EXPERIMENTAL CONDITIONS CONCERNING POTENTIOMETRIC TITRATION OF HUMIC ACID

The humic acids of four soils from Denmark have been extracted by EDTA. The humic acids were separated from EDTA by precipitation with Ba²⁺. The ash content was lowered by treatment with HF and HC1. The ash content in the four humic acids was less than 0.6 per cent. Chemical analysis of the humic acids supply some evidence for the suggestion that EDTA extracted organic matter is a more definite fraction than humic acid extracted by NaOH. It was shown that an alkaline humate solution stored in sterile, sealed ampoules under N₂ does not change its initial pH, indicating that the protolytic equilibrium is established instantly. It is therefore proposed that the titration of humic acid should be carried out as quickly as a normal acid-base titration.     

PHENOLIC HYDROLYSIS PRODUCTS FROM GEL CHROMATOGRAPHIC FRACTIONS OF SOIL HUMIC ACIDS

Humic acids extracted from the Bh horizon of a kauri (Agathis australis) podzol and the A horizon of a yellow-brown earth under hard beech (Nothofagus truncata), both New Zealand soils, were fractionated by a ‘salt boundary’ technique using a dextran gel, and the fractions hydrolysed with 6 M hydrochloric acid. Lignin-derived phenolic acids were analysed by gas chromatography of the ether-soluble hydrolysis products of the humic acids. The lignin derivatives from the kauri podzol humic acid are probably modern products derived from the present-day scrub vegetation, whereas those from the yellow-brown earth humic acid are derived from the deciduous vegetation.     

Contribution to the quantification of humic acids by thin layer chromatography

Increasing amounts from 2.5 to 45 μg of one synthetic and seven natural humic acids were chromatographed on silica gel thin layers using ammonia 25% and propanol in the ratio 70:30 v/v as mobile phase. The fragments of humic acids produced under the influence of the alkaline mobile phase were separated in three band-shaped chromatographic fractions, whose lengths were transverse to the direction of the mobile phase. Since the fragments were not formed in constant ratios from different quantities of the same humic acid, the length of a fraction could only reflect its content of humic substance, whereas the sum of lengths of the three fractions (F) reflected quantities of the humic acid (x) at starting points. Similar F-x curves were obtained from humic acids extracted from similar origins, even when the locations of the samples, particle weights of the humic acids or the pH values at which they were extracted were different. The mathematical relation between F and x for quantities of humic acids up to 15–20 μg possessed high correlation coefficients and may be thus applied for the estimation of unknown concentrations of humic acids extracted from similar origins.     

Persulfate oxidation of humic acids extracted from three different soils

Three soil humic acids were degraded by a new mild chemical oxidation method using potassium persulfate at pH 2.0. The method degraded 30–40% of the starting material. The type and relative quantities of the products or fragments released as determined by GC/MS varied with the source of the polymers. Humic acid extracted from an Inceptisol yielded fatty, benzenecarboxylic and phenolic acids; humic acid from a Typic Chromoxerert produced largely dialkyl phthalates, and humic acid from an Humic Haplorthod gave only branched and straight-chain fatty acids. It is suggested that the method may be used to advantage as a first oxidant in a sequential degradation.     

Humic matter isolated from soils and water by the XAD‐8 resin and conventional NaOH methods

Abstract

Differences were studied in humic (HA) and fulvic acid (FA) extracted from soils and streams in South Georgia by the Amberlite XAD‐8 resin and conventional NaOH method. Characterization analysis was performed by liquid ¹³C NMR, infrared (IR) spectroscopy, scanning electron microscopy (SEM), and chemical analysis. The NMR spectra indicated that the resin method yielded black water HA and FA with spectroscopic, chemical and elemental characteristics different from those isolated by the conventional NaOH method. Humic acids from both the resin and conventional NaOH methods were composed of aliphatic, aromatics and carboxyl groups, but the “resin”; HA contained more aliphatic groups. These differences were also noticed between the FA fractions obtained by the two methods. The differences corresponded to differences in IR spectra. The IR spectrum of “resin”; FA exhibited only a weak shoulder at 1625/cm for the COO”; stretching vibration, in contrast to that of FA isolated by the conventional NaOH procedure. Apparently, the high aliphatic‐CH₃ group content has blocked the vibration above, as evidenced by methylation of HA. Fulvic acid extracted by the resin method was also higher in total acidity, but considerably lower in N content than FA obtained by the conventional NaOH method. Both methods yielded black water FA which was less aromatic in nature than black water HA, or soil FA.     

