Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm^− 2. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg^− 1 B, 3.0 mg kg^− 1 Cu, 3.6 mg kg^− 1 Fe, 1.8 mg kg^− 1 Mn and 1.2 mg kg^− 1 Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition.     

2-D analysis of Ge implanted SiO2 surfaces by laser-induced breakdown spectroscopy

2-D elemental distribution of Ge in silicon oxide substrates with differing implantation doses of between 3 × 10¹⁶ cm^− 2 and 1.5 × 10¹⁷ cm^− 2 has been investigated by Laser-Induced Breakdown Spectroscopy (LIBS). Spectral emission intensity has been optimized with respect to time, crater size, ablation depth and laser energy. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive X-Ray Spectroscopy (EDX) have been utilized to obtain crater depth, morphology and elemental composition of the sample material, respectively. LIBS spectral data revealed the possibility of performing 2-D distribution analysis of Ge atoms in silicon oxide substrate. EDX analysis results confirmed that LIBS is capable to detect Ge atoms at concentrations lower than 0.2% (atomic). LIBS as a fast semi-quantitative analysis method with 50 µm lateral and 800 nm depth resolution has been evaluated. Results illustrate the potential use of LIBS for rapid, on-line assessment of the quality of advanced technology materials during the manufacturing process.     

Real time and in situ determination of lead in road sediments using a man-portable laser-induced breakdown spectroscopy analyzer

In situ, real time levels of lead in road sediments have been measured using a man-portable laser-induced breakdown spectroscopy analyzer. The instrument consists of a backpack and a probe housing a Q-switched Nd:YAG laser head delivering 50 mJ per pulse at 1064 nm. Plasma emission was collected and transmitted via fiber optic to a compact cross Czerny-Turner spectrometer equipped with a linear CCD array allocated in the backpack together with a personal computer. The limit of detection (LOD) for lead and the precision measured in the laboratory were 190 μg g⁻¹ (calculated by the 3σ method) and 9% R.S.D. (relative standard deviation), respectively. During the field campaign, averaged Pb concentration in the sediments were ranging from 480 μg g⁻¹ to 660 μg g⁻¹ depending on the inspected area, i.e. the entrance, the central part and the exit of the tunnel. These results were compared with those obtained with flame-atomic absorption spectrometry (flame-AAS). The relative error, expressed as [100(LIBS result − flame AAS result)/(LIBS result)], was approximately 14%.     

Assessment of statistical uncertainty in the quantitative analysis of solid samples in motion using laser-induced breakdown spectroscopy

Statistical uncertainty in the quantitative analysis of solid samples in motion by laser-induced breakdown spectroscopy (LIBS) has been assessed. For this purpose, a LIBS demonstrator was designed and constructed in our laboratory. The LIBS system consisted of a laboratory-scale conveyor belt, a compact optical module and a Nd:YAG laser operating at 532 nm. The speed of the conveyor belt was variable and could be adjusted up to a maximum speed of 2 m s^− 1. Statistical uncertainty in the analytical measurements was estimated in terms of precision (reproducibility and repeatability) and accuracy. The results obtained by LIBS on shredded scrap samples under real conditions have demonstrated that the analytical precision and accuracy of LIBS is dependent on the sample geometry, position on the conveyor belt and surface cleanliness. Flat, relatively clean scrap samples exhibited acceptable reproducibility and repeatability; by contrast, samples with an irregular shape or a dirty surface exhibited a poor relative standard deviation.     

Determination of total arsenic in seawater by hydride generation atomic fluorescence spectrometry

In this work, the determination of total As in seawater by hydride generation atomic fluorescence spectrometry was studied. The influence of the chemical, flow and instrumental parameters were investigated and optimized. The pre-reduction of As(V) to As(III) was performed using KI plus ascorbic acid in 3.5 mol L^− 1 HCl medium. No multiplicative interference was present and external aqueous calibration could be used. The limit of detection was 36 ng L^− 1, while the repeatability was 2% (n = 10), at a 500 ng L^− 1 concentration level. The sample throughput was 15 h^− 1 if triplicate measurements were made. The accuracy was assessed by the analysis of a seawater certified reference material and excellent agreement between the obtained and certified values was verified. The procedure was used for the analysis of seawater offshore samples collected at the Brazilian coast and results ranging from 860 to 1200 ng L^− 1 were found.     

