Ion-Selective Electrode Determination of Sodium and Potassium in Blood and Urine

Abstract

The Beckman Electrolyte 2 Analyzer (E2A) has been studied for its response to sodium and potassium content in various laboratory prepared pH-adjusted mixtures of metal chlorides in the absence and presence of albumin and α-, β-and γ -globulins. These mixtures also included MITS, a Mock Ionic Test Serm, containing sodium chloride (15OmM), potassium chloride (4mM), calcium chloride (1mM) and magnesium chloride (1mM). Results for sodium and potassium are often low for these non-clinical standards.

Responses have also been studied for patient blood serum and urine samples. Some comparisons have been made with data obtained by flame photometry. The blood serum data obtained with the Electrolyte 2 Analyzer are statistically compared with those obtained by flame photometry.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Three component flow injection analysis with on-line dialysis. Simultaneous determination of free calcium, total calcium and total chloride in milk by flow injection analysis and on-line dialysis

Summary A fast and reliable fully automated three-component flow injection procedure for the simultaneous determination of free calcium, total calcium and total chloride in milk is described where the three components from a single sample injection (30 l milk samples) are determined at a sampling rate of 60 samples per hour. The samples are directed to three different channels by using two dialysers in series. Interferences in the determination of free calcium are eliminated by using a dialyser (first in the series) which also separates the total and free calcium. Free calcium is determined by UV/VIS spectrophotometry at 580 nm and total calcium by atomic absorption spectrometry (AAS) at 422.7 nm. Interferences from phosphates in milk in the determination of total calcium by AAS are overcome by using a nitrous oxide-acetylene flame with the necessary suppression with potassium ions. A second dialyser in series is used to eliminate interferences, especially the interference of casein, before the dialysed chloride is measured with a coated tubular chloride-selective electrode. The results obtained for the free calcium, total calcium and total chloride in milk at a sampling rate of 60 samples per hour compared well with data obtained by standard methods. With 30 l samples the relative standard deviation for milk samples having different concentrations of free calcium (110–170 mg/l free calcium), total calcium (1000–1500 mg/l total calcium) and total chloride (1000–1800 mg/l total chloride) were better than 0.37, 1.01 and 0.25, respectively.     

Isolation of Lipophilic Persistent Organic Pollutants From Human Breast Milk

Background: Lipid removal from biological samples can be achieved by addition of concentrated sulfuric acid. However, certain persistent organic pollutants (POPs) such as chlorophenols are decomposed by sulfuric acid treatment and, thus, a more gentle lipid reduction method is needed for extraction of many environmental contaminants from biological samples. Membrane dialysis extraction (MDE) is a non-disruptive method to extract POPs from biological matrices.

Methods: Human breast milk samples were spiked with radiolabelled p,p′-dichlorodiphenyl trichloroethane ([C-14]-DDT) as a POP proxy and extracted using solid phase extraction (SPE). The extracts obtained were dialyzed by MDE in low-density polyethylene tubings containing a mixture of n-hexane and dichloromethane for 24 h, 48 h, or 72 h.

Results: The lipid content was reduced by 86.2% after one dialysis cycle of 24 h using MDE, and 87.1% recovery of the [C-14]-DDT standard was obtained. The DDT recovery could be further increased up to 96.3% and 98.1% by repeating the dialyses for one or two more cycles, respectively. However, the increased [C-14]-DDT recovery includes a concomitant increase in lipid carryover from 13.8% with one dialysis cycle to 22.1% with three cycles.

Conclusion: An SPE procedure for extracting POPs from breast milk and dialytic conditions for isolation of the extracted POP with minimal lipid carryover was established. The method is nondestructive and acceptable recoveries can be obtained within a single solvent shift as demonstrated by spiking standards. The lipid carryover was minimized, and the method may be considered for lipid removal before HPLC or GC analysis of environmental contaminants.     

