Slurry sampling for determination of lead in marine plankton by electrothermal atomic absorption spectrometry

A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO₃ by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO₃)₂, Mg(NO₃)₂, Pd(NO₃)₂, Pd(NO₃)₂ + Mg(NO₃)₂, and Mg(NO₃)₂ + NH₄H₂PO₄, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO₃ and HF were examined as suspension medium. Dilute HNO₃ (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L^− 1 and 32 pg for the conventional method and 0.62 μg L^− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval.     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.     

Comparative study of conventional and multivariate methods for aluminum determination in soft drinks by graphite furnace atomic absorption spectrometry

In the present study, conventional and multivariate methods were used to optimize conditions for direct determination of aluminum in soft drinks by electrothermal atomic absorption spectrometry. For the conventional method, the optimized experimental parameters were: pyrolysis and atomization temperatures and chemical modifier. A multivariate study was performed using factorial design and the optimized parameters were the same employed in the univariate method including pyrolysis time. For the conventional method, the optimal conditions obtained were: pyrolysis temperature of 1600 °C, atomization temperature of 2700 °C, and Zr as permanent modifier. For the factorial design in the multivariate optimization, the Pareto´s chart showed that the atomization temperature, the modifier, and the pyrolysis temperature presented a significant effect on the integrated absorbance and the interaction between pyrolysis temperature and pyrolysis time also had a significant effect on the signal. Better results were obtained using Zr as modifier. The surface response indicates that the lowest pyrolysis (1100 °C) and atomization temperatures (2350 °C) provide higher absorbance for aluminum in soft drinks. Characteristic mass of 23.4 and 19.4 pg and LOD of 17.9 and 11.3 μg L^− 1 was obtained to conventional and multivariate methods, respectively. The calibration was accomplished with standard addition in a range of 60–200 μg L^− 1 for conventional method and of 38–200 μg L^− 1for multivariate method with R higher than 0.99 for both conditions. Recoveries in both studies were nearly 100% with adequate precision for GFAAS analysis. For the Al concentrations level found in soft drinks, both experimental conditions are adequate as good results were obtained in recovery studies. The Al concentrations in different soft drinks range from 147.9 to 599.5 μg L⁻¹. Higher concentrations were found in soft drinks sold in Al cans than in PET bottles, indicating that contamination can occur.     

Real-time monitoring of metal deposition and segregation phenomena during preparation of PdCu membranes

The N₂ and H₂ evolution, respectively, were monitored during deposition of Pd and Cu from electroless plating baths to obtain in-process control of the composition during preparation of 3–7 μm thick PdCu membranes on tubular ceramic substrates. Compositions estimated by gas evolution compare favorably to those measured in post-mortem XRD and EDS analyses, mostly differing by not more than 1 at.%. This result suggests that use of gas evolution measurements to enable in-process control of composition to within 1 at.% is feasible. Annealing experiments in an H₂ atmosphere demonstrated that, at 893 K, only 48 h are needed to form a stoichiometrically homogeneous, 9.5 μm thick, face centered cubic (fcc) Pd₆₃Cu₃₇ membrane from sequentially deposited layers; at 723 K, the same transformation requires over 2 weeks. The appearance of transient body centered cubic (bcc) and fcc phases with lower Pd contents signaled compositional segregation in the initial stages of alloy formation at 723 and 773 K and could be a source of persistent stoichiometric heterogeneity particularly in bcc PdCu membranes. The H₂ fluxes of fcc Pd₅₈Cu₄₂ and Pd₇₀Cu₃₀ membranes were J_H2=(1.6±1.1) mol m⁻² s⁻¹ exp[(−24.8±0.4)kJ mol⁻¹/RT] and J_H2=(3.7±0.6) mol m⁻² s⁻¹ exp[(−21.3±1.0)kJ mol⁻¹/RT], respectively, at 100 kPa H₂ pressure difference.     

