Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.     

Colorimetric Determination of Propofol in Bulk form,Dosage Form and Biological Fluids

ABSTRACT

Propofol is coupled with 2, 6-dichloroquinone-4-chlorimide (DCQ) in a reaction buffered at pH 9.6 to give a colored product having an analytically useful maximum at 635 nm. The factors affecting the color generation were optimized and incorporated in the procedure. The reacted propofol has a molar absorptivity of 3.9 × 10^?4 L mol^?1 cm^?1, and Beer's law is obeyed for concentrations 1-5 μg ml^?1 with detection limit 0.25 μg ml^?1. The method was found applicable to biological fluids (plasma and urine) spiked with propofol at concentration levels 1-5 μg ml^?1 for plasma and 1-5 μg 0.5 ml^?1 urine (less sensitivity is obtained with urine volumes above 0.5 ml) with detection limits 0.28 μg ml^?1 for plasma and 0.4 μg 0.5 ml^?1 urine. The average recovery for the commercial preparation (1% w/v propofol emulsion intravenous injection for infusion) was 99.54% with an RSD of 1.05%. The method was validated by an adopted HPLC method. The results obtained by the HPLC method for the commercial preparation were statistically compared with the proposed method and evaluated at the 95% confidence limits.     

Enhancement of ruthenium determination by inductively coupled plasma/atomic emission spectrometry by addition of periodic acid

A sensitive method for the determination of ruthenium involving the formation of volatile species in solution and subsequent nebulization for inductively coupled plasma/atomic emission spectrometry is proposed. The sensitivity of the determination of ruthenium was increased by a factor of 70 with the addition of 1×10^?2 M periodic acid as an oxidizing agent. The detection limit was 5 ng ml^?1 of ruthenium and the calibration was linear over the range 0.01–0.5 μg ml^?1 of ruthenium. Serious interferences were not found except from reducing agents.     

Sensitivity enhancement by palladium addition in the electrothermal atomic absorption spectrometry of mercury

In graphite-furnace atomic absorption spectrometry of mercury, addition of 50 μg ml^?1 palladium improves the peak height for 5 μg Hg ml^?1 50 times. Further addition of 20 μg ml^?1 platinum doubles the enhanced peak height. The effect is due to amalgam formation. The best sensitivity is 0.3 ng (1% absorption) and the detection limit is 0.1 ng. The method allows higher ashing temperatures than for solutions without noble metal addition and can be applied to solutions containing substantial amount of organic matter.     

Adsorptive stripping voltammetric determination of ofloxacin

The fluoroquinolone antibacterial agent ofloxacin was studied by adsorptive stripping voltammetry. Controlled interfecial accumulation of ofloxacin on a static mercury drop electrode in the hanging mercury drop mode provides high sensitivity. The linear concentration range was 0.079–197.5 μg ml^?1 when using a 60-s preconcentration at ?1 V vs. Ag/AgCl in Britton-Robinson buffer of pH 6.00. The detection limit of ofloxacin was 1 ng ml^?1. The precision is excellent with a relative standard deviation of ca. 0.75% at a concentration of 0.848 μg ml^?1.     

Interactions of Nile Blue Sulphate with Nucleic Acids as Studied by Resonance Light-Scattering Measurements and Determination of Nucleic Acids at Nanogram Levels

