Absence Of Matrix Interferences Research Articles

Extraction and determination of free glutathione and its disulfide in various flour samples using liquid chromatography and on-line post column derivatization

In the present report we propose an HPLC method coupled to on-line post column derivatization for the simultaneous determination of glutathione and its disulfide in flour samples. The extraction of the analytes from the sample matrix was investigated in terms of efficiency, stability and compatibility with the analytical method. The selection of o-phthalaldehyde at high alkaline medium as post column reaction system enabled the determination of both analytes in a single run at reasonable separation times (<10 min). Fluorimetric detection allowed determination at the low nmol g−1 (5–75 nmol g−1) levels in the absence of matrix interferences from endogenous compounds. The LOD values were 1.2–1.3 nmol g−1 and the precision better than 7.2% in all cases. Various commercially available flour samples (wheat, corn, rice) were analyzed and were found to contain glutathione and its disulfide in the ranges of 29–243 and 8–84 nmol g−1 respectively. Only in one rice flour sample the levels of GSH were < LOQ of the method.

Applicable pharmacokinetic study: Development and validation of bioanalytical LC-MS/MS method for the simultaneous quantification of cytarabine and glasdegib used for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is characteristic by high concentrations of immature bone marrow myeloid cells. Glasdegib (DaurismoTM, GSB) in combination with low dose cytarabin (DepocytTM, CTB) have recently been approved by the US Food and Drug Administration for the treatment of newly diagnosed AML in patients over 75 years of age or who have comorbidities that are prohibitive to intensive induction chemotherapy. However, the pharmacokinetic characteristics of the CTB and GSB is yet unknown. This study developed a selective, sensitive and fast analytical method using liquid chromatography-electrospray ionization (ESI) with tandem mass spectrometry (LC-MS/MS) to simultaneously quantify of CTB and GSB in rat plasma using duvelisib as internal standard (IS). The LC-MS/MS instrument was performed in the ESI interface operating at positive ionization and multiple reaction monitoring (MRM) mode. The CTB and GSB with the IS were extracted from rat plasma by using cation exchange solid-phase extraction cartridge before the analysis. The cartridge gave high recovery rates for both drugs without interference from plasma endogenous. Chromatographic separation was performed on reversed-phase polar-100 column (100 mm × 2.1 mm, 3 µm), with an isocratic mobile phase consisted of a mixture of water containing 0.1% formic acid and acetonitrile (85:15, v/v, pH 3.2) at a flow rate of 0.4 mL/min and the process of analysis was run for 3.5 min. The developed method was validated as per the FDA guidelines over a linear concentration range of 5–3000, for both CTB and GSB with high correlation coefficient (r2 ≥ 0.99). The lower limits of detection (LLOD) were 2.0 ng/mL for both drugs. The overall recoveries of CTB and GSB from rat plasma were in the range of 93.93–101.43%, and the mean relative standard deviation (RSD) of the results was 2.99%. The validated-method was successfully applied for the first time, to a pharmacokinetic study on concurrent oral administration of CTB and GSB in rats (12.0 mg/kg of CTB and 8.5 mg/kg of GSB). The maximum plasma concentration (Cmax) for CTB and GSB was 2312.23 ± 448.26 ng/mL and 1710.61 ± 166.04 ng/mL achieved at 2.83 ± 0.14 h and 2.39 ± 0.10 h, respectively. The AUC0-∞ for CTB and GSB was found to be 8592.49 ± 1714.12 and 4527.67 ± 390.01 ng/mL.h; respectively. The elimination half-life (t1/2kel) of CTB and GSB in rat plasma, were determined to be 2.00 ± 0.19 h and 1.58 ± 0.13 h, respectively. The newly developed approach stands out for its high extraction recovery and absence of matrix interference. Findings further demonstrated the high sensitivity of the developed method, which allowed for effective routine tests in pharmacokinetic investigations with LLOD of 2.0 ng/mL and a run time of 3.5 min.