Soluble Phosphorus Released by Poultry Wastes in Acidified Aqueous Extracts

Abstract

Research has shown that measured water‐soluble phosphorus (WSP) from poultry litter might have been less than that released in the field. The effects of acidified extractions on soluble P (SP) concentrations were studied, and a buffer was selected to measure SP at pH 6.0, which is a target value for soil management in Georgia.

Soluble P concentrations were extracted from poultry wastes at three pHs: 1) at natural pH, using deionized water (DI_w); 2) after titrating DI_w suspensions with 0.5N hydrochloric acid (HCl) to pH end‐points 3.0, 4.0, and 6.0; and 3) at pH 6.0 with buffers of sodium (Na) acetate, potassium hydrogen phthalate (KHP), 2‐(N‐morpholino) ethanesulphonic acid (MES), Na cacodylate, imidazole, N‐(2‐acetamido)‐2‐aminoethansulphonic acid (ACES), N‐(carbamoyl‐methyl) iminodiacetic acid (ADA), bis‐(2‐hydroxyethyl) imino]‐tris‐[(hydroxymethyl) methane (Bistris), and 1,4 piperazine‐bis‐(ethane sulphonic acid) (PIPES).

Total SP increased 60% to 140% in suspensions acidified with HCl to pH 6.0 compared to suspensions at pH≥8. Dissolved unreactive P responded more (2× to 30×) than molybdate reactive P (20–100%). Buffers extracted more soluble minerals than suspensions acidified with HCl, probably because of their complexation ability. The most effective buffer was MES, because its effects seemed mainly due to acidification.     

Characterization of lake sediment humic acids from the Ćelije Lake system near Kruševac (Central Serbia) by13C and 1H solution NMR and 13C cpmas NMR

Humic acids were extracted from the bottom sediment of the three lakes (Zlatari, Vasici and Vodozahvat) that together comprise Lake ?elije a regional drinking water reservoir. The humic acids were examined by high resolution ¹³C and ¹H solution NMR and ¹³C CPMAS. The aromaticity expressed as the number of benzene rings per 1000 g of humic acid is 1.8 for Zlatari, 2.3 for Vasici and 1.9 for Vodozahvat. Oxygen-substituted aromatic carbon structures in humic acids from the first two lakes (Zlatari and Vasici) are similar and resemble p-coumaryl units in lignin while those in Lake Vodozahvat more closely resemble coniferyl or sinapyl units in lignin. The aromatic rings of all three humic acids are highly substituted. Humic acids from the first two lakes have very similar carbohydrate carbon contents (19.9 and 19.5% respectively) compared to 23.3% for Vodozahvat humic acid. Zlatari and Vodozahvat humic acids have a higher alkyl chain content which indicates a greater potential for forming hydrophobic cavities. The carboxyl and aromatic OH group content of each humic acid influences their capacity for forming complexes with metal ions.     

固态13C和15N核磁共振法研究15N标记土壤的腐殖质组分

Five humic fractions were obtained from a uniformly ^15N-labelled soil by extraction with 0.1 mol L^-1 Na4P2O7,0.1mol L^-1 NaOH ,and HF/HCl-0.1 mol L^-1 NaOH,consecutively,and analyzed by ^13C and ^15N CPMAS NMR (cross polarization and magic angle spinning nuclear magnetic resonace).Compared with those of native soils humic fractions studied as a whole contained more alkyls ,methoxyls and O-alkyls,being 27%-36%,17%-21%and 36%-40%,respectively,but fewer aromatics and carboxyls(bein 14%-20% and 13%-90%,respectively),Among those humic fractions ,the humic acid(HA)and fulvic acid(FA) extracted by 0.1 mol L^-1 Na4P2O7 contained slightly more carboxyls than corresponding humic fractions extracted by 0.1 mol L^-1 NaOH ,and the HA extacted by 0.1 mol L^-1 NaOH after treatment with HF/HCl contained the least aromatics and carboxyls.The distribution of nitrogen functional groups of soil humic fractions studied was quite similar to each other and also quite similar to that of humic fraction from native soils.More than 75% of total N in each fraction was in amide from,with 9%-13% present as aromatic and /or aliphatic amines and the remainder as heerocyclic N.     