ABSTRACT

The interactions of nile blue sulphate (NBS) with nucleic acids, including calf thymus DNA, fish sperm DNA and yeast RNA, were characterized with resonance light-scattering (RLS) measurements by using a common spectrofluorometer. Accordingly a method for the determination of nucleic acids at nanogram levels was established. At pH's of 7.20～7.60 and ionic strengths lower than 0.012, the interactions of NBS with nucleic acids result in three characteristic RLS peaks at 293.4 nm, 349.4 nm and 560.4 nm. Mechanism study shows that these peaks are ascribed to the long range assembly of NBS on the molecular surface of nucleic acids, which depends on pH, ionic strength and the stranded structure of nucleic acids. A Scatchard plot was constructed by using the RLS data, yielding the assembly number and assembly constant being 6.4 and 7.13x10⁶ mol^?1 1 for NBS assembly on the molecular surface of calf thymus DNA. The same parameters are 6.6 and 4.58x10⁶ mol^?1 1 for the assembly on that of fish sperm DNA, 3.9 and 1.67x10⁶ mol^?1 1 on that of yeast RNA, respectively. Linear relationships were found between the enhanced RLS intensity at 293.4 nm and nucleic acid concentration. If 1.2x10^?5 mol I^?1 NBS was employed, 0～0.80 μg ml^?1 calf thymus DNA and fish sperm DNA, 0.20～0.60 μg ml^?1 yeast RNA can be determined with the determination limits being 3.2 ng ml^?1 for calf thymus DNA, 11.5 ng ml^?1 for fish sperm DNA and 38.3 ng ml^?1 for yeast RNA, respectively. Four synthetic samples were determined with satisfaction.     

A Fluorosensor with Immobilized Cyclodextrin As A Substrate

Abstract

A flow-through optosensor for phenylalanine and tyrosine is described in this paper. The sensor is developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The analytical performance characteristics of the proposed sensor for analysis of very low levels of phenylalanine and tyrosine were as follows: the detection limits for phenylalanine and tyrosine were 0.20 μg ml^?1 and 8.9 ng ml^?1, respectively. The observed relative standard deviations were 1.03% for 50 μg ml^?1 of phenylalanine (n = 7) and 3.6% for 0.1 μg ml^?1 of tyrosine (n = 7), respectively.     

Direct determination of biacetyl in fats by sensitized room temperature phosphorescence

A direct method for the determination of biacetyl in butter and margarine by sensitized room temperature phosphorescence (SRTP) is described. After dissolution of the sample in hexane, biacetyl is isolated by distillation, and its native phosphorescence is sensitized by a non-polar linear furocoumarin, 4′5′-dihydro-3-carbethoxypsoralen. The limit of detection is 0.05 ng ml^?1 biacetyl, with a linear response from 1 × 10^?4 to 1 μg ml^?1 (r = 0.999). The RSD is 3.5% at 100 ng ml^?1.     

Sensitivity enhancement for inductively-coupled plasma atomic emission spectrometry of cadmium by suction-flow on-line ion-exchange preconcentration

A column of iminodiacetate chelating resin is used to preconcentrate cadmium by a factor of 25-fold for a 5-ml sample. The sampling rate was 25 h^?1, and the detection limit 0.05 ng Cd²⁺ ml^?1. The r.s.d. for 0.1 μg Cd²⁺ ml^?1 was 2.2% (n = 10). This technique was applied to the determination of cadmium in certified biological reference materials and waste-water samples.     

Square‐Wave Adsorptive‐Stripping Voltammetric Detection in the Quality Control of Fluoxetine

ABSTRACT

A simple and sensitive extraction-spectrophotometric method for the determination of barium and potassium is reported. The 18C6-Barium-Orange II (18C6-Ba-(OR II)₂) and 18C6-Potassium-Orange II (18C6-K-OR II) ternary complexes are quantitatively extracted into dichloromethane and their absorbances are measured at 483 nm. Linear calibration graphs were obtained over the barium concentration range of 0.1-5 μg ml^?1 and potassium concentration range of 1-8 μg ml^?1. The relative standard deviation for 2.0 μg ml^?1 barium and pottasium are, respectively, 4.16% and 3.60%. The interfering effect of a large number of diverse ions on the determination of barium and potassium was studied. The method was applied to a synthetic sample with natural matrix effects of tap water and the results showed high potential of the recommended method for the determination of Ba and K in water samples.     

