Total iodine in nutritional and biological reference materials using neutron activation analysis and inductively coupled plasma mass spectrometry

In a recent collaborative study intended to extend the variety of reference materials certified for iodine, three mineralization methods were developed to quantify the total iodine content of biological and nutritional materials by inductively coupled plasma mass spectrometry (ICP-MS). A mixture of water-soluble tertiary amines was used as the matrix solution for two oxygen combustion methods and for a simple extraction at room temperature. Calibrations with matrix-matched standards, internal calibration, and isotope dilution with ¹²⁹I were used. Good agreement between neutron activation analysis (NAA) and the two combustion methods was observed except for < 0.1 mg kg^–1 iodine concentrations. The amine extraction method gave the most reliable results for the mixed diet, milk powder, and infant formula samples but low recoveries for other biological materials owing to an incomplete extraction and solubilization of iodine. The NAA method, with its freedom from reagent blank, is a useful technique for the independent determination of iodine in biological, environmental and food matrices, especially for verification of iodine results obtained by ICP-MS.     

Iodine determination in biological materials Options for sample preparation and final determination

This paper describes the development of various new acid sample decomposition methods, as well as an extraction (leaching) method and compares them with the “Sch?niger Combustion” technique. The methods have been developed as sample preparation techniques for iodine determination in biological materials, especially in solid samples. ICP-MS (inductively coupled plasma mass spectrometry) and a catalytic technique are employed and discussed for the final determination of iodine concentrations. Accuracy and reliability of the different analytical methods are shown in the examples of different CRMs (certified reference materials) available for iodine. The results of an interlaboratory comparison are specifically presented for the extraction (leaching) method. Received: 11 May 1998 / Revised: 14 June 1998 / Accepted: 16 June 1998     

Determination of total and non-water soluble iodine in atmospheric aerosols by thermal extraction and spectrometric detection (TESI)

Iodine has recently been of interest in atmospheric chemistry due to its role in tropospheric ozone depletion, modification of the HO/HO₂ ratio and aerosol nucleation. Gas-phase iodine chemistry is tightly coupled to the aerosol phase through heterogeneous reactions, which are dependent on iodine concentrations and speciation in the aerosol. To date, the only method available for total iodine determination in aerosols is collection on filters by impaction and quantification by neutron activation analysis (NAA). NAA is not widely available to all working groups and is costly to commission. Here, we present a method to determine total iodine concentrations in aerosol impact filter samples by combustion of filter sub-samples (∼5 cm²) at 1,000 °C, trapping in deionised water and quantification by UV/Vis spectroscopy. Both quartz and cellulose filters were analysed from four separate sampling campaigns. The method proved to be sensitive (3σ = 6 ng absolute iodine ≈ 3 pmol m⁻³) precise (RSD ∼ 5%) and accurate, as determined by external and standard addition calibrations. Total iodine concentrations ranged from 10 pmol m⁻³ over the Southern Ocean to 100 pmol m⁻³ over the tropical Atlantic, in agreement with previous estimates. The soluble iodine concentration (extracted with water and measured by ICP-MS) was then subtracted from the total iodine to yield non-water-soluble iodine (NSI). The NSI fraction ranged from 20% to 53% of total iodine, and thus can be significant in some cases.     

Epithermal instrumental neutron activation analysis of biological reference materials for iodine

Epithermal instrumental neutron activation analysis (EINAA) methods have been optimized and applied to several biological reference materials and selected food items for the determination of iodine. The method involves irradiation of the samples for different periods in epi-cadmium and/or epi-boron flux of the Dalhousie University SLOWPOKE-2 reactor and direct counting without any pre-treatment on a 25-cm³ hyperpure Ge detector. The 443 keV photopeak of ¹²⁸I is used for assaying the iodine content. Precision of measurements, expressed as the relative standard deviation, is 10–15% at 200–500 ppb and 3–12% at 500–6000 ppb levels of iodine. Accuracy of iodine measurements is within 5%. The detection limits for iodine in several biological materials with cadmium and boron, either alone or a combination of the two, as thermal neutron shields have been found to vary between 0.1 and 0.4 mg · kg^–1 for different periods of irradiation, decay and counting. The results suggest that the EINAA methods can be successfully applied to biological materials for routine analysis of iodine at levels higher than 200 ppb.     