Use of a Conditioning Buffer to Regenerate Gas Sensing Ion Selective Electrodes

Abstract

In the course of working with geothermal-geopressured brines we have developed a slight modification to the general procedure for the use of gas sensing ion selective electrodes which reduces the time between successive samples to about 10 minutes, as well as improving the precision and in the case of the ammonia electrode an improvement in the lower detection limit (to 0.1 ppm) was obtained. We have found that the modified procedure works equally well for both the Orion ammonia (Model 95–10) and the Orion carbon dioxide (Model 95–02) electrodes.     

Determination of Anticholinesterase Activity for Pesticides Monitoring Using a Thiocholine Sensor

Abstract

An acetylthiocholine sensor based on a disposable screen-printed carbon electrode has been assembled for measuring organophosphorus and carbamate pesticides in river water samples through the degree of inhibition of the enzyme acetylcholinesterase (AChE). The carbon working electrode surface was modified by deposition of a mediator, tetracyanoquinodimethane (TCNQ), and Nafion. Acetylcholinesterase catalyses the cleavage of acetylthiocholine to thiocholine, which is measured by differential pulse voltammetry and directly related to the enzyme activity. The scan speed, the pulse amplitude of the differential pulse voltammetry and several parameters in the procedure were optimised. An inhibition calibration curve was obtained using carbofuran. The method was also applied to water samples, showing its suitability as a rapid screening assay (15 min per test) for anticholinesterase activity detection.     

An Improved Gas-Liquid Chromatographic Method for the Analysis Of 1,1,1-Trichloro-2,2-BIS(p-Chlorophenyl) Ethane(p,p′-DDT) and Its Metabolites in Milk

Abstract

A rapid method has been developed, in which p,p′-DDT residues are extracted from milk samples with n-hexane, following treatment of the milk with concentrated sulfuric acid. The extract, containing p,p′-DDT residues is then cleaned up on a silica gel column. Electron capture gas chromatography was used to measure the efficiency of the extraction and cleanup procedure. An overall average recovery of 97% was obtained on samples at concentration levels of 0.05 to 1.00 ppm.     

In situ continuous monitoring of chloride, nitrate and ammonium in a temporary stream: Comparison with standard methods

A multi-parameter probe was used for in situ chloride, nitrate and ammonium measurements in a temporary stream (Ribeira da Pardiela, in the South of Portugal). Comparison with standard analytical methods was performed for all elements. For chloride, the results of the probe depicted the same behaviour as that obtained with the standard method, although it is clear that the matrix effects were present. For nitrate, the results obtained with the probe were in agreement with the other standard methods used, except for samples collected during drought, when the stream water became brownish and exhaled an offensive smell, due to the decomposition of organic matter. For ammonium, surprisingly the probe show to be the best option, the phenate method being affected by matrix effects. The results still suggest an interference of the bicarbonate ion on nitrate determination, but standard additions approach was shown to minimize most of the matrix effects. Recoveries were reasonable to good for all the three anions under scrutiny.     

Selenium speciation in cow milk obtained after supplementation with different selenium forms to the cow feed using liquid chromatography coupled with hydride generation-atomic fluorescence spectrometry

The purpose of this paper is to develop an easy and quick on-line selenium speciation method (LC-UV-HG-AFS) in cow milk obtained after different supplementation to cow feed. This study focuses on selenium speciation in cow milk after the use of different selenium species (organic selenium as selenised yeast and inorganic selenium as sodium selenite) in the supplementation of forages. Separation was carried out on a μBondapack C₁₈ column with the positively charged ion-pairing agent tetraethylammonium chloride in the mobile phase. The optimization of pre-reduction conditions was carried out; this step was done with UV irradiation and a heating block to improve the reduction of the different Se-compounds. Variables such as exposure time, hydrochloric acid concentration and temperature were studied. The detection limits for SeCyst₂, Se(IV), SeMet and Se(VI) were 0.4, 0.5, 0.9 and 1.0 μg l⁻¹, respectively. The proposed method was applied to cow milk samples. The milk samples obtained after an organic supplementation of feeding as selenised yeast present three species of selenium, SeCyst2, Se(IV) and SeMet, while only SeCyst2 and Se(IV) are present in milk samples obtained after an inorganic supplementation of feeding.     

