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.     

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. Received: 11 February 1998 / Revised: 21 April 1998 / Accepted: 16 June 1998     

Rapid IC-ICP/MS method for simultaneous analysis of iodoacetic acids, bromoacetic acids, bromate, and other related halogenated compounds in water

Haloacetic acids (HAAs) and bromate are toxic water disinfection by-products (DBPs) that the U.S. Environmental Protection Agency has regulated in drinking water. Iodoacetic acids (IAAs) are the emerging DBPs that have been recently found in disinfected drinking waters with higher toxicity than their corresponding chloro- and bromo-acetic acids. This study has developed a new rapid and sensitive method for simultaneous analysis of six brominated and four iodinated acetic acids, bromate, iodate, bromide, and iodide using ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). Mono-, di- and tri-chloroacetic acids are not detected by this method because the sensitivity of ICP-MS analysis for chlorine is poor. Following IC separation, an Elan DRC-e ICP-MS was used for detection, with quantitation utilizing m/z of 79, 127, and 74 amu for Br, I, and Ge (optional internal standard) species, respectively. Although the primary method used was an external standard procedure, an internal standard method approach is discussed herein as well. Calibration and validation were done in a variety of natural and disinfection-treated water samples. The method detection limits (MDLs) in natural water ranged from 0.33 to 0.72 μg L⁻¹ for iodine species, and from 1.36 to 3.28 μg L⁻¹ for bromine species. Spiked recoveries were between 67% and 123%, while relative standard deviations ranged from 0.2% to 12.8% for replicate samples. This method was applied to detect the bromine and iodine species in drinking water, groundwater, surface water, and swimming pool water.     

Room temperature acid sonication ICP-MS multielemental analysis of milk

Room temperature acid sonication of milk samples is proposed as a fast alternative methodology for the determination of the total content of 45 elements (Li, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Mo, Ag, Cd, In, Sn, U, Sb, Te, Cs, Ba, Hg, Pb, Bi, Th, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Hf and Ta) in milk by inductively coupled plasma mass spectrometry (ICP-MS). The aforementioned procedure involves a 10 min sample pre-treatment. Measurements were made in quantitative and semiquantitative (Totalquant^®) modes of analysis using Rh as internal standard and Be, Ge, Tb and Re for internal calibration of the equipment in the semiquantitative mode. The selected isotopes were in general the most abundant ones of each element, except in cases where polyatomic or isobaric interferences were detected. Results of total concentrations in 10 liquid and 11 powdered commercially available milk samples were presented. Method validation was performed by measuring a SRM NIST-1549 non-fat milk powder and through the use of recovery experiments. Additionally, the proposed methodology was compared with a method based on a previous microwave-assisted digestion of samples and a direct analysis of 1:4 diluted samples.     

Determination of urine melamine by validated isotopic ultra‐performance liquid chromatography/tandem mass spectrometry

Little is known about melamine (MEL) analysis in children's urine. In this study, an isotopic ultra‐performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and systematically validated for the analysis of MEL in urine. The method is easily performed and comprises acidification, solid‐phase extraction (SPE) and UPLC/MS/MS analysis. ¹³C₃N₃(¹⁵NH₂)₃ was used as the internal standard (IS) for calibration. Transition ions m/z 127 > 85 of MEL and m/z 133 > 89 of the IS were used for quantification and m/z 127 > 68 of MEL was used for quantitative confirmation. Recovery and precision were assessed to guarantee the applicability of the method. The limit of quantification (LOQ) was 0.01 µg/mL while the calculated method detection limit was 0.006 µg/mL. The mean recoveries ranged from 96–99%. The method was then applied to analyze urine samples from children who had potentially consumed MEL‐tainted dairy products during screening in Taiwan. Ten nephrolithiasis cases and 20 age‐ and gender‐matched controls were selected for this study. Three out of the 10 nephrolithiasis cases had elevated levels of MEL. Comparatively, twenty age‐ and gender‐matched non‐nephrolithiasis controls consuming Taiwan brand milk powder all showed MEL levels lower than the detection limit except for two children with background levels of 0.02 µg/mL. The background level in these children urine samples was established by UPLC/MS/MS analysis. Positive results of urine MEL tests might be associated with nephrolithiasis in these candidates. Measurement of urine MEL concentration can be helpful in confirming MEL‐related nephrolithiasis, but its clinical application needs further clarification. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Iodine-129 in Missouri rain and milk

A combination of neutron activation and mass spectrometry was used to measure¹²⁹I and¹²⁷I in local samples of rain and milk. The general distribution of values for the¹²⁹I/¹²⁷I ratio in these samples can be understood in terms of well established geochemical and biological cycles of iodine, but the origin of high¹²⁹I/¹²⁷I ratios in a few of the samples collected in 1976 is not understood. The procedures used to extract and purify iodine were tested by monitoring¹³¹I in rain and milk following the Chinese atmospheric bomb test of September 17, 1977.     

