Spectrophotometric determination of some vic-diols

Conditions have been established for the determination of mannitol and sorbitol (0.4–14 μg), mannose (3.6–18 μg), myoinositol (1.5–6 μg) and pinacol (11–70 μg) by periodate oxidation. The iodate formed is determined spectrophotometrically by reaction with iodide to form tri-iodide. Exce'ss of periodate is masked with molybdate.     

Application of ion-exchange cartridge clean-up in food analysis I. Simultaneous determination of thiabendazole and imazalil in citrus fruit and banana using high-performance liquid chromatography with ultraviolet detection

A simple, rapid and reproducible analytical method for thiabendazole (TBZ) and imazalil (IMA) in citrus fruit and banana has been developed. The method involves the use of an ion-exchange cartridge for sample clean-up followed by ion-pair high-performance liquid chromatography with ultraviolet detection. The recoveries of TBZ and IMA from citrus fruits spiked at levels of 10 μg/g and 5 μg/g were in the range of 94–98% and 93–98% with coefficients of variation of 0.5–2.2% and 1.6–2.7%, respectively. The recoveries of TBZ and IMA from banana spiked at levels of 3 μg/g and 2 μg/g were 94% and 94% with coefficients of variation 1.1% and 4.9%, respectively. The detection limits for TBZ and IMA were 0.1 μg/g in citrus fruit and 0.05 μg/g in banana.     

Simultaneous spectrophotometric determination of cadmium, copper and zinc

A method for the simultaneous spectrophotometric determination of cadmium, copper and zinc based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide is proposed. The absorption curves of these complexes overlap severely in the scanning range 380–480 nm. The analyte concentrations are calculated by a least squares fit of the pure spectra to the mixture spectra. A linear determination range of 0.1–1.7 μg/ml for cadmium, 0.1–1.3 μg/ml for copper and 0.2–1.2 μg/ml for zinc were obtained. The effect of interference was studied. The method has been applied to the determination of these metal ions in various type of materials.     

Application of extraction disks in dissolution tests of clenbuterol and levothyroxine tablets by capillary electrophoresis

Sample preparation procedures using octadecyl (C₁₈) extraction disks were developed to obtain accurate and reproducible results for determinations of clenbuterol (20 μg per dose) and levothyroxine (100 μg per dose) in dissolution media of solid oral dosage forms. Preconcentration of samples allowed final concentrations of 1.1 μg/ml of clenbuterol and 4.0 μg/ml of levothyroxine to be reached prior to CE analysis. The results obtained by CE were in good agreement with those of HPLC. The precision of the migration time, peak area, peak height and accuracy were determined in both intea-day (n = 6) and inter-day (n =18) assays. Linearity was demonstrated over the ranges 0.5–80.0 μg/ml of clenbuterol and 1.0–30.0 μg/ml of levothyroxine. The mean recoveries were higher than 94.0%, ranging from 50 to 125% levels with respect to dose potencies. The proposed methodology may be generally applied to determine drugs at ng/ml concentrations.     

Nitrofuran antibiotic residues in pork: The FoodBRAND retail survey

Use of nitrofuran drugs in food-producing animals has been prohibited within the EU because they may represent a public health risk. Monitoring compliance with the ban has focused on the detection of protein-bound nitrofuran metabolites which, in contrast to the parent compounds, are stable and persist in animal tissues. As part of the “FoodBRAND” project, an extensive survey of pork was undertaken across 15 European countries. Samples (n = 1500) purchased at retail outlets were analysed for the nitrofuran metabolites AOZ, AMOZ, AHD and SEM using LC–MS/MS determination of nitrobenzaldehyde derivatives. Limits of quantification for the method were 0.1 μg/kg (AOZ, AMOZ), 0.2 μg/kg (SEM) and 0.5 μg/kg (AHD). Of the 1500 samples tested, measurable residues of nitrofuran metabolites were confirmed in 12 samples (0.8% incidence overall) of which 10 samples were purchased in Portugal (AOZ, 0.3 μg/kg; AMOZ, 0.2–0.6 μg/kg) and one sample each in Italy (AMOZ, 1.0 μg/kg) and Greece (AOZ, 3.0 μg/kg).     

