Determination of Nitrilotriacetic Acid in Waters and Waste Waters by Gas-Liquid Chromatography,Differential Pulse Polarography and a Colorimetric Method

Abstract

A comparison of gas-liquid chromatography, differential-pulse polarography and a colorimetric method for the determination of nitrilotriacetic acid in settled sewage, sewage effluent, potable water, soil extracted water and deionised water has been undertaken. Differential-pulse polarography has also been applied to the determination of nitrilotriacetic acid in saline samples. By statistical analysis of replicate determinations, accuracy and precision have been evaluated, and calibration linearity assessed. Interferences were observed for sewage samples when analysed by all three methods. Precision was generally higher for differential-pulse polarography down to 100 μgl^?1, although only gas-liquid chromatography is applicable to concentrations below 25μgl^?1 in non-saline samples. The colorimetric method was not applicable to concentrations below 500 μgl^?1 of nitrilotriacetic acid.     

Electroreduction and pulse-polarographic determination of nicotinamide in multivitamin tablets

The electroreduction of nicotinamide has been investigated by d.c., a.c. and pulse polarography, cyclic voltammetry and coulometry. A single well-defined polarographic wave is obtained from 2 M sulphuric acid and from 0.1 M sodium hydroxide. In both media, nicotinamide undergoes an irreversible 2-electron reduction; 3 hydrogen ions are consumed in acidic medium and two hydrogen ions in alkaline medium. The current is diffusion-controlled and proportional to the concentration in the range 0.6–120 μg ml^?1. Reduction mechanisms are proposed. A simple and rapid method for the determination of nicotinamide in multivitamin tablets by differential pulse polarography is described.     

Electrochemical determination of N,N-dimethyl-4-amino-4′-aminoazobenzene

N,N-Dimethyl-4-amino-4′-aminoazobenzene has been determined using differential pulse polarography. Fast-scan modification and linear-scan voltammetry at a hanging mercury drop electrode was used with a detection limit of less than 10⁻⁸ mol liter⁻¹. Differential pulse polarography was then used to analyze mixtures of the above depolarizer with azobenzene and N,N-dimethyl-4-aminoazobenzene, either directly, or after a TLC separation.     

Spectrometric evidence ford-orbital participation in the lowest excited singlet states of naphthalenethiols

Tellurium can be determined polarographically in the range 10^?5–10^?8M by means of the Te⁰_ads→Te^2- reduction in 1M perchloric acid as supporting electrolyte. Pulse polarography, a.c. polarography and linear sweep cyclic voltammetry can be used to determine tellurium in the p.p.b. range. Copper(II), arsenic(III) and selenium(IV) interfere, but the interferences can be overcome by a standard addition method.     

Determination of pseudouridine at submicromolar concentrations by cathodic stripping voltammetry at a mercury electrode

Pseudouridine (5-ribosyluracil), uridine (N,1-ribosyluracil), deoxyuridine (N,1-deoxyribosyluracil) and uracil are investigated by means of d.c. polarography and by differential and normal pulse polarography. Pseudouridine, which is known to be a cancer marker, yields anodic polarographic currents in the pH range 7–11, whereas uridine and deoxyuridine are inactive under the same conditions. The polarographic response of pseudouridine obtained is due to the formation of a sparingly soluble mercury compound. Pseudouridine can be determined by differential pulse polarography in the concentration range 2–6 × 10^?6 M and by differential-pulse cathodic stripping voltammetry at concentrations two orders of magnitude lower. Small excesses of uridine, deoxyuridine or proteins do not interfere with the determination.     

Anomalies in Faradaic rectification polarography of aromatic compounds in non-aqueous solvents

The electrode reaction of p-dicyanobenzene^O/? in N,N-dimethylformamide is studied with the aid of the galvanostatic double pulse (GDP) method and faradaic rectification (FR) polarography. The results of the GDP measurements obey the theoretical requirements in all aspects. Conversely, the FR polarogram can be fitted with the theoretical polarograms only in the potential range ?-50 mV vs. the reversible half-wave potential of this electrode. Furthermore, the most suitable k⁰ values used in this curve-fit analysis depends on the frequency of ac input and differ greatly from the value determined by the GDP method. Attention is called to the fact that the p-dicyanobenzene^0/? system is just one of the 16 redox systems of aromatic compounds which show this type of behaviour in FR and GDP experiments. Their kinetic parameters are also tabulated, with some comments on the anomalies in FR polarography.     