Selective preconcentration and determination of iodine species in milk samples using polymer inclusion sorbent

A method to determine low levels of iodine species namely I⁻ and IO₃⁻ in aqueous samples was developed and applied to milk and milk powder samples. It is based on selective preconcentration of I⁻ in polymer inclusion sorbent (PIS) and neutron activation analysis (NAA) of I⁻ sorbed in PIS. The PIS was found to be highly selective for I⁻ in presence of IO₃⁻ and other anions commonly present in the milk samples. In order to preconcentrate total I⁻ + IO₃⁻ content in the PIS, IO₃⁻ was reduced to I⁻ using a mixture of acetic acid and ascorbic acid. It was found that total iodine content in milk could be determined with epithermal neutron activation analysis (ENAA). A scheme was developed to determine I⁻, IO₃⁻ and total iodine. The developed method was applied to milk reference materials (NIST SRM-1549 and IAEA-RM-153 milk powder) and a commercially available milk powder. The scheme for estimation of iodine in different forms was validated by using reference material NIST SRM-1549.     

Determination of iodine and molybdenum in milk by quadrupole ICP-MS

A reliable method for the determination of iodine and molybdenum in milk samples, using alkaline digestion with tetramethylammonium hydroxide and hydrogen peroxide, followed by quadrupole ICP-MS analysis, has been developed and tested using certified reference materials. The use of He+O2 (1.0 ml min(-1) and 0.6 ml min(-1)) in the collision-reaction cell of the mass spectrometer to remove (129)Xe+-- initially to enable the determination of low levels of 129I--also resulted in the quantitative conversion of Mo(+) to MoO2+ which enabled the molybdenum in the milk to be determined at similar mass to the iodine with the use of Sb as a common internal standard. In order to separate and pre-concentrate iodine at sub microg l(-1) concentrations, a novel method was developed using a cation-exchange column loaded with Pd2+ and Ca2+ ions to selectively retain iodide followed by elution with a small volume of ammonium thiosulfate. This method showed excellent results for aqueous iodide solutions, although the complex milk digest matrix made the method unsuitable for such samples. An investigation of the iodine species formed during oxidation and extraction of milk sample digests was carried out with a view to controlling the iodine chemistry.     

Quantitative selenium speciation in human urine by using liquid chromatography–electrospray tandem mass spectrometry

A liquid chromatography–electrospray-tandem mass spectrometry (ES-MS/MS) method was developed for the speciation analysis of four organic selenium species of relevance to human urinary metabolism, namely trimethylselenomium ion (TMSe⁺), selenomethionine (SeMet) and the two selenosugars, methyl 2-acetamido-2-deoxy-1-seleno-β-d-galactos/-glucos-amine (SeGalNAc and SeGluNAc, respectively). Their chromatographic separation was achieved by using a cation exchange pre-column coupled in-series with a reversed-phase high-performance liquid chromatography column, along with an isocratic mobile phase. Online detection was performed using ES-MS/MS in selective reaction monitoring mode. SeGalNAc was detected as the major human urinary metabolite of selenium in the samples analysed, whereas TMSe⁺ was detected in the urine of one volunteer before and after receiving a selenium supplement. SeMet was not detected as a urine excretory metabolite in this study. Spiking experiments performed with the urine samples revealed significant signal suppression caused by coeluting matrix constituents. To overcome such interferences, isotopically labelled ¹³CD₃⁸²SeGalNAc was used as an internal standard, whereas in the absence of an isotopically labelled internal standard for TMSe⁺, the standard addition method was applied. Quality control for the accurate quantitation of TMSe⁺ and SeGalNAc was carried out by analysing spiked human urine samples with appropriate selenium standards over a concentration range of 10–50 μg Se L⁻¹. The method has achieved a limit of detection in the presence of urine matrix comparable to that of HPLC-inductively coupled plasma-mass spectrometry for the four selenium species: 1.0 μg Se L⁻¹ for TMSe⁺, 5.6 μg Se L⁻¹ for SeMet, and 0.1 μg Se L⁻¹ for both SeGalNAc and SeGluNAc.     

Routine clinical determination of lead,arsenic, cadmium,and thallium in urine and whole blood by inductively coupled plasma mass spectrometry

For the measurement of As, Cd, Pb, and Tl in urine or whole blood, judicious choices of internal standard elements for matrix correction and the development of a refined isobaric arsenic correction are necessary to produce accurate ICP-MS results. Ga and Rh are chosen as internal standards for As and Cd respectively. Bi is better for the correction of Pb and Tl than Re. An empirically derived equation relating the measurement of ¹⁶O³⁵Cl to the ⁴⁰Ar³⁵Cl contribution to the arsenic signal at mass 75 is refined by measuring the responses at mass 51 and 75 for urines with added hydrochloric acid. Overall, ICP-MS results for blood and urine are within 6% of Zeeman GFAAS results for patient samples. For surveys, the overall average of ICP-MS results is within 3% of target.     