Sensitive determination of ultra-trace nitric oxide in blood using derivatization-polymer monolith microextraction coupled with reversed-phase high-performance liquid chromatography

Nitric oxide (NO) plays a very important role in human blood system. In this work, a novel approach has been developed for the quantitation of ultra-trace NO derivatized with 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s- indacene (DAMBO) using a polymer monolith microextraction (PMME) with a poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith in conjunction with high-performance liquid chromatography (HPLC). Both derivatization and PMME conditions have been optimized in detail. The detection limit of derivatized NO was 2 × 10⁻¹² mol L⁻¹ (signal to noise = 3) and linear range was 9 × 10⁻¹¹-4.5 × 10⁻⁸ mol L⁻¹. The proposed DAMBO-based derivatization-PMME-HPLC-fluorescence detection method has been successfully applied for the determination of NO in 10 μL blood samples of healthy persons and patients suffering from ischemic cardio-cerebrovascular diseases with recoveries varying from 87.40 to 91.60%.     

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry

It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K, Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. In this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. The particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. The pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25 J cm⁻²). The plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 μs, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 μm. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity.     

A renewable copper electrode as an amperometric flow detector for nitrate determination in mineral water and soft drink samples

A novel approach was developed for nitrate analysis in a FIA configuration with amperometric detection (E = −0.48 V). Sensitive and reproducible current measurements were achieved by using a copper electrode activated with a controlled potential protocol. The response of the FIA amperometric method was linear over the range from 0.1 to 2.5 mmol L⁻¹ nitrate with a detection limit of 4.2 μmol L⁻¹ (S/N = 3). The repeatability of measurements was determined as 4.7% (n = 9) at the best conditions (flow rate: 3.0 mL min⁻¹, sample volume: 150 μL and nitrate concentration: 0.5 mmol L⁻¹) with a sampling rate of 60 samples h⁻¹. The method was employed for the determination of nitrate in mineral water and soft drink samples and the results were in agreement with those obtained by using a recommended procedure. Studies towards a selective monitoring of nitrite were also performed in samples containing nitrate by carrying out measurements at a less negative potential (−0.20 V).     

Nephelometry and turbidimetry with paired emitter detector diodes and their application for determination of total urinary protein

Two miniature and compact optoelectronic devices fabricated by means of integration of light emitting diodes have been developed for turbidimetric and nephelometric measurements. These devices are operating according to paired-emitter-detector-diode (PEDD) principle. The detectors have been characterized using bovine serum albumin and Exton protein assay as a model analyte and a model analytical method, respectively. The developed detectors have been adapted for measurements under conditions of flow injection analysis (FIA). Under optimized conditions the turbidimetric flow system offers the range of linear response up to 400 mg L⁻¹ with the detection limit at 20 mg L⁻¹. The linear range and detection limit found for optimized nephelometric FIA system are 15–500 mg L⁻¹ and 8 mg L⁻¹, respectively. The PEDD-based FIA systems with the detector operating according to both modes of measurements have been successfully applied for urinalysis offering total protein determination at physiological and pathological levels with high throughput (over 60 injections per hour).     

A ratiometric fluorescence sensor for Be based on Beryllon II/layered double hydroxide ultrathin films

A ratiometric fluorescence sensor for Be²⁺ has been fabricated via alternate assembly of 2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate (Beryllon II) and MgAl-LDH nanosheets on quartz substrates using the layer-by-layer (LBL) deposition technique. UV–vis absorption and the fluorescence emission spectroscopy indicate a stepwise and regular growth of the Beryllon II/LDH UTFs upon increasing deposition cycle. The film of Beryllon II/LDH possesses a periodic layered structure perpendicular to the substrate revealed by X-ray diffraction and scanning electron microscopy. Atomic force microscopy images show that the film surface is continuous and uniform. The Beryllon II/LDH UTFs display ratiometric fluorescence response for Be²⁺ with a linear response range in 1.0 × 10⁻⁷–1.9 × 10⁻⁶ mol L⁻¹ and a detection limit of 4.2 × 10⁻⁹ mol L⁻¹. Furthermore, the ratiometric sensor exhibits good repeatability, high stability (thermal, storage and mechanical) as well as excellent selectivity toward Be²⁺. XPS and Raman measurements demonstrate that the specific response of the sensor is attributed to the coordination between Be²⁺ and Beryllon II in the UTF. The Beryllon II/LDH UTFs in this work can be potentially used as a chemosensor for the detection of Be²⁺ in the environmental and biomedical field.     

