A comparative study of diffusion samplers for the determination of hexavalent chromium by sequential injection spectrophotometry

Carbon nanodots as a fluorescence sensor for rapid and sensitive detection of Cr(VI) and their multifunctional applications

In this work, carbon nanodots (CDs) were prepared via a green and convenient microwave assisted pyrolysis of ionic liquids (ILs) and ethylenediamine. It was found that the synthesized IL-based CDs (ILCDs) exhibited a superior selective sensitivity for Cr(VI). Photoluminescence (PL) properties of the ILCDs were applied to determine the concentration of Cr(VI), which showed a wide linear range and a low detection limit. We also received promising results by using the ILCDs for Cr(VI) detection in real samples. Moreover, the synthesized ILCDs can also work as a PL nanosensors to determine temperature and pH value in solution.

A novel fluorescent distinguished probe for Cr (VI) in aqueous solution

Salicylaldehyde rhodamine B hydrazone (SRBH) was developed as a new spectrofluorimetric probe for the selective and sensitive detection of CrO(4)(2-) in acidic conditions. The proposed method was based on the special oxidation reaction between non-fluorescent SRBH by potassium dichromate to produce a highly fluorescent rhodamine B, as a product. Under the optimum conditions described, the fluorescence enhancement at 591 nm was good linearly related to the concentration of CrO(4)(2-) from 1.0 x 10(-8) to 3.0 x 10(-7)M (0.42-12.6 ng mL(-1)) with a correlation coefficient of R(2)=0.9989 (n=10) and a detection limit of 1.5 x 10(-9)M (0.063 ng mL(-1)). The relative standard deviation (R.S.D.) was 2.0% (n=6). The proposed method was also successfully applied to the determination of chromium (VI) in drinking water, river water and synthetic samples.

An organic-reagent-free method for determination of chromium(VI) in steel alloys, sewage sludge and wastewater

One of the active areas of green chemistry research and development is in the development of new analytical methods and techniques that reduce and eliminate the use and generation of hazardous substances. In this work, a rapid and organic-reagent-free method was developed for the determination of chromium(VI) by sequential injection analysis (SIA). The method was based on the detection of a blue unstable intermediate compound resulting from the reaction of Cr(VI) with hydrogen peroxide (H(2)O(2)) in acidic medium. H(2)O(2) and its reaction products were environmentally friendly, and chromogenic reagents and organic solvents were not used in the proposed method. Different SIA parameters have been optimized and used to obtain the analytical figures of merit. Under the optimum experimental conditions, the linear range for Cr(VI) was 0.5-100.0 microg mL(-1), and the detection limit was 0.16 microg mL(-1). The sample throughput was 80 h(-1), and the total volume of only 145 microL was consumed in each determination of Cr(VI). The method was applied for the determination of Cr(VI) in seven real samples, including alloy steel, sewage sludge and wastewater samples, and the results were compared with those obtained by atomic absorption spectrometry as well as with the certified value of Cr(VI) in standard reference material. Statistical analysis revealed that there was no significant difference at 95% confidence level.

Rapid determination of chromium(VI) in electroplating waste water by use of a spectrophotometric flow injection system

A new rapid and sensitive FI method is reported for spectrophotometric determination of trace chromium(VI) in electroplating waste water. The method is based on the reaction of Cr(VI) with sodium diphenylamine sulfonate (DPH) in acidic medium to form a purple complex (lambda(max) = 550 nm). Under the optimized conditions, the calibration curve is linear in the range 0.04-3.8 microg ml(-1) at a sampling rate of 30 h(-1). The detection limit of the method is 0.0217 microg ml(-1), and the relative standard deviation is 1.1% for eight determinations of 2 microg ml(-1) Cr(VI). The proposed method was applied to the determination of chromium in electroplating waste water with satisfactory results.

Sensitive and selective spectrofluorimetric determination of chromium(VI) in water by fluorescence enhancement

A new fluorogenic method for the selective and sensitive determination of chromium(VI) in acidic water using rhodamine B hydrazide was developed. This method was based on the oxidation of non-fluorescent rhodamine B hydrazide by potassium dichromate in acidic aqueous conditions to give rhodamine B, which was highly fluorescent, as a product. With the optimum condition described, the fluorescence enhancement at 585 nm was linearly related to the concentration of chromium(VI) in the range of 5.0 x 10(-8) to 2.0 x 10(-6) mol L(-1) (2.60-104 ng mL(-1)) with a correlation coefficient of R(2)=0.9993 (n=18) and a detection limit of 5.5 x 10(-9) mol L(-1) (0.29 ng mL(-1)). The R.S.D. was 2.2% (n=5). The proposed method was also applied to the determination of chromium(VI) in drinking water, river water and synthetic samples.