Determination of the chemical forms of iodine with IC-ICP-MS and its application to environmental samples

An online analytical system using ion chromatography (IC) followed by inductively coupled plasma mass spectrometry (ICP-MS) was developed for the separate determination of I⁻ and IO₃⁻ in aqueous solutions with a detection limit 0.1–1 μg 1/1. The total iodine concentration was also directly determined by ICP-MS. Iodine in several environmental samples (i.e., rain, river water, brine, and soil solution) was successfully determined with information on its chemical form. The release of I⁻ into soil solution with decreasing Eh was observed in an incubation experiment with flooded soil. An iodine form other than I⁻ and IO₃⁻ was observed in several environmental samples.     

Development of a routine method for the simultaneous confirmation and determination of clenbuterol in urine by minimal labeling isotope pattern deconvolution and GC-EI-MS

A novel and fast routine method for the simultaneous determination and confirmation of clenbuterol in bovine and human urine samples by gas chromatography electron ionization mass spectrometry (GC-EI-MS) has been developed. The method employs isotope dilution mass spectrometry (IDMS) and is based on a combination of minimal labeling (a single ¹³C label in the molecule) and isotope pattern deconvolution (IPD). This new methodology does not require the construction of a methodological calibration graph, and was compared with the classical IDMS procedure employed in clenbuterol analysis based on the use of a deuterated compound as internal standard (d₉-clenbuterol) and a calibration curve. The sample preparation consists of simple extraction with dichloromethane, which was dried and derivatized with chloro(chloromethyl)dimethylsilane, generating a cyclic dimethylsilamorpholine (DMS) derivative suitable for GC(EI)MS detection and identification. This compound produces five intense ions in the electron ionization source, which allow the presence of clenbuterol to be confirmed in just one analysis, as demanded by European Union directives. The accuracy of the method was studied by performing recovery experiments at different concentration levels (from 0.3 to 5 ng g⁻¹) in 5 mL bovine urine samples using two labeled compounds: an in-house-synthesized ¹³C₁-clenbuterol and a commercially available d₉-clenbuterol. The detection limit of the method in human urine was 0.050 ng g⁻¹ with a sample volume of 10 mL, and is thus suitable for antidoping control purposes. Finally, the ¹³C₁-clenbuterol standard was employed for the determination of clenbuterol in two reference materials, BCR-503 and BCR-504 (lyophilized bovine urine). The concentrations obtained were in agreement with the certified values, with a reproducibility of below 1% RSD.     

Food safety evaluation: Detection and confirmation of chloramphenicol in milk by high performance liquid chromatography-tandem mass spectrometry

A simple and rapid procedure for extraction of chloramphenicol (CAP) in milk and analysis by high-performance liquid chromatography coupled with quadrupole mass spectrometry in tandem was developed. The method consisted of one step of liquid-liquid extraction using ethyl acetate and acidified water (10 mmol L⁻¹ formic acid) and HPLC-MS/MS detection. CAP-D5 was used as internal standard. The method was validated according to Commission Decision 2002/657/EC. The calibration curves were linear, with typical r² values higher than 0.98. Absolute recovery of CAP from milk proved to be more than 95%, however CAP-D5 absolute recovery was 75%. The method was accurate and reproducible, being successfully applied to the monitoring of CAP in milk samples obtained from the Brazilian market. Decision limit (CCα) was 0.05 ng mL⁻¹ and detection capability (CCβ) was 0.09 ng mL⁻¹.     

Direct quantification of 11‐nor‐Δ9‐tetrahydrocannabinol‐9‐carboxylic acid in urine by liquid chromatography/tandem mass spectrometry in relation to doping control analysis

An accurate and precise method for the quantification of 11‐nor‐Δ⁹‐tetrahydrocannabinol‐9‐carboxylic acid (THCA) in urine by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for doping analysis purposes has been developed. The method involves the use of only 200 µL of urine and the use of D₉‐THCA as internal standard. No extraction procedure is used. The urine samples are hydrolysed using sodium hydroxide and diluted with a mixture of methanol/glacial acetic acid (1:1). Chromatographic separation is achieved using a C8 column with gradient elution. All MS and MS/MS parameters were optimised in both positive and negative electrospray ionisation modes. For the identification and the quantification of THCA three product ions are monitored in both ionisation modes. The method is linear over the studied range (5–40 ng/mL), with satisfactory intra‐and inter‐assay precision, and the relative standard deviations (RSDs) are lower than 15%. Good accuracy is achieved with bias less than 10% at all levels tested. No significant matrix effects are observed. The selectivity and specificity are satisfactory, and no interferences are detected. The LC/MS/MS method was applied for the analysis of 48 real urine samples previously analysed with a routine gas chromatography/mass spectrometry (GC/MS) method. A good correlation between the two methods was obtained (r² > 0.98) with a slope close to 1. Copyright © 2010 John Wiley & Sons, Ltd.     

