An innovative nano-sorbent for selective solid-phase extraction and spectrophotometric determination of p-amino benzoic acid in cosmetic products.

OBJECTIVE: A novel nano-sorbent was developed for selective extraction and pre-concentration of p-amino benzoic acid (PABA) prior to determination by spectrophotometry. METHODS: Selective extraction of PABA from aqueous solutions was performed using a solid-phase extraction column packed with 200 mg of nickel-zinc-aluminium layered double hydroxide (Ni-Zn-Al LDH) as a nano-sorbent. Extraction procedure is based on the adsorption of p-amino benzoate ions on the Ni-Zn-Al-nitrate LDH and/or their exchanging with LDH interlayer nitrate ions. After elution of extracted analyte by 2.5 mL of 2 mol L(-1) NaCl solution, its concentration was determined spectrophotometrically at λmax = 268 nm. RESULTS: The spectrophotometry method gave a linear response for PABA within the range of 12.5-425.0 µg L(-1) with a correlation coefficient of 0.9994. In the optimum experimental conditions, the limit of detection and sorption capacity were 3.78 µg L(-1) and 21.25 mg g(-1) , respectively. CONCLUSION: The presented method uses mild separation conditions and is a sensitive, reproducible, simple, low-cost and environment-friendly technique that could be used for the extraction and determination of PABA in various cosmetic samples.

A nano-structured material for reliable speciation of chromium and manganese in drinking waters, surface waters and industrial wastewater effluents.

A simple solid phase extraction system based on the applying the nickel-aluminum layered double hydroxide (Ni-Al LDH) as a nano-sorbent was developed for the speciation analysis of chromium and manganese by flame atomic absorption spectrometry (FAAS). The method is based on the fact that Cr(VI) and Mn(VII) oxyanions could be adsorbed on the Ni-Al(NO(3)(-)) LDH and/or exchanged with LDH interlayer NO(3)(-) ions at pH 6.0, whereas Cr(III) and Mn(II) cations pass through the LDH-packed column without retention. The determinations of total Cr and Mn, and hence indirectly Cr(III) and Mn(II), involve the pre-oxidations of Cr(III) and Mn(II) to Cr(VI) and Mn(VII) with H(2)O(2) and acidic solution of KIO(4), respectively. Several important factors affecting the retention efficiency were investigated and optimized. In the optimum experimental conditions, the limits of detection (3S(b)/m) for Cr(VI) and Mn(VII) were 0.51 and 0.47 ng mL(-1), and the relative standard deviations were 2.5 and 3.2% (C=30.0 ng mL(-1), n=6), respectively. The presented method was validated by the analysis of a certified reference material, and applied to the speciation of Cr and Mn in drinking waters, surface waters and industrial wastewater effluents.

Nickel-aluminum layered double hydroxide as a nanosorbent for selective solid-phase extraction and spectrofluorometric determination of salicylic acid in pharmaceutical and biological samples.

The nickel-aluminum layered double hydroxide (Ni-Al LDH) was synthesized by a simple co-precipitation method and used as a solid-phase extraction (SPE) sorbent for separation and pre-concentration of trace levels of salicylic acid (SA) from aqueous solutions. Extraction of analyte is based on the adsorption of salicylate ions on the Ni-Al (NO(3)(-)) LDH and/or their exchanging with LDH interlayer NO(3)(-) ions. The retained analyte on the LDH was stripped by 3 mol L(-1) NaOH solution and its concentration was subsequently determined spectrofluorometrically at λ(em)=400 nm with excitation at λ(ex)=270 nm. Various parameters affecting the extraction efficiency of SA on the Ni-Al (NO(3)(-)) LDH, such as pH, amount of nano-sorbent, sample loading flow rate, elution conditions, sample volume and matrix effects were investigated. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 0.12 µg L(-1) and 40, respectively. The relative standard deviation (RSD) for six replicate determinations of 10 µg L(-1) SA was 2.3%. The calibration graph using the pre-concentration system was linear in the range of 0.3-45 µg L(-1) with a correlation coefficient of 0.9985. The optimized method was successfully applied to the determination of SA in blood serum, willow leaf and aspirin tablet.