Use of a graphite–polyurethane composite electrode for electroanalytical determination of indole-3-acetic acid in soil samples

A new electroanalytical methodology was developed for the quantification of the phytohormone indole-3-acetic acid (IAA), using a graphite–polyurethane composite electrode (GPU) and the square wave voltammetry (SWV), in 0.1 mol L^− 1 phosphoric acid solution (pH 1.6). Analytical curves were constructed under optimized conditions (f = 100 s^− 1, a = 50 mV, E_i = 5 mV) and the reached detection and quantification limits were 26 μg L^− 1 and 0.2 mg L^− 1, respectively. The developed methodology is simple and accurate for the routine determination of IAA. In order to verify the application of the electroanalytical methodology in fortified soil samples without previous treatment, an IAA assay was performed without serious interferences of the soil constituents.     

Development and critical comparison of greener flow procedures for nitrite determination in natural waters

Two greener procedures for flow-injection spectrophotometric determination of nitrite in natural waters were developed and critically compared. Replacement of toxic reagents, waste minimization and treatment were exploited to attend the standards of clean chemistry. The flow system was designed with solenoid micro-pumps in order to minimize reagent consumption and waste generation. The first procedure is based on the Griess diazo-coupling reaction with sulfanilamide and N-(1-naphthyl)ethylenediamine (NED) yielding an azo dye, followed by photodegradation of the low amount of waste generated based on the photo-Fenton reaction. The second procedure is based on the formation of iodine from nitrite and iodide in acid medium in order to avoid the use of toxic reagents. For Griess method, linear response was achieved up to 1.0 mg L^− 1, described by the equation A = − 0.007 + 0.460C (mg L^− 1), r = 0.999. The detection limit was estimated as 8 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.8% (n = 20). The sampling rate was estimated as 108 determinations per hour. The consumption of the most toxic reagent (NED) is reduced 55-fold and 20-fold in comparison to batch method and flow injection with continuous reagent addition, respectively. A colorless residue was obtained by in-line photodegradation with reduction of 87% of the total organic carbon content. The results obtained for natural water samples were in agreement with those achieved by the reference method at the 95% confidence level. For the nitrite–iodide method, linear response was observed up to 2.0 mg L^− 1, described by the equation A = − 0.024 + 0.148C (mg L^− 1), r = 0.999. The detection limit was estimated as 25 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.6% (n = 20). The sampling rate was estimated as 44 determinations per hour. Despite avoiding the use of toxic reagents, the nitrite–iodide method presented worst performance in terms of selectivity and sensitivity.     

On-line molecularly imprinted solid phase extraction for the selective spectrophotometric determination of catechol

A molecularly imprinted polymer has been synthesized for a selective on-line catechol extraction, followed by its spectrophotometric determination in guarana powder, mate tea and tap water samples. A clean-up column, containing a methacrylic polymer + C₁₈ solid phase, was also used in order to enhance selectivity. The imprinted polymer was prepared by bulk polymerization using catechol as template and 4-vinylpyridine as the functional monomer. Permanganate solution was used as spectrophotometric reagent, where Mn(VII) was reduced to Mn(II) by catechol in an acid medium, causing color loss, which was monitored at 528 nm. Physical (extraction flow rate, elution flow rate, coil length) and chemical (nature and concentration of the eluent, potassium permanganate concentration) variables were optimized, and the selectivity was appraised using three molecules (4-chloro-2-methylphenol, 2-cresol, 2-methoxyphenol) similar to catechol. These molecules did not present interference in 1:8, 1:10 and 1:10 (catechol/concomitant) proportions, respectively. The analytical calibration curve ranged from 3.0 up to 100 μmol L^− 1 (r > 0.999; seven concentrations levels, n = 3) and the limits of detection (LOD) and quantification (LOQ) were 0.8 and 2.7 μmol L^− 1, respectively. Precision, expressed as RSD, was of 3.0% (20 μmol L^− 1, n = 10), and the analytical frequency was 15 h^− 1. Accuracy was checked by the HPLC technique and the results did not present significant difference at 95% confidence levels according to the t test.     