氧化/磺化腐殖酸对潮土中Cu、Zn、Fe、Mn有效性的影响

【目的】研究比较改性腐殖酸对潮土微量元素有效性的影响及其作用机理,以期为开发提高微量元素有效性的专用腐殖酸功能材料提供科学依据。【方法】采用土壤培养法,将腐殖酸 (HA)、氧化腐殖酸 (YHA) 和磺化腐殖酸 (SHA) 分别按30、100、300 mg/kg用量与干土混匀装入培养瓶中,调节含水量至田间持水量的60%,置于25℃人工气候箱中进行恒温培养,并保持土壤湿度恒定。分别在培养第3、7、15、30、60天取样,测定土壤有效铜、锌、铁、锰含量。【结果】三种腐殖酸对土壤Cu、Zn、Fe、Mn有效性的影响大小依次为HA>YHA>SHA。施用30～300 mg/kg 腐殖酸 (HA) 可显著提高土壤有效铜含量,特别是在15～30天内,土壤有效铜含量提升幅度可达51.3%,明显优于氧化腐殖酸和磺化腐殖酸;施用三种腐殖酸30～300 mg/kg可在15天内增加土壤有效锌含量,其中以腐殖酸 (HA) 效果最好,土壤有效锌含量增幅可达11.8%～20.3%,优于氧化腐殖酸、磺化腐殖酸;30～100 mg/kg用量下,施用腐殖酸 (HA) 可在15天内使土壤有效锰含量提升5.6%,效果优于氧化腐殖酸和磺化腐殖酸,300 mg/kg用量下,磺化腐殖酸可使土壤有效锰含量提升13.6%;施用30～300 mg/kg的腐殖酸 (HA) 一周后,土壤有效铁含量提高4.3%～7.2%,磺化腐殖酸或氧化腐殖酸用量分别在30 mg/kg和300 mg/kg时可提高土壤铁有效性。【结论】施用腐殖酸可显著提升潮土铜的有效性,但对潮土锌、锰、铁有效性的影响呈现出阶段性变化,不同结构腐殖酸对潮土微量元素有效性的影响差异较大,以HA对元素有效性的影响最大。因此,腐殖酸应用于提升微量元素有效性时,需考虑腐殖酸本身性质及施用时期等因素。     

The alkaline hydrolysis of humic substances

A humic and a fulvic acid were subjected to four successive hydrolyses with 2NNaOH solution at 170°C for 3 h. Following each hydrolysis, the degradation products were extracted into ethyl acetate, methylated, separated by chromatographic techniques and identified by mass spectrometry and micro-IR spectrophotometry.One g of humic acid yielded 113.5 mg of aliphatic compounds (mainly n-C₁₆ and n-C₁₅) fatty acids), 72.1 mg of phenolics (principally guaiacyl and syringyl derivative) 17.1 mg of benzenepolycarboxylic acid esters and 30.4 mg of N-containing compounds (mainly secondary aromatic amides). Repeated attacks by the alkali on 1.0 g of fulvic acid released 103.8 mg of aliphatics, 133.8 mg of phenolics, 27.0 mg of benzenecarboxylic but 181.8 mg of N-containing compounds. Most of the latter appeared to have been formed during the second, third and fourth hydrolysis which produced reactive compounds that could abstract N from diazomethane which was used as methylating reagent. While 25.0% of the initial humic acid resisted repeated attacks by the alkali, practically all of the fulvic acid was converted into ethyl acetate-soluble products. The alkali-resistant humic acid residue produced high yields of benzenepolycarboxylic acids on alkaline permanganate oxidation.Alkaline hydrolysis, which is known to cleave CO bonds, was found to be relatively specific, although not very efficient, for the degradation of structural phenolic humic and fulvic acid components and for the concomitant liberation of adsorbed aliphatics and N-containing compounds, but was relatively ineffective for degrading aromatic structures linked by CC bonds.     