Critical study of fluorimetric determination of selenium in urine

Different steps for the fluorimetric determination of Se in urine have been investigated. A HNO₃---HClO₄ (4:1) mixture is useful for urine digestion, and reduction of Se(VI) to Se(IV) is effectively carried out with HCl (6M). Selenium(VI) present after the digestion process constitutes 14.5–36.6% of total Se. An optimum pH of 1.80±0.05 and the addition of 1 ml of 2,3-diaminonaphthalene (DAN) (0.1%, w/v) are established in the formation of Se—DAN complex. Heating to 60°C, a time of incubation of 15 min is recommended to assure the complete formation of Se—DAN complex. A volume of 5 ml of cyclohexane and vigorous shaking for 45 sec is necessary for the extraction process. With this optimized method, the detection limit of selenium was 0.82 μg/l., within-day precision for a 50.0 μg/l. standard solution and urine (27.3 μg/l.) were 2.4 and 2.7% and between-day for the urine was 3.9% (33.9 μg/l.). Analytical recovery of 0.5 ml of Se standard (250 μg/l.) added to 1 ml of urine was 99.9±2.9% (95.8–104.4, n = 12). Normal levels of selenium excretion in urine obtained from healthy people were 27.9±8.7 μg/day (13.2–44.1), not observing significant differences (P < 0.05) between sexes.     

Automated at-line solid-phase extraction-gas chromatographic analysis of micropollutants in water using the PrepStation

A fully automated at-line solid-phase extraction-gas chromatography procedure has been developed for the analysis of aqueous samples using the PrepStation. The sample extract is transferred from the sample preparation module to the gas chromatograph via an autosampler vial. With flame-ionization detection, limits of determination (S/N=10) of 0.05–0.13 μg/l were obtained for the analysis of HPLC-grade water when modifying the PrepStation by: (i) increasing the sample volume to 50 ml, (ii) increasing the injection volume up to 50 μl, and (iii) decreasing the desorption volume to 300 μl. The HP autosampler had to be modified to enable the automated “at-once” on-column injection of up to 50 μl of sample extract. The amount of packing material in the original cartridge had to be reduced to effect the decrease of the desorption volume. The total set-up did not require any further optimization after having set up the method once. The analytical characteristics of the organonitrogen and organophosphorus test analytes, i.e. recoveries (typically 75–105%), repeatability (2–8%) and linearity (0.09–3.0 μg/l) were satisfactory. The potential of the system was demonstrated by determining triazines and organophosphorus pesticides in river Rhine water at the 0.6 μg/l level using flame-ionization and mass-selective detection. No practical problems were observed during the analysis of more than 100 river water samples.     

Detection and spectrophotometric determination of EDTA with cobalt(II) and phosphomolybdic acid in urine and detergents

A simple, rapid, sensitive and selective method for the microgram detection and spectrophotometric determination of EDTA in water, human urine and detergents, based on its reaction with Co(II) and phosphomolybdic acid at pH 0.5–2.0 is reported. Absorbance is measured against Co(II)–phosphomolybdic acid reference solution at 750 nm. The effect of time, temperature, pH and Co(II) or phosphomolybdic acid concentration is studied, and optimum operating conditions are established. Beer's law is applicable in the concentration range 0.3–1.9 μg ml⁻¹ of 10⁻⁵M EDTA. Its detection limit is 0.14 μg in the solution phase and 0.03 μg in the resin phase. The relative standard deviation is ±0.13 μg. Ag(I), Zn(II), Cu(II), Ni(II), Pb(II), Cd(II), Ca(II), Mg(II), Fe(III), Cr(III), U(VI), chloride, nitrite, phosphate, oxalate, borate and amino acids do not interfere.     

