years for determination of soil organic carbon (SOC), but one of the main problems with WB method in operation is determination of titration end point by the observer. In the past several years some studies have been done to reduce the human role in determination of titration end point in WB method. In this study, in addition to the routine method of using an indicator for end point determination, a potentiometric and a spectrophotometric method was also employed for end point determination. The results indicated that these two methods are more accurate than the indicator method. Finally, a modified Walkley-Black (MWB) method employing a spectrophotometric procedure was proposed, which is more reproducible, easier in operation, and more economical.     

Colorimetric and volumetric assays of colchicine in galenicals and in pharmaceutical preparations.

In the method described the amide group in the colchicine molecule is reduced with lithium aluminum hydride to the corresponding secondary amine. The latter is extracted with chloroform and then determined either colorimetrically by the copper dithiocarbamate reaction or volumetrically by dissolving in acid and titrating with sodium hydroxide or perchloric acid. The results were comparable with those obtained by the Egyptian Pharmacopoeia spectrophotometric method.     

Spectrophotometric and Inductively Coupled Plasma–Optical Emission Spectroscopy Determination of Gallium in Natural Soils and Soils Polluted by Industry: Relationships between Elements

The aim of this work was to determine gallium contents in different soils of Poland using a sensitive spectrophotometric method based on the complex of Ga(III) with chrome azurol S and benzyldodecyldimethylammonium bromide and inductively coupled plasma–optical emission spectrometry technique. The total content of gallium in the soils clearly depends on the soil location and properties and ranged from 41.7 to 437 μg g^–1. The contents of gallium determined in 10% nitric acid and 1 M of magnesium chloride extract ranges respectively from 38.0 to 81.9% and 20–40% of the total content of this element. A strong correlation has been found between gallium and zinc, cadmium, lead, and copper. The high Pearson correlation coefficient values and the proportional relationship between the concentrations of Ga and these metals may make it possible to treat gallium as an indicator of soil contamination with heavy metals.     

Kinetic characterization of the oxidation of chlorogenic acid by polyphenol oxidase and peroxidase. Characteristics of the o-quinone

Chlorogenic acid is the major diphenol of many fruits, where it is oxidized enzymatically by polyphenol oxidase (PPO) or peroxidase (POD) to its o-quinone. In spectrophotometric studies of chlorogenic acid oxidation with a periodate ratio of [CGA]0/[IO4-]0 < 1 and [CGA]0/[IO4-]0 > 1, the o-quinone was characterized as follows: lambda(max) at 400 nm and epsilon = 2000 and 2200 M-1 cm-1 at pH 4.5 and 7.0, respectively. In studies of o-quinone generated by the oxidation of chlorogenic acid using a periodate at ratio of [CGA]0/[IO4-]0 > 1, a reaction with the remaining substrate was detected, showing rate constants of k = 2.73 +/- 0.17 M-1 s-1 and k' = 0.05 +/- 0.01 M-1 s-1 at the above pH values. A chronometric spectrophotometric method is proposed to kinetically characterize the action of the PPO or POD on the basis of measuring the time it takes for a given amount of ascorbic acid to be consumed in the reaction with the o-quinone. The kinetic constants of mushroom PPO and horseradish POD are determined.     

Nitrogen effects on total flavonoids,chlorogenic acid,and antioxidant activity of the medicinal plant Chrysanthemum morifolium

Chrysanthemum morifolium (Ramat.) has a long history of cultivation and use as a traditional medicine and tea plant in China. A greenhouse experiment with potted soil–quarz mixture studied the effects of nitrogen supply (0, 56, 112, 167, 224, 334, 501, 556, and 668 mg N kg^–1) on concentrations and ratios of total flavonoids and chlorogenic acid in the flowers of C. morifolium using spectrophotometric and HPLC methods. The antioxidant activity of the flowers was determined as the radical scavenging activities of hydroxyl, superoxide anion, and 2,2‐diphenyl‐1‐picrylhydrazyl hydrate (DPPH) free radicals. A high N supply decreased the concentrations of total flavonoids by 18%–35% and that of chlorogenic acid by 8%–60% compared to a low N‐supply rate. At the same time, increasing N supply significantly decreased the antioxidant activity of the flowers. The antioxidant activity of C. morifolium flowers was significantly positively correlated with the concentrations of total flavonoids and chlorogenic acid. We conclude that an N supply in excess of 300 mg (kg soil)^–1 will negatively affect the antioxidant activity and thereby reduce the quality of C. morifolium flowers.     

Spectrophotometric analysis of mixtures of acetaminophen, salicylamide, and codeine phosphate in tablets

A simple and accurate spectrophotometric procedure for the analysis of a mixture of acetaminophen, salicylamide, and codeine phosphate is described. Determination of the first 2 components depends on pH-induced differential spectral changes of their nitroso derivatives. The third component is assayed by the acid dye method. The proposed procedure was successfully applied to the analysis of laboratory-made and commercial tablets containing the ternary drug mixture.     

A rapid microwave digestion method for colorimetric measurement of soil organic carbon

Abstract

Soil organic matter is an active component of agroecosystems. Rapid and precise measurement of organic carbon (C_org) is essential to monitor changes in organic matter and soil quality. A new semi‐micro wet digestion method for the determination of C_org was developed using rapid microwave energy applied at 500 J mL^‐1 digestion mixture to enhance oxidation of C_org by K₂Cr₂O₇and conc. H₂SO₄. This proposed method and three existing methods of soil C determination were compared with the LECO dry combustion carbon analyzer. The r² value for the proposed microwave method regressed against LECO C was 0.9913. The recovery of C_org by the rapid microwave digestion method for spectrophotometric measurement was 91.7±1.2% (conversion factor 1.09) of C measured by the LECO dry combustion method. Compared to the traditional Walkley‐Black's method, the proposed spectrophotometric with microwave digestion method was rapid and more precise, used smaller reagent volumes, and produced less waste.     

Spectrophotometric determination of piperazine and its salts in pharmaceuticals

A spectrophotometric determination of piperazine and some of its salts is described. The method depends on the UV measurement of the N-nitroso derivatives formed by the interaction of piperazine with nitrous acid. The chromophore is developed by heating the reaction mixture at 80 degrees C for 15 min, at pH 2.3--2.6. Beer's law is obeyed in the range 1--15 micrograms/mL.     

New method to determine antioxidant activity of polyphenols

The capacity of polyphenolic compounds to reduce the beta-carotene-linoleic acid cooxidation enzymatically induced by soybean lipoxygenase was assayed to determine their comprehensive antioxidant ability. The inhibition of the coupled oxidation is a well-known spectrophotometric method for the antioxidant activity measurement. A modification of this method is proposed to reduce assay time and to gain simplicity. The antioxidant abilities of several polyphenols were determined, and quercetin and sinapic acid were most active. These results were compared to those obtained by the DPPH* procedure to evaluate the free radical scavenging contribution to the total protective action. The highest values of antiradical activity were found for ellagic and quercetin.