Dietary antioxidants interfere with Amplex Red-coupled-fluorescence assays

ROS produced by NOX promote the neurite growth in a PI3K/Akt independent manner

Reactive oxygen species (ROS) function as signaling molecules in several physiologic and pathologic processes. In central nervous system, ROS are critical for differentiation, migration, polarization, and neurite growth. These actions are mediated by reversible oxidation of target proteins. On the other hand, PI3K/Akt signaling pathway is susceptible to be modulated by ROS and it has been implicated in neurite growth. In this study, we evaluated the participation of ROS in the neurite growth of cultured rat cerebellar granule neurons (CGN), as well as the possible regulation of the PI3K/Akt pathway by ROS during neurite outgrowth. For this purpose, CGN were treated with cellular or mitochondrial antioxidants, or an NOX inhibitor and neurite growth was evaluated. Moreover, to assess the participation Akt in this process, the p-Akt levels were measured in CGN treated with antioxidants or a NOX inhibitor. The effect of antioxidants on the neurite growth in the presence of a PI3K inhibitor was also measured. We found that cellular antioxidants and the NOX inhibitor decreased the neurite growth, but not the mitochondrial antioxidant. Interestingly, the antioxidants increased the p-Akt levels; however, the effect of antioxidants on neurite growth was no dependent on the Akt activity since the inhibitor of PI3K did not modify the antioxidant action on neurite growth. Our results show that the PI3K/Akt pathway participates in neurite growth and that ROS produced by NOX could function as signals in this process; however, this action is not mediated by a redox regulation of Akt activity.

Novel fluorometric protocol for assessing myeloperoxidase activity

Neutrophil myeloperoxidase (MPO) is an essential enzyme for the innate immune system. Measuring MPO activity is vital for understanding neutrophil characteristics and functions in various diseases. MPO activity can be measured using several methods, including spectrophotometric and fluorometric protocols. This paper introduces a fluorometric method for specifically quantifying MPO activity based on the H2O2-dependent oxidation of thiamine. We optimized this new method using the robust statistical approach response surface methodology (RSM) and Box Benken Design (BBD). We extensively examined the effects of several experimental parameters using the RSM methodology and determined the best conditions for accurate and sensitive MPO activity measurement. The optimal conditions were determined using the analysis of variance (ANOVA) for second-order polynomial equations. The resulting F-value (4.86) indicated that the model was significant. However, the lack-of-fitness F-value (1.79) suggested it did not differ significantly from the corresponding p-value. The greatest MPO activity (30 ± 2 U L-1) was obtained under optimum conditions, which were 1000 µM of H2O2, 10 min incubation time, and 1000 µM of thiamine. Our results suggest that this advanced fluorometric method has significant accuracy, sensitivity, and linearity up to 60 IU. The new and standard colorimetric methods also showed a good correlation. These results indicate that the new fluorometric method can be dependable and efficient for assessing MPO activity. The new method is characterized by excellent accuracy, sensitivity, and linearity, making it a valuable protocol for researchers and clinicians interested in assessing MPO activity.

Phenolic compounds interfere in the Ampliflu Red/peroxidase assay for hydrogen peroxide

Methods employing horseradish peroxidase (HRP) are popular for quantification of hydrogen peroxide. This communication reports interference of the Ampliflu Red-HRP assay by phenolic compounds, abundant in food and beverages of plant origin. Concentrations of catechin, propyl gallate, quercetin and gallic acid lowering the yield of the product, resorufin, in this system by 50% were lower than 10 μM. The extent of inhibition increased with decreasing hydrogen peroxide concentration. These results point to the necessity of a careful interpretation of results concerning the quantification of hydrogen peroxide in materials containing phenolic compounds with methods employing HRP, especially when low concentrations of hydrogen peroxide are concerned.