Trace iodine quantitation in biological samples by mass spectrometric methods: The optimum internal standard

Accurate quantitation of iodine in biological samples is essential for studies of nutrition and medicine, as well as for epidemiological studies for monitoring intake of this essential nutrient. Despite the importance of accurate measurement, a standardized method for iodine analysis of biological samples is yet to be established. We have evaluated the effectiveness of ⁷²Ge, ¹¹⁵In, and ¹²⁹I as internal standards for measurement of iodine in milk and urine samples by induction coupled plasma mass spectrometry (ICP-MS) and of ³⁵Cl¹⁸O₄⁻, ¹²⁹I⁻, and 2-chlorobenzenesulfonate (2-CBS) as internal standards for ion chromatography-tandem mass spectrometry (IC-MS/MS). We found recovery of iodine to be markedly low when IC-MS/MS was used without an internal standard. Percent recovery was similarly low using ³⁵Cl¹⁸O₄ as an internal standard for milk and unpredictable when used for urine. 2-Chlorobenzebenzenesulfonate provided accurate recovery of iodine from milk, but overestimated iodine in urine samples by as much as a factor of 2. Percent recovery of iodine from milk and urine using ICP-MS without an internal standard was ∼120%. Use of ¹¹⁵In predicted approximately 60% of known values for both milk and urine samples. ⁷²Ge provided reasonable and consistent percent recovery for iodine in milk samples (∼108%) but resulted in ∼80% recovery of iodine from urine. Use of ¹²⁹I as an internal standard resulted in excellent recovery of iodine from both milk and urine samples using either IC-MS/MS and ICP-MS.     

Iodine determination in food by inductively coupled plasma mass spectrometry after digestion by microwave-induced combustion

Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour were completely combusted using the MIC system. Ammonium nitrate (6 mol l⁻¹ solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O₂. The use of H₂O, 0.9 mmol l⁻¹ H₂O₂, 10 to 50 mmol l⁻¹ (NH₄)₂CO₃ and 56 mmol l⁻¹ tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux step after the combustion process. Digestion of food samples by pressurized microwave-assisted acid digestion, microwave-assisted extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99% were obtained using MIC and 50 mmol l⁻¹ (NH₄)₂CO₃ or 56 mmol l⁻¹ tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification by MIC and further ICP-MS determination was 0.002 μg g⁻¹. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples by each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium for further iodine determination by ICP-MS.     

Boron determination in biological materials by inductively coupled plasma atomic emission and mass spectrometry: effects of sample dissolution methods

This study compares four sample dissolution methods for Boron determination in two National Institute of Standard and Technology (NIST) botanical Standard Reference Materials (SRMs) and three Agriculture Canada/NIST RMs, each having a reference (certified or best estimate) B concentration. The dissolution treatments consisted of: 1) dry ashing at 500° C, 2) wet digestion with HNO₃ + H₂O₂, 3) extraction with hot HNO₃ and 4) closed vessel microwave dissolution. The samples were spiked before and after imposing dissolution treatments to study B recovery by inductively coupled plasma mass spectrometric (ICP-MS) analysis. Microwave digests of NIST SRM 1515 and some in-house RMs were also used to compare the B values of ICP-MS and ICP-AES (atomic emission spectrometry). While all three digestion methods (dry ashing, wet ashing and microwave) dissolved botanical samples, only the microwave method worked well for animal tissues. In terms of B values in these materials, there was no significant difference among the three digestion treatments. Near 100% recovery of B spiked before and after the sample dissolution indicates that there may not be a significant loss of B during the dissolution process used in this study. Extraction with hot HNO₃ was as effective as the three digestion treatments, and B values for this method agreed well with reference values. For the botanical materials studied, the B values determined by ICP-AES were not significantly different from ICP-MS values. This study shows that a simple, time and labor efficient hot HNO₃ extraction is as effective as other digestion/dissolution methods for quantitative B recovery from biological materials. Received: 13 June 1996 / Revised: 17 September 1996 / Accepted: 19 September 1996     