Molecularly imprinted polymer coated magnetite nanoparticles as an efficient mefenamic acid resonance light scattering nanosensor

In this work, a mefenamic acid (MFA) nanosensor was synthesized by the aid of molecularly imprinted polymer (MIP) technique. MIP layer was coated on magnetite nanoparticles as magnetic nano-carriers. Synthesized nanoparticles were characterized using various measurements techniques. Light scattering properties of the synthesized nanoparticles in the presence or absence of MFA have been selected as the detection signal. In this regard, resonance light scattering has been used as the detection method. Various factors that can potentially affect light scattering efficiency (i.e., pH, ultrasonication time and nanoparticle dosage) were optimized using “one-at-a-time” method. A linear dynamic range was established from 100.0 to 2000.0 ng L⁻¹ of MFA and the limit of detection was found to be 50.0 ng L⁻¹ using the proposed method.     

Cobalt phthalocyanine as a novel molecular recognition reagent for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants

Cobalt(II) phthalocyanine [Co(II)Pc] is used as both an ionophore and chromogen for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants (SDS), respectively. The potentiometric technique involves preparation of a polymeric membrane sensor by dispersing [Co(II)Pc] in a plasticized PVC membrane. Under batch mode of operation, the sensor displays a near-Nernstian slope of −56.5 mV decade⁻¹, wide response linear range of 7.8 × 10⁻⁴ to 8.0 × 10⁻⁷ mol L⁻¹, lower detection limit of 2.5 × 10⁻⁷ mol L⁻¹ and exhibits high selectivity for anionic surfactants in the presence of many common ions. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range are −51.1 mV decade⁻¹, 5.6 × 10⁻⁷ and 1.0 × 10⁻³ to 1.0 × 10⁻⁶ mol L⁻¹, respectively. The spectrophotometric method is based on the use of [Co(II)Pc] solution in dimethylsulfoxide (DMSO) as a chromogenic reagent. The maximum absorption of the reagent at 658 nm linearly decreases with the increase of anionic surfactant over the concentration range 2-30 μg mL⁻¹. The lower limit of detection is 1 μg mL⁻¹ and high concentrations of many interfering ions are tolerated. Flow injection spectrophotometric measurements are carried out by injection of the surfactant test solution in a stream of the reagent in DMSO. The sample throughput, working range and lower detection limit are 25-30 samples h⁻¹, 4-60 and 2 μg mL⁻¹, respectively. The potentiometric and spectrophotometric techniques are applied to the batch and flow injection measurements of anionic surfactants in some commercial detergent products. The results agree fairly well with data obtained using the standard methylene blue spectrophotometric method.     

Development of a flow manifold for Fe(III) ion determination with a fluoride ion-selective electrode

Continuous-flow (CF) and flow-injection (FI) analysis using the fluoride ion-selective electrode (FISE) as detector have been investigated. The measurements were performed in a home-made cell under appropriate flow conditions (2.86 or 3.45 ml min⁻¹, 0.2 ml samples, 10⁻⁶ M sodium fluoride). The calibration graph was obtained by plotting the signal height versus concentration of iron in the range of Fe(III) concentration from 10⁻⁵ to 10⁻¹ M in acetate buffer (pH 2.8 or 3.4). In all described procedures, the range of linear response extends to the Fe(III) concentration from 1×10⁻³ to 1×10⁻¹ M, with detection limit 9×10⁻⁵ M. The effect of double-line, two-line flow manifold and CF was investigated and discussed.     

