Isotope-dilution Chromatography-tandem Mass Research Articles

Comparison of Automated 25-OH Vitamin D Immunoassays with Liquid Chromatography Isotope Dilution Tandem Mass Spectrometry

Comparing two fully automated 25-OH-D immunoassays with a validated liquid chromatography isotope dilution tandem mass spectrometry (LC-IDMS/MS) method in human serum samples. 180 samples were analyzed with the Liaison TOTAL Vitamin D, the IDS-iSYS 25-Hydroxy Vitamin D, and a validated LC-IDMS/MS 25-OH D method. The Liaison method mean +/- standard deviation (SD) was 64.3 +/- 23.5 nmol/L; the IDS-iSYS 70.1 +/- 27.0 nmol/L, and the LC-IDMS/MS 68.9 +/- 24.6 nmol/L. The correlation coefficient (r) between the Liaison and LC-IDMS/MS was 0.723, and the r between the IDS-iSYS and LC-IDMS/MS was 0.799. When the samples were grouped by females and males, the r between the Liaison and LC-IDMS/MS was 0.680 and 0.846, being 0.781 and 0.863 between the IDS-iSYS and LC-IDMS/MS, respectively. With the Passing-Bablok analysis, only the IDS-iSYS gave equivalent results to LC-IDMS/MS. The automated 25-OH-D immunoassays were in clinically good overall agreement with the LC-IDMS/MS method.

Quantification of nerve agent adducts with albumin in rat plasma using liquid chromatography–isotope dilution tandem mass spectrometry

A sensitive method for the determination of the organophosphorus nerve agents sarin, soman and VX adducts with tyrosine residue of albumin in rat plasma has been developed and validated using liquid chromatography–isotope dilution tandem mass spectrometry (LC–IDMS/MS). O-(O-Alkyl methylphosphonyl) tyrosine adducts and their deuterated products that were used as the internal standards were synthesised to establish the quantitative isotope-dilution method. Protein purification and solid-phase extraction (SPE) were applied to improve the recovery efficiency, reduce interference and achieve high sensitivity. The method provided a detection limit of 0.01ng/mL for sarin and soman adducts and 0.05ng/mL for the VX adduct. The value of the intra-day relative standard deviation over the calibration range was less than 6.16% (n=6), and that of the inter-day was less than 12.7% (n=6). The recovery varied from 86% to 111%. This sensitive method was successfully applied to the analysis of adducts in rat plasma after nerve agent exposure, and the results demonstrated the dose–effect relationships.

Detection and Quantitation of Bacterial Acylhomoserine Lactone Quorum Sensing Molecules via Liquid Chromatography–Isotope Dilution Tandem Mass Spectrometry

A range of acylhomoserine lactones (AHLs) are used as intraspecies quorum sensing signals by Gram-negative bacteria, and the detection and quantitation of these molecules is of interest. This manuscript reports a liquid chromatographic-isotope dilution tandem mass spectrometric method for the quantitation of these molecules. A divergent solid-phase synthesis of stable-isotope-labeled AHLs suitable for use as an internal standard is reported. This route relies on the biomimetic conversion of a dideuterated methionine equivalent, N-Fmoc-(4,4-(2)H(2))methionine, to the desired labeled AHL, and a representative series of eight of these molecules was produced in >95% purity and yields up to ~50%. The representative AHL internal standards were then used to develop an optimized liquid chromatography-tandem mass spectrometric (LC-MS/MS) separation and detection protocol for these molecules, which relies on a high-efficiency C18 core-shell column to minimize the time necessary for separation. The addition of internal standards at different steps during sampling was also found to affect the analysis for hydrophobic AHLs with addition prior to cell removal giving the most accurate results. Taken together, the use of the internal standards and separation method reported herein provides a rapid and quantitative method for the study of AHL production in bacteria.

Personal care product use and urinary levels of phthalate metabolites in Mexican women