Polarographic behaviour and hydrolysis of midazolam and its metabolites

The electrochemical behaviour of midazolam [7-chloro-5-(o-fluorophenyl)-3H-(2′- methyllimidazo) [1,5-a]-benzodiazepine was studied by polarography and cyclic voltammetry. The irreversible two-electron were is not strongly affected by the imidazole ring or the 5-o-fluorophenyl substituent, but the latter increases the rate of the hydrolysis in acidic media. Kinetic parameters are evaluated for midazolam and three of its hydroxylated metabolites. The hydrolysis is a first-order reaction initially but becomes second order. The 3-hydroxy matabolites are more easily hydrolyzed than midazolam. Midazolam (10^?4–10^?7 M) can be quanitified by using differential-pulse polarography; the detection limit is 6 × 10^?8 M.     

Determination of soluble cyanide in soil samples by differential pulse polarography

Soluble cyanide can be determined ins oil samples by differential pulse polarography. Interference from sulphide is avoided by treating the alkali-stabilized sample solutions with lead carbonate prior to distillation of cyanide from the soil extract. Less than 10 μg l^?1 cyanide can be determined accurately, depending on teh weight of sample taken and the final collection volume. For a 100-g soil sample, the detection limit is 5 ng g^?1, which is similar to the limit of a standard spectrophotometric method. Relative standard deviations are 1–3%.     

Dosage direct du paracetamol dans les milieux biologiques par polarographie sinusoidale

(The direct determination of paracetamol in biological fluids by a.c. polarography). Paracetamol can be determined rapidly in biological fluids (blood serum and urine) by a.c. polarography. After elimination of protein by perchloric acid, followed by reaction with nitrous acid in acidic medium, the nitro derivative is measured at pH 10. As little as 4 × 10^-6 M paracetamol (0.6 μg ml^-1) in serum can be determined.     

Kinetic study of the reduction of hydroxylamine by Cu(I)

We have studied the reduction of Se^IV in acidic medium (1 M HCl and 1 M HClO₄) by classical and alternating current polarography and single sweep linear voltammetry with dropping mercury electrode and hanging mercury drop (HMDE). Two steps are observed distinctly: (1) The reduction of Se^IV→Se^o leads to a deposit of adsorbed elementary selenium. A mathematical expression is shown for the variation of current which is related to the surface covered at the HMDE. (2) The second step is the reduction of Se^o→Se^2? which takes place at more negative potentials. The accumulation of Se^o may be used for the determination of traces in trace analysis by cathodic stripping. It appears that the behavior of selenium in these two mineral acids is similar. But sometimes it behaves in a different manner, especially in a.c. polarography (in this connection the influence of frequency and demodulation angle are important).     

Electrochemical study and analytical applications for new biologically active 2-nitrophenylbenzimidazole derivatives

The present study addresses the electrochemical behavior and the analytical applications of six 2-nitrophenylbenzimidazole derivatives with activity against Trypanosoma cruzi. When studied in a wide range of pH, by differential pulse polarography, tast polarography and cyclic voltammetry, these compounds exhibited two irreversible cathodic responses. With analytical purposes, the differential pulse polarography mode was selected, which exhibited adequate analytical parameters of repeatability, reproducibility and selectivity. The percentage of recovery was in all cases over 99%, and the detection and quantitation limits were at the level of 1 × 10⁻⁷ mol L⁻¹ and 1 × 10⁻⁶ mol L⁻¹, respectively. In addition, the differential pulse polarography method was successfully applied to study the hydrolytic degradation kinetic of one of the tested compounds. Activation energy, kinetic rate constants at different temperatures and half-life values of such application are reported.     

Polarographic determination of chlorpheniramine maleate in pharmaceuticals

The electroreduction of chlorpheniramine maleate has been investigated by a.c. and d.c. polarography, coulometry and cyclic voltammetry. Polarograms recorded from 0.2 M sulphuric acid exhibit a single well-defined 2-electron wave. The current is diffusion-controlled and proportional to the concentration in the entire range 0.3–400 μg ml^?1. A simple and rapid method for the determination of chlorpheniramine maleate in tablets is described.     

Polarographie radiochimique des solutions acides de TeIV

With ¹²¹Te (T_1/2=17 days) radiochemical polarography of [Te^IV]≤10^?9M is possible with negligible surface coverage. Deposition of Te is diffusion controlled. The potential range of Te⁰ formation is limited at negative potential by its reduction to HTe^?.     

The determination of uranium by cathode-ray polarography

The determination of uranium in the concentration range 2.10^-6–4.10^-3M has been studied by using both conventional and cathode-ray polarography, The prefeircd supporting electrolyte is 1 M perchloric acid, molybdenum is the only element which will cause serious interference at levels of the saine order as that of the uranium.     