The Non-Specific Drp1 Inhibitor Mdivi-1 Has Modest Biochemical Antioxidant Activity

Mitochondrial division inhibitor-1 (mdivi-1), a non-specific inhibitor of Drp1-dependent mitochondrial fission, is neuroprotective in numerous preclinical disease models. These include rodent models of Alzheimer’s disease and ischemic or traumatic brain injury. Among its Drp1-independent actions, the compound was found to suppress mitochondrial Complex I-dependent respiration but with less resultant mitochondrial reactive oxygen species (ROS) emission compared with the classical Complex I inhibitor rotenone. We employed two different methods of quantifying Trolox-equivalent antioxidant capacity (TEAC) to test the prediction that mdivi-1 can directly scavenge free radicals. Mdivi-1 exhibited moderate antioxidant activity in the 2,2′-azinobis (3-ethylbenzothiazoline 6-sulfonate) (ABTS) assay. Half-maximal ABTS radical depletion was observed at ~25 μM mdivi-1, equivalent to that achieved by ~12.5 μM Trolox. Mdivi-1 also showed antioxidant activity in the α, α-diphenyl-β-picrylhydrazyl (DPPH) assay. However, mdivi-1 exhibited a reduced capacity to deplete the DPPH radical, which has a more sterically hindered radical site compared with ABTS, with 25 μM mdivi-1 displaying only 0.8 μM Trolox equivalency. Both assays indicate that mdivi-1 possesses biochemical antioxidant activity but with modest potency relative to the vitamin E analog Trolox. Future studies are needed to evaluate whether the ability of mdivi-1 to directly scavenge free radicals contributes to its mechanisms of neuroprotection.

Simple kinetic method for assessing catalase activity in biological samples

A novel kinetic method for measuring catalase activity in biological samples was evaluated. The principle of the current method is based on the oxidation effect of unreacted hydrogen peroxide (H₂O₂) on pyrogallol red (PGR) using the catalytic effects of molybdenum. The decrease in the absorbance of PGR in the presence of H₂O₂ with time from 0.5 to 4.5 min was directly proportional to the concentration of H₂O₂, and, in turn, directly proportional to catalase activity. Erythrocyte lysate homogenates were used to measure catalase activity and the results of the current method were significantly correlated to those of the ammonium peroxovanadate method. The 3.1% within run and 4.7% between run coefficients of variation indicated the high precision of the present novel method. The validation process confirmed that the diagnostic method is appropriate for different types of biological samples. Here, we describe a rapid, relatively easy, and reliable method for measuring catalase activity. The assay could be applied as a diagnostic tool and is suitable in research contexts.•

A novel kinetic method for measuring catalase activity in biological samples was evaluated.

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The validation process confirmed that the diagnostic method is appropriate for different types of biological samples.

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The assay could be applied as a diagnostic tool and is suitable in research contexts.

Spatial Heterogeneity in Particle-Associated, Light-Independent Superoxide Production Within Productive Coastal Waters

In the marine environment, the reactive oxygen species (ROS) superoxide is produced through a diverse array of light-dependent and light-independent reactions, the latter of which is thought to be primarily controlled by microorganisms. Marine superoxide production influences organic matter remineralization, metal redox cycling, and dissolved oxygen concentrations, yet the relative contributions of different sources to total superoxide production remain poorly constrained. Here we investigate the production, steady-state concentration, and particle-associated nature of light-independent superoxide in productive waters off the northeast coast of North America. We find exceptionally high levels of light-independent superoxide in the marine water column, with concentrations ranging from 10 pM to in excess of 2,000 pM. The highest superoxide concentrations were particle associated in surface seawater and in aphotic seawater collected meters off the seafloor. Filtration of seawater overlying the continental shelf lowered the light-independent, steady-state superoxide concentration by an average of 84%. We identify eukaryotic phytoplankton as the dominant particle-associated source of superoxide to these coastal waters. We contrast these measurements with those collected at an off-shelf station, where superoxide concentrations did not exceed 100 pM, and particles account for an average of 40% of the steady-state superoxide concentration. This study demonstrates the primary role of particles in the production of superoxide in seawater overlying the continental shelf and highlights the importance of light-independent, dissolved-phase reactions in marine ROS production.

