HR-CS GF AAS Research Articles

High-resolution continuum source graphite furnace atomic absorption spectrometry for direct analysis of solid samples and complex materials: a tutorial review

This work tries to provide guidance for the development of new methods aiming at the direct analysis of solid samples or complex liquid materials using HR CS GFAAS.

Simultaneous determination of Mo and Ni in wine and soil amendments by HR-CS GF AAS

Mo and Ni have been determined simultaneously in wine and soil amendment samples.

Determination of Lead in Eye Shadow and Blush by High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry Employing Direct Solid Sampling

−1 , respectivamente. Direct solid sampling is proposed for Pb determination in eye shadow and blush samples by high- resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). A mixture of Pd(NO3)2 + Mg(NO3)2 was employed as chemical modifier, and aqueous calibration (0.25-2.5 ng Pb, r = 0.998) was obtained. Accuracy of the determination of Pb in eye shadow and blush samples by the proposed method was verified by line source graphite furnace AAS as a comparative technique employing digested samples. The results obtained by the two methods were in agreement at a 95% confidence level (paired t-test). The limit of quantification (dry mass) was 0.020 ng mg −1 . The Pb content in the eye shadow and blush samples varied between 1.222 and 9.632 ng mg −1 and 0.362 and 28.091 ng mg −1 , respectively.

Determination of macro and trace elements in multivitamin dietary supplements by high-resolution continuum source graphite furnace atomic absorption spectrometry with slurry sampling

In this research, three different commercially available multivitamin dietary supplements were analyzed by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) with slurry sampling. The concentrations of Cr, Cu, Fe, Mn, and Se were determined and compared to the amounts stated by producers. The safety of multivitamin dietary supplements depends on various factors including the manufacturing process and the purity and origins of the raw ingredients. For this reason, this research determined concentrations of several toxic elements (As, Cd, and Pb). Microwave-assisted high pressure Teflon bomb digestion was used to determine total amounts of elements in samples. Samples were prepared as slurries at a concentration of 0.1% (m/v) for macro elements (Cr, Cu, Fe, Mn, and Se) and at a concentration of % (m/v) for trace elements (As, Cd, and Pb) in acidic media (3M HNO3). The influence of acid concentration, Triton X-100 addition, sonication time, and sonication power on absorbance was investigated. The accuracy of this method was validated by analyses of NRCC LUTS-1 (Lobster hepatopancreas), NRCC DORM-1 (Dogfish Muscle), NRCC DOLT-2 (Dogfish Liver), NBS SRM 1570 (Spinach Leaves) and NBS SRM 1573 (Tomato Leaves) certified reference materials. The measured elements contents in these reference materials (except NRCC DOLT-2) were in satisfactory agreement with the certified values according to the t-test for a 95% confidence level.

Determination of iron in biodiesel based on fluorescence quenching of CdTe quantum dots

The determination of trace elements in biodiesel is essential to assess oil qualities, identify adulterations and prevent undesirable effects in environment and in humans. However, due to the low sample concentration, sensitive instrumental techniques are required.In this work an effective and simple quantification method using water-soluble mercaptopropionic acid (MPA)-capped CdTe quantum dots (QDs) was for the first time implemented for the fluorescence quantification of iron in biodiesel obtained from different vegetable oils and fat. The developed methodology was based on the iron capacity to establish surface interactions with the nanocrystals that result in a quenching of the fluorescence intensity (F0−F), proportional to the iron concentration. Size and concentration of QDs, concentration and pH of the buffer solution showed a strong effect on the quenching efficiency influencing linear working range and sensitivity of the methodology.An ultrasonic bath was used for the extraction of iron from oil samples with a mixture of 1:1 (v/v) concentrated HCl and H2O2. The extraction efficiency was approximately 100% after 50min of ultrasound.Under the optimized experimental conditions, a linear working range was obtained for iron concentrations from 4.16 to 100.0μgL−1 (R=0.9996, n=6). The determined detection limit (LOD) was about 1.25μgL−1. Six biodiesel samples were analyzed by the proposed methodology, and the results revealed good agreement with those obtained through a high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) comparison procedure. Relative deviations lower than 4.5% were achieved, and the application of a paired Student’s t-test, confirmed the absence of any statistical difference for a confidence level of 95% (n=5). Recoveries varied from 90.2% to 105.2%. The slopes of the analytical curves obtained with different matrices showed that the quantification of the analytes was not influenced by matrix effects. The quenching mechanism of CdTe QDs is discussed. The accuracy, precision and operational simplicity of the method, without additional electronic devices, demonstrated an excellent alternative for determination of iron in biodiesel samples.

