Isotope Dilution Mass Spectrometry Technique Research Articles

Development of cancer biomarker heat shock protein 90α certified reference material using two different isotope dilution mass spectrometry techniques.

Heat shock protein 90α (HSP90α) has been regarded as an important indicator for judging tumor metastasis and prognosis due to its significant upregulation in various tumors. Therefore, the accurate quantification of HSP90α is of great significance for clinical diagnosis and therapy of cancers. However, the lack of HSP90α certified reference material (CRM) leads to the accuracy and consistency of quantification methods not being effectively evaluated. Besides, quantitative results without traceability make comparisons between different studies difficult. In this study, an HSP90α solution CRM was developed from the recombinant protein raw material. The recombinant protein is adimer, and the purity of the CRM candidate reached 96.71%. Both amino acid analysis-isotope dilution mass spectrometry (AAA-IDMS) and unique peptide analysis-isotope dilution mass spectrometry (UPA-IDMS) were performed to measure the content of HSP90α in the solution CRM candidate, and the certified value was assessed to be 66.2 ± 8.8µg/g. Good homogeneity of the CRM was identified, and the stability examination suggested that the CRM was stable for at least 4months at - 80°C and for 7days at 4°C. With traceability to SI unit (kg), this CRM has potential to help establish ametrological traceability chain for quantification of HSP90α, which will make the quantification results standardized and comparable regardless of the quantitative methods.

Determination of methenamine residues in edible animal tissues by HPLC-MS/MS using a modified QuEChERS method: Validation and pilot survey in actual samples

A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method was developed for the determination of methenamine in edible animal tissues by high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Samples were extracted with acetonitrile, and cleaned with anhydrous sodium sulfate and primary secondary amine (PSA) sorbent. An isotope dilution mass spectrometry technique was applied to compensate for matrix effect. The separation was performed on a HILIC column, and the mobile phase composed of acetonitrile-0.1% of formic acid and 5.0 mmol/L of ammonium acetate in water. The method showed a linear relationship in the range of 1.0–20.0 μg/L for methenamine, and the determination coefficients (R2) ranged from 0.9939 to 0.9995. The limit of detection (LOD) and quantification (LOQ) for methenamine in animal tissues sample was 1.5 μg/kg and 5.0 μg/kg, respectively. The average recoveries were 86.7–109.5% at spiked levels of 5.0, 25.0, 100.0 μg/kg. The intra-day precision ranged from 2.6 to 7.0%, and the inter-day precision ranged from 4.9 to 11.3%. The validated method was successfully applied to determination of methenamine in swinish muscle, kidney and liver.

Determination of phthalate esters in Chinese spirits using isotope dilution gas chromatography with tandem mass spectrometry.

Phthalate esters are additives used in polyvinylchloride and are found as contaminants in many food products. An isotope dilution mass spectrometry technique has been developed for accurate analysis of 16 phthalate esters in Chinese spirits by adopting the 16 corresponding isotope-labeled phthalate esters. The ethanol in the spirit sample was first removed by heating with a water bath at 100°C with a stream of nitrogen, after which the residue was extracted with n-hexane twice. The phthalates collected were identified and quantified by gas chromatography with tandem mass spectrometry in multiple reaction monitoring mode. The spiking recoveries of 16 analytes ranged from 94.3 to 105.3% with relative standard deviation values of <6.5%. The detection limits for 16 analytes were <10.0 ng/g. The expanded relative uncertainties were from 3.0 to 14%. A survey was performed on Chinese spirits from the market. Six of the nine analyzed samples were contaminated by phthalates. Di-n-butyl phthalate and di-2-ethylhexyl phthalate showed higher detection frequency and concentrations. This isotope dilution gas chromatography with tandem mass spectrometry method is simple, rapid, accurate, and highly sensitive, which qualifies as a candidate reference method for the determination of phthalates in spirits.

