Use of a capacitively coupled microwave plasma (CMP) with Ar, N2 and air as working gases for atomic spectrometric elemental determinations in aqueous solutions and oils

A comparative study was performed of 600 W capacitively coupled microwave plasmas (CMP) with different plasma gases (Ar, N₂ and air) and aerosol generation with the aid of a Légère pneumatic nebulizer. Detection limits with the different working gases are in the order of 15–4000 ng/mL for Fe, Cr, Zn, Mg and Ca in aqueous solutions. The influence of organic solutions on the stability of the plasma is discussed. The determination of Co, Cr, Fe, Mg and Ni in different oil samples by OES is described, using an air-CMP and pneumatic nebulization after dilution of the oils by 20% with cyclohexane. The detection limits for these elements are in the 100–400 ng/g range. Results obtained for a waste motor oil for the elements mentioned in the concentration range of 4–50 μg/g were found to be in good agreement with those obtained by ICP-OES after digestion of the oils at high pressure in PTFE vessels. Received: 10 March 1997 / Revised: 23 May 1997 / Accepted: 30 May 1997     

The application of butanol as dilution agent for the inductively coupled plasma-atomic emission spectrometric determination of boron and phosphorus in lubricating oils

An evaluation of butanol-1 as dilution solvent for the determination of boron (B) and phosphorus (P) in lubricating oils by inductively coupled plasma-atomic emission spectrometry (ICP-AES) has been performed. Standard solutions of boric acid and tri-n-butyl phosphate (TBP) in butanol were employed as calibrants for B and P, respectively. Solutions of phosphoric acid and tris(2-ethylhexyl)phosphate (TEHP) in butanol were also tested as possible P standards. Increased concentrations of oil in the sample in the range of 0 to 20% showed no significant effects on B and P emission intensities indicating that matrix matching is not required for lubricating oils of about 2–15 cPoise. Detection limits in absence of spectral interferences were 0.06 μg B/g oil and 2 μg P/g oil. Overall estimated precision was 2.5% for B concentrations above 4 μg/g oil, and 6.5% for P concentrations above 20 μg/g oil. We evaluated the performance of a high resolution scanning spectrometer for mitigating the effects of overlapping spectral interferences from iron (Fe) and copper (Cu) on B and P emission lines. An interference from Fe 249.782 nm on the primary B line at 249.773 nm is observed for Fe concentrations higher than 100 μg/g oil, but a secondary B line at 249.678 nm is completely resolved from Fe 249.653 nm. In the case of P 213.618 nm, a contribution of the right wing of a Cu line at 213.598 nm generates a signal equivalent to P 18 μg/g oil for Cu 1000 μg/g oil. Received: 25 June 1997 / Revised: 16 September 1997 / Accepted: 7 October 1997     

The application of butanol as dilution agent for the inductively coupled plasma-atomic emission spectrometric determination of boron and phosphorus in lubricating oils

An evaluation of butanol-1 as dilution solvent for the determination of boron (B) and phosphorus (P) in lubricating oils by inductively coupled plasma-atomic emission spectrometry (ICP-AES) has been performed. Standard solutions of boric acid and tri-n-butyl phosphate (TBP) in butanol were employed as calibrants for B and P, respectively. Solutions of phosphoric acid and tris(2-ethylhexyl)phosphate (TEHP) in butanol were also tested as possible P standards. Increased concentrations of oil in the sample in the range of 0 to 20% showed no significant effects on B and P emission intensities indicating that matrix matching is not required for lubricating oils of about 2–15 cPoise. Detection limits in absence of spectral interferences were 0.06 μg B/g oil and 2 μg P/g oil. Overall estimated precision was 2.5% for B concentrations above 4 μg/g oil, and 6.5% for P concentrations above 20 μg/g oil. We evaluated the performance of a high resolution scanning spectrometer for mitigating the effects of overlapping spectral interferences from iron (Fe) and copper (Cu) on B and P emission lines. An interference from Fe 249.782 nm on the primary B line at 249.773 nm is observed for Fe concentrations higher than 100 μg/g oil, but a secondary B line at 249.678 nm is completely resolved from Fe 249.653 nm. In the case of P 213.618 nm, a contribution of the right wing of a Cu line at 213.598 nm generates a signal equivalent to P 18 μg/g oil for Cu 1000 μg/g oil. Received: 25 June 1997 / Revised: 16 September 1997 / Accepted: 7 October 1997     