Carbon Black Integrated Polylactic Acid Electrodes Obtained by Fused Deposition Modeling: A Powerful Tool for Sensing of Sulfanilamide Residues in Honey Samples

Sulfanilamide (SFL) is used to prevent infections in honeybees. However, many regulatory agencies prohibit or establish maximum levels of SFL residues in honey samples. Hence, we developed a low-cost and portable electrochemical method for SFL detection using a disposable device produced through 3D printing technology. In the proposed approach, the working electrode was printed using a conductive filament based on carbon black and polylactic acid and it was associated with square wave voltammetry (SWV). Under optimized SWV parameters, linear concentration ranges (1-10 μmol L-1 and 12.5-35.0 μmol L-1), a detection limit of 0.26 μmol L-1 (0.05 mg L-1), and suitable RSD values (2.4% for inter-electrode; n = 3) were achieved. The developed method was selective in relation to other antibiotics applied in honey samples, requiring only dilution in the electrolyte. The recovery values (85-120%) obtained by SWV were statistically similar (95% confidence level) to those obtained by HPLC, attesting to the accuracy of the analysis and the absence of matrix interference.

3D-printed carbon black/polylactic acid electrochemical sensor combined with batch injection analysis: A cost-effective and portable tool for naproxen sensing

Additive manufacturing has emerged as an innovative technology for the large-scale development of low-cost and disposable electrochemical devices. Hence, in this paper, we highlight the use of a 3D-printed electrode using carbon black integrated polylactic acid (CB/PLA) conductive filament for electrochemical detection of naproxen (NPX), a highly consumed non-steroidal anti-inflammatory drug used in the treatment of rheumatoid arthritis, osteoarthritis, nonrheumatic inflammation, and migraine. Two designs of electrodes were fabricated using an extrusion-based 3D printer and a 3D pen (cylindrical and planar shapes) and both required only simple electrochemical surface treatment to improve their electrochemical activity towards the oxidation of NPX. The planar-shape sensor was incorporated into a 3D-printed Batch-injection analysis (BIA) cell to carry out amperometric detection (+1.3 V vs. Ag|AgCl|KCl(sat)) which provided sensing features comparable to more sophisticated sensors reported in the literature for NPX detection. Characteristics such as linear range (2 to 50 µmol L-1), limit of detection (0.9 µmol L-1), precision (RSD less than 6.7%, n = 20), high analytical frequency (105 injections h−1), and selectivity in relation to other electroactive species were achieved. Moreover, the method was applied in pharmaceutical, urine, and water samples and recovery values in the range of 88 to 105%, attesting to the accuracy and absence of matrix interference. For urine analysis, the selective detection of NPX was attained by using sequential amperometric detection to overcome the interference of electroactive species in the sample matrix. Thus, due to the great performance, the 3D-printed CB/PLA electrode proves to be an affordable and reliable platform for clinical, pharmaceutical and environmental purposes.

Determination of molecular mass 302 polycyclic aromatic hydrocarbons in Standard Reference Material 1597a by reversed-phase liquid chromatography and constant energy synchronous fluorescence spectroscopy

High-performance liquid chromatography with fluorescence detection is often used for the analysis of polycyclic aromatic hydrocarbons (PAHs) in environmental extracts. Since fluorescence chromatograms are usually recorded at a single set of excitation and emission wavelengths, qualitative parameters for PAH identification are restricted to characteristic retention times. The research presented here explores the use of constant energy synchronous fluorescence spectroscopy (CESFS) for the analysis of co-eluting PAHs with similar chromatographic behaviors under normal and reversed-phase conditions. Twenty-one PAH isomers with molecular mass (MM, g/mol) 302 were studied. Synchronous fluorescence spectra were recorded under stop-flow conditions with the aid of a commercial HPLC system. PAHs were extracted from a coal tar sample (Standard Reference Material 1597a) and fractionated by normal-phase liquid chromatography (NPLC). Qualitative and quantitative analysis of NPLC fractions was carried out via reversed-phase liquid chromatography-CESFS (RPLC-CESFS). Of the 21 isomers investigated in the coal tar sample, 16 were spectrally identified in the absence of matrix interference. Three of the remaining isomers were tentatively identified in the presence of moderate spectral interference. Thirteen isomers were used to investigate the accuracy of the RPLC-CESFS approach. Mass fractions statistically equivalent to the NIST reported values (P = 95%; N1 = N2 = 3) were obtained for ten isomers ranging from 2.04 (dibenzo[a,h]pyrene) to 10.41 mg/kg (naphtho[2,1-a]pyrene). The non-destructive nature of CESFS provides an additional layer of selective and accurate information to the analysis of PAH isomers with MM 302.