Spectrophotometric determination of terfenadine in pharmaceutical preparations by charge-transfer reactions

A simple, rapid and accurate method for the spectrophotometric determination of terfenadine has been developed. The proposed method based on the charge-transfer reactions of terfenadine, as n-electron donor, with 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as π-acceptors to give highly colored complexes. The experimental conditions such as reagent concentration, reaction solvent and time have been carefully optimized to achieve the highest sensitivity. Beer's law is obeyed over the concentration ranges of 3–72, 3–96, 12–168 and 24–240 μg mL⁻¹ terfenadine using TCNQ, TCNE, DDQ and p-CLA, respectively, with correlation coefficients 0.9999, 0.9974, 0.9997 and 0.9979 and detection limits 0.3, 0.4, 2.6 and 12.3 μg mL⁻¹, for the reagents in the same order. DDQ and p-CLA react spontaneously with terfenadine to give colored complexes that can be applied for the flow injection analysis of terfenadine in the concentration ranges 2.4–120 and 24–240 μg with correlation coefficients 0.9990 and 0.9985 and detection limits 0.8 and 2.7 μg for DDQ and p-CLA, respectively, in addition to the high sampling through output of 40 sample h⁻¹.     

Determination of trace level perchlorate in drinking water and ground water by ion chromatography

Ammonium perchlorate, a key ingredient in solid rocket propellants, has recently been found in ground and surface waters in the USA in a number of states, including California, Nevada, Utah, and West Virginia. Perchlorate poses a health risk and preliminary data from the US Environmental Protection Agency reports that exposure to less than 4–18 μg/l provides adequate human health protection. An ion chromatographic method was developed for the determination of low μg/l levels of perchlorate in drinking and ground waters based on a Dionex IonPac AS11 column, a 100 mM hydroxide eluent, large loop (1000 μl) injection, and suppressed conductivity detection. The method is free of interferences from common anions, linear in the range of 2.5–100 μg/l, and quantitative recoveries were obtained for low μg/l levels of perchlorate in spiked drinking and ground water samples. The method detection limit of 0.3 μg/l permits quantification of perchlorate below the levels which ensure adequate health protection. A new polarizable anion analysis column, the IonPac AS16, and its potential applicability for this analysis is also discussed.     

Effects of γ-irradiation on caprolactam level from multilayer PA-6 films for food packaging: Development and validation of a gas chromatographic method

A gas chromatographic method to determine caprolactam in multilayer PA-6 films used for meat foodstuffs and cheese was developed and validated. A wide linear range (0.8–400 μg/ml), RSD4.1% and recovery higher than 90.0% were obtained for the chromatographic system, while precision and accuracy of the method showed RSD3.8%, recovery from 95.5–100.0% and LOQ of 32 μg/g. Irradiated (3, 7 and 12 kGy) and non-irradiated commercial films were analyzed. Most of them increased caprolactam levels with the increase of irradiation doses.     

Comparison of three post-column reaction methods for the analysis of bromate and nitrite in drinking water

Three post-column ion chromatographic methods (i.e., a sodium bromide–sodium nitrite method, an o-dianisidine method, and a potassium iodide–ammonium heptamolybdate method) were compared for bromate and nitrite analysis. Also, the effect of direct mixing of the reagents without ion suppressors for the sodium bromide–sodium nitrite method and the potassium iodide–ammonium heptamolybdate method was investigated. For the analysis of bromate, the three methods showed similar method detection limits (0.17–0.24 μg/l) with pneumatic reagent delivery systems. Direct reagent mixing achieved comparable detection limits to the suppressor configuration. The three methods are also compatible with conductivity detection. When used in combination with conductivity detection, this compatibility allows simultaneous analysis of bromate, nitrite, and other common ions in drinking water, such as bromide. It was found that the o-dianisidine method achieves μg/l-level detection of nitrite and bromate with a simpler configuration than the potassium iodide–ammonium heptamolybdate method, while the sodium bromide–sodium nitrite method was not sufficiently sensitive for nitrite analysis at the μg/l level.     

Determination of gamma-hydroxybutyric acid in human urine by capillary electrophoresis with indirect UV detection and confirmation with electrospray ionization ion-trap mass spectrometry

γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ.     