The micro-scale synthesis of 117Sn-enriched tributyltin chloride and its characterization by GC–ICP-MS and NMR techniques

Organotin compounds (OTCs) are among the most toxic substances ever introduced to the environment by man. They are common pollutants in marine ecosystems, but are also present in the terrestrial environment, accumulated mainly in sewage sludge and landfill leachates. In investigations of the degradation and methylation processes of OTC in environmental samples, the use of enriched isotopic tracers represents a powerful analytical tool. Sn-enriched OTC are also necessary in application of the isotope dilution mass spectrometry technique for their accurate quantification. Since Sn-enriched monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) are not commercially available as single species, “in house” synthesis of individual butyltin-enriched species is necessary.In the present work, the preparation of the most toxic butyltin, namely TBT, was performed via a simple synthetic path, starting with bromination of metallic Sn, followed by butylation with butyl lithium. The tetrabutyltin (TeBT) formed was transformed to tributyltin chloride (TBTCl) using concentrated hydrochloric acid (HCl). The purity of the synthesized TBT was verified by speciation analysis using the techniques of gas chromatography coupled to inductively coupled plasma mass spectrometry (GC–ICP-MS) and nuclear magnetic resonance (NMR). The results showed that TBT had a purity of more than 97%. The remaining 3% corresponded to DBT. TBT was quantified by reverse isotope dilution GC–ICP-MS. The synthesis yield was around 60%. The advantage of this procedure over those previously reported lies in its possibility to be applied on a micro-scale (starting with 10mg of metallic Sn). This feature is of crucial importance, since enriched metallic Sn is extremely expensive. The procedure is simple and repeatable, and was successfully applied for the preparation of 117Sn-enriched TBTCl from 117Sn-enriched metal.

Comparison of Different Extraction Techniques of PCBs from Sediment Samples Using the Isotope Dilution Mass Spectrometry Technique

In this work, problems that may occur during determination of trace levels of polychlorinated biphenyls in sediment samples are described. The main error sources are connected with extraction of analytes prior to final determination. During model studies, polychlorinated biphenyls have been extracted from sediment reference material (METRANAL 2) with the use of different solvents (dichloromethane, hexane, and toluene); the process has been enhanced by mechanical shaking or ultrasound. Seven selected PCBs (PCB 28, 52, 101, 118, 138, 153, and 180, according to IUPAC) were determined in extract samples by the GC-MS technique and using the isotope dilution mass spectrometry (IDMS) technique. The results suggest that the best solvents for the isolation of PCB group compounds from sediment samples are dichloromethane and toluene. On the basis of results obtained it can be stated that increasing the number of extraction cycles to 10 and prolonging the sample ultrawave bath to 40 min do not affect the results obtained; thus, the accuracy of the procedure doesn't change from the statistical point of view.

A pilot study (APMP.QM-P19) for the measurement of melamine in milk powder

A pilot study (APMP.QM-P19) of the Asia Pacific Metrology Program for the determination of melamine at two different levels in milk powder was organized in 2010. It was the first interlaboratory comparison programme in measuring melamine in food matrices for metrology institutes in the region. Melamine was chosen as the target analyte because of the recent crises that happened in 2007 and 2008 had caused substantial concern from consumers, food manufacturers, policy makers on food safety and the food testing communities. The objectives of APMP.QM-P19 were to evaluate the testing capability of participants on the quantification of trace level melamine in milk and milk products and to investigate the degree of equivalence with respect to the assigned values. In total, 19 laboratories (11 metrology institutes and eight food testing institutes) enrolled in the study. Analytical techniques reported by participants included liquid chromatography with ultra-violet and tandem mass spectrometry, gas chromatography with high-resolution mass spectrometry and enzyme-linked immunosorbent assay. Dispersion of analytical data in the two test materials was significant, and normal Gaussian distribution of data was not observed. The median was agreed to be used as the assigned values in the programme. Metrology institutes who employed isotope dilution mass spectrometry technique were found to give more consistent results and higher degree of equivalence than others. The performance of most of the food testing institutes was not satisfactory, and they were encouraged to have a thorough review of their validation procedure and estimation of uncertainty.

Development of melamine certified reference material in milk using two different isotope dilution mass spectrometry techniques