Low-Temperature Phosphorescence Analysis of Mebendazole and Related Imidazoles

Abstract

Native low-temperature phosphorescence of mebendazole and flubendazole in ethanol is used for the determination of these imidazoles in anthelmintic preparations with wavelength maxima and detection limits of λ_EXC = 322 nm, λ_EM = 454 nm; 10 ng ml^?1 and λ_EXC = 325 nm, = λ_EM = 455 nm; 5 ng ml^?1, respectively, with linear response up to 8 μg ml^?1 and 9 μg ml^?1, respectively. The structural basis of these phenomena is discussed for both compounds and for related imidazoles and benzimidazoles. Apart from good sensitivity and excellent specificity offered by the technique, the use of cryogenic equipment (liquid nitrogen, special cuvettes, expensive dewar cells) implies some disadvantages for routine analyses.     

Cyclodextrin Enhanced Spectrofluorimetric Determination of Melatonin in Pharmaceuticals and Urine

ABSTRACT

Melatonin forms a 1:1 inclusion complex with methyl-β-cyclodextrin with an association constant of 139 ? 30 M^?1 at 20 °C. The effect of several cyclodextrins and derivatives on the fluorescence spectra of melatonin was studied with a great increase of fluorescence signal when methyl-β-cyclodextrin was employed. Optimal conditions of the method were: [methyl-β-cyclodextrin] = 0.01 M and temperature 20 °C; the pH does not affect the luminescence emission. The linear dynamic range (LDR) was 50-3000 ng ml^?1 and a limit of detection of 10 ng ml^?1 of melatonin was obtained with a relative standard deviation (RSD) of 0.77% (at 0.3 μg ml^?1 level). This simple method was satisfactorily applied to the determination of melatonin in pharmaceutical preparations and urine.     

Spectrophotometric Studies on the Proton Transfer from the Protonated DNA to 5,10,15,20-Tetrakis[4-(trimethyammonio)-phenyl]porphine

Abstract

The interaction of nucleic acids with 5, 10, 15, 20-tetrakis[4-trimethy-ammonio)phenyl]porpine (TAPP) were investigated on the basis of a mechanistic discussion, and a spectrophotometric method for DNAs was accordingly proposed in the present paper. Depending on the acidity of the solution, TAPP can interact with nucleic acids, producing different absorption features. When the pH of the solution is higher than 6.39, TAPP can interact with both DNAs and RNA, giving a new absorption band at 420.3 nm. If the pH is lower than 6.39, however, the interactions with DNAs (but not RNA) can give an absorption band centered at 436.3 nm. It was found that the absorption band at 436.3 nm originates from the proton transfer from the protonated double-stranded structure of DNA to TAPP. At optimal conditions, the absorbance at 436.3 nm is in proportion to the concentration of the DNAs. Calibration curves were linear in the range of 0±3.0 μg.ml^?1 for calf thymus and 0±3.2 μg.ml^?1 for fish sperm DNA. No interference of 4-fold of RNA was found for the determination of DNAs. The limits of determination (3[sgrave]) were 34.6 ng.ml^?1 for calf thymus DNA and 33.2 ng.ml^?1 for fish sperm DNA, respectively. Four synthetic samples were determined with satisfaction.     

Simultaneous Determination of Valsartan and Hydrochlorothiazide in Tablets by High-Performance Liquid Chromatography

ABSTRACT

A method for the simultaneous determination of valsartan and hydrochlorothiazide in tablets is described. The procedure, based on the use of reversed-phase high-performance liquid chromatography, is linear in the concentration range 5.0-10.0 μg ml^?1 for valsartan and 0.5-2.0 μg ml^?1 for hydrochlorothiazide, is simple and rapid and allows accurate and precise results. The limit of detection was 1.0 μg ml^?1 for valsartan and 0.05 μg ml^?1 for hydrochlorothiazide.     

Determination of technetium based on quenching of the fluorescence of some organic compounds,with application to vegetation

Technetium is an effective quencher of the fluorescence produced by 2,5-diphenyloxazole (PPO), 1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (POPOP) and 2,2′-pyridil [1,2-dioxo-1,2-bis(2-pyridyl)ethane]. Spectrofluorimetric procedures for 0.01–12 μg Tc ml^?1 with PPO and 0.1–12 μg ml^?1 with 2,2′-pyridil, and a spectrophotometric method for 1–15 μg ml^?1 are described. The distribution of technetium in vegetation is measured by applying the PPO method.     