腐植酸土壤调理剂对酸化果园土壤理化性状及苹果产量和品质的影响

为研究不同类型土壤调理剂对酸化果园土壤的改良效果,本试验采用普通土壤调理剂和腐植酸土壤调理剂,设置普通土壤调理剂+常规施肥、腐植酸土壤调理剂+常规施肥、腐植酸土壤调理剂减量15%+常规施肥和等养分肥料+常规施肥4个处理,在胶东酸化果园进行了为期两年的试验。结果表明:施用2种土壤调理剂均能改善酸化土壤的理化性状。在土壤物理性状方面,与普通土壤调理剂相比,施用腐植酸土壤调理剂的土壤容重降低2.72%～4.76%,粉粒含量增加3.12%～5.28%,孔隙度提高1.74%～3.54%;在土壤化学性状方面,施用腐植酸土壤调理剂的土壤速效钾含量增加3.74%～10.57%,pH提高0.07～0.45个单位。施用2种土壤调理剂均能提高苹果产量,相比于普通土壤调理剂,施用全量腐植酸土壤调理剂可增产4.84%,减量15%施用仍增产2.87%,而二者间差异未达显著性水平。此外,连续两年施用腐植酸土壤调理剂可以改善苹果的品质,其中总糖含量提高9.35%～15.46%,糖酸比提高21.84%～46.58%。综上,胶东酸化果园(pH4.5)在常规施肥下配施腐植酸土壤调理剂1 275 kg/hm2可作为短期内改良酸化土壤、提高苹果产量和品质的有效途径。     

Evaluation of the possibilities of using humic acids obtained from lignite in the production of commercial fertilizers

Purpose

Technological progress and high market demand contributed to a significant interest in the production of fertilizers based on humic acids. The aim of this study was to evaluate the possibilities of using humic acids obtained from lignite in the production of new commercial products. For this purpose, it is necessary to determine the quality standard requirements for such material. Properties of humic acids depend on source of origin as well as method of its extraction.

Materials and methods

The humic acids were extracted from polish deposit of lignite–Sieniawa Lubuska by alkaline extraction using for this purpose six kinds of extractants: 0.1 M NaOH and 0.25 M NaOH, 0.1 M KOH and 0.25 M KOH, and 0.1 M Na₄P₂O₇ and 0.25 M Na₄P₂O₇. The humic samples were used in solid powder form and characterized by UV-Vis spectroscopy, ¹³C NMR spectroscopy, fluorescence spectroscopy, and thermal analysis.

Results and discussion

The determining factor influencing a degree of humic acids extraction from lignite and their structure is type of extractant. The largest efficiency of extraction (about 50%) was obtained with the use of NaOH solutions. All examined humic acids were generally characterized by simple and heterogeneous molecularly structure with low molecular weight and low aromatic polycondensation. Therefore, it can be concluded that humic acids extracted with NaOH and KOH solutions are less condensed than those extracted with Na₄P₂O₇ solutions. It can suggest that humic acids obtained from lignite using solutions of Na₄P₂O₇ are characterized by a low transformation degree and greater amount of carboxyl groups.

Conclusions

Low rank coal can be successfully used in agriculture as a rich source of humic acids. Reagent used in their extraction, apart from high efficiency should have a neutral impact on their structure. Studies on the physicochemical properties of humic acids can be helpful in predicting behaviors of such fertilizer components in the environment and in inventing new products taking the principles of sustainable development into consideration.

     

Effects of humic acids from vermicomposts on plant growth

The interactions between earthworms and microorganisms can produce significant quantities of plant growth hormones and humic acids which act as plant regulators. Experiments were designed to evaluate the effects of humic acids extracted from vermicompost and compare them with the action of commercial humic acid in combination with a commercial plant growth hormone, indole acetic acid (IAA) which is a commonly found in vermicomposts. In the first experiments, humic acids were extracted from cattle, food and paper waste vermicomposts. They were applied to a plant growth medium, Metro-Mix360 (MM360), at rates of 0, 250 or 500 mg humates kg⁻¹ dry wt. of MM360, to marigold, pepper, and strawberry plants in the greenhouse. Substitution of humates ranging from 250 to 1000 mg kg⁻¹ MM360 increased the growth of marigold and pepper roots, and increased the growth of roots and numbers of fruits of strawberries significantly. In other experiments, humic acids extracted from food waste vermicomposts were applied at a rate of 500 mg kg⁻¹ dry wt. of MM360, singly or in combination with IAA at a rate of 10⁻⁵ μM, to pepper seedlings. This experiment was designed to compare the differences in effects between the most effective dosage rate of humic acid from food waste, a phytohormone (IAA), and a commercial source of humic acid. The numbers of pepper flowers and fruits increased significantly in response to treatment with humic acid, IAA and a combination of humic acid and IAA. Peppers treated with humic acids extracted from food waste vermicomposts produced significantly more fruits and flowers than those treated with commercially-produced humic acids.     

