Determination of ultratrace boron concentrations in uranium oxide by isotope dilution-thermal ionization mass spectrometry using a simplified separation procedure

Boron was determined at sub-ppm levels in uranium oxide by ID-TIMS. Following nitric acid dissolution, a solvent extraction method was adapted for extraction of boron by 5% 2-ethylhexane-1,3-diol in chloroform followed by evaporation of the extractant in presence of sodium carbonate and mannitol. This procedure allowed TIMS analysis of boron by monitoring the Na₂BO ₂ ⁺ ions formed from the sodium borate salt in the ion source. Reproducibility of about 1% was obtained for boron determination in the three different uranium oxide samples containing sub-ppm amounts of boron.     

Isotope dilution-thermal ionisation mass spectrometric analysis for tin in a fly ash material

Isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) analysis has been applied to the determination of tin in a fly ash sample supplied by the EC Joint Research Centre (Ispra, Italy). The proposed procedure includes the silica gel/phosphoric acid technique for tin thermal ionisation activation and a strict heating protocol for isotope ratio measurements. Instrumental mass discrimination factor has been previously determined measuring a natural tin standard solution. Spike solution has been prepared from ¹¹²Sn-enriched metal and quantified by reverse isotope dilution analysis. Two sample aliquots were spiked and tin was extracted with 4.5 M HCl during 25 min ultrasound exposure time. Due to the complex matrix of this fly ash material, a two-step purification stage using ion-exchange chromatography was required prior TIMS analysis. Obtained results for the two sample-spike blends (10.11 ± 0.55 and 10.50 ± 0.64 μmol g⁻¹) are comparable, both value and uncertainty. Also a good reproducibility is observed between measurements. The proposed ID-TIMS procedure, as a primary method and due to the lack of fly ash reference materials certified for tin content, can be used to validate more routine methodologies applied to tin determination in this kind of samples.     

Determination of K-factors for isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry

K-factors (= certified isotope ratio/observed isotope ratio) are determined for the isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry. An mdf of 0.07% and 0.18% per mass unit differing by a factor of about 3, is obtained for uranium and plutonium, respectively, employing double rhenium filament assembly in the ion source and Faraday cup as the detector using the presently available isotopic reference materials of uranium and plutonium.     

Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF₂ as sample compound. With the help of a fluorinating agent negatively charged MgF₃ molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF₂ molecules. The MgF₂ technique has been applied in the certification of a candidate ²⁶Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS.     

Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF₂ as sample compound. With the help of a fluorinating agent negatively charged MgF₃ molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF₂ molecules. The MgF₂ technique has been applied in the certification of a candidate ²⁶Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS. Received: 14 December 1998 / Revised: 5 March 1999 / Accepted: 11 March 1999     

Determination of Ba, Cd, Cu, Pb and Zn in saliva by isotope dilution direct injection inductively coupled plasma mass spectrometry

Trace elements in small sample volumes of saliva were determined by coupling a high efficiency direct injection nebulizer to inductively coupled plasma mass spectrometry and employing quantification by isotope dilution. Aliquots of 0.4 ml of human saliva were mixed with 0.1 ml of concentrated nitric acid and diluted to 2 ml with water. Sample solutions were spiked with an isotopic solution enriched in 135Ba, 112Cd, 65Cu, 206Pb and 66Zn. The amount of each isotope added to the samples and the measurement procedure were adjusted to attain precise analytical results calculated from the isotope ratios 135Ba/138Ba, 112Cd/114Cd, 65Cu/63Cu, 206Pb/208Pb and 66Zn/68Zn. Data acquisition for Ba, Cu and Zn isotopes was performed for a single sample injection of 50 microl and in another sample injection the Cd and Pb isotopes were measured. Concentrations ranging from 5.0 to 16 microg l(-1) for Ba, from 0.50 to 1.1 microg l(-1) for Cd, from 6.0 to 50 microg l(-1) for Cu, from 0.8 to 18.8 microg l(-1) for Pb and from 46.0 to 230 microg l(-1) for Zn were found in saliva samples. Detection limits of 0.11, 0.03, 0.40, 0.05 and 0.59 microg l(-1) were determined for Ba, Cd, Cu, Pb and Zn, respectively. The concentrations found by isotope dilution were in agreement with those of the completely digested samples quantified by external calibration. The direct analysis of 30 samples per hour was attained with the proposed procedure, avoiding time-consuming digestion steps, contamination risks and matrix effects.     