Reverse flow injection spectrophotometric determination of iron(III) using norfloxacin

A reversed flow injection colorimetric procedure for determining iron(III) at the μg level was proposed. It is based on the reaction between iron(III) with norfloxacin (NRF) in 0.07 mol l⁻¹ ammonium sulfate solution, resulting in an intense yellow complex with a suitable absorption at 435 nm. Optimum conditions for determining iron(III) were investigated by univariate method. The method involved injection of a 150 μl of 0.04% w/v colorimetric reagent solution into a merged streams of sample and/or standard solution containing iron(III) and 0.07 mol l⁻¹ ammonium sulfate in sulfuric acid (pH 3.5) solution which was then passed through a single bead string reactor. Subsequently the absorbance as peak height was monitored at 435 nm. Beer's law obeyed over the range of 0.2–1.4 μg ml⁻¹ iron(III). The method has been applied to the determination of total iron in water samples digested with HNO₃–H₂O₂ (1:9 v/v). Detection limit (3σ) was 0.01 μg ml⁻¹ the sample through of 86 h⁻¹ and the coefficient of variation of 1.77% (n=12) for 1 μg ml⁻¹ Fe(III) were achieved with the recovery of the spiked Fe(III) of 92.6–99.8%.     

Determination of fenpyroximate in apples by supercritical fluid extraction and packed capillary liquid chromatography with UV detection

A method using off-line supercritical fluid extraction (SFE) and micro liquid chromatography (μLC) with UV detection at 260 nm, was developed for selective determination of fenpyroximate in apple samples. The packed capillary liquid chromatography method utilises 20 μl injection volumes with on-column focusing. A 350×0.32 mm capillary column packed with Kromasil 100-C₁₈ of 5 μm particle size was used with a mobile phase of acetonitrile–10 mM ammonium acetate (85:15, v/v) at a flow of 5 μl/min. A two-step SFE procedure was used to extract fenpyroximate selectively in 2 g apple samples, with Hydromatrix (HMX) added as a water absorbent at a 1:1 (w:w) ratio. Fenpyroximate was extracted at 200 bar and 90°C for 15 min using carbon dioxide at a flow of 2 ml/min, and solvent trapping collection in 10 ml acetonitrile. The volume of the acetonitrile extract was reduced by evaporation and water was added to a final composition of acetonitrile–water (40:60, v/v). The resulting 2.0 ml solution was filtered using a 0.45 μm poly(vinylidene difluoride) syringe filter before μLC analysis. Validation of the method was accomplished with apple samples spiked with fenpyroximate, covering the range of 0.1 to 1.0 μg/kg. The within-day and between-day repeatabilities were in the range 4–18% relative standard deviation. Accuracy, measured as recovery, was found to be approximately 60%. Apple samples from a field treated with fenpyroximate were analysed. None of the samples contained fenpyroximate above the quantification level.     

Spectrophotometric determination of iron and cobalt with Ferrozine and dithizone

Procedures are described whereby iron (1–50 μg) and cobalt (1–25 μg) are determined spectrophotometrically, iron as iron(II) with the disodium salt of 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine (Ferrozine) and cobalt as the cobalt(III) dithizonate complex. The reduction to iron(II) prevents interference of iron(III) in the cobalt determination, and both metals can be determined in the same portion of sample solution. Removal of interference by other metal ions is described.     

Application of colloidal palladium modifier for the determination of As, Sb and Pb in a spiked sea water sample by electrothermal atomic absorption spectrometry

Colloidal palladium was used as a chemical modifier for analysis of complex samples by electrothermal atomic absorption spectrometry. In order to demonstrate high potential of the modifier, optimization of the time–temperature program of the atomizer was limited with only pyrolysis and atomization temperatures. Fixed palladium modifier masses were applied (6 μg for pure analyte solutions and 15 μg for matrix-containing solutions). It was shown that in the presence of colloidal palladium, interference-free determinations of As, Sb and Pb are possible up to at least 450 μg of chloride ion, or 40 μg of sulfate ion (as their sodium salts) in the atomizer. Colloidal palladium was used for the direct determination of As, Sb and Pb in a spiked sea water sample (from Bosphorus channel near Istanbul) by means of the calibration graphs prepared with pure analyte solutions. The detection limits for As, Sb and Pb in a sea water matrix calculated according to 2σ criteria are 5.4, 3.6 and 1.1 ng ml⁻¹, respectively (for sample volume 10 μl). In unspiked sea water, the contents of As, Sb and Pb were found to be below the detection limits. Recoveries of spiked analytes (25 and 50 ng ml⁻¹) were in the region of 98–112% depending on the nature of analyte and the concentration of spike.     