Determination of metals and metalloids in light and heavy crude oil by ICP-MS after digestion by microwave-induced combustion

A method for light and heavy crude oil digestion using microwave-induced combustion (MIC) in closed vessels is described for further determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V, and Zn by inductively coupled plasma mass spectrometry (ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels and analyte determination by inductively coupled plasma optical emission spectrometry (ICP OES) were also used for results comparison. For MIC procedure, samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 µl of 6 mol l^− 1 ammonium nitrate as aid for ignition. The concentration of nitric acid used as absorbing solution was evaluated (1, 2, 4, 7, 10 and 14 mol l^− 1) using an additional reflux step after combustion. Accuracy was evaluated for As, Ba, Ni, Se V, and Zn using certified reference material (CRM) with similar matrix composition and for Cr, Fe, K, Mg, Mn, and Mo by neutron activation analysis (NAA). Recovery tests were also performed for all the analytes by MIC and they were better than 97% using 2 mol l^− 1 nitric acid as absorbing solution (with reflux step). Agreement with certified values and NAA results was better than 95%. Using MIC it was possible to obtain lower limits of detection (LODs) by ICP-MS and also by ICP OES in comparison with those obtained by MW-AD. In spite of both sample preparation techniques were apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using diluted nitric acid as absorbing solution that is an important aspect to minimize interferences by ICP-MS and ICP OES. In order to avoid polyatomic interferences on ⁵²Cr and ⁵⁶Fe determinations by ICP-MS, a dynamic reaction cell with ammonia gas was used. Residual carbon content in digests obtained by MW-AD and MIC was 15% and < 1%, respectively. Using MIC the simultaneous digestion of 8 samples was possible in less than 30 min.     

Multielement neutron activation analysis of biological materials using chemical group separation and Ge(Li) gamma spectrometry

Neutron activation analysis (NAA) for the determination of some trace elements in biological materials is described. The method presented permits the simple and rapid determination of Se, Ag, Au, Sb, Pt (via¹⁹⁹Au), Hg, Co, Ni (via⁵⁸Co), Fe, Zn, Mo, Sn, Cr, Cd, Cu and As after radiochemical separation from Na, K, Cs, Rb and partially Br. For this purpose, postirradiation separation by extraction with mercury or zinc amalgam was used. Separation of gold by extraction with ethyl acetate or by precipitation with dimethylglyoxime was applied for the determination of gold and platinum in biological materials.     

Determination of iodine in diverse botanical and dietary matrices by pre-irradiation combustion followed by neutron activation analysis

Summary The method chosen for determination of iodine in this investigation is an extension of an existing analytical technique to food samples which was developed for environmental samples. The method is based on pre-irradiation combustion of the sample to liberate iodine, trapping the iodine on charcoal, and quantitating the element by neutron activation analysis (NAA). Existing botanical and dietary reference materials were used to check the validity of the method. Several mixed diet samples with high fat content from the U.S. Total Diet Study and composites of cereals with both low and high iodine content were analyzed. This method of pre-irradiation combustion followed by NAA has been shown to be a viable technique for the determination of iodine in dietary samples. However, with a detection limit of about 50 ng of iodine, large amounts of sample (>1 g) are typically required for each determination.     