Determination of ochratoxin A in meat products by high-performance liquid chromatography coupled to electrospray ionisation sequential mass spectrometry

A method based on liquid chromatography with electrospray ionisation ion trap mass spectrometry, for the determination of ochratoxin A (OTA) in meat products using ochratoxin B (OTB) as an internal standard, is described. Fragmentation patterns of OTA and OTB were studied by sequential mass spectrometry. Trace determination was then accomplished by consecutive reaction monitoring (CRM) of a fragment obtained by MS(3) experiments. This led to a better signal-to-noise ratio and to a higher specificity of the technique. The response to OTA was linear over at least one concentration decade with a limit of detection of 0.6 ng/g. The method was applied to pig tissue samples naturally contaminated by OTA.     

Determination of IGF-I in horse plasma by LC electrospray ionisation mass spectrometry

The insulin-like-growth factor (IGF-I) peptide is considered to be the main indirect marker for growth hormone administration (GH) in a horse. Further to a previous investigation on measurement of IGF-I in plasma samples by mass spectrometry, this study focuses on quantitative and qualitative analysis of intact IGF-I in horse plasma. First, protein-transposing software has been developed for IGF-I to facilitate its quantification by HPLC–electrospray–ion-trap mass spectrometry. Second, product-ion scan experiments on IGF-I have been conducted on standard samples, non-fortified equine plasma samples, fortified plasma samples, and equine GH post-administration samples. This “top-down” approach method enables characterisation of fragment ions corresponding to the carboxy terminal end, which can be useful for the confirmation of the presence of IGF-I in plasma samples. Figure Structure of IGF-I and amino acid sequences of IGF-I and R3 IGF-I. Deconvolution mass spectra of the IGF-I and R3 IGF-I mixture     

Determination of cyanuric acid using exact matching isotope dilution mass spectrometry

A high‐accuracy double isotope dilution mass spectrometric method using an exact matching approach with GC coupled to a mass spectrometer for the analysis of cyanuric acid in fortified milk powder was developed. Various parameters for sample clean‐up such as the type of SPE cartridge, GC column and type of derivatizing agent used were investigated. The method was found to be linear in the concentration range of 0.03 to 2 mg/kg of cyanuric acid in milk powder. LOD and LOQ were found to be 0.9 and 3 μg/kg, respectively. Recoveries in the range of 95.7 to 102.2% were obtained for the in‐house fortified milk powder samples, with RSD of measurements in the range of 0.2 to 3.0%. A metrological approach was undertaken to examine all possible biases that contributed to the combined measurement uncertainty of the method. This high‐accuracy method can serve as a reference method for techniques commonly applied in routine testing laboratories.     

Determination of the plutonium concentration by isotope dilution mass spectrometry using239Pu as a spike

A method is described for the determination of plutonium concentration in the presence of a bulk of other impurities by isotope dilution mass spectrometry /IDMS/ using²³⁹Pu as a spike. The method involves the addition of²³⁹Pu spike / 90 atom%/ to samples with²³⁹Pu / 70 atom%/ and vice versa. After ensuring chemical exchange between the sample and the spike isotopes, plutonium is purified by conventional anion exchange procedure in 7M HNO₃ medium.²³⁹Pu/²⁴⁰Pu atom ratio in the purified spiked sample is determined with high precision /better than 0.1%/ using a thermal ionization mass spectrometer. Concentration of plutonium in the sample is calculated from the changes in²³⁹Pu/²⁴⁰Pu atom ratio in the spiked mixture. Results obtained on different plutonium samples using²³⁹Pu as a spike are compared with those obtained by the use of²⁴²Pu spike. Precision and accuracy comparable to those achieved by using²⁴²Pu are demonstrated. The method provides an alternative in the event of non-availability of enriched²⁴²Pu or²⁴⁴Pu required in IDMS of plutonium and at the same time, offers certain advantages over the use of²⁴²Pu or²⁴⁴Pu spike.     

