Optical detection of phenolic compounds based on the surface plasmon resonance band of Au nanoparticles

An indirect colorimetric method is presented for detection of trace amounts of hydroquinone (1), catechol (2) and pyrogallol (3). The reduction of AuCl4(-) to Gold nanoparticles (Au-NPs) by these phenolic compounds in the presence of cetyltrimethylammonium chloride (CTAC) produced very intense surface plasmon resonance peak of Au-NPs. The plasmon absorbance of Au-NPs allows the quantitative colorimetric detection of the phenolic compounds. The calibration curves derived from the changes in absorbance at lambda = 568 nm were linear with concentration of hydroquinone, catechol and pyrogallol in the range of 7.0 x 10(-7) to 1.0 x 10(-4)M, 6.0 x 10(-6) to 2.0 x 10(-4)M and 6.0 x 10(-7) to 1.0 x 10(-4)M, respectively. The detection limits were 5.3 x 10(-7), 2.5 x 10(-6) and 3.2 x 10(-7)M for the hydroquinone, catechol and pyrogallol, respectively. The method was applied satisfactorily to the determination of phenolic compounds in water samples and pharmaceutical formulations.     

Simultaneous capillary electrophoretic separation and detection of P(V) and As(V) As heteropoly-blue complexes

A capillary electrophoretic (CE) method was developed for the simultaneous determination of P(V) and As(V). A Mo(VI)-ascorbic acid reagent reacted with a mixture of trace amounts of P(V) and As(V) to form the corresponding heteropoly-blue complexes in 0.05 M acetate buffer (pH 3.5). When 0.05 M malonate buffer was used as a migration buffer, the peaks due to their migrations were well separated in the electropherogram, and the pre-column complex-formation reaction was applied to the simultaneous CE determination of P(V) and As(V) with direct UV detection at 220 nm. With the proposed method, the calibration curves were linear in the concentration range of 5 x 10(-7) - 1 x 10(-4) M, with a detection limit of 1 x 10(-7) M (a signal-to-noise ratio of 3). Interference from foreign ions was also discussed.     

Biosensor based on paraffin/graphite modified with sweet potato tissue for the determination of hydroquinone in cosmetic cream in organic phase

An organic-phase biosensor based on paraffin/graphite modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was developed and used for determining hydroquinone in cosmetic creams. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone which electrochemical reduction back to hydroquinone was obtained at a peak potential of -0.22 V. The recovery of hydroquinone from two samples ranged from 99.1 to 104.1% and a rectilinear analytical curve for hydroquinone concentration from 7.5x10(-5) to 1.6x10(-3) M (r=0.9991) were obtained. The detection limit was 8.1x10(-6) M and relative standard deviation was <1.0% for a solution containing 7.3x10(-4) M hydroquinone and 1.0x10(-3) M hydrogen peroxide in 0.10 M tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n=10). The results obtained for hydroquinone in cosmetic creams using the proposed biosensor are in close agreement with those obtained using a Pharmacopoeia procedure at the 95% confidence level.     

Study on electrochemical oxidation behaviors and the diffusion mechanism of hydroquinone at pre-anodized carbon paste electrode by cyclic voltammetry

A functional pre-anodized carbon paste electrode (PACPE) was constructed by using successive cyclic voltammetry. The electrochemical oxidation behaviors of hydroquinone (HQ) were carefully investigated by various electrochemical techniques. The diffusion mechanism of HQ has been put forward for the first time. The driving force for the HQ transport towards anode not only related to the concentration diffusion but also depended on the transport of H(+) in the feed phase along a concentration gradient towards the cathode. The results indicated that the PACPE exhibited excellent electrocatalytic activity towards the oxidation of HQ. Compared with the bare carbon paste electrode, the oxidation and reduction peak separation (ΔE(p)) of HQ at the PACPE has been decreased from 578 to 83 mV. Under the optimum conditions, the oxidation peak current was linear with HQ concentration in the range of 4 × 10(-7) to 1.0 × 10(-4) M with the linear correlation coefficient of 0.9986. The detection limit was 1.05 × 10(-7) M. This method can be successfully applied to the determination of HQ in wastewater.     