Determination of naturally occurring radionuclides in ultrapure organic liquids

For the determination of trace elements in organic liquids radiochemical neutron activation analysis has been combined with counting methods geared to various decay modes of indicator radionuclides leading to a high sensitivity required for ultrapure samples. The activation parameters such as irradiation time, sample mass and neutron flux have been enlarged to the maximum possible in the available irradiation facility. Separation yields and adsorption losses have been studied in detail for a set of elements in order to rule out losses during the separation process. The attainable limits of detection are 2 · 10^–16g/g for U and Lu, in the 5 · 10^–15g/g range for Th and Sm, in the 1 · 10^–14g/g region for La, 5 · 10^–13g/g for Rb, Cd and 2 · 10^–12g/g for K and In. Although the analysis focused on traces of naturally occurring radioisotopes, results for Cr, Fe, W and Zn are presented as well. Received: 14 May 1997 / Revised: 28 August 1997 / Accepted: 9 September 1997     

Availability of essential trace elements in medicinal herbs used for diabetes mellitus and their possible correlations

Four plant parts (leaves, roots, fruits and seeds) of twenty samples of sixteen antidiabetic herbs including three commercially marketed capsules have been analyzed for 6 minor (Na, K, Ca, Cl, Mg, and P) and 21 trace (As, Ba, Br, Ce, Co, Cr, Cs, Cu, Eu, Fe, Hg, La, Mn, Rb, Sb, Sc, Se, Sm, Th, V and Zn) elements by instrumental neutron activation analysis (INAA). Further, Ni, Cd and Pb contents were determined by AAS. Elemental data were validated by simultaneously analyzing reference material (RM), MPH-2 Mixed Polish Herbs. Several elements such as Cr and V (1–2 μg/g), Rb (10–40 μg/g), Cs (80–300 ng/g), Se (∼100 ng/g) and Zn (25–60 μg/g) play an important role in diabetes mellitus. Interelemental linear correlations have been observed for Cu vs. Zn (r = 0.89) and Rb vs. Cs (r = 0.87). K/P ratio varies in a narrow range with a mean value of 6.2 ± 1.4. Toxic elements As and Hg were found in <1 μg/g whereas Cd and Pb were in ∼5 μg/g and <10 μg/g, respectively.     

Determination of trace amounts of rare earth and other elements in rice samples by ICP-AES with sample introduction by tungsten-coil electrothermal vaporization

Summary A device with tungsten-coil electrothermal vaporization for sample introduction into ICP has been proposed. It was applied to the determination of trace amounts of rare earth and other elements in rice samples. Several influencing factors were investigated in detail, such as drying and vaporization parameters, carrier gas flow rate, volume of vaporization chamber and matrix effects. Under optimal experimental conditions, the detection limits for Mg, Cu, Mn, Cr, Fe, Co, Ni and eight rare earth elements are of the order of 10⁻⁹−10⁻¹¹ g. The detection limits for the rare earth elements tested by the present method are comparable to and, in most instances, exceed those for the GFAAS and conventional pneumatic nebulisation-ICP-AES. A precision with RSD<6% was obtained.     

Determination of Wear Metals in Marine Lubricating Oils by Microwave Digestion and Atomic Absorption Spectrometry

 The difficulties associated with the development of a microwave-assisted acid digestion of lubricating oils in determination of wear metals are presented. The interest of this sample treatment lies in its basis for determining the total metal contents with enough sensitivity by flame atomic absorption spectrometry (FAAS). It allows earlier diagnosis of the engine state than is obtained by the widely applied simple dilution procedure. Another advantage is the avoidance of contamination and loss of the metals to be determined. The procedure employs nitric acid and hydrogen peroxide in a four-stage programme. Fe, Cu, Cr and Pb are determined by FAAS as representative of engine wear. The limits of detection are 0.1 μg/g for Fe and Cr and 0.05 μg/g for Cu and Pb. A comparison with other procedures is presented for spiked samples. Different types of used lubricating oils supplied by an oil company were analysed to prove the suitability of the procedure proposed. Received November 11, 1998. Revision Februray 20, 1999.     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Application of a hexapole collision and reaction cell in ICP-MS Part II: Analytical figures of merit and first applications