Kinetic-coulometric determination of mercury in biological samples

A simple approximate calculation method is given which permits determina-tion of the maximal scan rates of potential allowable for distortion-free recording of current-voltage curves with X-Y recorders. For the calculations only the response time of the recorder, the wave shape and the scan rate of potential need be known. Stationary mercury electrodes and rapid polarography with a dropping mercury electrode at controlled drop times were examined. Electroanalytical implications are discussed, with particular emphasis on the rapid a.c. polarographic method with short controlled drop times and on stationary-electrode fundamental and second harmonic a.c. voltammetry. Theoretically and experimentally it has been shown that an X-Y recorder with 0.5–1.0-s response time can be used for scan rates up to about (50/nt') mV s^-1 with a.c. techniques and about (100/nt') mV s^-1 with d.c. polarography (t'= response time of recorder, n = number of electrons).     

Zur Bestimmung von β-Aminocrotonsäureester nach Migration in Lebensmittel

β-Aminocrotonic esters are of great importance as stabilizers for the production of clearly transparent food packaging of PVC. For the purpose of studying the migration into foods a thin-layer Chromatographic and a polarographic method were elaborated. The TLC method consists of the visual comparison of the intensity of the spots after treatment with Fast Blue B salt. The polarographic determination is carried out after nitrosation of the stabilizer. By the TLC method 10^?7 g of ester per spot are still detectable; the concentration which is still determinable by cathode-ray polarography is 5×10^?7 g of ester and by conventional d.c. polarography 5×10^?6g of ester per ml of final solution. After extraction with acetonitrile traces of the stabilizer which are migrated into edible oil are still determinable down to 2 ppm by the methods described.     

Electroanalytical procedure and sorption studies for imazaquin in different soils

The objective of the present work is to determine sorption coefficients of the herbicide imazaquin using the differential pulse polarography in the major soil classes occurring in the State of São Paulo, Brazil. This study contributes to the predictions of pesticide fate and transport mechanisms in the environment as well as its exposure and interactions with different soil materials. Imazaquin was analysed directly in soil samples (scan rate 2 mV s^–1, mercury drop size 0.37 mm, and pulse height 50 mV) and the detection limits varied from 42 to 58 g L^–1 for different soils. Imazaquin showed the K_F values varying from 0.8 (for the sandy soil) to 35.5 L kg^–1 (for the medium textured soil), with a significant dependence on the soil pH, organic matter content, and clay minerals. The study demonstrates the practical utilisation of the electroanalytical methodology to determine the imazaquin adsorption in soil and consequently assess the impact of this herbicide in the environment, especially for the evaluation of the potential risk of surface and groundwater contamination.     

Electroanalytical studies of the pesticides menazon and its hydrolysis products

An electroanalytical study based on d.c. polarography, differential pulse polarography (d.p.p.) and coulometry is described for Menazon, S-[4, 6-diamino-1,3,5-triazin-2-yl)- methyl]-O,O-dimethylphosphorodithioate, and its alkaline hysdrolysis products in a (1 + 4) methanol/water medium. The responses of the different species are studied for analytical utility. Menazon itself produces two diffusion-controlled cathiodic waves or peaks at pH 4.78; the determination limit is 5.5 × 10^-7 M for the d.p. peak at about ?0.8 V vs. Ag/AgCl. The hydrolysis products obtained in 0.1 M sodium ydroxide give rise to four anodic waves. Acidification of the alkaline medium to pH 4.3 produces three well-defined waves; two cathodic and one anodic. The responses for the cathodic processes are linear with concentration over 2–2.5 orders of magnitude; the anodic wave is adsorption-controlled and provides linear response only at low concentrations. The detection limit for the hydrolysis products is 0.17 × 10^-6 M. Reaction mechanisms are proposed.     

The determination of chromium(VI) in natural waters by differential pulse polarography.

A method utilizing differential pulse polarography for the determination of chromium(VI) in natural water is described. Additions of 0.62 μg Cu(II) ml^-1 and 0.55 μg Fe(III) ml^-1 did not interfere with the determination of 0.050 μg Cr(VI) ml^-1. The natural water samples containing chromium(VI) were buffered to approximately pH 7 with 0.1 M ammonium acetate and 0.005 M ethylene diamine and analyzed. Natural water samples of chromium content from 0.035 μg ml^-1 to 2.0 μg ml^-1 may be analyzed directly without further preparation. The detection limit is 0.010 μg ml^-1.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.