Kinetics of autoxidation of tartaric acid in presence of iron

The kinetics of the autoxidation reaction of tartaric acid in an air-saturated solution in the presence of Fe(II) show autocatalytic behavior with distinct initiation, propagation, and termination phases. The initiation phase, which involves activation of dissolved oxygen, decreases with increasing pH, over the test range of pH of 2.5-4.5, indicating that activation of oxygen is catalyzed by an Fe(II)-tartrate complex. The autocatalytic nature of this reaction indicates the presence of a catalytic intermediate that is produced during the initiation phase and regenerated during the propagation phase. The addition of catalase, as well as direct measurements, provided evidence of the presence and kinetic action of hydrogen peroxide as one of the intermediates. Direct addition of hydrogen peroxide resulted in shortening of the initiation stage and the propagation phase with similar rates as in the autoxidation reaction at low pH. The propagation is approximately a zero order reaction with respect to oxygen and iron. The kinetic analysis suggests that an intermediate catalytic complex(s) involving a ferryl ion (FeO²⁺) controls the rate of the propagation reaction. The Fe(III) formation shows autocatalytic behavior that mirrors the dissolved oxygen consumption patterns under all pH conditions studied. At pH values of 2.5 and 3.0, Fe(III) accumulated to a maximum, before it was partially consumed. This maximum coincided with the depletion of dissolved oxygen. The consumption of Fe(III), or the reduction of Fe(III) back to Fe(II), reflects the catalytic nature of Fe(II) and the essential role of tartaric acid in the initiation phase of Fenton's original reaction.

Open Surface Droplet Microfluidic Magnetosensor for Microcystin-LR Monitoring in Reservoir

Establishing rapid, simple, and in situ detection of microcystin-LR (MC-LR) in drinking water sources is of significant importance for human health. To ease the situation that current methods cannot address, an open surface droplet microfluidic magnetosensor was designed and validated to quantify MC-LR in reservoir water, which is capable of (1) MC-LR isolation via MC-LR antibody-conjugated magnetic beads, (2) parallel and multistep analytical procedures in 15-array power-free and reusable active droplet microfluidic chips, (3) immunoassay incubation and fluorescence excitation within a miniaturized multifunctional 3D-printing optosensing accessory, and (4) signal read-out and data analysis by a user-friendly Android app. The proposed smartphone-based fluorimetric magnetosensor exhibited a low limit of detection of 1.2 × 10^-5 μg/L in the range of 10^-4 μg/L to 100 μg/L. This integrated and high throughput platform was utilized to draw an MC-LR contamination map for six reservoirs distributed in the Pearl River delta, Guangdong Province. It promises to be a simple and successful quantification method for MC-LR field detection, bringing many benefits to rapid on-site screening.

Small-molecule luminescent probes for the detection of cellular oxidizing and nitrating species

Reactive oxygen species (ROS) have been implicated in both pathogenic cellular damage events and physiological cellular redox signaling and regulation. To unravel the biological role of ROS, it is very important to be able to detect and identify the species involved. In this review, we introduce the reader to the methods of detection of ROS using luminescent (fluorescent, chemiluminescent, and bioluminescent) probes and discuss typical limitations of those probes. We review the most widely used probes, state-of-the-art assays, and the new, promising approaches for rigorous detection and identification of superoxide radical anion, hydrogen peroxide, and peroxynitrite. The combination of real-time monitoring of the dynamics of ROS in cells and the identification of the specific products formed from the probes will reveal the role of specific types of ROS in cellular function and dysfunction. Understanding the molecular mechanisms involving ROS may help with the development of new therapeutics for several diseases involving dysregulated cellular redox status.

Effects of Epigallocatechin Gallate on Tert-Butyl Hydroperoxide-Induced Mitochondrial Dysfunction in Rat Liver Mitochondria and Hepatocytes

Epigallocatechin gallate (EGCG) is a green tea antioxidant with adverse effects on rat liver mitochondria and hepatocytes at high doses. Here, we assessed whether low doses of EGCG would protect these systems from damage induced by tert-butyl hydroperoxide (tBHP). Rat liver mitochondria or permeabilized rat hepatocytes were pretreated with EGCG and then exposed to tBHP. Oxygen consumption, mitochondrial membrane potential (MMP), and mitochondrial retention capacity for calcium were measured. First, 50 μM EGCG or 0.25 mM tBHP alone increased State 4 Complex I-driven respiration, thus demonstrating uncoupling effects; tBHP also inhibited State 3 ADP-stimulated respiration. Then, the coexposure to 0.25 mM tBHP and 50 μM EGCG induced a trend of further decline in the respiratory control ratio beyond that observed upon tBHP exposure alone. EGCG had no effect on MMP and no effect, in concentrations up to 50 μM, on mitochondrial calcium retention capacity. tBHP led to a decline in both MMP and mitochondrial retention capacity for calcium; these effects were not changed by pretreatment with EGCG. In addition, EGCG dose-dependently enhanced hydrogen peroxide formation in a cell- and mitochondria-free medium. Conclusion. Moderate nontoxic doses of EGCG were not able to protect rat liver mitochondria and hepatocytes from tBHP-induced mitochondrial dysfunction.