Determination of Ag, Cd, Pb, Zn and Pd in sea-water by thermal-ionization isotope-dilution mass spectrometry

The concentrations of Ag, Cd, Pb, Zn and Pd in sea-water have been determined by thermal-ionization isotope-dilution mass spectrometry. The concentrations found, in ng/kg, were 0.6 +/- 0.4 Ag, 1.9 +/- 0.4 Cd, 18 +/- 8 Pb, 30 +/- 8 Zn and < 4 Pd. These levels are lower than some reported previously. Determination of Pd in sea-water is reported for the first time.     

Determination of benzidine in urine using capillary gas chromatography and negative-ion chemical ionisation mass spectrometry

Summary A highly sensitive and specific gas chromatographic-mass spectrometric (GC-MS) assay for the determination of benzidine in urine is reported. It is based on the solvent extraction of the hydrolysed benzidine conjugates, together with the deuterium-labelled benzidine-d₈ added as an internal standard, and a two-phase derivatisation procedure using pentafluoropropionic anhydride (PFPA) in the presence of pyridine as the phase-transfer catalyst. The reaction is complete within 5 min at room temperature. The pentafluoropropyl derivatives are quantified through capillary column GC-MS using selected ion monitoring (SIM) in the negative-ion chemical ionisation mode (NICI). The lower limit of detection for benzidine was 0.5 g/l and the calibration plot showed linearity between 2 g/l and 200 g/l. The recovery of the analyte added to pooled urine was above 82%. Analysis of 20 urine samples from un-exposed persons and 20 urine specimens of workers employed in a polyurethane-making plant using this procedure showed no substances likely to manifest false positive results in the range of interest.     

Determination of niacin in food materials by liquid chromatography using isotope dilution mass spectrometry

The availability of deuterium-labeled nicotinic acid makes stable isotope dilution mass spectromerty (MS) coupled with liquid chromatography (LC) an attractive option for the determination of the water-soluble B-vitamin niacin in food samples. A method was developed based on acid digestion, solid-phase extraction with a strong cation exchange column, and reversed-phase chromatography with a C18 column. Detection is by positive ion electrospray MS. Analysis in selected ion recording mode is subject to interference problems similar to those found with other LC determinations of niacin, but the additional selectivity of multiple reaction monitoring mode largely eliminates interference problems. The method was applied to 6 different food matrixes and to appropriate reference materials, including milk samples with niacin levels near 1 ppm. The method exhibited good accuracy, based on levels obtained for the reference materials, and relative standard deviations in the range of 0.5-5%.     

Determination of fission product ruthenium by isotope dilution mass spectrometry

Isotope dilution mass spectrometry using enriched isotope⁹⁶Ru as a spike was applied to the determination of ruthenium as a fission product. Ruthenium in the solution was oxidized to RuO₄ by Ce/IV/ and separated from coexisting metal elements by distillation. Silica-gel technique was employed to enhance ion current of ruthenium in the mass spectrometric measurement. The lower detection limit was 0.005 g ml^–1 and the relative standard deviations /n=3/ for 1.2 and 0.05 g ml^–1 of ruthenium were 0.2 and 0.5%, respectively.     

Characterisation of nicotine and related compounds using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their detection by liquid chromatography/electrospray ionisation mass spectrometry