Simultaneous determination of catecholamines by ion chromatography with direct conductivity detection

A simple method for simultaneous determination of three catecholamines using ion chromatography (IC) with direct conductivity detection (CD) based on the ionization of catecholamines in acidic medium without chemical suppression is developed in the present paper. The method could be used for the determination of these catecholamines in pharmaceutical preparations for the purpose of drug quality control. The recovery of catecholamines was more than 97% (n=3) and the relative standard deviation (R.S.D.) (n=11) was less than 2.1%. In a single chromatographic run, norepinephrine (NE), epinephrine (E) and dopamine (DA) can be determined in less than 10 min. The detection limits were found to be 0.001 μg/ml for NE, 0.01 μg/ml for E and DA respectively. Linear ranges were 0.01–50 μg/ml for NE (r²=0.9998), 0.1–50 μg/ml for E (r²=0.9995) and DA (r²=0.9999), respectively.     

Resin bead detection and spectrophotometric determination of oxyphenbutazone with p-dimethylaminocinnamaldehyde: Application to bulk drug and dosage forms

An analytical method for resin bead detection and spectrophotometric determination of oxyphenbutazone with p-dimethylaminocinnamaldehyde as a reagent is described. Acid hydrolysed product of oxyphenbutazone produced a red color product with p-dimethylaminocinnamaldehyde that absorbs maximally at 520 nm. The detection limit is 0.8 μg in resin phase and 4.0 μg in aqueous phase. Beer's law is obeyed in the concentration range of 0.4–4.0 μg/ml of oxyphenbutazone. The method is unaffected by the presence of acetylsalicylic acid, salicylamide, phenylbutazone and number of other excipients but paracetamol gives a positive reaction and novalgin being reductone interferes with the test, both should be removed by extraction with dilute sulfuric acid.     

Analysis of acidic drugs in the effluents of sewage treatment plants using liquid chromatography-electrospray ionization tandem mass spectrometry

Azaspiracid poisoning (AZP) is a new human toxic syndrome that is caused by the consumption of shellfish that have been feeding on harmful marine microalgae. A liquid chromatography–mass spectrometry (LC–MS) method has been developed for the determination of the three most prevalent toxins, azaspiracid (AZA1), 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3) as well as the isomeric hydroxylated analogues, AZA4 and AZA5. Separation of five azaspiracids was achieved on a C₁₈ column (Luna-2, 150×2 mm, 5 μm) with isocratic elution using acetonitrile–water containing trifluoroacetic acid and ammonium acetate as eluent modifiers. Using an electrospray ionisation (ESI) source with an ion-trap mass spectrometer, the spectra showed the protonated molecules, [M+H]⁺, with most major product ions due to the sequential loss of two water molecules. A characteristic fragmentation pathway that was observed in each azaspiracid was due to the cleavage of the A-ring at C₉–C₁₀ for each toxin. It was possible to select unique ion combinations to distinguish between the isomeric azaspiracids, AZA4 and AZA5. Highly sensitive LC–MS³ analytical methods were compared and the detection limits were 5–40 pg on-column. Linear calibrations were obtained for AZA1 in shellfish in the range 0.05–1.00 μg/ml (r²=0.9974) and good reproducibility was observed with a relative standard deviation (%RSD) of 1.8 for 0.9 μg AZA1/ml (n=5). The %RSD values for the minor toxins, AZA4 and AZA5, using LC–MS³ (A-ring fragmentation) were 12.3 and 8.1 (0.02 μg/ml; n=7), respectively. The selectivity of toxin determination was enhanced using LC–MS–MS with high energy WideBand activation.