Piceatannol and resveratrol share inhibitory effects on hydrogen peroxide release, monoamine oxidase and lipogenic activities in adipose tissue, but differ in their antilipolytic properties

Piceatannol is a hydroxylated derivative of resveratrol. While both dietary polyphenols coexist in edible plants and fruits, and share equivalent concentrations in several wines, the influence of piceatannol on adiposity has been less studied than that of resveratrol. Though resveratrol is now recognized to limit fat deposition in various obesity models, the benefit of its dietary supplementation remains under debate regarding human obesity treatment or prevention. The research for more potent resveratrol analogs is therefore still undergoing. This prompted us to compare various effects of piceatannol and resveratrol directly on human adipose tissue (hAT). Hydrogen peroxide release was measured by Amplex Red-based fluorescence in subcutaneous hAT samples from obese patients. Interactions of stilbenes with human amine oxidases and quinone reductase were assessed by radiometric methods, computational docking and electron paramagnetic resonance. Influences on lipogenic and lipolytic activities were compared in mouse adipocytes. Resveratrol and piceatannol inhibited monoamine oxidase (MAO) with respective IC50 of 18.5 and 133.7 μM, but not semicarbazide-sensitive amine oxidase (SSAO) in hAT. For both stilbenes, the docking scores were better for MAO than for SSAO. Piceatannol and resveratrol similarly hampered hydrogen peroxide detection in assays with and without hAT, while they shared pro-oxidant activities when incubated with purified quinone reductase. They exhibited similar dose-dependent inhibition of adipocyte lipogenic activity. Only piceatannol inhibited basal and stimulated lipolysis when incubated at a dose ≥100 μM. Thus, piceatannol exerted on fat cells dose-dependent effects similar to those of resveratrol, except for a stronger antilipolytic action. In this regard, piceatannol should be useful in limiting the lipotoxicity related to obesity when ingested or administered alone - or might hamper the fat mobilization induced by resveratrol when simultaneously administered with it.

Dietary Phenolic Compounds Interfere with the Fate of Hydrogen Peroxide in Human Adipose Tissue but Do Not Directly Inhibit Primary Amine Oxidase Activity

Resveratrol has been reported to inhibit monoamine oxidases (MAO). Many substrates or inhibitors of neuronal MAO interact also with other amine oxidases (AO) in peripheral organs, such as semicarbazide-sensitive AO (SSAO), known as primary amine oxidase, absent in neurones, but abundant in adipocytes. We asked whether phenolic compounds (resveratrol, pterostilbene, quercetin, and caffeic acid) behave as MAO and SSAO inhibitors. AO activity was determined in human adipose tissue. Computational docking and glucose uptake assays were performed in 3D models of human AO proteins and in adipocytes, respectively. Phenolic compounds fully inhibited the fluorescent detection of H2O2 generated during MAO and SSAO activation by tyramine and benzylamine. They also quenched H2O2-induced fluorescence in absence of biological material and were unable to abolish the oxidation of radiolabelled tyramine and benzylamine. Thus, phenolic compounds hampered H2O2 detection but did not block AO activity. Only resveratrol and quercetin partially impaired MAO-dependent [(14)C]-tyramine oxidation and behaved as MAO inhibitors. Phenolic compounds counteracted the H2O2-dependent benzylamine-stimulated glucose transport. This indicates that various phenolic compounds block downstream effects of H2O2 produced by biogenic or exogenous amine oxidation without directly inhibiting AO. Phenolic compounds remain of interest regarding their capacity to limit oxidative stress rather than inhibiting AO.

Direct oxidative pathway from amplex red to resorufin revealed by in situ confocal imaging

The conversion of Amplex Red (AR) to the fluorescent dye resorufin (RS) is employed in many biochemical assays. Here, direct generation of RS from AR at a mild oxidation potential is proven by a series of in situ electrochemical techniques.