Sources of phthalates other than Polyvinyl chloride (PVC) related products are scarcely documented in Mexico. The objective of our study was to explore the association between urinary levels of nine phthalate metabolites and the use of personal care products.Subjects included 108 women who participated as controls in an ongoing population-based case-control study of environmental factors and genetic susceptibility to breast cancer in northern Mexico. Direct interviews were performed to inquire about sociodemographic characteristics, reproductive history, use of personal care products, and diet. Phthalate metabolites measured in urine by high performance liquid chromatography–isotope dilution tandem mass spectrometry were monoethyl phthalate (MEP), monobenzyl phthalate (MBzP), mono-n-butyl phthalate (MBP), mono-isobutyl phthalate (MiBP), mono-3-carboxypropyl phthalate (MCPP) as well as mono-2-ethylhexyl phthalate (MEHP), mono-2-ethyl-5-oxohexyl phthalate (MEOHP), mono-2-ethyl-5-hydroxyhexyl phthalate (MEHHP), mono-2-ethyl-5-carboxypentyl phthalate (MECPP) that are metabolites of di-ethylhexyl phthalate (DEHP). Detectable urinary concentrations of phthalate metabolites varied from 75% (MEHP) to 100% (MEP, MBP, MEOHP, MEHHP and MECPP).Medians of urinary concentrations of some phthalate metabolites were significantly higher among users of the following personal care products compared to nonusers: body lotion (MEHHP, MECPP and sum of DEHP metabolites (ΣDEHP)), deodorant (MEHP and ΣDEHP), perfume (MiBP), anti-aging facial cream (MEP, MBP and MCPP) and bottled water (MCPP, MEHHP and MEOHP). Urinary concentrations of MEP showed a positive relationship with the number of personal care products used.Our results suggest that the use of some personal care products contributes to phthalate body burden that deserves attention due to its potential health impact.

Quantification of VX Vapor in Ambient Air by Liquid Chromatography Isotope Dilution Tandem Mass Spectrometric Analysis of Glass Bead Filled Sampling Tubes

An analysis method has been developed for determining low parts-per-quadrillion by volume (ppqv) concentrations of nerve agent VX vapor actively sampled from ambient air. The method utilizes glass bead filled depot area air monitoring system (DAAMS) sampling tubes with isopropyl alcohol extraction and isotope dilution using liquid chromatography coupled with a triple-quadrupole mass spectrometer (LC/MS/MS) with positive ion electrospray ionization for quantitation. The dynamic range was from one-tenth of the worker population limit (WPL) to the short-term exposure limit (STEL) for a 24 L air sample taken over a 1 h period. The precision and accuracy of the method were evaluated using liquid-spiked tubes, and the collection characteristics of the DAAMS tubes were assessed by collecting trace level vapor generated in a 1000 L continuous flow chamber. The method described here has significant improvements over currently employed thermal desorption techniques that utilize a silver fluoride pad during sampling to convert VX to a higher volatility G-analogue for gas chromatographic analysis. The benefits of this method are the ability to directly analyze VX with improved selectivity and sensitivity, the injection of a fraction of the extract, quantitation using an isotopically labeled internal standard, and a short instrument cycle time.

Bisphenol a exposure in Mexico City and risk of prematurity: a pilot nested case control study

BackgroundPresence of Bisphenol A (BPA) has been documented worldwide in a variety of human biological samples. There is growing evidence that low level BPA exposure may impact placental tissue development and thyroid function in humans. The aim of this present pilot study was to determine urinary concentrations of BPA during the last trimester of pregnancy among a small subset of women in Mexico City, Mexico and relate these concentrations to risk of delivering prematurely.MethodsA nested case-control subset of 60 participants in the Early Life Exposure in Mexico to ENvironmental Toxicants (ELEMENT) study in Mexico City, Mexico were selected based on delivering less than or equal to 37 weeks of gestation and greater than 37 weeks of gestation. Third trimester archived spot urine samples were analyzed by online solid phase extraction coupled with high performance liquid chromatography isotope dilution tandem mass spectrometry.ResultsBPA was detected in 80.0% (N = 48) of the urine samples; total concentrations ranged from < 0.4 μg/L to 6.7 μg/L; uncorrected geometric mean was 1.52 μg/L. The adjusted odds ratio of delivering less than or equal to 37 weeks in relation to specific gravity adjusted third trimester BPA concentration was 1.91 (95%CI 0.93, 3.91, p-value = 0.08). When cases were further restricted to births occurring prior to the 37th week (n = 12), the odds ratio for specific-gravity adjusted BPA was larger and statistically significant (p < 0.05).ConclusionsThis is the first study to document measurable levels of BPA in the urine of a population of Mexican women. This study also provides preliminary evidence, based on a single spot urine sample collected during the third trimester, that pregnant women who delivered less than or equal to 37 weeks of gestation and prematurely (< 37 weeks) had higher urinary concentrations of BPA compared to women delivering after 37 weeks.