Determination of catecholamines and serotonin by micellar electrokinetic chromatography with laser-induced fluorescence detection

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl) fluorescein, a new synthesized fluorescent reagent, was established for the first time as a label for the sensitive analysis of catecholamines (CAs) and serotonin (5-HT) by micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence detection. After careful study on the derivatization conditions such as pH value, reagent concentration, temperature and reaction time, the labeling reaction was accomplished as quickly as 7 min with stable yield. The separation parameters for the CAs and 5-HT were also optimized in detail. The derivatives were baseline separated in a running buffer containing 30 mM boric acid and 15 mM sodium dodeculsulfate at pH 9.0. The detection limits ranged from 5 x 10(-10) to 2 x 10(-9) M (signal-to-noise ratio = 3). The rapid and sensitive method was also applied to the determination of the CAs and 5-HT of urine samples.     

Trace analysis of aluminum in natural waters with rubeanic acid by adsorption chronopotentiometry

The determination of trace levels of aluminum in natural waters with rubeanic acid (RA) by adsorption chronopotentiometry is developed in this paper. Optimum experimental conditions include an accumulation potential of -0.40 V, accumulation time of 60 s, and a RA concentration of 6x10(-6) M in 0.2 M NaAc-HAc buffer solution (pH 4.6). The response is linear over the 1x10(-8) approximately 4x10(-7) M concentration range. The detection limit is 5.6x10(-9) M and the relative S.D. (at the 3x10(-7) M level) is 2.6%. Possible interferences are evaluated. The method has been applied to the determination of trace levels of Al in various real samples. Direct determination of toxic forms of Al in surface waters by this technique is also explored.     

Kinetic enzymatic determination of ethanol/methanol mixtures by the stopped-flow technique

The analytical use of the enzymatic oxidation of alcohols by alcohol oxidase was assessed applying the stopped-flow technique for mixing sample and reagents, and the DTNB (5,5'-dithiobis-(2-nitrobenzoic acid)/L-cysteine system as a new chromogenic reagent. The oxidation reaction was monitored by measuring the rate of absorbance decrease at 412 nm, the wavelength of maximum absorption of the reduced form of DTNB. The calibration graphs for the individual determination of the alcohols were linear over the range 1.0 x 10(-6)-1.0 x 10(-5)M, and the precision ranged between 2.1 and 4.8%. A differential rate principle was applied to the determination of ethanol/methanol mixtures involving mutual kinetic effects which allowed mixtures in molar ratios between 25:1.0 and 1.0:1.0 to be accurately resolved with good precision (r.s.d. less than 9 and 5%, respectively). Compared to the flow-injection analysis method, the proposed approach offers higher sensitivity and sample throughput, as well as the wider concentration ratio range for mixture resolution.     

金电极上苯二酚异构体的电化学性质及同时测定

采用循环伏安法研究了邻苯二酚(CAT)、间苯二酚（RE）和对苯二酚(HQ)在0.5 mol/L硫酸水溶液中的电化学行为,循环伏安法和差分脉冲伏安法研究了CAT、RE 和HQ共存体系的伏安行为。 实验结果表明,在pH=0的硫酸水溶液中,扫描速率为10 mV/s,循环伏安法扫描电位在0～1.2 V（vs.Ag/Cl）时,分离效果明显。 本文采用差分脉冲伏安法,测定了CAT、RE和HQ的混合物,检出限依次为3.9×10-6、3.9×10-6和7.8×10-6 mol/L。 将该方法用于合成样品测定,其精密度和准确度均满足分析要求。     

Oxidation of alkylarenes by nitrate catalyzed by polyoxophosphomolybdates: synthetic applications and mechanistic insights

