Keiitsu Saito

Selective determination method for measurement of nitrite and nitrate in water samples using high-performance liquid chromatography with post-column photochemical reaction and chemiluminescence detection

A simple, sensitive and selective method for the simultaneous determination of nitrite and nitrate in water samples has been developed. The method is based on ion-exchange separation, online photochemical reaction, and luminol chemiluminescence detection. The separation of nitrite and nitrate was achieved using an anion-exchange column with a 20mM borate buffer (pH 10.0). After the separation, these ions were converted to peroxynitrite by online UV irradiation using a low-pressure mercury lamp and then mixed with a luminol solution prepared with carbonate buffer (pH 10.0). The calibration graphs of the nitrite and nitrate were linear in the range from 2.0 x 10(-9) to 2.5 x 10(-6)M and 2.0 x 10(-8) to 2.5 x 10(-5)M, respectively. Since the sensitivity of nitrite was about 10 times higher than that of nitrate, the simultaneous determination of nitrite and nitrate in the water samples could be efficiently achieved. This method was successfully applied to various water samples--river water, pond water, rain water, commercial mineral water, and tap water--with only filtration and dilution steps.

Liquid—liquid extraction of metal ions by the thiacrown compound 1,4,8,11-tetrathiacyclotetradecane

The possibilities of thiacrown compounds in liquid—liquid extraction were tested by using 1,4,8,11-tetrathiacyclotetradecane (TTCT). Class a metals were not extracted at all; of the class ab metals, only copper(II) was extracted. Class b metals were extracted but their extractabilities varied considerably. The relationship between the distribution ratio of the b metal and its softness is discussed. The extraction behavior of copper(I) with TTCT was studied in detail. The copper(I)—TTCT cation was completely extracted at pH > 4.0 as an ion-pair with perchlorate, picrate or tetraphenylborate. The extraction of copper(I) with TTCT and picrate into different solvents decreased in the order nitrobenzene >1,2-dichloroethane > chloroform > carbon tetrachloride. A study of the extraction equilibria for copper(I) with TTCT in the presence of the picrate (Pic−) showed that copper(I) and TTCT form a 1:1 cation complex [Cu(TTCT)]+, which reacts with picrate to form the 1:1 ion-pair [Cu(TTCT)] +Pic−. The extraction constants are log Kex = 7.3 ± 0.3 and 9.0 ± 0.2 for chloroform and 1,2-dichloroethane, respectively, as the organic solvent.

Highly sensitive method for determination of N-nitrosamines using high-performance liquid chromatography with online UV irradiation and luminol chemiluminescence detection.

A new method for the measurement of N-nitrosamines in part-per-trillion concentrations from water samples without preconcentration steps has been developed. This method is based on online UV irradiation after high-performance liquid chromatographic separation and subsequent luminol chemiluminescence detection without addition of an oxidant. It was confirmed that N-nitrosamines in basic aqueous solution were transformed to peroxynitrite by UV irradiation. The detection limits for this method were 1.5 ng/L, 2.9 ng/L, 3.0 ng/L, and 2.7 ng/L for N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine, respectively, at a signal-to-noise ratio of 3. The calibration graphs were linear in the range of 5-1000 ng/L for these N-nitrosamines. This method was used for the determination of N-nitrosamines in tap water, river water, and industrial plant effluent samples. The recoveries of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine present in tap water sample at a concentration of 10 ng/L (mean+/-standard deviation, n=4) were (94.8+/-2.7)%, (102.0+/-6.9)%, (99.3+/-3.9)%, and (102.8+/-2.5)%, respectively. These results indicate that our proposed method can be applied satisfactorily to the determination of N-nitrosamines in water samples.

Development of a novel running buffer for the simultaneous determination of nitrate and nitrite in human serum by capillary zone electrophoresis.

In order to improve NO2- peak height and obtain a convenient buffer system for the assay of nitrogen monooxide metabolites, we developed a novel running buffer for the simultaneous determination of nitrite and nitrate in human serum by capillary electrophoresis. The addition of cetyltrimethylammonium chloride to the running buffer resulted in high-speed separation using reverse electroosmotic flow. Highly sensitive determination was also achieved using stacking with 10-fold diluted sample solutions. The samples were injected hydrodynamically for 100 s into a 50 cm x 75 microm I.D. capillary. The separation voltage was 10 kV (negative polarity). UV detection was performed at 214 nm. We obtained complete separation of nitrite and nitrate in deproteinized human serum within 6 min with optimum analytical conditions. Linear calibration curves for nitrite and nitrate for both peak height and peak area were obtained with standard addition method. The limits of detection obtained at a signal-to-noise ratio of 3 for nitrite and nitrate were 4.1 and 2.0 microM, while the values of relative standard deviation of peak height were 2.4 and 2.6%, respectively.

Extraction behaviour of copper(II) and silver(I) with a thiacrown ether carboxylic acid, 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid

The extraction behaviour of copper(II) and silver(I) with 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid (TTCTOHA) was investigated at 25+/-0.1 degrees C and ionic strength of 0.1. The value of the logarithmic distribution coefficient, logK(DR) of TTCTOHA between octan-1-ol and aqueous phases was determined to be 4.13. Copper(II) was extracted with TTCTOHA into octan-1-ol as CuL(2), where L represents the anionic species of TTCTOHA. The logarithmic extraction constant, logK(ex(10)), was determined at -7.42. Silver(I) was extracted with TTCTOHA into octan-1-ol as AgL and Ag(2)L(2). The logarithmic distribution constant, logK(DC), of AgL was estimated to be 0.49. On the other hand, silver(I) was extracted into 1,2-dichloroethane as AgL and the logarithmic extraction constant, logK(ex(10)), was determined to be -2.24.

Determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater by capillary zone electrophoresis with artificial seawater as the background electrolyte using transient isotachophoresis

We describe a combination of selected ions as a terminating ion which is useful for transient isotachophoresis (ITP) in capillary zone electrophoresis (CZE) for the determination of nitrite and nitrate in seawater. In addition to 150 mM sulfate as the principal terminating ion, 10 mM bromate was added to a sample solution as the additional terminating ion. Artificial seawater containing 3 mM cetyltrimethylammonium chloride (CTAC) was adopted as a background electrolyte (BGE). The limits of detection (LODs) for nitrite and nitrate were 2.2 and 1.0 νg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.9 and 1.4%. The RSDs of peak height were 1.7 and 1.9%, the RSDs of migration time 0.11%. The proposed method was applied to the determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS‐1, distributed by the National Research Council of Canada (NRC). The results almost agreed with the assigned tolerance interval.

Liquid-liquid extraction of platinum(II) with cyclic tetrathioethers.

The liquid-liquid extraction of platinum(II) with 12-, 14- and 16-membered cyclic tetrathioethers from chloride solution was studied. Bromocresol Green ion as a counter anion and 1,2-dichloroethane as an extraction solvent were used. The effect of thiourea on the extraction rate of platinum(II) was examined. Platinum(II) was hardly extracted with macrocyclic tetrathioethers in the absence of thiourea because of the slow extraction rate. The extraction rate of platinum(II) was considerably enhanced by the addition of thiourea. The extraction rate of platinum(II) with 16-membered cyclic tetrathioether was faster than that with 12- and 14-membered ones. Platinum(II) was quantitatively extracted with 16-membered cyclic tetrathioether into 1,2-dichloroethane within 5 h in the presence of thiourea.

Analysis of highly saline samples by capillary zone electrophoresis: enhanced direct UV detection of inorganic anions using on-capillary preconcentration and clean-up techniques

The ability to analyze samples with disparate levels of analyte and matrix ions is among the important benefits defining the practical utility of modern capillary electrophoresis. To compensate for the sensitivity limitations regarding trace-level inorganic anions, a number of on-line approaches that should offer an improved S/N ratio in direct UV detection were examined. The novel use of reversed pre-electrophoresis (at the applied voltage opposite to the separation voltage) made it possible to efficiently remove the most part of high chloride levels from the sample and hence to lower the background signal and to inject increased quantities of fast analyte anions. Specifically, by taking these advantages the sensitivity response of iodide was improved by a factor of 5 over normal CE mode. Using isotachophoretic sample stacking, a two-fold increase in detectability was obtained for moderately mobile anions, nitrate and nitrite, that corresponds to the minimum detectable concentrations close to their natural occurrences in seawater. Furthermore, field-amplified sample injection at increased electrolyte-to-sample matrix concentration ratios enabled the maximum S/N enhancement, with detection limits at the level of 10(-6) M and lower in the presence of > or = 5 x 10(4)-fold molar excess of chloride.

Extraction behaviour of silver(I) with some cyclic tetrathioethers

Abstract The extraction behaviour of silver(I) with 12-, 13-, 15- and 16-membered cyclic tetrathioethers (n-ane-S4, where n represents the total number of carbon and sulphur atoms in the cyclic ligand ring) was examined stoichiometrically using the picrate ion (Pic−) for the formation of the ion pair and chloroform and 1,2-dichloroethane as solvents. The composition of the extracted species and the extraction constant were determined. Silver(I) was extracted with these four ligands (L) into chloroform and 1,2-dichloroethane as the ion-pair compound [AgL]+Pic−. The extracted species with these four ligands is different from that previously reported for 14-ane-S4, [AgL2]+Pic−.

Liquid-liquid extraction of copper(II) with cyclic tetrathioethers

Abstract Liquid-liquid extraction of the divalent metal ions manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) with 1,4,8,11-tetrathiacyclotetradecane was examined using the tetraphenylborate ion (TPB − ) for the formation of the ion pairs. Copper(II) was quantitatively extracted into 1,2-dichloroethane, whereas the other metals were hardly extracted. The extraction behaviour of copper(II) with 12–16-membered cyclic tetrathioethers ([ n ]aneS 4 , where n represents the total number of carbon and sulphur atoms int he cyclic ligand ring) was examined. Chloroform and 1,2-dichloroethane were used as extraction solvents. The order of the extractability of copper(II) was as follows: [15]aneS 4 > [16]aneS 4 > [14]aneS 4 > [13]aneS 4 > [12]aneS 4 > at 2.5 × 10 −4 M of ligands, [16] aneS 4 > [15]aneS 4 > [14]aneS 4 > [13]aneS 4 > [12]aneS 4 at 2.5 × 10 −5 M of ligands. The extracted species were examined at ligand concentrations higher than 2.5 × 10 −4 M. Copper(II) was extracted with [13]aneS 4 and [16]aneS 4 as [CuL 2 ] 2+ (TPB − ) 2 and [CuL 4 ] 2+ (TPB − ) 2 depending upon the relative concentration of the ligand to copper(II). Where L represents cyclic tetrathioethers. The extracted species with [14]aneS 4 and [15]aneS 4 were [CuL 2 ] 2+ (TPB − ) 2 and [CuL 4 ] 2+ (TPB − ) 2 , respectively. In case of [12]aneS 4 , the following three species were observed depending upon concentrations of the ligand and TPB − : [CuL 2 (OH)] + TPB − , [CuL 2 ] 2+ (TPB − ) 2 and [CuL 4 ] 2+ (TPB − ) 2 .