Development and validation of a rapid liquid chromatography isotope dilution tandem mass spectrometry (LC-IDMS/MS) method for serum creatinine

Objectives: To develop an isotope dilution liquid chromatography tandem mass spectrometry (LC-IDMS/MS) method for the standardization of serum creatinine. Design and methods: Supernatants obtained by protein precipitation were injected into a LC-MS/MS. Chromatography was performed on a cation exchanger pre-column in normal phase isocratic mode. Creatinine and creatinine-D 3 were quantified using ion transitions of m/z 114→44 and 117→47, respectively. Results: The method was calibrated with the NIST Standard Reference Material 914a and was found to be exact in analyzing the certified reference material SRM 967 from NIST (97.1 ± 0.9% and 102.1 ± 0.9% of target value for levels 1 and 2, respectively) and by calculating recuperation of spiked creatinine in 10 different patient samples (103.6 ± 4.1%). Intra-assay imprecision was 0.9% at both 64.6 and 354 μmol/L creatinine, while inter-assay imprecisions were 1.9% and 1.8%. Absence of ion suppression was confirmed by spiking experiments. The method was shown to be free of carryover. A good correlation was obtained between the LC-MS/MS method and a Jaffe method run on an automated analyzer ( r = 0.999). Conclusions: We have developed a fast and simple method for the quantification of serum creatinine by isotope dilution tandem mass spectrometry (IDMS/MS) and we propose that this method can be used as a reference method by laboratories that wish to validate their serum creatinine automated assay.

Analysis of blood spots for polyfluoroalkyl chemicals

Polyfluoroalkyl chemicals (PFCs) have been detected in humans, in the environment, and in ecosystems around the world. The potential for developmental and reproductive toxicities of some PFCs is of concern especially to children's health. In the United States, a sample of a baby's blood, called a “dried blood spot” (DBS), is obtained from a heel stick within 48 h of a child's birth. DBS could be useful for assessing prenatal exposure to PFCs. We developed a method based on online solid phase extraction coupled with high performance liquid chromatography–isotope dilution tandem mass spectrometry for measuring four PFCs in DBS, perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate, perfluorooctanoate (PFOA), and perfluorononanoate. The analytical limits of detection using one whole DBS (∼75 μL of blood) were <0.5 ng mL −1. To validate the method, we analyzed 98 DBS collected in May 2007 in the United States. PFOS and PFOA were detected in all DBS at concentrations in the low ng mL −1 range. These data suggest that DBS may be a suitable matrix for assessing perinatal exposure to PFCs, but additional information related to sampling and specimen storage is needed to demonstrate the utility of these measures for assessing exposure.

Determination of serum creatinine by liquid chromatography isotope dilution tandem mass spectrometry (LC–IDMS/MS): A candidate reference method

Determination of serum creatinine by liquid chromatography isotope dilution tandem mass spectrometry (LC–IDMS/MS): A candidate reference method

Detection of SERUM testosterone by liquid chromatography–isotope dilution tandem mass spectrometry

Detection of SERUM testosterone by liquid chromatography–isotope dilution tandem mass spectrometry

Ultraperformance Liquid Chromatography Isotope Dilution Tandem Mass Spectrometry for the Absolute Quantification of Proteins and Peptides

Ultraperformance Liquid Chromatography Isotope Dilution Tandem Mass Spectrometry for the Absolute Quantification of Proteins and Peptides

Quantification of DNA damage products resulting from deamination, oxidation and reaction with products of lipid peroxidation by liquid chromatography isotope dilution tandem mass spectrometry

The analysis of damage products as biomarkers of inflammation has been hampered by a poor understanding of the chemical biology of inflammation, the lack of sensitive analytical methods and a focus on single chemicals as surrogates for inflammation. To overcome these problems, we developed a general and sensitive liquid chromatographic tandem mass spectrometry (LC/MS-MS) method to quantify, in a single DNA sample, the nucleoside forms of seven DNA lesions reflecting the range of chemistries associated with inflammation: 2'-deoxyuridine, 2'-deoxyxanthosine and 2'-deoxyinosine from nitrosative deamination; 8-oxo-2'-deoxyguanosine from oxidation; and 1,N(2)-etheno-2'-deoxyguanosine, 1,N(6)-etheno-2'-deoxyadenosine and 3,N(4)-etheno-2'-deoxycytidine arising from reaction of DNA with lipid peroxidation products. Using DNA purified from cells or tissues under conditions that minimize artifacts, individual nucleosides are purified by HPLC and quantified by isotope-dilution, electrospray ionization LC/MS-MS. The method can be applied to other DNA damage products and requires 4-6 d to complete depending upon the number of samples.

Automated on-line column-switching HPLC–MS/MS method for measuring environmental phenols and parabens in serum