Alkylarenes were catalytically and selectively oxidized to the corresponding benzylic acetates and carbonyl products by nitrate salts in acetic acid in the presence of Keggin type molybdenum-based heteropolyacids, H(3+)(x)()PV(x)()Mo(12)(-)(x)()O(40) (x = 0-2). H(5)PV(2)Mo(10)O(40) was especially effective. For methylarenes there was no over-oxidation to the carboxylic acid contrary to what was observed for nitric acid as oxidant. The conversion to the aldehyde/ketone could be increased by the addition of water to the reaction mixture. As evidenced by IR and (15)N NMR spectroscopy, initially the nitrate salt reacted with H(5)PV(2)Mo(10)O(40) to yield a N(V)O(2)(+)[H(4)PV(2)Mo(10)O(40)] intermediate. In an electron-transfer reaction, the proposed N(V)O(2)(+)[H(4)PV(2)Mo(10)O(40)] complex reacts with the alkylarene substrate to yield a radical-cation-based donor-acceptor intermediate, N(IV)O(2)[H(4)PV(2)Mo(10)O(40)]-ArCH(2)R(+)(*). Concurrent proton transfer yields an alkylarene radical, ArCHR(*), and NO(2). Alternatively, it is possible that the N(V)O(2)(+)[H(4)PV(2)Mo(10)O(40)] complex abstracts a hydrogen atom from alkylarene substrate to directly yield ArCHR(*) and NO(2). The electron transfer-proton transfer and hydrogen abstraction scenarios are supported by the correlation of the reaction rate with the ionization potential and the bond dissociation energy at the benzylic positions of the alkylarene, respectively, the high kinetic isotope effect determined for substrates deuterated at the benzylic position, and the reaction order in the catalyst. Product selectivity in the oxidation of phenylcyclopropane tends to support the electron transfer-proton transfer pathway. The ArCHR(*) and NO(2) radical species undergo heterocoupling to yield a benzylic nitrite, which undergoes hydrolysis or acetolysis and subsequent reactions to yield benzylic acetates and corresponding aldehydes or ketones as final products.     

Iodnitrotetrazolium chloride-A new analytical reagent for determination of chromium

The extraction of chromium (VI) with iodnitrotetrazolium chloride (INT) was studied spectrophotometrically. The basic spectrophotometric characteristics of the ion associated formed were determined. Using different methods it was found that the ratio between chromium and INT was 1:1. The molar absorptivity of the associate is (250) = (3.70 +/- 0.08) x 10(4) 1.mole(-1).cm(-1). Performing the reaction in acid medium (0.1-1.1M hydrochloric acid) allowed the determination of chromium in the presence of large amounts of W(VI), Mo(VI), Fe(III) and V(V). Hence INT is suggested as a sensitive and selective reagent for extractive-spectrophotometric determination of microquantities of chromium(VI).     

On-Line Sensitive Chemiluminescence Detection of Trace Amounts of Polyphenols Using MEKC

A high–performance capillary electrophoresis with chemiluminescence detection (CE–CL) method has been developed for the determination of three polyphenols (catechol, hydroquinone and pyrogallol) in this work. The effects of several factors such as the acidity and concentration of running buffer, the applied voltage, the injection time, the pH and concentration of CL reagents were investigated in detail. Under the optimum conditions, the baseline separation of three polyphenols was obtained within 6 min. Detection limit (S/N = 3) was 1.0 × 10^?10 M for catechol, 1.0 × 10^?9 M for hydroquinone and 3.0 × 10 ^?11 M for pyrogallol, respectively. The excellent detection limits of the analytes were 1–5 order lower than that of methods reported in literatures.     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Potentiometric flow-injection determination of trace hydrogen peroxide based on its induced reaction in iron(III)-iron(II) potential buffer containing bromide and molybdenum(VI)