ANALYTICAL PERFORMANCE CHARACTERISTICS OF A PROTOTYPE IMMUNOASSAY FOR QUANTIFICATION OF ALPHA-SYNUCLEIN IN HUMAN CEREBROSPINAL FLUID

α-Synuclein is a pre-synaptic protein whose abnormal aggregation is the main characteristic of a sub-group of neurodegenerative disorders called α-synucleinopathies, including but not limited to Parkinson's disease (PD) and dementia with Lewy bodies (DLB). CFS α-Synuclein levels reflect the presence of Lewy bodies in the brain and have been shown to be decreased in PD and DLB patients as compared to healthy aging controls. Robust assays with good lot-to-lot consistency are required for integration into clinical trials. This study documents the analytical performance characteristics of a novel colorimetric ELISA targeting α-Synuclein in biological fluids, with a focus on cerebrospinal fluid (CSF). α-Synuclein concentrations have been determined using a colorimetric ELISA designed and developed by ADx NeuroSciences using two monoclonal antibodies. The assay was qualified for CSF, but can be modified for application for EDTA-plasma samples. After having performed familiarization runs and some adaptation of the test procedures to the needs of a service provider, the assay was challenged internally for its analytical performance characteristics such as precision, parallelism, spike-recovery, working range, sample stability, and interference using commercially available CSF samples (n=40). α-Synuclein is measured in undiluted CSF and 10–50-fold diluted EDTA-plasma using a 3-hour incubation period for the samples. The new assay format specifically quantifies α-Synuclein in the absence of matrix interference as verified after dilution in α-Synuclein low CSF. Spike/recovery testing revealed good recovery rates (93 % ± 7 %). Our internal precision experiments with CSF resulted in an intra- and inter-assay variability (% CV) below 12 % and 11 %, respectively. The working range is confirmed between 90 pg/mL (Lower Limit of Quantitation) to 6142 pg/mL (Upper Limit of Quantitation). The stability of CSF α-Synuclein was assessed with respect to freeze/thawing and short-term stability at room temperature. No major difference with the reference condition was observed. The newly developed α-Synuclein colorimetric ELISA assay meets all of our internal acceptance criteria for clinical trial sample testing and represents an additional tool for patient enrichment in clinical trials or treatment follow-up.

Multi-analyte methods for the detection of photoinitiators and amine synergists in food contact materials and foodstuffs – Part II: UHPLC-MS/MS analysis of materials and dry foods

The aim of this investigation was to develop a multi-analyte method for the analysis of a total of 53 photoinitiators and amine synergists in food contact materials and foodstuffs. As for many of these compounds a maximum LOD of 10 µg kg−1 food applies, a sensitive and selective detection method is needed to control at these limits. Here an UHPLC-MS/MS was chosen to achieve this object. In the end 49 compounds could be integrated into one analytical method. This is nearly twice as many compared with other by now available methods. Only 11.5 min are needed for the analysis of one sample, allowing a high sample throughput. The LODs, which were determined in acetonitrile in the absence of matrix interferences, are sufficient to control at the legally acceptable limits, except for five photoinitiators. The developed method was tested for the analysis of food contact materials and foodstuffs. In the latter case a muesli matrix was spiked at four different concentration levels to determine the recovery rates. Extractions were performed in each case with acetonitrile. For 87% of the photoinitiators and amine synergists recoveries from the muesli were in the range between 70% and 120%. Thus, a comprehensive detection method for the analysis of food contact materials and foodstuffs for these potential migrating substances is now available, allowing the safe identification and control of migration levels in foodstuffs for the majority of the tested compounds. In particular, this multi-analyte method is worthwhile for official control laboratories where normally no information about the composition of applied inks on the food contact materials is available and thus target analyses are not feasible.