A new certified reference material (CRM) of melamine in milk GLHK-11-02 was developed aiming to address the great demand from the testing community after the melamine crises. The material was prepared by adding an appropriate quantity of melamine into the skimmed milk samples and the final product was in the form of fine lyophilized powder. Characterization of the material relied on two newly developed gravimetric isotope dilution mass spectrometry (IDMS) methods, one using liquid chromatography–tandem mass spectrometry (LC–MS/MS) and another gas chromatography–mass spectrometry (GC–MS). Experimental parameters with crucial effects on the performance of the two IDMS methods were thoroughly investigated. These included purity of standard used, equilibration time of isotopes, efficiency of extraction methods as well as possible interferences from the matrix and melamine analogues. Precision was found to be excellent with a coefficient of variation of 2.5% for the LC–IDMS/MS ( n = 46) and 1.9% for the GC–IDMS ( n = 30) respectively. Using one-tail Student's t-test at 95% confidence interval, analytical data sets generated from the two methods were found to exhibit no significant difference. Measurement accuracy of the methods was further verified through an Asia Pacific Metrology Program (APMP) pilot study. Analytical results of the present LC–IDMS/MS for the two milk test samples at the concentration level of about 0.45 and 3.5 mg kg −1 were proven to be very good. There were excellent overlaps between our results and the assigned reference values, and the absolute deviation was less than 3.2%. Both the LC–IDMS/MS and GC–IDMS methods were shown to be sufficiently reliable and accurate for certification of the melamine CRM. Certified value of melamine in dry mass fraction in GLHK-11-02 was 1.14 mg kg −1. Expanded uncertainty due to sample inhomogeneity, long term and short term stability and variability in the characterization procedure was at 7.1% or 0.08 mg kg −1. The CRM is primarily used to provide a complete method validation for and to improve the technical competence of melamine analysis to food and chemical testing laboratories.

CORRECTION OF ANALYTICAL RESULTS FOR RECOVERY: DETERMINATION OF PAH s IN AMBIENT AIR, SOIL, AND DIESEL EMISSION CONTROL SAMPLES BY ISOTOPE DILUTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY

Results from soil, diesel emission and ambient air control particulate matter samples on the determination of 30 PAHs were evaluated to establish whether the use of recovery data would result in an improvement of the quantitation accuracy over the uncorrected data. The performance of the recovery-corrected technique was initially evaluated using recovery results from PAH standard reference material samples spiked with analogue deuterated isotopes. The results showed an excellent correlation between recoveries of natives and corresponding surrogates for all matrices studied. The practical merit of the isotope dilution mass spectrometry technique was further assessed by spiking control samples with corresponding isotopic analogues and comparing the measured concentration of natives obtained with uncorrected and recovery-corrected techniques. The data revealed that the use of recovery correction leads to results closer to the real values, thus decreasing the negative bias due to losses that occur during the analytical process. The mean accuracy difference between uncorrected and corrected data is more pronounced as the sample matrix becomes more complex, such as soil (15 ± 12%) or diesel emission (8 ± 11%), and less for simpler ambient air matrix samples (3 ± 16%). Precision between the two techniques was comparable within each matrix and relatively close between the different matrices.

High-accuracy IDMS analysis of trace elements in wheat flour for the provision of reference values to a proficiency testing scheme

Isotope dilution techniques were developed for the analysis of ten trace elements (Cd, Cu, Cr, Hg, Mo, Ni, Pb, Se, Sn and Zn) in a fortified wheat flour candidate sample for a proficiency testing scheme coordinated by NMI. The technique used was exact-matching double isotope dilution mass spectrometry (IDMS) by ICP-MS. A metrological approach was used to examine potential biases and ensure that this potentially primary method of analysis provided appropriate accuracy for the provision of reference values to the proficiency testing scheme. The exact-matching IDMS technique used in this study has been compared with the IDMS methods of other national metrology institutes in the CCQM-K24 and -P29 intercomparisons and the results produced were in very good agreement. Expanded relative uncertainties at the 95% confidence level for the ten elements in the wheat flour varied from 3.1%–14%. The results submitted from the participant laboratories for the proficiency testing scheme generally compared reasonably well with the NMI reference values.

High accuracy analysis by isotope dilution mass spectrometry using an iterative exact matching technique

The selection of an appropriate isotope dilution mass spectrometry technique for the practical application of this potentially primary method of analysis is highly important. The NARL approach for the application of the exact matching double isotope dilution mass spectrometry technique developed by Henrion is presented. NARL's approach utilises exact matching to minimise the effect of measurement biases within the method but also includes the thorough examination of all other biasing factors. The approach has been successfully tested in international CCQM intercomparisons with other national metrology institutes.

Precise isotope determination of trace amounts of Sr in Magnesium-rich samples.