A rapid and highly sensitive potentiometric flow-injection method for the determination of trace hydrogen peroxide was developed by use of an Fe(III)-Fe(II) potential buffer solution containing bromide and Mo(VI). The analytical method was based on a linear relationship between a concentration of hydrogen peroxide and a largely transient potential change of an oxidation-reduction potential electrode due to bromine generated by the reaction of hydrogen peroxide with the potential buffer solution. The oxidation of bromide to bromine by hydrogen peroxide occurred very rapidly with the assistance of Mo(VI) when Fe(II) existed in the potential buffer solution. It was estimated by batchwise experiments that hydroxyl radical, OH., was generated by the reaction of hydrogen peroxide with Fe(II) as an intermediate, and subsequently oxidized bromide to bromine. In a flow system, analytical sensitivities to hydrogen peroxide obtained by the detection of the transient change of potential were enhanced about 75 fold compared with those obtained by using the potential change caused by the reaction of hydrogen peroxide with the potential buffer solution without bromide and Mo(VI). Sensitivities increased with decreasing concentration of the Fe(III)-Fe(II) buffer in the reagent solution. The detection limit (S/N = 3) of 4 x 10(-7) M (13.6 ppb) was achieved by using the 1 x 10(-4) M Fe(III)-Fe(II) buffer containing 0.4 M NaBr, 1.0 M H(2)SO(4) and 0.5% (NH(4))(6)Mo(7)O(24). Analytical throughput was approximately 40 h(-1) and the RSD (n = 6) was 0.6% for measurement of 4 x 10(-6) M hydrogen peroxide. The proposed method was applied to the determination of hydrogen peroxide in real rainwater samples, and was found to provide a good recovery for H(2)O(2) added to rainwater samples.     

A simple vapour phase decomposition (VPD) of quartz powder in a polypropylene vessel and determination of phosphorus by spectrophotometry

A simple, low pressure, low temperature vapour phase decomposition (VPD) of quartz powder has been developed for the determination of phosphorus. A platinum dish containing the quartz or silicon powder was placed inside a polypropylene vessel containing 40 ml of 1:1 mixture of HF and HNO(3). After capping the vessel, the entire assembly was heated on a water bath at approximately 90 degrees C for 8 h. The platinum dish was removed from the vessel, the sample solution was treated with 0.5 ml of H(2)SO(4) and 0.5 ml of HClO(4) and was heated on a hot plate till HClO(4) fumed out. The resultant solution was diluted to 40 ml ( approximately 0.4N), analysed for phosphorus by spectrophotometry as an ion-pair of molybdophosphate with crystal violet. Phosphorus contamination by reagents has been drastically reduced (around 250 times) compared to the conventional dissolution procedure. The optimum reaction conditions were [H(+)]=0.42N, [H(+)]/Mo=62 for the formation of molybdophosphate and its extraction into n-butyl acetate. No interferences due to fluoride, silicate (active silica) and arsenic (V) upto 6.7x10(3),2.7x10(3) and 2.0x10(3) times the content of phosphorus, respectively were observed. The LOD was found to be 0.066 mug g(-1) (+/-3 s). RSD is 0.4-2.3% and the molar absorptivity is 2.7x10(5) l mole(-1) cm(-1).     

石墨烯/铁氰化钴复合膜修饰玻碳电极同时测定对苯二酚、邻苯二酚和间苯二酚

采用滴涂法和电沉积法制备了石墨烯/铁氰化钴复合膜修饰玻碳电极. 用扫描电镜对该纳米复合膜进行了表征.用循环伏安法研究了对苯二酚(HQ)、邻苯二酚(CT)和间苯二酚(RS)在修饰电极上的电化学行为. 实验结果表明, 相对于裸玻碳电极和石墨烯修饰电极, HQ, CT 和RS 在石墨烯/铁氰化钴修饰电极上的氧化峰电流显著提高. 利用差分脉冲伏安法测定, HQ, CT 和RS 分别在1.0×10^－6～1.5×10^－4 mol/L, 1.0×10^－6～2.0×10^－4 mol/L 和3.5×10^－6～2.5×10^－4 mol/L浓度范围内与氧化峰电流呈良好的线性关系, 相关系数分别为0.991, 0.993 和0.992. 信噪比为3 时, HQ, CT 和RS 检出限分别为2.0×10^－7, 2.1×10^－7 和3.5×10^－7 mol/L. 将该方法用于水样分析, 回收率为95.6%～106.1%.     

Capillary electrophoretic determination of phosphate based on the formation of a Keggin-type [PMo12O40]3- complex.