Spatial Emission Profiles for Flagging Matrix Interferences in Axial-Viewing Inductively Coupled Plasma-Atomic Emission Spectrometry: 2. Statistical Protocol

A statistical protocol was developed and verified for automated signaling of matrix interferences in inductively coupled plasma-atomic emission spectrometry (ICP-AES). Spatial emission profiles in ICP-AES are versatile indicators for flagging matrix interference. A family of calibration curves is first generated by measurements of standard solutions at different spatial locations in the plasma. The determined-concentration profile of the analyte along a spatial measurement axis of the plasma is then obtained by analyzing the sample at each spatial location by reference to the respective calibration curve. The absence or presence of a matrix interference is gauged from the shape of the determined-concentration profile of the analyte. A flat determined-concentration profile indicates absence of matrix interference, whereas a dissimilar (i.e., curved) concentration profile offers a clear warning signal that the analytical results are compromised by interferences. The developed protocol automatically classifies a spatial profile as flat or curved; it involves the computation of three statistical parameters: relative range(0.05-0.95), σ(sample), and σ(successive). The term relative range(0.05-0.95) refers to the ratio of the range to the mean of the relative-intensity (or determined concentration) values between the 5th and 95th percentiles in a spatial profile, whereas σ(sample) and σ(successive) refer to the sample standard deviation and the standard deviation of successive values, respectively, of all values in a spatial profile. It was found that whenever the relative range(0.05-0.95) of a spatial profile is below 1.5%, the profile can be considered to be flat and no further statistical testing is needed. If relative range(0.05-0.95) > 1.5%, the σ(successive)/σ(sample) ratio provides useful information on the flatness of the profile. If the profile is flat, σ(successive) will be statistically equivalent to σ(sample) (i.e., σ(successive)/σ(sample) = 1). In contrast, if curvature is present in the profile, σ(successive) will be statistically smaller than σ(sample) (i.e., σ(successive)/σ(sample)< 1). A statistical test, based on the transformation of the experimental σ(successive)/σ(sample) ratio to the z value of a standard normal distribution, was used to judge if the difference between σ(successive) and σ(sample) is statistically significant. This statistical protocol for characterization of flatness in a spatial profile was verified in experiments carried out under the influence of various matrix interferences and different plasma operating conditions.

A fast, simple, and reliable hydrophilic interaction liquid chromatography method for the determination of ascorbic and isoascorbic acids

A reliable method for the determination of total vitamin C must be able to resolve ascorbic acid (AA) and the epimeric isoascorbic acid (IAA) and determine the sum of AA and its oxidized form dehydroascorbic acid. AA and IAA are polar molecules with a low retention time in conventional reversed phase systems, and hence of difficult resolution. Hydrophilic interaction chromatography using a TSKgel Amide-80 stationary phase with isocratic elution was successful in resolving the two epimers. The column was compatible with injections of high concentrations of metaphosphoric acid, tris(2-carboxyethyl)-phosphine, and EDTA without drift of baseline and retention time. Total AA and IAA were extracted, stabilized, and reduced in one step at 40 °C, using 5% m-phosphoric acid, 2 mM of EDTA, and 2 mM of tris(2-carboxyethyl)-phosphine as reducing agent. This simple, fast, and robust hydrophilic interaction chromatography-DAD method was applied for the analysis of food products namely fruit juices, chestnut, and ham and also in pharmaceutical and multivitamin tablets. Method validation was performed on the food products, including parameters of precision, accuracy, linearity, limit of detection, and quantification (LOQ). The absence of matrix interferences was assessed by the standard addition method and Youden calibration. The method was fast, accurate, and precise with a LOQ(AA) of 1.5 mg/L and LOQ(IAA) of 3.7 mg/L. The simple experimental procedure, completed in 1 h, the possibility of using IAA as an internal standard, and low probability of artifacts are the major advantages of the proposed method for the routine determination of these compounds in a large number of samples.