Determination of fluazifop-butyl and fluazifop acid in soybeans and soybean oil using liquid chromatography with oxidative amperometric detection

A new method is described for the determination of the herbicide fluazifop-butyl, and its metabolite fluazifop acid, in soybeans and soybean oil as fluazifop acid. Liquid chromatography with amperometric detection (LC/AD) is used to determine fluazifop acid produced from the metabolism or base hydrolysis of fluazifop-butyl in soybeans and soybean oil. These foods were spiked with fluazifopbutyl at 0.05, 0.10, and 0.50 ppm and hydrolyzed with 0.2N NaOH in methanol. The hydrolysate (adjusted to pH less than or equal to 1) is extracted with dichloromethane and the extract is washed with 1.0% NaHCO3. The NaHCO3 is acidified to pH less than or equal to 1 and extracted with dichloromethane; the partitioning is repeated 2 more times. The dichloromethane is removed, mobile phase solvent is added, and aliquots are injected onto a PRP-1 liquid chromatographic column; fluazifop acid is separated from coextracted compounds and detected at an applied potential of + 1.25 V, using an amperometric electrochemical detector in the oxidation mode. Recoveries ranged from 69 +/- 6.5 to 101 +/- 18% and from 72 +/- 7.5 to 88 +/- 11% for soybeans and soybean oil, respectively. Accuracy of these recoveries was confirmed by use of 14C-radiolabeled fluazifop-butyl and by liquid scintillation spectrometry of the 14C-fluazifop acid released.     

Decomposition and distribution of residual activity of some 13C-microbial polysaccharides and cells,glucose, cellulose and wheat straw in soil

Studies were made to determine the rate of decomposition of some ¹⁴C-labeled microbial polysaccharides, microbial cells, glucose, cellulose and wheat straw in soil, the distribution of the residual ¹⁴C in various humic fractions and the influence of the microbial products on the decomposition of plant residues in soil. During 16 weeks from 32 to 86 per cent of the C of added bacterial polysaccharides had evolved as ¹⁴CO₂. Chromobacterium violaceum polysaccharide was most resistant and Leuconostoc dextranicus polysaccharide least resistant. In general the polysaccharides, microbial cells, and glucose exerted little effect on the decomposition of the plant products. Upon incubation the ¹⁴C-activity was quickly distributed in the humic. fulvic and extracted soil fractions. The pattern of distribution depended upon the amendment and the degree of decomposition. The distribution was most uniform in the highly decomposed amendments. After 16 weeks the bulk of the residual activity from Azotobacter indicus polysaccharide remained in the NaOH extracted soil. From C. violaceum polysaccharide both the extracted soil and the humic acid fraction contained high activity. About 50–80 per cent of the residual activity from the ¹⁴C-glucose, cellulose and wheat straw amended soils could be removed by hydrolysis with 6 n HCl. The greater part of this activity in the humic acid fraction was associated with the amino acids and that from the fulvic acids and residual soils after NaOH extraction with the carbohydrates. About 8 16 per cent of the activity of the humic acid fraction was present in substances (probably aromatic) extracted by ether after reductive or oxidative degradation.     

Alkalinity destruction by sediment organic matter dissolution during neutralization of acidified lakes

In this study we report on the effect of sediment, from an acidified lake, on the neutralization of the acidified water column. The results of this experimental study show that organic acids (presumably humic or fulvic acids) can dissolve from the sediment and destroy alkalinity as measured by a Gran plot analysis. Alkalinity destruction by organic acid dissolution was shown to be a function of pH. Some Na ion exchange for sediment H⁺ was also observed. This ion exchange was shown to be a function of pH and Na concentration.     