Based on the formation of a Keggin-type [PMo12O40]3- complex, a sensitive capillary electrophoresis (CE) method was developed for the determination of P(V) with direct UV detection at 220 nm. A mixture of alpha- and beta-Keggin-type [PMo12O40]3- complexes was readily formed in a sample solution consisting of a trace amount of P(V), 2.5 mM Mo(VI), 0.050 M p-C6H3(CH3)-2-SO3H (XSA), and 60% v/v CH3CN. When a 0.05 M HCl and 60% v/v CH3CN solution was used as a migration electrolyte, the Keggin complexes exhibited a sharp and well-defined peak in the electropherogram. The peak area was linearly dependent on the P(V) concentration in the range of 5 x 10(-7)-5 x 10(-5) M; a detection limit of 1 x 10(-7) M was achieved. In comparison with indirect UV detection, the direct UV detection is about ten times more sensitive, because the Keggin complexes possess high molar absorptivities. The developed CE method was applied to the determination of P(V) in river water, and the results were in good agreement with those obtained by ion chromatography (IC) and colorimetry (COL) based on the formation of mixed-valence heteropoly blue species.     

Simultaneous kinetic spectrophotometric determination of periodate and iodate based on their reaction with pyrogallol red in acidic media by chemometrics methods

The univariate and multivariate calibration methods were applied for the simultaneous determination of iodate and periodate in water. The method is based on the reaction of periodate and iodate with pyrogallol red in sulfuric acid media. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of pyrogallol red at 470 nm. The calibration curve was linear over the concentration ranges of 0.1-12 and 0.1-14 μg ml⁻¹ for iodate and periodate, respectively. The experimental calibration matrix for partial least squares (PLS) and orthogonal signal correction (OSC-PLS) method was designed with 35 mixtures. The results obtained by the PLS and OSC-PLS were statistically compared. The effects of various cations and anions on iodate and periodate determination have been investigated.     

Selective Determination of Catechol in the Presence of Hydroquinone at Bare Indium Tin Oxide Electrodes via Peak‐Potential Separation and Redox Cycling by Hydrazine

The electrochemical, selective determination of catechol (CT) in the presence of hydroquinone (HQ) is not readily achieved, because the formal potentials of two phenolic compounds are very close. Here, we have developed a simple electrochemical method for the selective determination of CT by using bare indium tin oxide electrodes and employing CT redox cycling by hydrazine. The cyclic voltammetry of CT and HQ was investigated in Tris buffer (pH 9.0), phosphate buffered saline buffer (pH 7.4), and acetate buffer (pH 4.5). Especially in Tris buffer, the anodic peak potential of CT is much lower than that of HQ, resulting in a large difference between two peak potentials (ca. 0.4 V). The difference allows the selective determination of CT in the presence of excess HQ. The anodic current of CT is amplified using CT redox cycling by hydrazine, which also helps to stabilize CT and HQ in Tris buffer for several hours. The detection limits of CT in Tris buffer containing 0.1 mM HQ are 1 μM and 10 μM in the presence and absence of hydrazine, respectively.     

Chemiluminescence (CL) emission generated during oxidation of pyrogallol and its application in analytical chemistry. I. Effect of oxidant compound