Layered double hydroxides: a novel nano-sorbent for solid-phase extraction.

The nickel-aluminum layered double hydroxide (Ni-Al LDH) was synthesized by a simple co-precipitation method with controlled pH and followed by hydrothermal treatment. The obtained nano-structured inorganic material was employed, for the first time, as a new solid-phase extraction (SPE) sorbent for the extraction and pre-concentration of trace levels of fluoride ions from aqueous solutions. An indirect method was used for monitoring of extracted fluoride ions. The method is based on the quenching effect of extracted fluoride ions upon the fluorescence intensity of Al-oxine complex via the forming of AlF(6)(3-), which was determined spectrofluorometrically at λ(em)=510 nm with excitation at λ(ex)=404 nm. The effect of several parameters such as type of interlayer anion in Ni-Al LDH structure, pH, sample flow rate, elution conditions, amount of nano-sorbent, sample volume and co-existing ions on the extraction efficiency of the analyte were investigated. The results showed that fluoride ions could be retained on the Ni-Al (NO(3)(-)) LDH at pH 6.0 and stripped by 1.2 mL of 3.0 mol L(-1) NaOH. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 9.0 ng mL(-1) and 50, respectively. The optimized method was successfully applied to the determination of fluoride concentration in various water samples. The results obtained from the proposed method were successfully compared with those provided by standard SPADNS method.

Combination of ionic liquid-based dispersive liquid-liquid micro-extraction with stopped-flow spectrofluorometry for the pre-concentration and determination of aluminum in natural waters, fruit juice and food samples.

In this research, we combined ionic liquid-based dispersive liquid-liquid micro-extraction (IL-based DLLME) with stopped-flow spectrofluorometry (SFS) to evaluate the concentration of aluminum in different real samples at trace level. 1-Hexylpyridinium hexafluorophosphate [Hpy][PF(6)] ionic liquid and 8-hydroxyquinoline (oxine), which forms a highly fluorescent complex with Al(3+), were chosen as the extraction solvent and chelating agent, respectively. The hydrophobic Al-oxine complex was extracted into the [Hpy][PF(6)] and separated from the aqueous phase. Then, the concentration of the enriched aluminum in the sediment phase was determined by SFS. Some effective parameters that influence the SFS signals and the micro-extraction efficiency, such as the suction and sending time, the concentration of the chelating agent, pH, the amount of the ionic liquid, the type of disperser solvent and diluting agent, ionic strength, extraction time, equilibration temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 0.05microgL(-1) and 100, respectively. The relative standard deviation (RSD) for six replicate determinations of 6microgL(-1) Al was 1.7%. The calibration graph using the pre-concentration system was linear in the range of 0.06-15microgL(-1) with a correlation coefficient of 0.9989. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of aluminum in several water, fruit juice and food samples.

A novel microextraction technique based on 1-hexylpyridinium hexafluorophosphate ionic liquid for the preconcentration of zinc in water and milk samples.

A simple dispersive liquid-liquid microextraction methodology based on the application of 1-hexylpyridinium hexafluorophosphate [HPy][PF6] ionic liquid (IL) as an extractant solvent was proposed for the preconcentration of trace levels of zinc as a prior step to determination by flame atomic absorption spectrometry (FAAS). Zinc was complexed with 8-hydroxyquinoline (oxine) and extracted into ionic liquid. Some effective factors that influence the microextraction efficiency such as pH, oxine concentration, amount of IL, ionic strength, temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and the enhancement factor were 0.22 microg L(-1) and 71, respectively. The relative standard deviation (RSD) for six replicate determinations of 13 microg L(-1) Zn was 1.92%. In order to validate the developed method, a certified reference material (NIST SRM 1549) was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the trace determination of zinc in water and milk samples.