Pyrohydrolysis of carbon nanotubes for Br and I determination by ICP-MS

Bromine and iodine determination was performed in carbon nanotubes (CNTs) by inductively coupled plasma mass spectrometry (ICP-MS) after sample preparation using pyrohydrolysis. Samples of CNTs (up to 500 mg) were mixed with 750 mg of V₂O₅ and heated at 950 °C during 12.5 min in a quartz tube under water vapor and air. The main operational conditions of pyrohydrolysis (carrier gas, absorbing solution, heating time, sample mass and use of V₂O₅) were evaluated. Accuracy was evaluated using certified reference materials (CRM) with similar matrix and also by comparison of results obtained after digestion of samples by microwave-induced combustion (MIC) and determination by ICP-MS. Agreement with CRM values was higher than 97% for Br and better than 96% in comparison with reference values (MIC/ICP-MS) of Br and I in CNTs samples. The limit of detection of the method for Br and I determination by ICP-MS was 0.05 and 0.004 μg g^? 1, respectively. Using a relatively simple and low cost pyrohydrolysis apparatus up to four samples can be processed per hour. The pyrohydrolysis sample preparation procedure is easy to be performed and provide a clean solution for analysis by ICP-MS, which is very attractive for Br and I control in CNTs.     

Iodine determination in biological materials by ICP-MS

The present work describes an analytical procedure for the determination of the total iodine content in biological materials (serum, milk, plants, tissues etc.). Liquid samples can be directly analyzed after dilution, if necessary, by ICP-MS. Milk powder, plants and tissues were dissolved by using a modified simple Schöninger combustion, subsequently the residue was taken up in 0.1 mol/l NaOH and this solution was analyzed by ICP-MS. The detection limit is in the range of 0.01 g/l. The method was tested using different CRMs certified for the iodine content.     

Comparison of the TEVA-Spec resin and liquid-liquid extraction methods for the separation of technetium in soil samples

When ICP-MS is used for⁹⁹Tc measurements, elements which interfere with⁹⁹Tc counting should be removed. In this study, a separation method using a novel chromatographic resin (TEVA·Spec^® resin) was compared with a liquid-liquid extraction (LLX) method for separation and concentration of⁹⁹Tc which was trapped in a solution after combustion of environmental soil samples. The results showed that Tc could be separated from Ru at high recoveries with both separation methods. Molybdenum, however, was not removed by LLX, while more than 99% of Mo in soil samples were removed by TEVA·Spec resin.     

Determination of iodine in biological materials by pseudo-cyclic epithermal INAA using anti-coincidence gamma-ray spectrometry and estimation of expanded uncertainties

Epithermal instrumental neutron activation analysis (EINAA) technique in conjunction with anti-coincidence gamma-ray spectrometry (AC) has been applied for the determination of ppm to ppb levels of iodine in biological materials containing high levels of Al, Br, Cl, K, Mn, and Na. Both conventional EINAA-AC and pseudo-cyclic EINAA-AC (PC-EINAA-AC) methods using a combination of Cd and B filters have been developed using Dalhousie University SLOWPOKE-2 reactor (DUSR) facility. The expanded uncertainties (EU), at about 95% confidence level, for iodine in biological materials by EINAA-AC varied between 6 and 10%. The advantages of the non-destructive PC-EINAA-AC method has been successfully demonstrated by analyzing the NIST Pine Needles (SRM 1575) containing a low amount of iodine in presence of high quantities of Mn and other interfering elements where an iodine content of 92.8 μg kg⁻¹ with an EU of 6.1 μg kg⁻¹ and a detection limit of 40 μg kg⁻¹ has been obtained at the end of fourth cycle.     

