Determination of submicromolar amounts of uranium(VI) by compleximetric titration with pyridine-2,6-dicarboxylic acid

Uranium(VI) is selectively determined by a compleximetric titration with pyridine-2,6-dicarboxylic acid, using arsenazo-I indicator and hexamethylenetetramine buffer at pH 4.9. Cyclohexanediaminetetraacetic acid and diethylenetriaminepentaacetic acid provide masking of interfering metal ions. A probe colorimeter apparatus is recommended for end-point detection. The relative standard deviation is 0.6% for 0.17–0.76 μmol of uranium.     

Oxidations with alkaline permanganate using formic acid for back-titration: Determination of lead and thallium

Pb⁺² (~37-0.6mg) and Tl⁺ (45-0.9 mg) can bc estimated by mixing with KmnO₄ in presence of Ba⁺² ions and I_NNaOH. The excess KmnO₄ is then titrated with formic acid.A mixture of Pb⁺² and Tl⁺ is oxidized simultaneously with KMn0₄ in 0.1N NaOH. Pb⁺² interferes also when precipitated as sulphate or tellurate. In presence of SO₄^-2 and telluric acid, thallium can be titrated only when its concentration is not less than 30 mg, below which lead seriously interferes. Tl⁺ can be accurately determined in the filtrate from the PbS0₄ precipitate.     

Determination of ethylenediaminetetraacetic acid in sea water by solid-phase extraction and high-performance liquid chromatography

The chelating agent EDTA is widely used, and as a result is showing up widely in the aquatic environment. Here we describe a preconcentration procedure for measuring EDTA concentration in sea water samples by HPLC. The procedure consists of forming an Fe(III) complex followed by solid-phase extraction using an activated carbon cartridge. After the preconcentration, EDTA was quantified by HPLC with ultraviolet detection (260 nm). The enrichment permitted the determination of EDTA at concentrations as low as 1 nM. Good recoveries were obtained for both brackish and full-strength sea water with high repeatability (RSD < 6%). The method was applied to sea water samples taken from near the mouth of the Oyabe River in Japan.     

Determination of pantothenic acid in foods by optical biosensor immunoassay

An optical biosensor inhibition immunoassay was developed using a specific pantothenic acid-binding protein for the quantitation of free pantothenic acid (vitamin B5) in foodstuffs. Samples were prepared by a simple extraction procedure in buffer, and vitamin content was estimated against authentic calibrants in the same buffer. Performance parameters included a working range of 10-5000 ng/mL, a limit of detection of 4.4 ng/mL, precision relative standard deviation of 5.4-7.1% over a range of concentrations, and recoveries > 95% in the matrixes tested. A wide range of foodstuffs, including National Institute of Standards and Technology reference samples, were tested in 3 independent laboratories and the results were compared with microbiological assay and liquid chromatography/mass spectrometry (LC/MS) methods. The results indicate that the biosensor technique is appropriate for the estimation of pantothenic acid in a wide range of foodstuffs.     

The determination of copper by complexometric titration with ethylenediaminetetraacetic acid

A method has been developed for the determination of cupric copper by complexometric titration with ethylen.ediaminetctraacetic acid. The titrations were followed potentiometrically, and were effected at pH 5–6 in the presence of an ammonium acetate buffer. Interfering metals such as ferric iron, aluminium, cadmium, zinc, manganese, nickel, cobalt and lead must be removed by a preliminary separation.     

High frequency titrations involving chelation with ethylenediaminetetraacetic acid: Determination of uranyl ion

It has been shown that for the pH range of 3.5 to 4.0, ethylenediaminetetraacetic acid reacts with uranyl ion to form a stable salt. The reacting ratio was found to be 2 : 1 (metal to addendum) which is in contrast to the usual reacting ratio of 1 : 1 obtained with ethylenediaminetetraacetic acid and other heavy metals. The chelate obtained with uranyl ion is probably a pseudo salt.A high frequency titration employing tri-sodium ethylenediaminetetraacetate is suggested for the determination of uranyl ion.     