Ultra-trace determination of iodine in sediments and biological material using UV photochemical generation-inductively coupled plasma mass spectrometry

Several sample preparation techniques have been evaluated for the determination of iodine using UV-photochemical generation-quadrupole inductively coupled plasma mass spectrometry. Thermal decomposition of samples at 1000 °C followed by capture of the liberated iodine in dilute acetic acid permitted subsequent UV-photochemical generation of a volatile iodine species that serves to enhance sensitivity 25-fold over conventional solution nebulization, delivering reagent blank detection limits of 8.75 pg g^{–1 127}I and 0.075 pg g^–1 129I for solid samples (400 mg test mass). The methodology was validated through determination of total iodine in several Standard Reference Materials, including NIST 1572 Citrus leaves, NIST 1549 Non-fat milk powder, NIST 1566a Oyster tissue and NIST 2709 San Joaquin Soil. Liberation of iodine from samples and its collection as well as photochemical generation were quantitative, permitting calibration to be achieved using standards prepared in dilute acetic acid.     

Internal standardization in graphite furnace atomic absorption spectrometry: Comparative use of As and Ge to minimize matrix effects on Se determination in milk

Arsenic and germanium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium in milk by graphite furnace atomic absorption spectrometry (GFAAS) using tubes with integrated platform, pre-treated with W together with Pd as chemical modifier. The efficiency of As and Ge as internal standards for 25 μg L^− 1 Se plus 500 μg L^− 1 As or Ge in diluted (1 + 9 v/v) milk plus 1.0% (v/v) HNO₃ was evaluated by means of correlation graphs plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x). The equations that describe the linear regression were: A^As = − 0.004 ± 0.019 + 1.02 ± 0.019 A^Se (r = 0.9967 ± 0.005); A^Ge = − 0.017 ± 0.015 + 1.01 ± 0.015 A^Se (r = 0.9978 ± 0.004). Samples and reference solutions were automatically spiked with 500 μg L^− 1 Ge or As and 1.0% (v/v) HNO₃ by the autosampler. For 20 μL of aqueous standard solutions, analytical curves in the 5.00–40.0 μg L^− 1 Se range were established using the ratio of Se absorbance to internal standard absorbance (A^Se / A^IS) versus analyte concentration, and good linear correlations were obtained. The characteristic mass was 40 pg Se. Limits of detection were 0.55 and 0.40 μg L^− 1 with As and Ge as the internal standard, respectively. Relative standard deviations (RSD) for a sample containing 25 μg L^− 1 Se were 1.2% and 1.0% (n = 12) using As and Ge, respectively. The RSD without internal standardization was about 6%. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 99–105% range with IS and in the 70–80% range without IS. Using Ge as the internal standard, results of analysis of standard reference materials were in agreement with certified values at a 95% confidence level. The selenium concentration for 10 analyzed milk samples varied from 5.0 to 20 μg L^− 1.     

Analysis of low-level 129I in brine using accelerator mass spectrometry

An improved solvent extraction procedure for iodine separation from brine samples has been applied at Xi’an Accelerator Mass Spectrometry (AMS) center. Oil in the brine sample has to be removed to avoid appearance of the third phase during solvent extraction and to improve the chemical yield of iodine. The small amount of oil remained in the water phase was first removed by phase separation through settling down sufficiently based on their immiscibility, and then by filtration through a cellulose filter, on which oil was absorbed and removed. After oil removed, extraction recovery of iodine could achieve more than 90 %. The sodium bisulfite as an effective reductant should be added before acidification to avoid loss of iodine by formation of I₂ in sample via reaction of iodate and iodide at pH 1–2, and then pH was adjusted to 1–2 to reduce the iodate to iodide followed by oxidation of iodide to I₂ and solvent extraction to separate all inorganic iodine. As a pre-nuclear era sample, ¹²⁹I/¹²⁷I ratio in brine is normally more than two orders of magnitude lower than that in present surface environmental samples, so prevention of cross-contamination and memory effect in apparatus during processing procedure are very critical for obtaining reliable results, and monitoring the procedure blank is very important for analytical quality of ¹²⁹I. The ¹²⁹I/¹²⁷I isotopic ratio in the brine samples and procedure blank of iodine reagents were measured to be (1.9–2.7) × 10^?13 and 2.08 × 10^?13, respectively, 3–4 orders of magnitudes lower than that in environmental samples in Xi’an, and the result of procedure blank is in the same level as the previous experiments in past 3 years, indicating contamination is not observed in our method.