Microwave assisted extraction of iodine and bromine from edible seaweed for inductively coupled plasma-mass spectrometry determination

The feasibility of microwave energy to assist the solubilisation of edible seaweed samples by tetramethylammonium hydroxide (TMAH) has been investigated to extract iodine and bromine. Inductively coupled plasma-mass spectrometry (ICP-MS) has been used as a multi-element detector. Variables affecting the microwave assisted extraction/solubilisation (temperature, TMAH volume, ramp time and hold time) were firstly screened by applying a fractional factorial design (2^5-1 + 2), resolution V and 2 centre points. When extracting both halogens, results showed statistical significance (confidence interval of 95%) for TMAH volume and temperature, and also for the two order interaction between both variables. Therefore, these two variables were finally optimized by a 2² + star orthogonal central composite design with 5 centre points and 2 replicates, and optimum values of 200 °C and 10 mL for temperature and TMAH volume, respectively, were found. The extraction time (ramp and hold times) was found statistically non-significant, and values of 10 and 5 min were chosen for the ramp time and the hold time, respectively. This means a fast microwave heating cycle. Repeatability of the over-all procedure has been found to be 6% for both elements, while iodine and bromine concentrations of 24.6 and 19.9 ng g⁻¹, respectively, were established for the limit of detection. Accuracy of the method was assessed by analyzing the NIES-09 (Sargasso, Sargassum fulvellum) certified reference material (CRM) and the iodine and bromine concentrations found have been in good agreement with the indicative values for this CRM. Finally, the method was applied to several edible dried and canned seaweed samples.     

Iodine separation procedure for the determination of129I and127I in soil by neutron activation analysis

A radiochemical neutron activation analytical method for the determination of¹²⁹I and¹²⁷I in soil samples was studied. Iodine was separated from the sample prior to the irradiation by volatilization, i.e. by combustion of the sample and trapping of the iodine in an alkaline solution together with a reducing agent. This method enables one to digest samples containing up to 100 g dry matter. The chemical yield was mostly more than 90%. After irradiation the iodine fraction was further purified by solvent extraction. The detection limit of the¹²⁹I/¹²⁷I ratio was 1×10^–9.     

Microwave-assisted solid phase extraction prior to ICP-MS determination of Pd and Pt in environmental and biological samples

A sensitive and selective microwave-assisted solid phase extraction procedure coupled to inductively coupled plasma-mass spectrometry (ICP-MS) is proposed for palladium (Pd) and platinum (Pt) quantification in environmental and biological samples. Pd and Pt were quantitatively retained on commercial thioureido propyl functionalised silica gel packed inside a home-made glass microcolumn, and later eluted with 0.5% thiourea solution under microwave irradiation, followed by ICP-MS determination. The main variables affecting the procedural stages (i.e., sorption and desorption) and ICP-MS determination were optimised. The best conditions found were: (a) sorption: sample acidity, 1?M HCl; sample flow rate, 3?mL?min^?1; (b) desorption: microwave radiation, power 800?W; eluent concentration, 0.5% thiourea; eluent flow rate, 0.5?mL?min^?1; (c) ICP-MS determination: nebuliser feeding, free aspiration (0.3?mL?min^?1); internal standard, Rh (5?µg?L^?1). Analyte recoveries were higher than 90% and concentration factors up to 90 and 92 were achieved for Pd and Pt, respectively. Depending on the conditions, the methodological limits of detection were down to 0.2?ng?L^?1 for both analytes and repeatability, expressed as RSD%, varied between 1.3 and 11.0%. A method selectivity evaluation showed that most of the ICP-MS interferents were either quantitatively separated or more than 86% eliminated, except for Cu (elimination efficiency around 30%). Finally, the method was successfully used to determine Pd in certified reference materials (i.e. human urine and serum) and Pd and Pt in PM₁₀ airborne particulate matter fractions.     

Feasibility of ultra-trace determination of bromine and iodine in honey by ICP-MS using high sample mass in microwave-induced combustion