Stripping voltammetry of silver ions at polythiophene-modified platinum electrodes

The present work describes the development of a modified platinum electrode for stripping voltammetric determination of silver. The deposition of films based on electropolymerisation of the monomer thiophene was carried out by cycling the potential towards positive values between 0 and 1.6 V.The preconcentration process of silver ions was initiated on the surface of the modified electrode by complexing silver with polythiophene (PTH) when a negative potential (−0.5 V) was applied; then the reduced products was oxidized by means of differential pulse stripping voltammetry and the peak was observed at 0.17 V. Parameters such as pH, supporting electrolyte and number of electropolymerisation cycles were studied. A linear relation between current peak and concentration of Ag(I) was obtained in the range 0.07-1.0 mg L⁻¹. The detection limit for Ag(I) was evaluated to be 0.06 mg L⁻¹. The reproducibility was tested carrying out 11 measurements at different electrodes and the relative standard deviation was 1.5%. The interference of several metals was investigated and showed negligible effect on the electrode response.     

Determination of poisonous metals in wastewater collected from paint manufacturing plant using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) system was developed for determination of toxic metals in wastewater collected from local paint manufacturing plant. The plasma was generated by focusing a pulsed Nd:YAG laser at 1064 nm on the solid residue from wastewater collected from paint industry. The concentration of different elements of environmental significance like, lead, copper, chromium, calcium, sulphur, magnesium, zinc, titanium, strontium, nickel, silicone, iron, aluminum, barium, sodium, potassium and zirconium, in paint wastewater were 6, 3, 4, 301, 72, 200, 20, 42, 4, 1, 35, 120, 133, 119, 173, 28 and 12 mg kg⁻¹, respectively. The evaluation of potential and capabilities of LIBS as a rapid tool for paint industry effluent characterization is discussed in detail. Optimal experimental conditions were evaluated for improving the sensitivity of our LIBS system through parametric dependence study. The laser-induced breakdown spectroscopy (LIBS) results were compared with the results obtained using standard analytical technique such as inductively coupled plasma emission spectroscopy (ICP). The relative accuracy of our LIBS system for various elements as compared with ICP method is in the range of 0.03-0.6 at 2.5% error confidence. Limits of detection (LOD) of our LIBS system were also estimated for the above mentioned elements.     

An amperometric sensor based on hemin adsorbed on silica gel modified with titanium oxide for electrocatalytic reduction and quantification of artemisinin

The present work describes the development of an amperometric sensor based on hemin immobilized on a titanium oxide modified silica toward detection of artemisinin (ARN) in neutral medium at an applied potential of −0.5 V vs. Ag/AgCl. The sensor presented its best performance in 0.1 mol L⁻¹ phosphate buffer solution, at pH 7.0. After optimizing the operational conditions, the sensor provided a linear response range for ARN reduction from 50 nmol L⁻¹ to 1000 nmol L⁻¹ with a sensitivity, detection and quantification limits of 24.66 A L mol⁻¹, 15 nmol L⁻¹ and 52 nmol L⁻¹, respectively. The proposed sensor showed a stable response for at least 80 successive determinations. The repeatability of the measurements with the sensor and the preparation of a series of electrodes, evaluated in terms of relative standard deviation, were 4.1% and 5.0%, respectively, for n = 10. The developed sensor was applied for the determination of ARN in the crude extracts of A. vulgaris L and the average recovery for these samples is 101.4 (± 3.1)%.     

Laser-induced breakdown spectroscopy in analysis of Al3+ liquid droplets: on-line preconcentration by use of flow-injection manifold

Laser-induced breakdown spectroscopy (LIBS), combined with a flow-injection system, is demonstrated to analyze liquid droplets of aluminum salt, as generated with an electrospray ionization device. The spray needle also serves as the anode, through which the analyte solution is spread toward the other metal base as the cathode. Along the passage of the FI manifold, the Al-sample loading speed is controlled at 0.15 mL min⁻¹, restricted to the small diameter of the spray needle, and the loading volume amounts to 0.1 mL. The metal ion is retained in a cation-exchange resin microcolumn immobilized with Chromotrope 2B chelating agent, followed by elution with a 0.5 M HCl solution into LIBS. Upon laser irradiation at the preconcentrated liquid droplets, the time-resolved laser-induced breakdown (LIB) emission and plasma-induced current signals are acquired concurrently on a single-shot basis. The area under the LIB/current distribution increases in linear proportion as the concentration of the sample solution increases. The detection limit thus obtained can reach 1.5 mg L⁻¹, about an order of magnitude lower than those achieved previously using single-laser ablation without involvement of preconcentration. The linear dynamic range is more than two orders of magnitude.     