Determination of Trace Amount of Silver by Atomic-Absorption-Spectrometry-Coupled Flow Injection On-Line Coprecipitation Preconcentration Using DDTC–Copper as Coprecipitate Carrier

A flow injection on-line coprecipitation preconcentration system with diethyldithiocarbamate (DDTC) chelate of copper used as the coprecipitate carrier was coupled with flame atomic absorption spectrometry (FAAS) for the determination of trace silver. Silver was on-line coprecipitated with DDTC-Cu(II) in 0.5 moL · L⁻¹HCl, and the precipitate was collected in a knotted reactor. The precipitate was then dissolved by isobutyl methyl ketone and transported directly into the nebulizer–burner system of a flame atomic absorption spectrometer. A detection limit (3ς) of 0.6 μg · L⁻¹was achieved for a loading period of 30 s, a relative standard derivation of 2.0% was obtained for 11 determinations of 20 μg · L⁻¹Ag(I). Interference-free levels were 10 mg · L⁻¹for Cd²⁺, 50 mg · L⁻¹for Cu²⁺, 50 mg · L⁻¹for Mn²⁺, 25 mg · L⁻¹for Ni²⁺, 100 mg · L⁻¹for Pb²⁺, 50 mg · L⁻¹for Zn²⁺, 500 mg · L⁻¹for Fe³⁺, and 2000 mg · L⁻¹for Fe²⁺reduced from Fe³⁺by ascorbic acid. The developed method has been successfully applied to the determination of trace amount of silver in geological samples.     

Analysis of BTEX, PAHs and metals in the oilfield produced water in the State of Sergipe, Brazil

During oil and gas exploitation, large amounts of produced water are generated. This water has to be analyzed with relation to the chemical composition to deduce the environmental impact of its discharge after a treatment process. Therefore, a study was carried out to evaluate preliminarily the BTEX (benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and metals contents in produced water samples taken from effluents of the Bonsucesso treatment plant located in the city of Carmópolis, the most important oil and gas producer in the State of Sergipe, North-east of Brazil. Three methods were optimized to determine the target compounds. Polycyclic aromatic hydrocarbons were determined by gas chromatography with mass spectrometric detection (GC/MS), volatile aromatic hydrocarbons (BTEX) by gas chromatography with photoionization detector (GC/PID) and metals were analyzed by flame atomic absorption spectrometry (FAAS). The results showed that concentrations of the target compounds in these samples ranged from 96.7 to 1397 μg L^− 1 for BTEX, from 0.9 to 10.3 μg L^− 1 for PAHs and from 0.003 to 4540 mg L^− 1 for metals.     

Speciation analysis of selenium enriched green onions (Allium fistulosum) by HPLC-ICP-MS

Green onions (Allium fistulosum) enriched with 10 or 100 μg mL^− 1 Se(IV) or SeMet were analyzed for total selenium and species distribution. Anion and cation exchange chromatographies were applied for the separation of selenium species with mass spectrometric detection. Two different sample preparation methods (NaOH and enzymatic) were compared from the Se extraction efficiency point of view. Total selenium concentration accumulated by the onions reached the 200 μg g^− 1 level expressed for dry weight when applying SeMet at a concentration of 100 μg mL^− 1 as the source of Se. Speciation studies revealed that both in onion bulbs and leaves the predominant form of organic selenium is Se-methyl-selenocysteine (MeSeCys). When Se(IV) was applied for Se-enrichment at a concentration level of 100 μg mL^− 1 both onion leaf and bulb contained a significant amount of inorganic selenium. An unknown compound was also detected.     