Influence of Crystalline Forms of Titania on Desorption/Ionization Efficiency in Titania-Based Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

In surface-assisted laser desorption/ionization mass spectrometry using titania (TiO2) films (TiO2-SALDI-MS), one of the most important aspects is the absence of matrix interferences in the low-mass region. Therefore, in TiO2-SALDI, the detectable mass range for small biomolecules, pharmaceutical compounds, amino acids, and oligopeptides can be extended to below m/z 500. The physicochemical properties of titania are dependent on the crystalline form of the material; however, thus far, very little attention has been given to the effect of the crystalline form of titania on titania-based SALDI-MS. We investigated the influence of crystalline forms on the desorption/ionization efficiency of TiO2-based SALDI-MS using different crystalline forms such as rutile, anatase, and a non-crystalline amorphous structure. On the basis of survival yield measurements using benzylpyridium chloride, and the desorption/ionization efficiency of peptides (angiotensin II and gly-gly-tyr-arg) and saccharides (cellobiose and hexa-N-acetyl-chitohexaose), it was found that the anatase-type TiO2 is suitable for the TiO2-based SALDI-MS. Rutile-type TiO2 lost the SALDI activity compared with TiO2 in other crystalline forms, although rutile-type TiO2 showed the highest UV absorbance.

Enantiomeric separation of chiral polycyclic musks by capillary electrophoresis: Application to the analysis of cosmetic samples

The enantiomeric separation of four chiral polycyclic musks (Galaxolide, Tonalide, Traseolide and Phantolide) using CE was achieved for the first time in this work. Two chiral methodologies were developed by CD-MEKC using SDS as surfactant in a CHES buffer (pH 9.0). One methodology enabled the fast enantiomeric separation of individual polycyclic musks with analysis times lower than 10 min for Tonalide, 13 min for Traseolide and Phantolide, and 17 min for Galaxolide. Enantiomeric resolutions obtained were higher than 1.5 using different separation media for each compound. A second methodology was also developed enabling the simultaneous enantioseparation of the four musks. In this case, the use of a dual CD system containing two neutral CDs was necessary to achieve the separation of all enantiomers from three out of four musks in 45 min. Although a coelution between Galaxolide and Phantolide was observed, the use of different UV absorption wavelengths allowed the simultaneous analysis of both musks. In addition, a sweeping strategy was performed in order to increase the sensitivity of the method. Appropriate analytical characteristics (linearity, LOD and LOQ, precision and absence of matrix interferences) were obtained for conventional and sweeping methodologies. Finally, the usefulness of the method was demonstrated in the determination of the enantiomers of the polycyclic musks in personal care products as perfumes.

Determination of l- and d-carnitine in dietary food supplements using capillary electrophoresis–tandem mass spectrometry