Glitazones inhibit human monoamine oxidase but their anti-inflammatory actions are not mediated by VAP-1/semicarbazide-sensitive amine oxidase inhibition

Glitazones are peroxisome proliferator-activated receptor gamma (PPARγ) agonists widely used as antidiabetic drugs also known as thiazolidinediones. Most of them exert other effects such as anti-inflammatory actions via mechanisms supposed to be independent from PPARγ activation (e.g., decreased plasma monocyte chemoattractant protein-1 (MCP-1) levels). Recently, pioglitazone has been shown to inhibit the B form of monoamine oxidase (MAO) in mouse, while rosiglitazone and troglitazone were described as non-covalent inhibitors of both human MAO A and MAO B. Since molecules interacting with MAO might also inhibit semicarbazide-sensitive amine oxidase (SSAO), known as vascular adhesion protein-1 (VAP-1), and since VAP-1/SSAO inhibitors exhibit anti-inflammatory activity, our aim was to elucidate whether VAP-1/SSAO inhibition could be a mechanism involved in the anti-inflammatory behaviour of glitazones. To this aim, MAO and SSAO activities were measured in human subcutaneous adipose tissue biopsies obtained from overweight women undergoing plastic surgery. The production of hydrogen peroxide, an end-product of amine oxidase activity, was determined in tissue homogenates using a fluorometric method. The oxidation of 1 mM tyramine was inhibited by pargyline and almost resistant to semicarbazide, therefore predominantly MAO-dependent. Rosiglitazone was more potent than pioglitazone in inhibiting tyramine oxidation. By contrast, benzylamine oxidation was only abolished by semicarbazide: hence SSAO-mediated. Pioglitazone hampered SSAO activity only when tested at 1 mM while rosiglitazone was inefficient. However, rosiglitazone exhibited anti-inflammatory activity in human adipocytes by limiting MCP-1 expression. Our observations rule out any involvement of VAP-1/SSAO inhibition and subsequent limitation of leukocyte extravasation in the anti-inflammatory action of glitazones.

Resveratrol directly affects in vitro lipolysis and glucose transport in human fat cells

Resveratrol is a naturally occurring polyphenol found in many dietary sources and red wine. Recognized as a cancer chemoprevention agent, an anti-inflammatory factor and an antioxidant molecule, resveratrol has been proposed as a potential anti-obesity compound and to be beneficial in diabetes. Most of the studies demonstrating the anti-adipogenic action of resveratrol were performed as long-term treatments on cultured preadipocytes. The aim of this study was to analyse the acute effects of resveratrol on glucose uptake and lipolysis in human mature adipocytes. Samples of subcutaneous abdominal adipose tissue were obtained from overweight humans and immediately digested by liberase. Fat cells were incubated (from 45 min to 4 h) with resveratrol 1 μM-1 mM. Then, glycerol release or hexose uptake was determined. Regarding lipolysis, the significant effects of resveratrol were found at 100 μM, consisting in a facilitation of isoprenaline stimulation and an impairment of insulin antilipolytic action. At 1 and 10 μM, resveratrol only tended to limit glucose uptake. Resveratrol 100 μM did not change basal glucose uptake but impaired its activation by insulin or by benzylamine. This inhibition was not found with other antioxidants. Such impairment of glucose uptake activation in fat cells may led to a reduced availability of glycerol phosphate and then to a decreased triacylglycerol assembly. Therefore, resveratrol increased triacylglycerol breakdown triggered by β-adrenergic activation and impaired lipogenesis. Consequently, our data indicate that resveratrol can be considered as limiting fat accumulation in human fat cells and further support its use for the mitigation of obesity.

Highly sensitive determination of hydrogen peroxide and glucose by fluorescence correlation spectroscopy

Background

Because H₂O₂ is generated by various oxidase-catalyzed reactions, a highly sensitive determination method of H₂O₂ is applicable to measurements of low levels of various oxidases and their substrates such as glucose, lactate, glutamate, urate, xanthine, choline, cholesterol and NADPH. We propose herein a new, highly sensitive method for the measurement of H₂O₂ and glucose using fluorescence correlation spectroscopy (FCS).