Determination of ethylenediaminetetraacetic acid, ethylenediaminedisuccinic acid and iminodisuccinic acid in cosmetic products by capillary electrophoresis and high performance liquid chromatography

A capillary electrophoresis (CE) and a high performance liquid chromatography (HPLC) method are described for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA), S,S′-ethylenediaminedisuccinic acid (EDDS) and R,S-iminodisuccinic acid (IDS) complexing agents as their Fe(III) complexes in cosmetics like shower cream and foam bath. The non-biodegradable EDTA is used in combination with biodegradable analogues like EDDS and IDS in many commercial products. The HPLC method involves separation by reversed-phase ion pair chromatography on a C₁₈ column using methanol-formate buffer (20 mM tetrabutylammonium hydrogen sulfate, 15 mM sodium formate adjusted to pH 4.0 with formic acid) (10:90, v/v) as mobile solvent at a flow rate of 0.8 mL min⁻¹ at 24 °C using UV detection at 240 nm. The CE separation was performed in a fused silica capillary of 50 μm i.d. with the total length of 50 cm with a 10 mM MES and MOPSO (pH 5.5) at an applied voltage of −25 kV. The samples were introduced by applying a 50 mbar pressure for 2 s. Absorbances at 215 and 225 nm were monitored for the detection of the complexes. The methodology performance of the two methods was evaluated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility. The LOD values obtained from HPLC are low when compared with CE. The applicability of both the methods was demonstrated for the analysis of cosmetic products such as shower cream and foam bath. The results obtained by both CE and HPLC were found to be comparable and in good agreement.     

气相色谱-质谱联用法检测母乳脂肪中反式脂肪酸

建立了母乳中反式脂肪酸(TFAs)的气相色谱-质谱(GC-MS)检测方法,并应用于母乳脂肪中TFAs的检测。母乳用氨水水解,乙醚和石油醚提取脂肪,提取的脂肪加入C21: 0内标,用三氟化硼甲醇溶液在80℃水浴中冷凝回流15 min进行甲酯化,正己烷提取,上清液用GC-MS分析,内标法定量。在低、中、高加标水平上验证方法的准确度与精密度,结果显示该方法可用于母乳中18种TFAs及其同分异构体的检测,其中12种TFAs在母乳脂肪中的方法检出限为4.0~47.1 mg/kg,回收率为80%~113%, RSD为2.9%~14.5%(n=6)。TFAs在部分母乳脂样品中检出,含量为9.54~6.9 mg/kg。该方法定性、定量准确,可有效用于母乳中TFAs的检测,但仍存在脂肪酸本底干扰等问题,可结合银离子固相萃取柱预分离技术进一步完善。     

Large-volume sample stacking for analysis of ethylenediaminetetraacetic acid by capillary electrophoresis

A simple, quick, and sensitive capillary electrophoretic technique-large volume stacking using the electroosmotic flow (EOF) pump (LVSEP) - has been developed for determining ethylenediaminetetraacetic acid (EDTA) in drinking water for the first time. It is based on a precapillary complexation of EDTA with Fe(III) ions, followed by large-volume sample stacking and direct UV detection at 258 nm. The curve of peak response versus concentration was linear from 5.0 to 600.0 microg/L, and 0.7 to 30.0 mg/L. The regression coefficients were 0.9988 and 0.9990, respectively. The detection limit of the current technique for EDTA analysis was 0.2 microg/L with an additional 10-fold preconcentration procedure, based on the signal-to-noise ratio of 3. As opposed to the classical capillary zone electrophoresis (CE) method, the detection limit was improved about 1000-fold by using this LVSEP method. To the best of our knowledge, it represents the highest sensitivity for EDTA analysis via CE. Several drinking water samples were tested by this novel method with satisfactory results.     

Determination of nitrite in foods by single-sweep polarography

In an acid medium, nitrite diazotized with p-rosaniline and then coupled with 8-hydroxyquinoline in a weak alkaline medium produces azo compounds. The azo compounds produce a very sensitive polarographic wave at -0.70 V (versus the saturated calomel electrode). The height of the peak is linear with the concentration of nitrite in the range of 5 x 10(-9) to 5 x 10(-7) g/mL. The detection limit is 3 x 10(-9) g/mL. The electrochemical characteristics of the polarographic wave are also discussed. The method was used to determine nitrite in sausage. The results agree well with those obtained by spectrophotometry.     