This paper reports the application of a capillary electrophoresis–electrospray ionisation-tandem mass spectrometry methodology for the unequivocal identification and the quantitative determination of the two enantiomers of the non-protein amino acid carnitine ( l- and d-Carn) in 22 dietary food supplements, including drinks, biscuits, capsules and tablets. MS/MS experiments were optimised to achieve the high sensitivity and selectivity required for food analysis. A comparison of the slopes obtained by the external standard and the standard additions calibration methods indicated the absence of matrix interferences in these food samples. Good precision (RSDs ranged from 2.3% to 4.3% for migration times, and from 2.1% to 10.5% for corrected peak areas) and acceptable accuracy established by means of recovery studies (from 85% to 102%) were obtained. The limit of detection was about 10 ng/mL ( S/ N = 3) enabling the determination of enantiomeric impurities ( d-Carn) up to 0.025% of Carn in foods. This chiral method illustrated is suitable for routine qualitative and quantitative analyses of Carn in foods. The results showed contents for l-Carn comprised from 47% to 115% with respect to the labelled content of l-Carn. Percentages obtained for the d-enantiomer ranged from 0.4% to 5.9%, except for one of the samples analysed, that contained the racemate (49.3% d-Carn). The use of the racemate is not allowed by legislation, which corroborated the high potential of the developed method in the control of the quality and safety of foods containing Carn.

Development of an in‐capillary derivatization method by CE for the determination of chiral amino acids in dietary supplements and wines

A fast in-capillary derivatization method by CE with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate was developed for the first time for the determination of amino acid enantiomers (arginine, lysine, and ornithine) in dietary supplements and wines. Because of the initial current problems due to the formation of precipitates into the capillary during the derivatization reaction, a washing step with an organic solvent as DMSO between injections was necessary. Different approaches were also investigated to enhance the sensitivity of detection. A derivatization procedure, where plugs of ACN, derivatizing agent (10 mM 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate), and sample in borate (1:1 v/v) were injected in tandem (2, 3, and 6 s, respectively, at 50 mbar), was selected because it enabled to obtain the most sensitive and reproducible results. Appropriate analytical characteristics (linearity, LOD and LOQ, precision, absence of matrix interferences, and accuracy) were obtained for this method. Finally, the optimized method was successfully applied to the determination of the enantiomers of arginine, lysine, and ornithine in food samples of different complexities (dietary supplements and wines).

Biochemical and biological assays of endocrine disrupting compounds in various manure matrices

Wastes generated by animal agriculture have complex matrices and present a significant challenge for achieving accurate measurements of estrogens. The objective of this study was to compare two different extraction methods and two different biochemical and biological estrogen assays on two dairy manure matrices. The two extraction methods studied in this research were a two-step base-toluene extraction and a one-step cyclohexane extraction. The two assays assessed were an enzyme-linked immunosorbent assay (ELISA) and a yeast estrogen screen (YES) bioassay. Estrogenic activity was measured directly as 17β-estradiol (E2) through the ELISA method or as E2 equivalents (E2-eq) through the YES bioassay. Both extraction methods yielded reasonable recoveries from distilled water in the absence of matrix interferences. In manure samples, ELISA resulted in recoveries slightly higher than 100% in two types of dairy manures, but YES recoveries varied. The YES bioassay detected much higher estrogenic activities in dairy manure compared to the E2 concentrations measured by ELISA. The base-solvent extraction yielded higher E2 concentrations in dairy manure compared to the one-step cyclohexane extraction. These results suggest that manure matrices vary sufficiently that extraction methods must be optimized for specific assays utilized to quantify estrogens in manures.

Simultaneous determination of DTPA, EDTA, and NTA by UV–visible spectrometry and HPLC