Determination of Lead in Lipstick by Direct Solid Sampling High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry: Comparison of Two Digestion Methods

A new analytical procedure for the determination of lead in lipstick has been developed using direct solid sampling high resolution continuum source graphite furnace atomic absorption spectrometry (SS HR CS GFAAS). The performance of this method has been compared to acid digestion methods for sample preparation, with or without hydrofluoric acid (HF) with inductively coupled plasma mass spectrometry (ICP-MS) detection. Good reliability was obtained for all three methods; the results obtained for certified reference materials with concentrations between 1 and 20 ppm were in agreement with the certified values. However, for materials with complex matrices, such as pearl or Ca-Na borosilicate, only ICP-MS with HF sample digestion or AAS with direct solid sampling allowed complete recovery of lead. To avoid the use of hazardous acids, the development of SS HR CS GFAAS is an interesting alternative. With the AAS method, a characteristic mass of 13.2 pg of lead was obtained, and the limit of detection was 0.005 µg/g. The performance of the method was evaluated by determining lead in lipstick. The use of the solid sampling technique constitutes a good alternative for accurate and rapid determination of lead content in lipstick and cosmetic raw materials, with a suitable limit of detection and a reduced risk of contamination or of analyte loss. Another alternative would be to use ICP-MS determination in conjunction with microwave-assisted acid digestion without the use of HF, which implies accepting a quantification of “nearly total” lead, closer to a “bio-extractible” fraction.

Determination of Cd, Cu, Ni, and Pb in Black Tea from Saudi Arabia using Graphite Furnace Atomic Absorption Spectrometry after Microwave-Assisted Acid Digestion

A method has been developed for the determination of Cd, Cu, Ni, and Pb in black tea samples from Saudi Arabia using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS). It was found that chemical modifiers were not required for this analysis. The determination of Cd and Cu was free of spectral interferences. In the case of Ni, a strong iron line appeared close to the main nickel line, and in the case of Pb, the well-known absorption spectrum of the PO molecule was present, both of which would cause spectral interferences when deuterium background correction is used. This kind of fine-structured absorption does not cause any problems in HR CS GFAAS, as the analytical lines were separated from the background absorption. The optimum pyrolysis temperatures were 600, 1100, 1300, and 700°C and the atomization temperatures were 1200, 2000, 2550, and 1700°C for Cd, Cu, Ni, and Pb, respectively. The limits of detection were 0.03 µg L−1, 11 µg L−1, 0.9 µg L−1, and 0.27 µg L−1 for Cd, Cu, Ni, and Pb, respectively; the limits of quantification were 0.1 µg L−1, 33 µg L−1, 2.8 µg L−1, and 0.8 µg L−1 for Cd, Cu, Ni, and Pb, respectively. The results of the analysis of a green tea certified reference material confirmed the validity of the proposed method. The concentrations of Cd, Cu, Ni, and Pb found in this study were among the lowest reported in the literature for tea samples.

Potential of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry to monitor the Ag body burden in individual Daphnia magna specimens exposed to Ag nanoparticles

This work evaluates the potential of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) for the direct determination of the Ag body burden in individual specimens of Daphnia magna (a small aquatic invertebrate of approx. 2 mm length typically used in ecotoxicological studies) exposed to different Ag species, and particularly to Ag nanoparticles (NPs). It is shown that this technique offers unique features for this type of application, permitting the direct analysis of these organisms in a very straightforward way (only approx. 2–3 min are required for the analysis of every individual) and constructing the calibration curve with aqueous standards. Moreover, appropriate selection of the detector pixels used for signal quantification makes it feasible to achieve a very broad linear range for any set of experimental conditions, contrary to what occurs for traditional line source-GFAAS. This feature is particularly important for this application, as every Daphnia magna specimen can be measured only once and its Ag content is not known in advance. In this case, the use of central and/or side pixels permits achieving a working range between 3 pg and 1 μg for the 328.068 nm Ag line, thus allowing analysis of all the samples of interest with the same experimental settings.