Selective fluorescence determination of chromium (VI) in water samples with terbium composite nanoparticles

The strong fluorescence Tb/acetyl acetone (acac)/Poly (Acrylamide) (PAM) composite nanoparticles have been prepared under ultrasonic radiation. The nanoparticles were water-soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. Based on the fluorescence quenching of Tb/acac/PAM by Cr (VI), a method for the selective determination of Cr (VI), without separation of Cr (III) in water, was developed. The reaction condition between Cr (VI) and Tb/acac/PAM were investigated in detail. Under optimal experimental conditions, the linear calibration curve was obtained over the concentration range of 5-600 ng mL(-1) with a correlation coefficient of 0.9939. The corresponding detection limit is 0.8 ng mL(-1) and the relative standard deviation is 1.5% for 0.05 microg mL(-1) (n=7). The proposed method has been applied to the selective quantification of Cr (VI) in synthetic samples and waste-water samples with the satisfactory results. The assay is characterized by short reaction time, very few interference, stable fluorescence signals, simple instrument and simplicity.

A remote in situ monitor based on continuous flow analysis for the quantitation of sub-micromolar levels of hexavalent chromium in natural waters

We describe the design, optimization, and application of a small, lightweight, deployable monitoring instrument for accurately measuring parts-per-billion levels of hexavalent Cr in surface waters at hourly intervals. The monitor quantifies Cr(vi) using a standard molecular absorbance spectroscopic method, i.e. by formation of a complex with 1,5-diphenylcarbazide (DPC). The continuous flow analysis (CFA) design uses narrow conduits (0.90 mm) that are hot-forged onto poly(methyl methacrylate) ('Plexiglas') plates based on the method of Jannasch et al.(Anal. Chem., 1994, 66, 3352). The sample stream is drawn through the manifold at 25 microl min(-1) using a mini-peristaltic pump; osmotic pumps (10 microl h(-1)) are used to continuously inject reagent (2.0 mM DPC, 0.60 M HNO(3), 5.0% w/v acetone, and 0.10% w/v Brij-35) and to periodically introduce quality control standards and a cleaning solution (0.50 M HNO(3)). The 'Z-type' optical cell uses a liquid-core waveguide (10 mm) to collimate the light-emitting diode source beam (lambda(max) 574 nm) to a broadband photodiode detector. Figures of merit are: 7 min cycle time, response within 28 min and clear-down within 31 min, low waste generation (<40 ml d(-1)), detection limit (3sigma) of 48.4 microg l(-1) as Cr(vi) or 0.411 microM as chromic acid, 1.54% relative standard deviation at 100 microg l(-1), and selectivity for dissolved Cr(vi) in authentic surface water samples containing moderate levels (>0.21% w/v) of total particulate matter. Using a test chamber containing Milwaukee Harbor water that was periodically fortified with Cr(vi) standards, continuous testing over a 15 day period (354 h) yielded results that were in excellent agreement (<5% variation) with measurements made using an ICP-MS reference method. Drift in the calibration model over the test period was 1.23% and the variation in a 0.50 mg l(-1) Cr(vi) standard was 3.8%(n= 11). Known interferences to the DPC chemistry (Mo, V, and Hg at >5 mg l(-1)) were undetected in the harbor water by ICP-MS.

Passive sampling and/or extraction techniques in environmental analysis: a review

The current state-of-the-art of passive sampling and/or extraction methods for long-term monitoring of pollutants in different environmental compartments is discussed in this review. Passive dosimeters that have been successfully used to monitor organic and inorganic contaminants in air, water, sediments, and soil are presented. The application of new approaches to the determination of pollutants at the sampling stage is discussed. The main milestones in the development of passive techniques for sampling and/or extraction of analytes, and in biomonitors used in environmental analysis, are summarized in this review. Passive samplers and biomonitors are compared.