In this study, UV-visible spectrophotometry (UV-Vis) and high-performance liquid chromatography (HPLC) were used for simultaneous analysis of chelating agents diethylenetriamine pentaacetic acid (DTPA), ethylenediamine tetraacetic acid (EDTA), and nitrilotriacetic acid (NTA), as their metal chelates in dishwashing detergents, natural waters, and pulp mill water. The total amounts of the chelating agents in dishwashing detergents were verified by potentiometric titration with Fe(III) solution. Nickel(II) chelates were determined by UV-Vis and iron(III)chelates by HPLC and titration. Recoveries of DTPA, EDTA, and NTA from a standard mixture of analytes by UV-Vis were 107+/-7, 101+/-12 and 94+/-13%, respectively, and the recovery of the total amount of complexing agents was 99+/-4%. The limits of detection for DTPA, EDTA, and NTA were 667, 324, and 739 micromol L(-1), respectively. In HPLC measurements the optimized mobile phase contained 0.03 mol L(-1) sodium acetate, 0.002 mol L(-1) tetrabutylammonium bromide, and 5% methanol at pH 3.15 and the detection was by UV-Vis detection at 254 nm. All three complexing agents could be separated from each other in a simultaneous analysis in less than 5 min. The limits of detection were 0.34, 0.27, and 0.62 micromol L(-1) for DTPA, EDTA, and NTA, respectively. The total amounts of the analytes measured in the dishwashing detergents by the three techniques were found to be highly comparable (ANOVA: F=0.04, P=0.96). R(2) values were 0.99 for EDTA, 0.99 for NTA, and 0.99 for all the results when UV-Vis and HPLC determinations were compared using regression lines. The UV-Vis and HPLC methods were proved to be viable also for analyses of natural and pulp mill waters. The absence of matrix interferences was verified by the standard addition technique.

Desorption/ionization on silicon time-of-flight/time-of-flight mass spectrometry.

Desorption/ionization on silicon (DIOS) tandem time-of-flight (TOF/TOF) mass spectrometry (MS) provides high accuracy and significant fragmentation information, particularly in the characterization of biomolecules. DIOS TOF/TOF offers a high-throughput surface-based ionization platform as well as complete fragmentation through high collision energies. The absence of matrix interference in DIOS allows for the MS and MS/MS analysis of small molecules well below m/z 300. In addition, sample preparation is minimal, and the DIOS chips can be stored and reanalyzed for fragmentation information or accurate mass measurements. The combined benefits of robustness, minimal sample preparation, good sensitivity, high throughput, and sequencing capability make DIOS TOF/TOF a powerful tool for small molecule characterization and protein identification.

Selective determination of arsenite by flow injection spectrophotometry

This paper describes the application of the well-known Molybdenum Blue method for selective determination of arsenite in a flow injection system. Selectivity is achieved by on-line separation of the main interferents phosphate, arsenate and silicate using a strong anion-exchange microcolumn located in the aspiration line of injection valve. Arsenite passing through the microcolumn unretained is determined using Molybdenum Blue method following in-line oxidation to arsenate by permanganate. A thorough investigation of optimal experimental conditions for both, the separation of interferents and sensitive detection of arsenite is presented. The method developed permits arsenite to be determined in the concentration range 5–500 μg/l with high precision and reliability. A sample throughput of 20 hr −1 is achieved. Phosphate, arsenate and silicate do not interfere at concentration levels significantly higher than that of arsenite. The application to real water samples reveals excellent recovery of spiked samples and the absence of matrix interferences.

Determination of monovalent and divalent cations and chloride in the carbacephalosporin loracarbef by ion chromatography

Sensitive determination of monovalent and divalent cations and chloride in the carbacephalosporin antibiotic loracarbef can be achieved by separation on a high-capacity cation-exchange column followed by chemically suppressed conductivity detection. The methods developed in our laboratory for these determinations are characterized by the absence of matrix interference, rapid separation, ease of sample preparation and good sensitivity. Of these benefits, it is the minimization of matrix interference supplied by micromembrane chemical suppression that has made this technique so powerful for this application. Advantage is taken of the acid-base chemistry of loracarbef, resulting in a drastic reduction in its concentration in the eluent prior to detection of the analytes of interest. Linearities in the presence of the matrix (coefficient of determination ⪢ 0.995) and recoveries from the matrix are excellent (100 ± 2%). However, when the suppression components exhibit decreased efficiency, systems employing eluents composed of both hydrochloric and diaminopropionic acids are susceptible to problems such as poor peak shape, high background conductivity, and noise thus making accurate determinations difficult. Both the suppression system and the eluent are assessed in relation to the sources of high background conductivity and noise.