An investigation of chemiluminescence (CL)-emission generated by the oxidation of pyrogallol using various inorganic oxidant compounds is reported in this F.I.A.-merging zone application. The oxidant compounds that showed measurable CL-emission were permanganate, periodate, hypochlorite anions, cerium(IV) and hydrogen peroxide. The different oxidant compounds showed CL-emissions at different pH-ranges. The CL-emission was limited by the inner filter effect and this was more intense for oxidants of selective oxidation. Kinetic effects were also found in the case of oxidation by permanganate. Plots of CL-emission against pH give evidence of speciation and or deactivation mechanism effects. The analytical parameters for the determination of the oxidants are given. Sensitivities of 895 600, 19 500, 33 723, 10 680 and 56 703 mV M(-1) were found for the determination of permanganate, cerium(IV), periodate, hypochlorite and hydrogen peroxide, respectively. The calibration curves of the oxidant determination were generally S-shaped; the S-shaped calibration curve of periodate was closer to a straight line relationship while that of hypochlorite was almost a straight line; detection limits in the range of 10(-4) M oxidant concentration were found for nearly all oxidants. The analytical parameters for determination of pyrogallol by the CL-emission generated through oxidation by the different oxidants at optimum conditions were 1.16x10(6) mV M(-1) for permanganate; 0.086x10(6) mV M(-1) for cerium(IV); 0.91x10(6) mV M(-1) for periodate; 0.012x10(6) mV M(-1) for hypochlorite; and 0.25x10(6) mV M(-1) for hydrogen peroxide. The detection limit was 1.0x10(-4) M. The nearly straight-line relationship (initial part of the plot) for CL-emission with oxidant concentration gives an indication that the CL-reaction of pyrogallol oxidation by hypochlorite proceeds through a process that involves energy transfer while the pronounced S-shaped curve produced by permanganate gives the indication that the reaction proceeds through a process that does not involve energy transfer according to the mathematical model of CL-emission that controls the F.I.A.-merging zone technique of the flow apparatus used in this work. The sequence of completeness of the oxidation process by each oxidant was MnO(4)(-)>H(2)O(2)>IO(4)(-)>OCl(-); the stoichiometric quantity of the oxidant per pyrogallol molecule for the rapid part of the overall oxidation by each different oxidant was attempted; this is an index-value of the oxidation state of the fluorescent excited molecule. Finally, the impact of the above findings for further analytical applications is discussed.     

Generation of bis(dithiolene)dioxomolybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media

Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum(iv) (Mo(IV)OL(x)) complexes is studied as a model of oxidative-half reaction of arsenite oxidase molybdenum enzymes. The reactions are revealed to involve proton-coupled electron transfer. Electrochemical oxidation of Mo(IV)OL(x) yields the corresponding bis(dithiolene)dioxomolybdenum(vi) complexes in basic solution, where the conversion of Mo(IV)OL(dmed) supported by a smaller electron donating dithiolene ligand (1,2-dicarbomethoxyethylene-1,2-dithiolate, L(dmed)) to Mo(VI)O(2)L(dmed) is faster than that of Mo(IV)OL(bdt) with a larger electron donating dithiolene ligand (1,2-benzenedithiolate, L(bdt)) under the same conditions. Titration experiments for the electrochemical oxidation reveal that the reaction involves two-electron oxidation and two equivalents of OH(-) consumption per Mo(IV)OL(x). In the conversion process of Mo(IV)OL(x) to Mo(VI)O(2)L(x), the five-coordinate bis(dithiolene)monooxomolybdenum(v) complex (Mo(V)OL(x)) being a one-electron oxidized species of Mo(IV)OL(x) is suggested to react with OH(-). Mo(V)OL(x) reacts with OH(-) in CH(3)CN or C(2)H(5)CN in a 2?:?2 ratio to give one equivalent Mo(IV)OL(x) and one equivalent Mo(VI)O(2)L(x), which is confirmed by the UV-vis and IR spectroscopies. The low temperature stopped-flow analysis allows investigations of the mechanism for the reaction of Mo(V)OL(x) with OH(-). The kinetic study for the reaction of Mo(V)OL(dmed) with OH(-) suggests that Mo(V)OL(dmed) reacts with OH(-) to give a six-coordinate oxo-hydroxo-molybdenum(v) species, Mo(V)O(OH), and, then, the resulting species undergoes successive deprotonation by another OH(-) and oxidation by a remaining Mo(V)OL(dmed) to yield the final products Mo(IV)OL(dmed) and Mo(VI)O(2)L(dmed) complexes in a 1?:?1 ratio. In this case, the Mo(V)O(2) species are involved as an intermediate in the reaction. On the other hand, in the reaction of Mo(V)OL(bdt) with OH(-), coordination of OH(-) to the Mo(V) centre to give a six-coordinate Mo(V)O(OH)L(bdt) species becomes the rate limiting step and other intermediates are not suggested. On the basis of these results, the ligand effects of the dithiolene ligands on the reactivity of the bis(dithiolene)molybdenum complexes are discussed.