Determination of Ciprofloxacin,Enrofloxacin, and Marbofloxacin in Bovine Urine,Serum, and Milk by Microextraction by a Packed Sorbent Coupled to Ultra-High Performance Liquid Chromatography

This article reports new, easy, and rapid microextraction by packed sorbent (MEPS)–ultra high performance liquid chromatography with photodiode array detection for the simultaneous determination in bovine urine, serum, and milk of three antibiotics belonging to the class of the fluoroquinolones, namely ciprofloxacin, enrofloxacin, and marbofloxacin, approved for veterinary and human use (ciprofloxacin). The chromatographic separation of the analytes and all aspects influencing the MEPS performance were optimized for the extraction from the considered biological samples. The optimized procedure required simple sample pretreatment, a short (<8?min) isocratic elution, and provided sufficient sensitivity for the determination of the analytes at trace levels in compliance with current legislation. Limits of quantitation were in the range from 0.002 (ciprofloxacin, urine) to 0.048?μg/mL (enrofloxacin, milk). Recoveries from 79% (enrofloxacin, milk) to 88% (ciprofloxacin, urine/serum) were obtained on spiked samples. The within-day (n?=?6) and between-day (n?=?6 over 3?days) relative standard deviation percentages in bovine urine, serum, and milk samples ranged from 2.2 (ciprofloxacin, urine) to 2.5 (enrofloxacin, serum) and from 3.1 (ciprofloxacin, urine) to 3.7 (enrofloxacin, milk), respectively, and were not concentration dependent. To the best of our knowledge, this is the first study describing a fast and simple method for the determination of fluoroquinolones in bovine biological samples.     

Chemiluminescent Detection of Gatifloxacin Residue in Milk

Abstract

An indirect competitive chemiluminescent enzyme-linked immunosorbent assay (CL-ELISA) for detection of gatifloxacin residue in milk was developed in this study. Compared with conventional colorimetric ELISA using the same antibody, the developed CL immunoassay shows a significant improvement in sensitivity and detectability with an IC₅₀ of 0.4 ng mL^?1 and a detection limit of 0.001 ng mL^?1 and thus is suitable to be used as a highly sensitive screening method to detect and regulate illegal use of gatifloxacin in food and food products. The test kit was applied to detect milk samples spiked by gatifloxacin, and satisfactory results were obtained.     

FIA-potentiometry in the sub-Nernstian response region for rapid and direct chloride assays in milk and in coconut water

A simple and reliable FIA-potentiometric system for rapid assays of chloride in certain food samples is described and evaluated. The system is constituted by an aquarium air pump to propel the carrier solution, a manually operated injector, a homemade dialysis flow cell, a solid-state chloride detector (Ag/AgCl), a reference electrode and a multimeter connected to a microcomputer for data acquisition. The dialysis unit enables direct analysis of liquid food samples without any other previous treatment. The principal novelties are the precision (R.S.D. of 1.2% for whole milk) and rapidity (90 determinations/h) of FIA measurements near and below the lower end of the linear (Nernstian) response region of the chloride ion-selective electrode (ISE), with an estimated detection limit (3 s) of 0.4 mg L⁻¹ Cl⁻ in the sample injected in donor stream. Data of peak potential versus sample chloride concentration (donor stream) was accurately fitted with a quadratic polynomial over the range between 4 and 1000 mg L⁻¹ (r² = 0.9999) and used as a calibration curve. The method was applied to the determination of chloride in milk and in coconut water samples. The validation of the results was done by comparison with a NIST reference material (milk) or by capillary electrophoresis (coconut water). For all analysis, no significant difference at a 95% confidence level was observed.     