Vertical Distribution of Trace Metals in Natural Soil Horizons from Japan Part 2: Effects of Organic Components in Soil

The association of Al, Mn, Fe, Ba, Zn, Cr, Ni, Co and Pb withsoil organic matter (SOM) was investigated in three Japanesesoils. Organically bound metals were assayed by elementalanalysis of a fraction extracted with acidified hydrogenperoxide (H₂O₂) and the humic acid extracted withalkaline reagent, from soil sampled at various depths of solums.A Dystric Cambisol showed higher extractability with acidifiedH₂O₂ for most of the metals than a Humic Andosol and an Orthic Acrisol. A Humic Andosol had more metals associated with humicacid than the other two soils.Cu showed high extractability with acidified H₂O₂ andalso significant association with humic acid, while Pb showedhigh extractability with acidified H₂O₂ but itsassociation with humic acid was relatively low among the metalsinvestigated. As humic acid is highly resistant to weathering,retention of Cu with SOM may last longer than that of Pb.The binding of metals with SOM probably has contributed to theaccumulation of some metals in organic-rich shallow horizons of soil. Such metals were Zn, Cu, Ni and Pb in a Dystric Cambisol,Cu in a Humic Andosol, and Pb and Cu in an Orthic Arisol.     

AUTOXIDATION OF HUMIC ACID UNDER ALKALINE CONDITIONS

Humic acid was treated for 30 days with normal NaOH under either N₂ or O₂. In both cases some acid-soluble material resulted which was enriched with free and peptide α-amino N and also with total N. The molecular weight of the humic acid fell under alkaline conditions, while there was a decrease in total UV and visible absorption due to the production of less-coloured material which was largely present in the acid soluble fraction. Under O₂ these effects were considerably enhanced and simultaneously a significant arnount of O₂ was consumed. Other changes produced by O₂ were an increase in the cation-exchange capacity, particularly of the acid-soluble fraction, the production of carbonate, an increase in the Oxidation state of the acid, and a lessening of the resemblance of the acid to lignin as shown by the infra-red and UV spectra. In the main the changes produced by O₂ are similar to those observed for humic acids of decreasing molecular weight that can be extracted from a soil, either by differential extraction or by extraction followed by fractionation into different molecular-weight classes.     

Chemical heterogeneity of humic substances: characterization of size fractions obtained by hollow-fibre ultrafiltration

To investigate the chemical heterogeneity of humic substances in relation to molecular size, fulvic and humic acids were extracted and purified from the surface horizon of a Humic Gleysol in northern Switzerland. A fractionation scheme using hollow‐fibre ultrafiltration cartridges was developed and used to obtain four size fractions of the humic acid with nominal molecular weight ranges > 300 kDa, 100–300 kDa, 30–100 kDa, and 10–30 kDa. The fulvic acid and all humic acid fractions were characterized by size exclusion chromatography, elemental analysis (C, H, N, S), as well as spectroscopic techniques including UV‐VIS, CP‐MAS ¹³C‐NMR, FT‐IR, and fluorescence spectroscopy. Clear chemical differences between the humic acid size fractions were observed. Smaller size fractions of the soil humic acid contained more chargeable functional groups and a larger percentage of aromatic carbon than the larger size fractions. Conversely, the percentage of aliphatic carbon increased with increasing apparent molecular weight. The chemical composition of the smallest humic acid fraction differed clearly from the fulvic acid fraction, despite similar apparent molecular size and carboxyl carbon content. Small humic acids contained much more aromatic carbon and less aliphatic carbon than the fulvic acid fraction. Apparently, humic size fractions differ in their chemical composition, which can have important implications for their environmental behaviour.     

电荷辅助氢键对腐殖酸分子量和溶解性的影响

采用体积排阻色谱和总有机碳分析法,分别测定腐殖酸体系中加入盐酸、甲酸、乙酸和丙酸后其分子量和溶解性发生的变化;通过分析抗坏血酸、苯甲酸、苯酚和邻苯二酚4种模型化合物在甲酸影响下的紫外光谱,以验证电荷辅助氢键的存在。结果表明:小分子有机酸能够明显降低腐殖酸的分子量;此外,当腐殖酸体系pH接近小分子有机酸的pKa时(DpKa<0.5),腐殖酸溶解性明显增大。小分子有机酸可能与腐殖酸之间形成电荷辅助氢键,从而打破弱作用力维持的腐殖酸超分子的稳态结构,导致腐殖酸分子量的降低和溶解性的增加;且弱酸与有机物之间的pKa相差越小,形成的电荷辅助氢键能量越高,腐殖酸分子结构受到的扰动程度越大。一维紫外光谱和同步二维相关紫外光谱分析进一步表明,小分子有机酸可能与pKa接近的化合物之间形成电荷辅助氢键,整体跃迁所需能量提高,造成低波长吸收增大而高波长吸收减小的结果。