Determination of linuron in water samples by high performance liquid chromatography after preconcentration with octadecyl silanized magnetite

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of linuron. Linuron was preconcentrated on octadecyl silanized (ODS) magnetite as an adsorbent and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain sufficient preconcentration efficiency when the solution pH was 6 using 100 mL of sample solution containing 1.0 μg of linuron and 3 mL of ethanol as a desorption solution. Recovery of linuron was 50.7 ± 1.9% with a relative standard deviation for five determinations of 3.0% under optimum conditions. The calibration curve of linuron was linear up to 200 ng mL^− 1 with a correlation coefficient of 0.998 and the detection limit (3S/N) was 1.0 ng mL^− 1. The capacity of the adsorbent was also examined and found to be 0.15 mg g^− 1 for linuron. ODS-magnetite is suitable for repeated use without decreasing recovery at least 4 adsorption–desorption cycles. The proposed method was successfully applied to the determination of linuron in river water with high precision and accuracy.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Coupling on-line preconcentration by ion-exchange with microwave plasma torch-atomic emission spectrometry for the determination of cobalt and nickel

In the present work, a simple and sensitive preconcentration-microwave plasma torch-atomic emission spectrometric procedure was carried out for the determination of cobalt and nickel. The method was based upon a flow-injection system with on-line preconcentration of the metal ions on a minicolumn of a strong acid cation-exchange resin. The operation parameters including sample acidity, flow rate, loading time, and eluent concentration, flow rate were studied and optimized. Under the optimal experimental conditions the enrichment factors were calculated as 13.58 and 17.65 for cobalt and nickel, respectively. The relative standard deviations, 3.73% for cobalt and 4.23% for nickel (n = 7), and a sample throughput of 40 h^− 1 were obtained. Furthermore, the limits of detection were shown to be 1.28 and 1.80 μg·L^− 1 for cobalt and nickel, respectively. The method was applied to the determination of cobalt and nickel in tea samples and the accuracy was assessed through recovery experiments.     

Indirect atomic absorption spectrometry (IAAS) as a tool for the determination of iodide in infant formulas by precipitation of AgI and redissolution with cyanide

A method to determine iodide in infant formula samples by indirect atomic absorption spectrometry (IAAS) was developed. The iodide in solution resulting from an alkaline digestion (Na₂CO₃–NaOH) of the sample is precipitated with silver; the precipitate is redissolved by adding cyanide solution, and this solution is subjected to GF-AAS. Temperatures of 1000 and 2100°C were selected for the ashing and atomization steps, respectively, using a mixture of Pd and Mg(NO₃)₂ as a matrix modifier (at concentrations of 36 and 16 μg ml⁻¹, respectively). The sensitivity, LOD, LOQ and characteristic mass obtained were, respectively, 1.12×10⁻² l μg⁻¹, 3.1 μg g⁻¹ and 10.4 μg g⁻¹ and 7.3 pg, referred to sample. The linear interval of concentrations extends up to 10 μg l⁻¹ of iodide, with no need to use the standard addition method; the mean R.S.D. of data within this range is 3.4%, with 2.9% over the whole procedure. No interfering effects were observed among the foreign ions studied, and 100.0% was the mean analytical recovery achieved within the linear range of concentrations. The application of the method to seven real samples gave a mean content of 12.8 μg g⁻¹ of iodide, as well as less than 3.1 μg g⁻¹ in eight other samples.     

Simultaneous determination of pethidine and methadone by capillary electrophoresis with electrochemiluminescence detection of tris(2,2′-bipyridyl)ruthenium(II)

In this paper, we described a simple and rapid method, capillary electrophoresis with electrochemiluminescence (CE–ECL) detection using tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺), to simultaneously detect pethidine and methadone. Analytes were injected to separation capillary of 67.5 cm length (25 μm i.d., 360 μm o.d.) by electrokinetic injection for 10 s at 10 kV. Under the optimized conditions: ECL detection at 1.20 V, 30 mM sodium phosphate (pH 6.0) as running buffer, separation voltage at 14.0 kV, 5 mM Ru(bpy)₃²⁺ with 50 mM sodium phosphate (pH 6.5) in the detection cell, the linear range from 2.0 × 10^− 6 to 2.0 × 10^− 5 M for pethidine and 5.0 × 10^− 6 to 2.0 × 10^− 4 M for methadone and detection limits of 0.5 μM for both of them were achieved (S/N = 3). Relative standard derivations of the ECL intensity were 2.09% and 6.59% for pethidine and methadone, respectively.     