Spectrophotometric determination of beryllium in water samples after micelle-mediated extraction preconcentration

A new micelle-mediated phase preconcentration method for preconcentration of ultra-trace quantities of beryllium as a prior step to its determination by spectrophotometry has been developed. Chrome Azurol S (CAS) and cetyltrimethylammonium bromide (CTAB) were used as chelating agent and cationic surfactant, respectively. The method evaluates and eliminates the blank bias error present in such procedures using mean centering of ratio spectra. This procedure gives more accurate results than the traditional approach using absorbance values against reagent blank. The optimal extraction and reaction conditions were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration and improvement factors) were obtained. Linearity was obeyed in the range of 0.9-18.0 ng mL⁻¹ (1.00 × 10⁻⁷-2.00 × 10⁻⁶ mol L⁻¹) of beryllium. The detection limit of the method is 0.51 ng mL⁻¹ (5.66 × 10⁻⁸ mol L⁻¹) of beryllium. The interference effect of some anions and cations was also tested. The method was applied to the determination of beryllium in spring water samples.     

Column preconcentration of mercury as HgI4 using methyltrioctylammonium chloride-naphthalene adsorbent with subsequent anodic stripping-differential pulse voltammetric determination

A sensitive and selective preconcentration method has been developed for mercury using naphthalene-methyltrioctylammonium chloride (Aliquat 336s) as an adsorbent. Mercury as HgI₄²⁻ was retained by the adsorbent in the column at a flow rate of 1 ml min⁻¹. The column was washed by a solution of sodium tetraphenylborate and sodium iodide to elute the adsorbed mercury. The eluents were collected in a 10 ml volumetric flask and diluted to the mark with water, transferred to a voltammetric cell and anodic stripping-differential pulse voltammetry was performed. Preconcentration factors of 40 and 80 could be achieved when using a 10 and 5 ml voltammetric cell, respectively. The calibration graph was linear in the range of 1.2-8.7 ng ml⁻¹ Hg(II) in the initial solution with r=0.9998 (n=6) and the 3 s detection limit was 0.13 ng ml⁻¹ when using a 10 ml cell. The relative standard deviation for eight replicate measurements of 1.2, 5.0 and 8.7 ng ml⁻¹ of Hg(II) in the initial solution was 0.51, 0.71 and 0.80%, respectively. The proposed method was successfully applied to determination of mercury in natural waters, wastewater and synthetic samples.     

Optimization of experimental parameters in single-drop microextraction-gas chromatography-mass spectrometry for the determination of periodate by the Malaprade reaction, and its application to ethylene glycol

The aim of present work was to optimize the experimental parameters in single drop microextraction under solution immersion (SDME) and headspace (HS-SDME) extraction modes for the determination of periodate using guaifenesine [3-(2′-methoxyphenoxy)-1,2-propane diol] and norephedrine (phenylpropanolamine) as new and alternative reagents for the Malaprade reaction. The reactions were complete within 5 min resulting in the formation of 2-(2′-methoxyphenoxy)-acetaldehyde and benzaldehyde, respectively. SDME/HS-SDME of oxidation products with 2 μl of anisole or 1 μl of toluene, respectively, has permitted the determination of periodate at μg l⁻¹ concentration levels. The results indicated that HS-SDME (range 0.01-10 mg l⁻¹, r² = 0.9990; limit of detection 1.55 μg l⁻¹) was more sensitive than SDME (range 0.05-50 mg l⁻¹, r² = 0.9984; limit of detection 3.42 μg l⁻¹), and was inexpensive, rapid and convenient. Tolerance of excess of iodate has permitted the application of this method in the determination of ethylene glycol in motor oil; the average recovery on spiked sample was 98.6% with R.S.D. of 4.2%.