Determination of Lead in Human Hair by High Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry with Microwave Digestion and Solid Sampling

The content of lead in human hair was measured by high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) combined with microwave-assisted digestion (MAD) and direct solid sampling (DSS). Hair strands were washed, dried, and then cut into three parts (root, middle portion, and tip). For MAD-GFAAS assays, approximately 0.25 g of hair was completely digested using a mixture of concentrated nitric acid and hydrogen peroxide in a closed system. In the DSS-GFAAS assays, 0.1–0.2 mg of dried hair was directly introduced into a graphite furnace using a solid autosampler. The temperature programs were optimized and the effects of various added modifiers were compared. The results indicated that NH4H2PO4 was the optimal modifier for analysis of Pb using GFAAS. Use of the optimal modifier and temperature program gave similar limits of detection for MAD-GFAAS and DSS-GFAAS of 1.16 ng/g and 0.82 ng/g, respectively. Both methods also produced satisfactory recoveries ranging from 98.69% to 103.14%. There was no significant difference observed between the Pb contents of hair strands determined by the MAD-GFAAS and DSS-GFAAS assays, which both indicated that the Pb levels increased along the hair strands. Comparison of the two methods revealed that DSS-GFAAS had several advantageous characteristics over MAD-GFAAS, including the need for much less sample material and having a less time-consuming procedure, lower sample blank absorbance, lower memory effect, and no risk of environmental pollution by digesting chemicals. The direct solid sampling technique can be employed as a good alternative to conventional wet digestion in AAS assays.

Determination of lead in medicinal plants by high-resolution continuum source graphite furnace atomic absorption spectrometry using direct solid sampling

A procedure is proposed for Pb determination in medicinal plants by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) using direct solid sampling. Among Pd(NO3)2, Pd/Mg(NO3)2, NH4H2PO4 and the W-coated platform tested as chemical modifiers, Pd(NO3)2 presented the best performance. Calibration plots (10–1000pg Pb) with regression coefficients better than 0.999 were typically obtained. Accuracy was checked for Pb determination in five plant certified reference materials. Results were in agreement with reference values at a 95% confidence level (paired t-test). Medicinal plant samples were analyzed by the proposed procedure and line-source GF AAS using slurry sampling as a comparative technique. The RSD was 10% (n=3) for a sample containing 0.88μgg−1 Pb. The limit of quantification (dry mass) was 0.024μgg−1. The contents of Pb in medicinal plant samples varied in the 0.30–1.94μgg−1 range.

Graphite tubes with small internal diameters tailored for high-resolution continuum source graphite furnace atomic absorption spectrometry

Graphite tubes with internal diameters of 1 mm, 1.5 mm and 2 mm (mini tubes) were developed and adapted for use in high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The applicability and analytical performance of the mini tubes were tested. Use of a 2 mm tube resulted in no loss of lamp radiation when compared to the use of a 5.8 mm standard tube, while the use of 1.5 mm and 1 mm tubes resulted in about 20% and 70% loss of lamp radiation, respectively. One to several microlitres of liquid samples were introduced to the tube through an end hole using a conventional autosampler. Due to the smaller atomizer volume, analytical sensitivity was significantly improved. For 51 of the 62 elements tested, the improvement in sensitivity of a 2 mm tube over a 5.8 mm tube met or exceeded the values expected (factors 6 to 12). The feasibility of the mini tube concept for sample analysis was demonstrated by the determination of elements in model and real sample solutions under the influence of inorganic and organic matrices, yielding reliable results in all cases. The mini tubes provide high absolute sensitivity and can be used for ultra-trace analysis of small samples.

Comparison of three different sample preparation procedures for the determination of traffic-related elements in airborne particulate matter collected on glass fiber filters

Three different procedures for sample preparation have been compared for the determination of Cu, Mo and Sb in airborne particulate matter (APM) collected on glass fiber filters using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). Direct solid sample analysis of the ground filters was compared with microwave-assisted acid leaching with aqua regia and ultrasound-assisted extraction also using aqua regia. The main absorption line at 324.754nm or the secondary line at 216.509nm was used for the determination of Cu, depending on the analyte content in the samples. The primary absorption line at 313.259nm was used for Mo and the secondary line at 212.739nm for Sb determination. The limits of detection (LOD, 3σ) found for the direct solid sampling method, based on ten atomizations of an unused filter were 15μgg−1 for all three analytes, corresponding to 40ngm−3 for a typical air volume of 1440m3 collected over a period of 24h. The LOD for the other two methods were less than a factor of two inferior, but the total time required for an analysis was significantly longer. The repeatability of the measurements was between 3 and 9% (n=5), and the results obtained with the three methods did not show any significant difference. The ratio between the three analytes on the filters from areas of intense traffic was found to be around Cu:Mo:Sb≈4:1:1.4, which suggests that the source of all three elements is brake linings, i.e., related to automobile traffic. When the ratio deviated significantly from the above values, the source of contamination was assumed to be of different origin.