The application of an ion-guiding gas-filled hexapole collision/reaction cell in ICP-MS has been studied to characterize the analytical figures of merit that can be achieved with this approach. For the elements investigated, application of a buffer and a reaction gas resulted in improved sensitivities which are lowest for Be with about 7 · 10⁷ cps per μg mL^–1 and highest for Ba with about ?6 · 10⁸ cps per μg mL^–1. Relative standard deviations (RSD) < 0.1% were obtained. Application of the reaction gas H₂ was used to suppress polyatomic ions caused by argon. The reduction amounted up to four orders of magnitude so that elements such as Ca, K, Cr, Fe, As and Se could be analyzed in nitric and hydrochloric acid or in methanol. Detection limits of 6 pg mL^–1 for Cr in 2% methanol, 23 pg mL^–1 for As and 9 pg mL^–1 for Se in 0.28 M HCl were achieved. For other elements detection limits ?< 1 pg mL^–1 were realized in the medium and high mass range. Accuracy was proved using the NIST 1643d standard reference material. Received: 10 May 1999 / Revised: 4 June 1999 / Accepted: 12 June 1999     

Application of nondestructive X-ray fluorescence analysis to determine the element composition of medicinal plants

A nondestructive X-ray fluorescence technique has been developed to determine Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Ba, and Pb in plants. The line element intensities were measured by an S4 Pioneer X-ray sequence spectrometer (Bruker AXS, Germany). The inversely proportional relationship was obtained between the analyte line intensity and mass of the plant, pressed on boric acid backing, for elements with an atomic number 11 < Z < 20. It was found that reduction of plant mass from 6 to 1 g leads to an increase in element determination sensitivity. The detection limits for 1 g of pressed plant were evaluated as μg/g: 5–20 (Na, Mg, Al); 1–4 (Si, P, S, Cl, K, Ca, Ti, Ba, Pb); 0.4-0.8 (Cr, Mn, Fe, Ni, Br, Cu, Zn, Rb and Sr). This technique was applied to determine the element composition of violets of Violaceae family, which are used in medicine.     

Flame AAS/flame AES for trace determination in fresh and used lubricating oils with sample introduction by hydraulic high-pressure nebulization

In hydraulic high-pressure nebulization (HHPN) an aerosol is produced by means of an HPLC-pump and a special nebulization nozzle, applying a pressure of about 200 bar. This spray technique has been employed for sample introduction of mineral oil samples in flame atomic absorption/flame emission spectrometry. The determination of the trace elements Al, Cr, Cu, Fe, K, Na, Ni, Pb, Si and V has been investigated. Viscosity hardly acts upon the sensitivity of the determination, thereby avoiding a time consuming dilution of oil samples. By means of two interconnecting sampling valves a calibration method based on the standard addition technique can be performed which is both simple and easy to carry out. In samples of used oils, results for Cu and Pb equalled those of XRF-analysis. Regarding Fe traces, data obtained from AAS and XRF measurement correlate. In comparison with sample uptake by pneumatic nebulization, which is restricted to diluted oil samples, detection limits decrease by a factor of 2 to 4, indicating the dilution required in pneumatic nebulization.     

Flame AAS/flame AES for trace determination in fresh and used lubricating oils with sample introduction by hydraulic high-pressure nebulization

In hydraulic high-pressure nebulization (HHPN) an aerosol is produced by means of an HPLC-pump and a special nebulization nozzle, applying a pressure of about 200 bar. This spray technique has been employed for sample introduction of mineral oil samples in flame atomic absorption/flame emission spectrometry. The determination of the trace elements Al, Cr, Cu, Fe, K, Na, Ni, Pb, Si and V has been investigated. Viscosity hardly acts upon the sensitivity of the determination, thereby avoiding a time consuming dilution of oil samples. By means of two interconnecting sampling valves a calibration method based on the standard addition technique can be performed which is both simple and easy to carry out. In samples of used oils, results for Cu and Pb equalled those of XRF-analysis. Regarding Fe traces, data obtained from AAS and XRF measurement correlate. In comparison with sample uptake by pneumatic nebulization, which is restricted to diluted oil samples, detection limits decrease by a factor of 2 to 4, indicating the dilution required in pneumatic nebulization.     

Slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry for the direct determination of metal impurities in aluminium oxide ceramic powders

A new analytical procedure for the direct determination of metal impurities (Cr, Cu, Fe and V) in aluminium oxide ceramic powders by slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) is reported. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of impurity elements in aluminium oxide ceramic powders from the graphite tube. A vaporization stage with a long ramp time and a short hold time provided the possibility of temporal analyte-matrix separation. The experimental results indicated that a 10 μL 1% m/v slurry of aluminium oxide could be destroyed and vaporized completely with 600 μg PTFE under the selected conditions. Two aluminium oxide ceramic powder samples were used without any additional pretreatment. Analytical results obtained by using standard addition method with aqueous standard solution were checked by comparison of the results with pneumatic nebulization (PN)-ICP-AES based on the wet-chemical decomposition and analyte-matrix separation. The limits of detection (LODs) between 0.30 μg g^–1 (Fe ) and 0.08 μg g^–1 (Cu) were achieved, and, the repeatability of measurements was mainly better than 10%. Received: 28 August 2000 / Revised: 1 November 2000 / Accepted: 12 November 2000     

A pilot study for the preparation of a new Reference Material based on antarctic krill

The preparation of new Certified Reference Materials (CRMs) of antarctic matrices forms the backbone of an ongoing project in the framework of the Italian National Program for Antarctic Research. The first CRM of this kind (MURST-ISS-A1 Antarctic Marine Sediment) is already available. The second phase focuses on the certification of antarctic krill, a small shrimp extremely abundant in the Southern Ocean. The total mass of krill available for this purpose is approximately 44 kg and results from the combination of three different catches (Ross Sea, Marguerite Bay and Livingston Island, respectively). The quantification of the following elements in the raw mass appears to be affordable by current analytical techniques, values being in the range of (in μg/g) 0.11–0.30 for As, 0.03–0.12 for Cd, 0.06–0.23 for Cr, 6.1–21 for Cu, 5.7–7.6 for Fe, 0.005–0.008 for Hg, 0.7–1.2 for Mn, 0.013– 0.077 for Ni, 0.04–0.57 for Pb and 12–16 for Zn. On the other hand, the average values ascertained in freeze-dried krill are as a rule one order of magnitude higher, i.e., (in μg/g), 3.2 for As, 0.6 for Cd, 1.8 for Cr, 75 for Cu, 61 for Fe, 0.025 for Hg, 4.6 for Mn, 0.7 for Ni, 2.1 for Pb and 81 for Zn. Information on the pretreatment of krill and details on the planned certification campaign are also given. Received: 10 June 1997 / Revised: 24 September 1997 / Accepted: 28 September 1997     

Multi-element trace determinations in pure alkaline earth fluoride powders by high-resolution ICP-MS using wet-chemical sample preparation and laser ablation

Four alternative analytical procedures for the determination of ten important trace impurities (Mg, Cr, Fe, Cu, Zn, Sr, Zr, Cd, Ba, and Pb) in pure alkaline earth fluoride powders were applied using high-resolution inductively coupled plasma mass spectrometry (ICP-MS). Two procedures are based on a wet-chemical microwave digestion with boric acid and quantification by the standard addition technique and isotope dilution mass spectrometry (IDMS), respectively. In addition, analyses are also performed by laser ablation as a direct solid sampling technique applying matrix-matched external calibration as well as isotope dilution of the powdered sample. For most elements good agreement between the different methods is found. Detection limits for laser ablation vary between 0.05 ng g^–1 for Zr and 20 ng g^–1 for Mg. They are about one to two orders of magnitude lower than those of the wet-chemical procedures, which is mainly due to the high dilution factor during the sample preparation step. Advantages and restrictions of the different analytical procedures are discussed with respect to their routine applicability. Due to its relatively high accuracy, low detection limits, and time-efficiency LA-ICP-IDMS is the preferred choice if no standard reference materials are available.     