Methodology/Principal Findings

FCS has the advantage of allowing us to determine the number of fluorescent molecules. FCS measures the fluctuations in fluorescence intensity caused by fluorescent probe movement in a small light cavity with a defined volume generated by confocal illumination. We thus developed a highly sensitive determination system of H₂O₂ by FCS, where horseradish peroxidase (HRP) catalyzes the formation of a covalent bond between fluorescent molecules and proteins in the presence of H₂O₂. Our developed system gave a linear calibration curve for H₂O₂ in the range of 28 to 300 nM with the detection limit of 8 nM. In addition, by coupling with glucose oxidase (GOD)-catalyzed reaction, the method allows to measure glucose in the range of 80 nM to 1.5 µM with detection limit of 24 nM. The method was applicable to the assay of glucose in blood plasma. The mean concentration of glucose in normal human blood plasma was determined to be 4.9 mM.

Conclusions/Significance

In comparison with commercial available methods, the detection limit and the minimum value of determination for glucose are at least 2 orders of magnitude more sensitive in our system. Such a highly sensitive method leads the fact that only a very small amount of plasma (20 nL) is needed for the determination of glucose concentration in blood plasma.

Knockdown of cytoglobin expression sensitizes human glioma cells to radiation and oxidative stress

Cytoglobin is a recently identified vertebrate globin whose functions include scavenging reactive oxygen and nitrosative species. In tumor cells, CYGB may function as a tumor suppressor gene. Here we show that knockdown of cytoglobin expression can sensitize human glioma cells to oxidative stress induced by chemical inhibitors of the electron transport chain and as well can increase cellular radiosensitivity. When treated with antimycin A, an inhibitor of the mitochondrial electron transport chain, cytoglobin-deficient cells showed significantly higher H₂O₂ levels, whereas H₂O₂ levels were significantly reduced in cytoglobin-overexpressing cells. In addition, cytoglobin knockdown significantly decreased the doubling time of glioma cell lines, consistent with a putative tumor suppressor function. These finding suggest that modulating cytoglobin levels may be a promising treatment strategy for sensitizing human glioma cells to oxidative stress that is induced by ionizing radiation, certain chemotherapies and ischemia-reperfusion.

Labeling live cells by copper-catalyzed alkyne--azide click chemistry

The copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, optimized for biological molecules in aqueous buffers, has been shown to rapidly label mammalian cells in culture with no loss in cell viability. Metabolic uptake and display of the azide derivative of N-acetylmannosamine developed by Bertozzi, followed by CuAAC ligation using sodium ascorbate and the ligand tris(hydroxypropyltriazolyl)methylamine (THPTA), gave rise to abundant covalent attachment of dye-alkyne reactants. THPTA serves both to accelerate the CuAAC reaction and to protect the cells from damage by oxidative agents produced by the Cu-catalyzed reduction of oxygen by ascorbate, which is required to maintain the metal in the active +1 oxidation state. This procedure extends the application of this fastest of azide-based bioorthogonal reactions to the exterior of living cells.

When cholesterol is not cholesterol: a note on the enzymatic determination of its concentration in model systems containing vegetable extracts

BACKGROUND

Experimental evidences demonstrate that vegetable derived extracts inhibit cholesterol absorption in the gastrointestinal tract. To further explore the mechanisms behind, we modeled duodenal contents with several vegetable extracts.

RESULTS

By employing a widely used cholesterol quantification method based on a cholesterol oxidase-peroxidase coupled reaction we analyzed the effects on cholesterol partition. Evidenced interferences were analyzed by studying specific and unspecific inhibitors of cholesterol oxidase-peroxidase coupled reaction. Cholesterol was also quantified by LC/MS. We found a significant interference of diverse (cocoa and tea-derived) extracts over this method. The interference was strongly dependent on model matrix: while as in phosphate buffered saline, the development of unspecific fluorescence was inhibitable by catalase (but not by heat denaturation), suggesting vegetable extract derived H(2)O(2) production, in bile-containing model systems, this interference also comprised cholesterol-oxidase inhibition. Several strategies, such as cholesterol standard addition and use of suitable blanks containing vegetable extracts were tested. When those failed, the use of a mass-spectrometry based chromatographic assay allowed quantification of cholesterol in models of duodenal contents in the presence of vegetable extracts.

CONCLUSIONS

We propose that the use of cholesterol-oxidase and/or peroxidase based systems for cholesterol analyses in foodstuffs should be accurately monitored, as important interferences in all the components of the enzymatic chain were evident. The use of adequate controls, standard addition and finally, chromatographic analyses solve these issues.