Search results for "Chemical analysis."

Removal of hexavalent chromium from wastewaters by bone charcoal

1999

The adsorption of hexavalent chromium onto bone charcoal was studied as a function of time, amount of charcoal, pH, concentration of chromium and sample volume. The cross interference with other elements was also investigated. Tests were carried out with solutions of chromium(VI) at concentrations between 5 and 25 mg · L–1. Chromium removal efficiencies higher than 90% were achieved at pH = 1 using 2 g of bone charcoal and a stirring time in the order of 30 min. Acid and alkaline pretreatments of bone charcoal did not improve the sorption capacity of bone charcoal against Cr(VI). The presence of other ions had practically no influence on the chromium removal. The presence of a matrix of tan…

A multiresidue analytical method for trace level determination of antibiotics and antiretroviral drugs in wastewater and surface water using SPE-LC-M…

2016

An analytical method for simultaneous determination of seven commonly used antibiotics and three antiretrovirals in surface water and urban wastewater at the ng L−1 level has been developed. The method involves concentration and clean-up by solid phase extraction (SPE) followed by identification and quantification by liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS). The use of matrix-matched calibration curves constructed by spiking surface water was evaluated for quantification and compared with the internal standard method using isotopically labelled compounds. The method gave absolute recoveries of 41–116% with most of the compounds having recoveries >50%. The LOQs ranged fr…

Some observations on the use of matrix modifiers in the determination of aluminum by electrothermal atomic absorption spectrophotometry

1989

Abstract Some evidence demonstrating that the use of matrix modifiers is necessary to obtain good calibration lines in the determination of aluminum by graphite furnace atomic absorption spectrophotometry is provided. It was found that the most sensitive results were obtained when Mg(NO 3 ) 2 was used instead of NH 4 H 2 PO 4 .

Erratum

2014

Stability of Cannabinoids in Hair Samples Exposed to Sunlight

2000

It has been well recognized that hashish and marihuana lose potency during storage because of a decrease in the content of tetrahydrocannabinol (THC), which is the major psychoactive constituent of cannabis (1). The effect of oxygen on stored plant and resin materials or solutions of pure cannabinoids seems much less significant than that of higher temperatures (≥37 °C) or light (2)(3)(4)(5)(6)(7). A few data are available on the stability of THC and major metabolites in blood (8)(9)(10)(11). However, the stability of cannabinoids in the hair shaft has not been addressed, although scalp hair represents one of the most exposed parts of the body. Therefore, a study was performed to elucidate …

High-performance liquid chromatographic determination of diuretics in urine by micellar liquid chromatography.

1992

The use of micellar liquid chromatography for the determination of diuretics in urine by direct injection of the sample into the chromatographic system is discussed. The retention of the urine matrix at the beginning of the chromatograms was observed for different sodium dodecyl sulphate (SDS) mobile phases. The eluent strengths of a hybrid SDS-methanol micellar mobile phase for several diuretics were compared and related to the stationary phase/water partition coefficient with a purely micellar mobile phase. The urine band was appreciably narrower with a mobile phase of 0.05 M SDS-5% methanol (v/v) at 50 degrees C (pH 6.9). With this mobile phase the determination of bendroflumethiazide an…

UV filters: From sunscreens to human body and the environment

2007

Recognition of the harmful effects of ultraviolet (UV) radiation on the skin has triggered development of organic chemicals (commonly referred as UV filters) that can absorb UV radiation and attenuate the negative effects of sunlight exposure. Depending on the properties and the intended degree of protection, a wide array of combinations is being marketed as delivering protection against most kinds of UV-induced skin damage. However, some UV filters have dermatological implications, so maximum applicable concentrations have been established. To monitor to what extent commercial products comply with the mandatory limits, several analytical methods have been used for their determination in co…

Selective Laser Sintering of Metal-Organic Frameworks: Production of Highly Porous Filters by 3D Printing onto a Polymeric Matrix.

2019

Metal‐organic frameworks (MOFs) have raised a lot of interest, especially as adsorbing materials, because of their unique and well‐defined pore structures. One of the main challenges in the utilization of MOFs is their crystalline and powdery nature, which makes their use inconvenient in practice. Three‐dimensional printing has been suggested as a potential solution to overcome this problem. We used selective laser sintering (SLS) to print highly porous flow‐through filters containing the MOF copper(II) benzene‐1,3,5‐tricarboxylate (HKUST‐1). These filters were printed simply by mixing HKUST‐1 with an easily printable nylon‐12 polymer matrix. By using the SLS, powdery particles were fused t…