This work demonstrates the feasibility of ultra-trace determination of halogens in biological samples by inductively coupled plasma mass spectrometry (ICP-MS) after decomposition by microwave-induced combustion (MIC). The conventional MIC method was improved to allow the combustion of samples with mass higher than that used in previous works in order to achieve better limits of detection (LODs). The applicability of the proposed method for ultra-trace determination of bromine and iodine in organic samples was demonstrated here using honey. It was possible to decompose up to 1000 mg of honey using microcrystalline cellulose as a combustion aid and polyethylene film for sample wrapping. After combustion, analytes were absorbed using 50 mmol L^?1 NH₄OH and recoveries for Br and I were between 99 and 104 %, and relative standard deviations were lower than 5 %. Microwave-assisted alkaline dissolution (MA-AD) was also evaluated for honey sample preparation using NH₄OH or tetramethylammonium hydroxide solutions. However, the LODs for the MA-AD method were unsuitable because the high carbon content in digests required a dilution step prior to the analysis by ICP-MS. The LODs obtained by MIC were improved from 1143 to 34 ng g^?1 for Br and from 571 to 6.0 ng g^?1 for I, when compared to the MA-AD method. Furthermore, it was possible to decompose up to eight samples simultaneously in 30 min (including the cooling step) with very low reagent consumption and consequently lower generation of effluents, making MIC method well suited for routine ultra-trace determination of Br and I in honey.

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Graphical Abstract A high mass of honey was efficiently digested by MIC for subsequent Br and I determination by ICP-MS

     

Online determination of copper in aluminum alloy by microchip solvent extraction using isotope dilution ICP-MS method

Isotope dilution mass spectroscopy (IDMS)/ICP-MS combined with microchip solvent extraction was successfully applied for the online determination of copper in an aluminum alloy. The microchip solvent extraction was developed for the separation of Cu from major element, and optimal pH range was wider than that of the batchwise extraction method. The dimensions of the microchip were 30 mm × 70 mm and that of micro-channel on the microchip was 180 μm wide and 40 μm deep. The copper complex with 8-hydroxyquinoline was extracted into o-xylene at pH 5.5 and back extracted with 0.1 mol l⁻¹ nitric acid at flow rate of 20 μl min⁻¹. The total extraction efficiency (water/organic solvent/nitric acid) was around 40%. IDMS/ICP-MS was coupled with solvent extraction for precise determination of Cu. The extraction and back-extraction on the microchip took about 1 s and the total measurement time for the IDMS/ICP-MS was about 40 s/sample. The blank value of this method was 0.1 ng g⁻¹. The proposed method was used for the determination of Cu in Al standard materials (JSAC 0121-C, The Japan Society for Analytical Chemistry and 7074 Al alloy, Nippon Light Metal Co. Ltd.). The obtained analytical results are in good agreement with the certified values.     

Robust microwave-assisted extraction protocol for determination of total mercury and methylmercury in fish tissues

A rapid and efficient closed vessel microwave-assisted extraction (MAE) method based on acidic leaching was developed and optimized for the extraction of total mercury (Hg), inorganic mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) from fish tissues. The quantitative extraction of total Hg and mercury species from biological samples was achieved by using 5 mol L⁻¹ HCl and 0.25 mol L⁻¹ NaCl during 10 min at 60 °C. Total Hg content was determined using inductively coupled plasma mass spectrometry (ICP-MS). Mercury species were measured by liquid chromatography hyphenated with inductively coupled plasma mass spectrometry (LC-ICP-MS). The method was validated using biological certified reference materials ERM-CE464, DOLT-3, and NIST SRM-1946. The analytical results were in good agreement with the certified reference values of total Hg and CH₃Hg⁺ at a 95% confidence level. Further, accuracy validation using speciated isotope-dilution mass spectrometry (SIDMS, as described in the EPA Method 6800) was carried out. SIDMS was also applied to study and correct for unwanted species transformation reactions during and/or after sample preparation steps. For the studied reference materials, no statistically significant transformation between mercury species was observed during the extraction and determination procedures. The proposed method was successfully applied to fish tissues with good agreement between SIDMS results and external calibration (EC) results. Interspecies transformations in fish tissues were slightly higher than certified reference materials due to differences in matrix composition. Depending on the type of fish tissue, up to 10.24% of Hg²⁺ was methylated and up to 1.75% of CH₃Hg⁺ was demethylated to Hg²⁺.