Fluorescent Complexes of Nucleic Acids/8-Hydroxyquinoline/Lanthanum(III) and the Fluorometry of Nucleic Acids

Abstract

The ternary fluorescent complexes of nucleic acids/8-hydroxyquinoline/ lanthanum (III) were studied. Nucleic acids in the study involve natured and thermally denatured calf thymus DNA, fish sperm DNA and yeast RNA. In the range of pH 8.0–8.4 (controlled by NH₃-NH₄Cl buffer) ternary fluorescent complexes are formed which emit at 485.0 nm for calf thymus DNA and at 480.0 nm for yeast RNA (when excited at 267.0 nm) and emits at 483.0 nm for fish sperm DNA when excited at 265.0 nm. Based on the fluorescence reactions sensitive fluorometric methods for nucleic acids were proposed. Using optimal conditions, the calibration curves were linear in the range of 0.4–3.6 μg˙ml^?1 for calf thymus DNA, 0.4–4.0 μg-ml^?1 for fish sperm DNA and 0.4–4.0 μg˙ml^?1 for yeast RNA, respectively. The limits of determination (3σ) were 0.076 μg˙ml^?1 for calf thymus DNA, 0.068 μg˙ml^?1 for fish sperm DNA and 0.329 μg˙ml^?1 for yeast RNA, respectively. Five synthetic samples were determined with satisfaction.

     

Spectrophotometric determination of trace amounts of beryllium using 1,8-dihydroxyanthrone as a new chromogenic reagent

A simple, rapid, and sensitive spectrophotometric method for the trace level determination of beryllium based on the formation of a 1:2 complex with anthralin (1,8-dihydroxyanthrone) as a new reagent is developed. A spectrophotometric method was used to determine the acidity constant and stepwise proton dissociation of the reagent. The experimental conditions for determining beryllium including the influences of pH, reagent concentration and time were evaluated and optimized. Under the optimum experimental conditions, the molar absorptivity of the complex is 0.47 × 10⁴ l mol^?1 cm^?1 at 545 nm. Calibration graph was linear in the range of 0.04–1.04 μg ml^?1 with a detection limit of 0.012 μg ml^?1 and a %RSD of 0.43%, for 5 replicate determinations at 0.48 μg ml^?1 of Be(II). The interferring effect of some cations and anions was also studied. The method was applied for the determination of beryllium in beryl, silicate rock and alloys. Ethylenediaminetetraacetic acid (EDTA) was used for masking interfering ions.     

The determination of uranium in aqueous samples by means of a pulsed-source fluorescence spectrometer

Luminescence from aqueous uranyl ions is examined by means of a fluorescence spectrometer with a pulsed xenon light source. Background fluorescence is reduced by using time-based discrimination of the uranyl emission, but interference can still occur from quenchers such as iron(III). Such interferences are reduced by extraction of the uranyl ion into hexane containing trin-n-butyl phosphate, with back-extraction into dilute phosphoric acid before measurement. A detection limit of 5 ng ml^?1 is found with a linear calibration range of 0–10 μg ml^?1.     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

Indirect determination of fluoride in waters with lanthanum alizarin complexone and inductively-coupled plasma emission spectrometry

Fluoride is determined indirectly by measurement of the La II 333.75-nm line in the lanthanum/alizarin complexone/fluoride complex. The ternary complex is extracted into hexanol containing N,N-diethylaniline and the extract is introduced directly into the plasma. Related to water samples, the detection limit (3σ, concentration factor 5) is 0.59 ng ml^?1 fluoride, calibration is linear up to 1.2 μg ml^?1 and the relative standard deviation for 0.04 μg ml^?1 is 2.6%. Alkali, alkali elements and most anions do not interfere. The method is applied in the analysis of river water, coastal seawater and drinking water.