Amperometric Determination of Lactic Acid. Applications on Milk Samples

Abstract

A hydrogen peroxide electrochemical sensor, coupled with immobilized lactate oxidase and covered with a cellulose acetate dialysis membrane has been applied in flow analysis of lactate in milk samples. The hydrogen peroxide produced by the enzymatic reaction is measured with a platinum electrode polarized at +650 mV versus Ag/AgCl. Milk samples were analyzed and compared with a spectophotometric reference method. The developed procedure is very simple and the short response time allows its use in assaying milk samples on dairy farms.     

On-line Chloride Interference Removal for Arsenic Determination in Waste Water and Urine by ICP-MS Using a Modified Capillary

The determination of arsenic in environmental samples like waste waters from industrial effluents and in biological samples like urine is very important due to the toxic nature of some of its species at moderate levels of exposure. The objective of this study was to evaluate the capability of modified anionic capillaries to remove chloride for ICP-MS determination of arsenic, which causes spectral interference due to formation of 40 Ar 35 Cl + . Also high chloride content gives non-spectral interferences. The results indicate that arsenic at a concentration higher than 1 µg L m 1 in a matrix with a chloride content up to 600 mg L m 1 can be accurately determined using a 3-aminopropyltrimethoxysilane (APTMS) modified capillary connected to a microconcentric nebuliser (MCN). The interference level of chloride is considerably reduced due to its retention in the capillary. The method has been successfully applied and validated for waste water and by recovery tests for urine (diluted 1 : 15) samples.     

Selective Liquid and (Vinyl-Chloride) Pentoxyverine Membrane Electrodes - Their Preparation and Use for the Potentiometric Determination of Pentoxyverine Citrate

Abstract

The use of liquid and poly(vinyl-chloride) membrane electrodes which are sensitive and reasonably selective for pentoxyverine determination is described here. The electrodes are based on the use of pentoxyverine-picrate, pentoxyverine-picrolonate and pentoxyverine-tetraphenylborate ion association complexes as electroactive materials in nitrobenzene or in poly(vinyl chloride) matrix. These electrodes show near Nernstian response values in different concentration ranges, depending on the nature of the used counter-ions, at 3.3–7.8 pH range. Potentiometric determination of pentoxyverine citrate with use of these electrodes gives good results which later on are compared with those obtained by non-aqueous titration.     

Flow injection spectrophotometric determination of calcium, phosphate and chloride ions in milk.

Flow injection procedures for the determination of calcium, phosphate and chloride ions in milk samples are described. The reactions are based on the formation of coloured complexes and their spectrophotometric monitoring. A sample pre-treatment with acetate buffer was carried out owing to the complexity of the sample matrix. For chloride, a rapid and reliable automated procedure for direct measurement of its content in milk (using a dialyser to eliminate interferences) is also described. After optimizing the sample pre-treatment and flow injection variables, the procedures were applied to commercial milk; the results obtained agreed satisfactorily with those of the reference methods. With 50 mm3 samples, a working range of 0-15 ppm for calcium, 50-150 ppm for phosphate and 5-100 ppm for chloride is covered with a precision of better than 1.1%. The sample throughput was higher than 50 samples h-1. These preliminary experiments are the basis for the automation of the determination of calcium, phosphate and chloride ions using a computer-controlled, self-designed and laboratory-built autoanalyser.     