Oxidation with alkaline permanganate using formic acid for the back-titration : Potentiometric determination of chromium

Determination of chromium by oxidation of chromite with permanganate does not give accurate results. KmnO₄ is reduced to MnO₂. Titration of KmnO₄ with Cr⁺³ solution in the presence of 0.8–1.5N NaOH and Ba⁺² ions yields manganate and gives good results. In the absence of Ba⁺² ions and in the presence of 0.5–2N NaOH reduction of KmnO₄ passes quantitatively to MnO₂.Cr⁺³ can be determined by adding the chromic solution to KmnO₄ while stirring in presence of 1N NaOH and Ba⁺² ions, or a. 2.5N NaOH in the absence ofBa⁺² ions. The excess KmnO₄ is then back-titrated with formic acid.     

Determination of magnesium in foods by single-sweep polarography

In KOH, the Mg(II)-bromopyrogallol red (BPR) complex produced a very sensitive polarographic wave at -1.30 V. The wave height was linear with the concentration of Mg(II) in the range of 0.05 to 2 microg/mL. The detection limit was 0.01 microg/mL. The electrochemical behavior of Mg(II)-BPR was studied by electrochemical and spectrophotometric methods. Experiments proved that the polarographic wave of Mg(II)-BPR was due to the reduction of BPR in the Mg(II)-BPR complex. The method, which was sensitive, selective, and simple to perform, was used to determine magnesium in foods, and the results were consistent with those obtained by atomic absorption spectroscopy.     

Indirect determination of fluoride by EDTA back-titration of lanthanum

Semimicro to macro amounts of fluoride ion (0.4-100 mg) are determined rapidly and accurately by precipitation with an excess of lanthanum at pH 2.5-2.8 by digestion on a water-bath, cooling to room temperature, addition of excess of EDTA and back-titration of the excess with zinc solution to the Xylenol Orange end-point at ph 5.8-5..9. Large amounts of chloride, acetate and perchlorate, and small amounts of sulphate and silicate do not interfere, but phosphate does. This method is much superior to the usual thorium nitrate titration method and can be applied after preliminary separation of fluorine by steam distillation or pyrolysis.     

Determination of acrylamide in starch-based foods by HPLC with pre-column ultraviolet derivatization

A new method is developed for the determination of acrylamide in starch-based foods. The method included the extraction of acrylamide with water, defatting with hexane, derivatization with potassium bromate (KBrO(3)) and potassium bromide (KBr), liquid-liquid extraction with ethyl acetate-hexane (4:1), and concentration. The final analyte (2-bromopropenamide, 2-BPA) is analyzed by high-performance liquid chromatography coupled with diode array detection for quantification and by gas chromatography coupled to mass spectrometry for confirmation. The chromatographic analysis is performed on an ODS-3 C(18) column, and good retention and peak response of acrylamide are achieved under the optimal conditions. The limit of detection and quantitation are estimated to be 15 and 50 μg/kg, respectively. The recoveries of acrylamide from the commercial samples are spiked at levels of 50-1000 μg/kg, and range between 89.6 and 102.0%. These results show that this method should be regarded as a new, low-cost, and robust alternative for conventional investigation of acrylamide.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%.     

Determination of carbaryl in foods by solid-phase room-temperature phosphorimetry

A phosphorimetric solid phase assay is proposed for the determination of the pesticide carbaryl (CBL) at room temperature. CBL was spotted on filter paper together with Tl(I) as heavy metal, and dried for 3 min, after which the diffuse transmitted phosphorescence was measured using two quartz plates to avoid the quenching effect produced by atmospheric oxygen. The linear dynamic range was 0.5–4.0 μg/mL and the detection and quantification limits were 0.09 and 0.31 μg/mL, respectively. The precision of the method, expressed as relative standard deviation, was 2.3% for a sample containing 2.0 μg/mL of CBL. The method was applied to the determination of CBL residues in cereals, potatoes and waters, obtaining recoveries ranging between 92 and 105%. Received: 10 October 1997 / Revised: 2 February 1998 / Accepted: 7 February 1998