Spectroscopic and analytical characteristics of an inductively coupled argon plasma combined with hydride generation with or without simultaneous introduction of the sample aerosol for optical emission spectrometry

A radially viewed inductively coupled argon plasma was used for optical emission spectrometry of volatile species formed by reaction with NaBH₄ (hydride generation). The volatile hydrides were either introduced into the plasma alone or at the same time as a sample aerosol generated by pneumatic nebulization with a commercially available Concomitant Metals Analyzer. The effects of the forward power, the presence of pre-reducing agents [(NH₂)₂SC, KI, KBr and hot HCl], the occurrence of easily ionized elements (Ca, K, Mg and Na) in the analyte solutions on the excitation temperature (as measured via Ar atomic lines) and the electron number density were investigated for both of the sample introduction modes applied. The detection limits and the signal-to-background intensity ratios for As, Bi, Sb, Se and Sn lines were also evalutated and were observed to deteriorate with increasing power. When simultaneous hydride generation and pneumatic nebulization was employed under optimized experimental conditions, detection limits of 3.5, 2.9, 4.3, 1.5 and 2.1 μg L⁻¹ for As, Bi, Sb, Se and Sn, respectively, were obtained, and the intensities of the analytical lines for elements that do not form volatile hydrides were found to be 40% (Cd), 30% (Ni), 20% (Co, Cr, Fe, Mn and Zn) and 10% (Cu, Mg, V) greater than those obtained when only pneumatic nebulization was used.     

Elemental composition of drinking water supplies in three states in Southeastern Nigeria

The levels of some trace elements; Co, Mn, Cu, Zn, Cr, Cd, Pb, Fe, Hg, Se, As, Ni and minor elements; Na, K, Ca and Mg were determined in public drinking water supplies (public taps and groundwaters) in three states in Southeastern Nigeria using energy dispersive X-ray fluorescence spectrometry (EDXRF) and flame atomic absorption spectrometry (FAAS). The mean levels of most of the trace elements in the groundwater samples were below the World Health Organization (WHO) drinking water quality limits, the only exception being Hg whose mean value of 3.69 μg/l exceeded the WHO limit of 1.0 μg/l. Violations of the WHO limits were also observed for Fe, Zn, Se and Pb in some of the groundwater samples. In the public tap samples only Hg violated the WHO limit.     

Trace analysis of gallium arsenide by selective evaporation of the matrix with bromine vapours

Gallium arsenide samples are analyzed by graphite furnace AAS after the selective evaporation of the matrix elements as bromides with bromine vapours in a simple apparatus. The evaporation step is carried out at 280–300 ° C and it is accomplished for 0.5 g sample within 1 h. Reproducibilities of 5 to 20% were obtained. Detection limits (3 s, in ng/g) are 20 (Fe), 5.0 (Ca), 3.0 (Mg), 2.0 (Ni, Cu), 1.0 (Al), 0.5 (Pb, Co), 0.2 (Mn, Cr).     

Multi-element analysis of Ghanaian crude oils by instrumental neutron activation analysis

Instrumental neutron activation analysis based on thermal neutrons from the Ghana Research Reactor-1 facility was utilized to analyze 18 trace elements namely Al, As, Br, Ca, Cd, Cl, Co, Cu, Fe, K, Mg, Mn, Na, Ni, S, Si, V, and Zn in two different crude oil samples from the Saltpond and Jubilee field in the Saltpond, Central region and Cape Three Points, Western region of Ghana, respectively. The sulfur concentration for both samples were low and within globally accepted range of 0.1–0.5%wt for sweet crude oil. The results of the elemental analysis showed that the two samples are relatively low in trace element concentrations compared to crude oils of other countries. Higher Fe concentration in the Jubilee crude oil indicates younger oil. The V/Ni ratios obtained for crude oils from both locations imply a possible marine organic origin and also suggest the Saltpond crude oil is more matured than the Jubilee crude oil.