Ion-Selective Electrode Determination of Calcium and Potassium in Bovine Skim-Milk Powder

Abstract

Ion-selective electrode determinations of potassium and calcium have been carried out on skim milk powder and the results compared with data obtained by flame emission spectroscopy for potassium and by atomic absorption spectroscopy for calcium. The data indicate that ion-selective electrodes can be used as an alternative to spectroscopic methods for determining these metals by using a dry-ashing pretreatment procedure. Acid digestion pretreatment is not recommended because of the ensuing high ionic strength and possible interferences. Sodium and magnesium contents obtained by spectroscopy are also quoted for interest. The various percentage metal contents are: potassium: 1.96 ± 0.155 (ISE direct) 1.81 ± 0.144 (ISE Gran) and 1.82 ± 0.076 (flame emission), sodium: 0.511 ± 0.017 (flame emission), calcium: 1.37 ± 0.095 (ISE direct), 1.36 + 0.079 (ISE Gran) and 1.41 ± 0.082 (flame aas), and magnesium 0.119 ± 0.003 (flame aas).     

Determination of organochlorine pesticides (OCPs) in breast milk from Rio Grande do Sul,Brazil, using a modified QuEChERS method and gas chromatography-negative chemical ionisation-mass spectrometry

ABSTRACT

The food chain is the main source of exposure to humans by organochlorine pesticides (OCPs) due to the bioaccumulation. Breast milk can accumulate OCPs, so this matrix is often used as an environmental bioindicator. The currently available methods for the determination of several OCPs and metabolites in breast milk involve, in general, multi-step sample preparation and quantification techniques with low selectivity, high cost and much time and labour. Thus, a fast and efficient method based on sample preparation using the quick, easy, cheap, effective, rugged and safe (QuEChERS) method combined with gas chromatography coupled to mass spectrometry with negative chemical ionisation (GC-NCI-MS) was developed, validated and applied for determination of 16 OCPs and metabolites in breast milk samples. The extract was cleaned by dispersive solid-phase extraction (d-SPE) using MgSO₄ and C18, evaporated in a Turbovap® system, redissolved and analysed by GC-NCI-MS. The method was validated showing acceptable recoveries (72–118%) and precision (RSD <19%). Method limits of detection (LODs) and quantification (LOQs) ranged from 0.75 to 7.5 ng g^?1 and from 2.5 to 25 ng g^?1 lipid, respectively. The method was successfully applied to 20 samples of breast milk from different regions of the Rio Grande do Sul state, Brazil, of which 75% contained residues below the LOQs.     

Coupling on-line of a dialyser with a flow-continuous system to separate Vitamin B(12) from milk

The use of membranes for on-line separations in flow-through dialyser as a part of a flow system is extremely useful for automated samples preparation. In this paper a method to couple the dialysis and the UV detection on-line of Vitamin B₁₂ from milk is proposed. Firstly, the milk samples were pre-treated with trichloroacetic and centrifuged (to eliminate proteins and fats) and later, using a dialyser coupled a flow-continuous manifold was possible dialyse the Vitamin B₁₂, which was monitored spectrophotometrically at 361 nm. On the other hand, the milk samples were also dialysed on-line but without the acid treatment and the results were compared. The influence of various parameters, including the pump speed for both the donor and acceptor stream, dialysis time, donor and acceptor loop volume on dialysis efficiency was studied. The method was applied to different kinds of milk (skimmed and semi-skimmed milk, evaporated milk, lactose free milk and liquid and powder whole milk). The relative standard deviation (R.S.D.) of the proposed method was of 0.45% and the obtained dialysis percentage was of 5.8%. The proposed method very easy permit a pre-treatment of the sample, quick and on-line with the detection. The dialysis process permitted the pass of vitamin and avoided the pass of other analytes as proteins in the case of the milk samples without acid treatment.     

Determination of Phosphate by Cathodic Stripping Voltammetry at a Glassy Carbon Electrode

Abstract

The oxidation of Fe(II) in the presence of phosphate results in a film of a sparingly soluble Fe(III) phosphate salt on a glassy carbon electrode. The reaction is used as the preconcentration step in a cathodic stripping method for phosphate. The recommended procedure yields working curves which are linear over single orders-of-magnitude down to 0.1 ppm, With a 40-minute preconcentration time, 40 ppb phosphate can be detected. The method is free of interference by chloride and sulfate.