Electrospray ionisation ion trap mass spectrometry (ESI-MS(n)) has been used to study the fragmentation patterns of nicotine and nine of its related compounds. From this study certain characteristic fragmentations are apparent with generally the pyrrolidine or piperidine ring being subject to chemical modifications. The structures of the product ions proposed for the ESI-MS(n) study have been supported by results from electrospray ionisation quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). Compounds with pyrrolidine and piperidine rings that possess an unsubstituted N atom have been shown to lose NH(3) at the MS(2) stage. Those compounds with N-methyl groups lose CH(3)NH(2) at the MS(2) stage. The loss of NH(3) or CH(3)NH(2) leaves the corresponding rings opened and this is followed by ring closure at the pyridine-2 carbon atom. Mono-N-oxides fragment in a similar way but the di-N-oxide can also fragment by cleavage of the bond between the pyridine and pyrrolidine rings. Cotinine also can undergo cleavage of this bond between the rings.This data therefore provides useful information on how substituents and the nature of the non-pyridine ring can affect the fragmentation patterns of nicotine and its related compounds. This information can be used in the characterisation of these compounds by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) which results in the separation of nicotine and its related compounds with limits of detection (LODs) ranging from 15 to 105 ng/mL. The use of LC/ESI-MS to study nicotine-containing samples resulted in the simultaneous and unambiguous identification of seven of the compounds discussed in this paper: cotinine identified at retention time 12.5 min (with its [M+H](+) ion at m/z 177), nornicotine 16.0 min (m/z 149), anatabine 18.0 min (m/z 161), myosmine 18.5 min (m/z 147), anabasine 20.4 min (m/z 163), nicotine 22.2 min (m/z 163), and nicotyrine 31.4 min (m/z 159). For quality control of nicotine replacement therapy products, these nicotine impurities can be readily identified and determined at levels up to 0.3% for single impurities and up to 1.0% for total impurities.     

萃取色层分离同位素稀释ICP-MS测定空气中费克 量钚

ICP-MS测定环境样品中超痕量^2^3^9Pu时,^2^3^8UH^+会对m/z239的测量带来干扰。测得UH^+的产生几率为4.6×10^-^5,通过三正辛胺色层分离后,对铀的去除率为10^4,可以有效地去除^2^3^8UH^+离子峰对^2^3^9Pu测定的干扰。钚的回收率为75%。同位素稀释法对^2^3^9Pu的检出限为4.5×10^-^1^5g/mL,方法的定量测定限为16×10^-^1^5g/mL。用所建立的方法测得我国某地区空气中^2^3^9Pu的浓度为4.8×10^-^1^7g/m^3。     

Determination of sites citrullinated by peptidylarginine deiminase using 18O stable isotope labeling and mass spectrometry

Peptidylarginine deiminase (PADI) is an enzyme which catalyzes conversion of arginine residues into citrulline residues in proteins. Citrullination is known to be related to autoimmune diseases including rheumatoid arthritis. Previous work in this laboratory succeeded in identifying citrullinated sites of human fibrinogen by mass spectrometry, but discrimination between citrullination and deamidation of asparagines and glutamine required time-consuming and labor-intensive inspection of tandem mass spectra. In this work a stable isotope is utilized to improve on a previous method for the determination of citrullinated sites by mass spectrometry. Since an oxygen atom is incorporated into the citrulline residue from H(2)O in citrullination by PADI, peptides citrullinated in 50% H(2)(18)O would show a characteristic isotope distribution different from natural abundance, and thus determination of citrullinated sites is expected to be much easier. To verify the utility of this new method, the sites of citrullination of human fibrinogen by human PADI4 were investigated using 50% H(2)(18)O. Compared with the previous method, this new method identified citrullinated sites more easily and effectively, while both the determined citrullinated sites and protein sequence coverage were unaltered.     

The characterisation of selected antidepressant drugs using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their determination by high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

The electrospray ionisation ion trap tandem mass spectrometry (ESI-MS(n)) of selected antidepressant drugs, i.e., citalopram, fluoxetine, mirtazapine, paroxetine, sertraline, and venlafaxine, has been investigated. Sequential product ion fragmentation experiments (MS(n)) have been performed in order to elucidate the degradation pathways for the [M+H](+) ions and their predominant product ions. These MS(n) experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as molecules such as H(2)O, amines and phenols. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with mirtazapine, fragmentation initially occurs at the latter ring with the former being predictably resistant to fragmentation. Also, when an amine-containing drug molecule such as fluoxetine also contains a functional group, which liberates a phenol with a significantly lower DeltaH(f) (0) value than that of the corresponding amine, the phenol is preferentially liberated. The structures of product ions proposed for ESI-MS(n) can be supported by electrospray ionisation quadrupole-time-of-flight tandem mass spectrometry (ESI-QToF-MS/MS). These molecules can be identified and determined in mixtures at low ng/mL concentrations by the application of high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry (HPLC/ESI-MS(2)), which can also be used for their analysis in hair samples.