Modular L-design of hydride atomizers for atomic absorption spectrometry

A novel modular L-shaped design of hydride atomizer for atomic absorption spectrometry is described. It makes it possible to replace the optical tube of the atomizer and, mainly, to employ optical tubes made also from other materials than fused quartz. The design is useful mainly for further improvement of hydride atomizers based on the multiatomizer concept. Employing selenium hydride as the analyte and arsine as the interferent, a preliminary evaluation of performance of three types of L-shaped multiatomizers based on various optical tubes in terms of sensitivity, linearity of calibration graph and resistance to atomization interferences is made. The “classical” T-shaped multiatomizer was employed as a reference.The L-shaped multiatomizer with the optical tube analogous to that employed in the “classical” T-shaped multiatomizer offers virtually the same performance as the reference multiatomizer. Optical tube made of fused quartz with holes with smaller diameters does not offer significantly better performance compared to the reference T-shaped multiatomizer. However, the L-shaped multiatomizer with optical tube fabricated from porous quartz glass overpowers all the other multiatomizers substantially in terms of the resistance against interferences: even the maximum As interferent concentration of 5 µg ml^− 1 does not significantly influence the observed signal. This should be compared with multiatomizers based on plain fused quartz tubes with holes: tolerance limit around 0.5 µg ml^− 1; interferent concentration of 1 µg ml^− 1 causing 20% signal depression.     

Indirect voltammetric determination of caffeine content in coffee using 1,4-benzoquinone modified carbon paste electrode

In this paper a simple and highly sensitive electroanalytical method for the determination of caffeine content using 1,4-benzoquinone modified carbon paste electrode is presented. The method is based on suppression of 1,4-benzoquinone peak current on addition of caffeine. Square-wave and cyclic voltammetric techniques were utilised for the investigation. The 1,4-benzoquinone modified electrode exhibited a well-defined peak with reproducible peak current values for repetitive measurements; and showed a decrease in peak current value with an increase in caffeine content. The result revealed two linear range regions between 0 mmol L⁻¹ and 0.5 mmol L⁻¹ and 0.5 mmol L⁻¹ and 8.0 mmol L⁻¹, with detection limits of 0.3 μmol L⁻¹ and 5.1 μmol L⁻¹, respectively. The method was then successfully applied to the determination of caffeine content in coffee samples. The effects of pH, electrode composition, step potential, pulse amplitude and square-wave frequency on the voltammetric responses were also investigated.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

Ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction combined with electrothermal atomic absorption spectrometry for a sensitive determination of cadmium in water samples

A new method was developed for the determination of cadmium in water samples using ionic liquid-based ultrasound-assisted dispersive liquid–liquid microextraction (IL-based USA-DLLME) followed by electrothermal atomic absorption spectrometry (ETAAS). The IL-based USA-DLLME procedure is free of volatile organic solvents, and there is no need for a dispersive solvent, in contrast to conventional DLLME. The ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF₆), was quickly disrupted by an ultrasonic probe for 1 min and dispersed in water samples like a cloud. At this stage, a hydrophobic cadmium–DDTC complex was formed and extracted into the fine droplets of HMIMPF₆. After centrifugation, the concentration of the enriched cadmium in the sedimented phase was determined by ETAAS. Some effective parameters of the complex formation and microextraction, such as the concentration of the chelating agent, the pH, the volume of the extraction solvent, the extraction time, and the salt effect, have been optimized. Under optimal conditions, a high extraction efficiency and selectivity were reached for the extraction of 1.0 ng of cadmium in 10.0 mL of water solution employing 73 µL of HMIMPF₆ as the extraction solvent. The enrichment factor of the method is 67. The detection limit was 7.4 ng L^− 1, and the characteristic mass (m₀, 0.0044 absorbance) of the proposed method was 0.02 pg for cadmium (Cd). The relative standard deviation (RSD) for 11 replicates of 50 ng L^− 1 Cd was 3.3%. The method was applied to the analysis of tap, well, river, and lake water samples and the Environmental Water Reference Material GSBZ 50009-88 (200921). The recoveries of spiked samples were in the range of 87.2–106%.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.