Complete separation of Sr for the isotopic analysis of Mg-rich samples, such as ultramafic rocks and their constituent minerals, was established by adopting a combination of cationexchange chromatography in H+ form and pyridinium form with a DCTA complex using extremely small volumes of cation-exchange resin (1ml and 0.5ml respectively), This method made it possible to efficiently separate nanogram sizes of Sr from coexisting large amounts of Mg and Ca with a reduced total elution volume of only 24ml. The method also resulted in the reduction of procedural blanks for Sr and Rb to 32 and 25 pg, respectively. Applying static multicollection mass spectrometry with Ta-oxide as an ionization activator on a V-shaped W single filament, the isotopic composition of 10 to 20 ng Sr samples separated from 40 to 55mg of ultramafic rock standard (PCC-1) was determined with analytical precision of<0.005% and reproducibility of<0.006%. These precise analyses were performed with a high 88Sr+ ion beam intensity (>1.5×10-11 A). Our efficient chemical separation procedure also ensured the absence of Ca and Mg interference to Sr ionization. The Ta-oxide readily eliminated Rb prior to the Sr isotopic analysis in the mass spectrometer. This improved the analytical reliability of isotope dilution mass spectrometry (IDMS) for the simultaneous determination of Sr isotopic composition and concentration. The measured isotopic compositions of spiked PCC-1 agreed within error with those obtained from unspiked measurements, Rb/Sr ratio analyses for PCC-1 using IDMS provided analytical reproducibilities of better than 2%. These achievements indicate that our IDMS technique is capable of yielding trace Rb and Sr concentrations simultaneously with Sr isotopic composition in Mg-rich samples with an analytical reliability similar to that obtained from larger samples ( ?? 1 μg) of common silicate rock samples.

Atmospheric Lead in Antarctic Ice during the Last Climatic Cycle

Concentrations of lead (Pb) have been measured by the ultra-clean isotope dilution mass spectrometry technique in various sections of the Antarctic Dome C and Vostok deep ice cores, whose ages range from 3.85 to 155 ka B.P., in order to assess the natural, pre-human, sources of this toxic heavy metal in the global troposphere. Pb concentrations were very low, as low as about 0.3 pg Pb/g during the Holocene and probably during the last interglacial and part of the last ice age. On the other hand, they were quite high, up to about 40 pg Pb/g, during the Last Glacial Maximum and at the end of the penultimate ice age. Wind-blown dust from crustal rock and soil appears to be the main natural source of Pb in the global troposphere. Pb contribution from volcanoes is significant during periods of low Pb only. Contribution from the oceans is insignificant.

Atmospheric Lead in Antarctic Ice during the Last Climatic Cycle

Concentrations of lead (Pb) have been measured by the ultra-clean isotope dilution mass spectrometry technique in various sections of the Antarctic Dome C and Vostok deep ice cores, whose ages range from 3.85 to 155 ka B.P., in order to assess the natural, pre-human, sources of this toxic heavy metal in the global troposphere. Pb concentrations were very low, as low as about 0.3 pg Pb/g during the Holocene and probably during the last interglacial and part of the last ice age. On the other hand, they were quite high, up to about 40 pg Pb/g, during the Last Glacial Maximum and at the end of the penultimate ice age. Wind-blown dust from crustal rock and soil appears to be the main natural source of Pb in the global troposphere. Pb contribution from volcanoes is significant during periods of low Pb only. Contribution from the oceans is insignificant.

Determination of steroid hormones by the use of isotope dilution-mass spectrometry: A definitive method in clinical chemistry

Isotope dilution-mass spectrometry (ID-MS) is a reliable analytical tool for the highly accurate measurement of volatile compounds in biological fluids. In the present investigation the technique of ID-MS has been applied to the specific and accurate determination of oestradiol-17β, oestriol, testosterone, progesterone, aldosterone and cortisol in human serum. The analytical procedure for the measurement of steroid hormones comprises the following steps: (1) addition of a 14C-labelled steroid to the serum sample; (2) extraction of the 14C-labelled and of the non-labelled steroid by the use of an organic solvent; (3) purification of the steroid fraction by column chromatography on Sephadex LH-20 or on Lipidex-5000; (4) formation of a derivative; (5) combined gas chromatography-mass spectrometry. During gas chromatography the mass spectrometer continuously records two m/ e values corresponding to the labelled and the non-labelled hormone. Quantitative determination is performed by comparing the peak heights of the hormone to be determined and of the labelled internal standard. The accuracy of the methods is based on the high specificity of mass spectrometry and on the exact control of recovery employing the principle of isotope dilution. Therefore, the analytical procedures described here may be recommended as definitive methods in clinical chemistry.