We developed a method using on-line solid phase extraction (SPE) coupled to high performance liquid chromatography–isotope dilution tandem mass spectrometry (HPLC–MS/MS) to measure the serum concentrations of seven environmental phenols and five parabens: bisphenol A; ortho-phenylphenol; 2,4-dichlorophenol; 2,5-dichlorophenol; 2,4,5-trichlorophenol; benzophenone-3; triclosan; and methyl-, ethyl-, propyl-, butyl-, and benzyl-parabens. The phenols and parabens present in serum were retained and concentrated on a C18 reversed-phase size-exclusion SPE column, back-eluted from the SPE column while the eluate was diluted through a mixing Tee (analyte peak focusing), separated using a pair of monolithic HPLC columns, and detected by isotope dilution-MS/MS. Sample preparation did not require protein precipitation, only dilution of the serum with 0.1 M formic acid. This method, which combines an on-line SPE with analyte peak focusing feature and the selective atmospheric pressure photoionization MS detection, resulted in limits of detection ranging from 0.1 to 0.5 ng/mL for most of the analytes. The high throughput and adequate sensitivity with yet a relative low serum volume used (100 μL) confirm that analytically it is possible to measure simultaneously these phenols and parabens with the precision and accuracy at sub-parts-per-billion levels required for biomonitoring. However, important additional factors, including validated sample collecting, handling, and storing protocols, as well as toxicokinetic data, are required if these measures are used for exposure assessment.

Ultra Performance Liquid Chromatography Isotope Dilution Tandem Mass Spectrometry for the Absolute Quantification of Proteins and Peptides

A selective, rapid, and sensitive 12.7-min ultra performance liquid chromatography-isotope dilution tandem mass spectrometry (UPLC-ID/MS/MS) method was developed and compared to conventional high-performance liquid chromatography-isotope dilution tandem mass spectrometry (HPLC-ID/MS/MS) for the absolute quantitative determination of multiple proteins from complex matrixes. The UPLC analysis was carried out on an Acquity UPLC ethylene-bridged hybrid (BEH) C18 reversed-phase column (50 x 2.1 mm i.d., 1.7-microm particle size) with gradient elution at a flow rate of 300 microL/min. For the HPLC separation, a similar gradient profile on a reversed-phase C18 column with dimensions of 150 x 1.0 mm at a flow rate of 30 microL/min was utilized. The aqueous and organic mobile phases were 0.1% formic acid in water and acetonitrile, respectively. Detection was performed on a triple-quadrupole mass spectrometer operated in the multiple reaction monitoring mode. Linear calibration curves were obtained in the concentration range of 10-90 fmol/microL. Relative standard deviation values equal to or less than 6.5% were obtained by the UPLC-ID/MS/MS method, thus demonstrating performance equivalent to conventional HPLC-ID/MS/MS for isotope dilution quantification of peptides and proteins. UPLC provides additional dimensions of rapid analysis time and high-sample throughput, which expands laboratory emergency response capabilities over conventional HPLC.

Quantification of the urinary concentrations of parabens in humans by on-line solid phase extraction-high performance liquid chromatography–isotope dilution tandem mass spectrometry

Parabens (alkyl esters of p-hydroxybenzoic acid) are widely used as antimicrobial preservatives in cosmetic products, pharmaceuticals, and food processing. However, weak estrogenicity of some parabens has been revealed from several studies. Human exposure to parabens may be assessed by measuring the conjugated or free species of these compounds or their metabolites in urine. We have developed a method using on-line solid phase extraction-high performance liquid chromatography–isotope dilution tandem mass spectrometry with peak focusing to measure the urinary concentrations of methyl, ethyl, propyl, n- and iso- butyl, and benzyl parabens. This method has good reproducibility and accuracy with detection limits for all analytes below 0.2 ng/mL in 100 μL of urine, and permits quick and accurate analysis of a large number of samples in epidemiologic studies for assessing the prevalence of human exposure to parabens. Using this method, we detected methyl, ethyl, and propyl parabens, mostly as conjugated species, in 22 urine samples collected from anonymous adults.

Measuring environmental phenols and chlorinated organic chemicals in breast milk using automated on-line column-switching–high performance liquid chromatography–isotope dilution tandem mass spectrometry

Breast milk is one possible route of exposure to environmental chemicals, including phenols and chlorinated organic chemicals for breast-fed infants. We developed a highly sensitive method of analyzing breast milk for triclocarban (3,4,4'-trichlorocarbanilide) and eight phenolic compounds: bisphenol A (BPA), 4-tert-octylphenol (4-tOP), ortho-phenylphenol (OPP), 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, and 2-hydroxy-4-metoxybenzophenone (BP-3). The method includes adding a solution containing a stable isotope of each chemical, enzymatic hydrolysis of the conjugated chemicals in the milk, and on-line solid-phase extraction coupled with high performance liquid chromatography-tandem mass spectrometry. It can also be used to measure the free (unconjugated) species by omitting the enzymatic deconjugation step. The method, validated using pooled breast milk samples, has inter-day coefficient of variations ranging from 4.8 to 18.9% for most analytes, and spiked recoveries generally about 100%. Detection limits for most analytes are below 1 ng/mL in 100 microL of breast milk. We tested the usefulness of the method by measuring concentrations of these nine compounds in 20 breast milk samples. BPA, OPP, and BP-3 were detected in more than 60% of the samples tested. The free species of these compounds appear to be most prevalent in milk.