Method development for the determination of cadmium in fertilizer samples using high-resolution continuum source graphite furnace atomic absorption spectrometry and slurry sampling

The determination of cadmium (Cd) in fertilizers is of major interest, as this element can cause growth problems in plants, and also affect animals and humans. High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) with charge-coupled device (CCD) array detection overcomes several of the limitations encountered with conventional line source AAS, especially the problem of accurate background measurement and correction. In this work an analytical method has been developed to determine Cd in fertilizer samples by HR-CS GF AAS using slurry sampling. Both a mixture of 10 μg Pd + 6 μg Mg in solution and 400 μg of iridium as permanent modifier have been investigated and aqueous standards were used for calibration. Pyrolysis and atomization temperatures were 600 °C and 1600 °C for the Pd-Mg modifier, and 500 °C and 1600 °C for Ir, respectively. The results obtained for Cd in the certified reference material NIST SRM 695 (Trace Elements in Multi-Nutrient Fertilizer) of 16.7 ± 1.3 μg g −1 and 16.4 ± 0.75 μg g −1 for the Pd–Mg and Ir modifier, respectively, were statistically not different from the certified value of 16.9 ± 0.2 μg g −1 on a 95% confidence level; however, the results obtained with the Ir modifier were significantly lower than those for the Pd–Mg modifier for most of the samples. The characteristic mass was 1.0 pg for the Pd–Mg modifier and 1.1 pg Cd for the Ir modifier, and the correlation coefficients (R 2) of the calibration were > 0.99. The instrumental limits of detection were 7.5 and 7.9 ng g −1, and the limits of quantification were 25 and 27 ng g −1 for Pd–Mg and Ir, respectively, based on a sample mass of 5 mg. The cadmium concentration in the investigated samples was between 0.07 and 5.5 μg g −1 Cd, and hence below the maximum value of 20 μg g −1 Cd permitted by Brazilian legislation.

Determination of Lead in Coal Using Direct Solid Sampling and High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry

A method has been developed for the determination of Pb in coal using direct solid sampling (SS) and high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The certified coal reference materials used in this study were ground in an agate mortar to particle size ≤50 µm. Mass aliquots between 0.1 and 1 mg were weighed onto pyrolytic graphite platforms, and inserted directly into the graphite tube. For pyrolysis temperatures lower than 600 °C, a continuous background due to radiation scattering at solid particles preceded the atomic signal, as the coal matrix could not be sufficiently eliminated under these conditions. An optimized pyrolysis temperature of 700 °C was adopted for Pb without the use of a modifier. The optimum atomization temperature was found to be 1700 °C. Under these conditions, interference-free determination could be performed with calibration against aqueous standards in 0.5% v/v HNO3. A total of six certified reference coal samples were analyzed, and the results obtained were all in good agreement with certified and informed values, respectively, according to a Student t-test at a 95% confidence level. A detection limit of 0.008 µg g−1 for Pb was obtained at the 217.000 nm resonance line, a value comparable to those obtained by other sensitive, but much more sophisticated techniques, showing that the absence of dilution in the SS-HR-CS GF AAS method allows at least equivalent detection performance.

Speciation analysis of volatile and non-volatile vanadium compounds in Brazilian crude oils using high-resolution continuum source graphite furnace atomic absorption spectrometry

A method is proposed that makes possible determining total and “thermally stable” vanadium in crude oil without prior separation, and to calculate “volatile” vanadium by difference. The volatile fraction is believed to be largely vanadyl porphyrine complexes. The method is based on the unsurpassed background correction capability of high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS), which allows pyrolysis temperatures as low as 300 °C to be used. The samples were prepared as oil-in-water emulsions, and aqueous standards emulsified in the same way were used for calibration. Total vanadium has been determined using a pyrolysis temperature of 400 °C, and “thermally stable” vanadium using a pyrolysis temperature of 800 °C. The content of total vanadium in 12 Brazilian crude oil samples was found to be between less than 0.04 and about 30 mg kg −1. The volatile fraction was between 5 and 51% of the total content, and there was no correlation between the total and the volatile vanadium content. The limits of detection and quantification were 0.04 and 0.12 mg kg −1 of V in crude oil, respectively, based on a mass of 2 g of oil in 10 mL of emulsion. The precision was better than 4% at the 3 mg kg −1 level and better than 1.5% at the 30 mg kg −1 level of V in crude oil.