Isotope Dilution Gas Chromatography-mass Spectrometry Research Articles

Improved Quantification of Geosmin and 2-Methylisoborneol in Farmed Fish Using Stable Isotope Dilution Gas Chromatography-Mass Spectrometry.

A requisite to improving the taste and odor attributes of farmed fish is the availability of accurate and practical analytical methods to quantify 2-methylisoborneol (MIB) and geosmin (GSM). Solid-phase microextraction (SPME) enables reliable measurement of nanogram per liter quantities of MIB and GSM in water. In contrast, direct headspace (HS)-SPME of biological matrices with variable proximate compositions can increase bias and uncertainty in off-flavor determinations. Analytical recovery plays a crucial role in the accurate determination of MIB and GSM in fish, and this study investigates strategies to maximize and account for this recovery factor. MIB and GSM values in off-flavor catfish and trout were measured using direct HS-SPME and distillation as sample preparation techniques. Trout samples prepared by distillation yielded 10-fold higher GSM recoveries than those from direct HS-SPME (31% versus 3%). A stable isotope dilution method (SIDM) was implemented by routinely spiking samples with known quantities of deuterium-labeled MIB and GSM, allowing for the correction of sample-to-sample recovery deviations. SIDM-determined GSM values generated recoveries of 106 and 95% for direct HS-SPME and distilled trout, respectively. Aspects of the strategies and techniques presented can be incorporated into existing analytical methods to improve the accuracy and sample throughput. Particularly, routine inclusion of SIDM in the evaluation of MIB and GSM can facilitate identification of reliable practices to control off-flavors in aquaculture.

Legacy Dichlorodiphenyltrichloroethane (DDT) Pollution in a River Ecosystem: Sediment Contamination and Bioaccumulation in Benthic Invertebrates

Dichlorodiphenyltrichloroethane (DDT) contamination in the Toce River in northern Italy was studied by collecting data from 2016 to 2021 upstream and downstream of a production factory which in the past had discharged technical DDT. Analysis of sediments and of bioaccumulation in different benthic invertebrate taxa (Gammaridae, Diptera, Ephemeroptera Baetidae and Heptageniidae) was carried out to assess the transfer of DDT from sediments to benthic invertebrates and the environmental risk of this legacy pollutant for the river ecosystem. DDT and its metabolites dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD), here called DDx, were analyzed by isotope dilution gas chromatography–mass spectrometry (GC-MS/MS). DDx values in sediments in upstream stations (1.14–2.25 ng g−1 1% Organic Carbon) were lower than downstream of the industrial site (5.60–7.60 ng g−1 1% Organic Carbon), often exceeding Sediment Quality Guidelines for total DDx. Peak levels derived from new inputs of parental DDT, as confirmed by fingerprint analysis. Bioaccumulation was higher at downstream sites (up to 5107 ng g−1 lipid weight), confirming the bioavailability of residual DDT as well as active metabolism, with the formation of DDD and DDE. The Biota-Sediment Accumulation Factor evidenced the highest values (over 4.2) for Diptera and Gammaridae, highlighting that invertebrates can transfer contamination from sediments to the trophic chain. Linear regression models were developed to estimate DDx concentrations in benthic invertebrates from DDx concentrations in sediments. However, determination coefficients R2 remained in the range of 0.36–0.51, highlighting the necessity of bioaccumulation analysis to fully estimate environmental risk. The results show that DDT contamination, even if residual, may still represent a risk due to its effective transfer to the trophic chain.

Fast and accurate isotope dilution mass spectrometry method for the assignment of trihalomethanes in water in an uncommon accuracy-based proficiency testing programme in Singapore

ABSTRACT In the light of the instability of trihalomethanes (THMs) in water, a fast and high accuracy method based on headspace gas chromatography-isotope dilution mass spectrometry (HS-GC-IDMS) technique was developed. The optimised method was validated using fortified water samples. Recoveries between 96.1% and 108.8% with an intermediate precision between 3.9% and 5.7% were achieved. The method was applied in the value assignment of THMs in water in an accuracy-based proficiency testing (PT) programme organised by the Health Sciences Authority (HSA) Singapore. The assigned values obtained for chloroform, bromodichloromethane, dibromochloromethane and bromoform were 73.6 ± 9.3 µg/L, 49.1 ± 5.2 µg/L, 47.7 ± 4.4 µg/L and 70.8 ± 6.8 µg/L, respectively. The PT programme was especially valuable and uncommon as it allowed local water testing laboratories to have access to traceable reference values for the benchmarking of their technical competencies. The procedure undertaken by the Laboratory to prepare a batch of PT sample comprising the unstable analytes, conduct homogeneity and stability testing, as well as value assignment, are presented. The between-samples relative standard deviations (RSDs) obtained in a feasibility batch of THMs concentrate in methanol were improved by four to six times compared to those from the first feasibility batch of THMs in water. Based on z-scores, evaluated using the assigned reference value determined by HS-GC-IDMS, 85% of the participating laboratories in the PT programme achieved satisfactory results. The provision of metrological assigned values heightened the testing laboratories’ awareness on the importance of accuracy-based PT programmes for evaluation of true method biases, which is particularly valuable for analytes with regulated limits.

Advances in the analytical methods for the determination of fluorinated aromatic carboxylic acids in aqueous matrices: A review.

Fluorobenzoic acids are critically important chemical tracers in hydrothermal, geothermal, leaching, and oilfield applications. Particularly in oilfield applications, these tracers are used to investigate fluid flow paths between injector wells and producer wells, providing valuable information about the enhanced oil recovery process of the oil reservoirs. The detection limit of tracers is a vital subject in field reservoir work because the amount of chemical tracer that must be injected into the injector well is directly related to the amount detected at the producer well after migration and diffusion. The popularity of fluorinated benzoic acids as the tracers is due to their non-toxicity over radioactive tracers and low detection limit, which is determined using analytical techniques. This review focuses on the improvements/developments in extraction techniques such as solid-phase extraction and determination techniques such as gas chromatography coupled with mass spectrometry, liquid chromatography with mass spectrometry, isotope dilution gas chromatography-mass spectrometry, high-performance liquid chromatography, ion chromatography coupled with electrospray mass spectrometry, and so on for the analysis of fluorinated benzoic acids to achieve the lowest possible limit of concentration.

Isotope-Dilution Gas Chromatography-Mass Spectrometry Method for the Selective Detection of Nicotine and Menthol in E-Cigarette, or Vaping, Product Liquids and Aerosols.

We developed a quantitative method for analyzing nicotine and menthol in e-cigarette, or vaping, products (EVPs). These products may adversely impact health through inhalational exposure to addictive and harmful chemicals. The presence of unknown substances in do-it-yourself e-liquids, counterfeits, or unregulated products may increase exposure to harmful chemicals, as underscored by the 2019 EVP use-associated lung injury (EVALI) outbreak. To minimize these risks, it is important to accurately quantify nicotine and menthol in e-liquids and aerosol emissions to evaluate EVP authenticity, verify product label accuracy, and identify potentially hazardous products. We developed a simple, versatile, high-throughput method using isotope-dilution gas chromatography-mass spectrometry for quantifying nicotine and menthol concentrations in both e-liquid contents and machine-generated aerosol emissions of EVPs. Rigorous validation has demonstrated that the method is specific, precise (CV<2.71%), accurate (percent error ≤7.0%), and robust. Linear calibration ranges from 0.01 to 1.00 mg/ml for both analytes was achieved, corresponding to expected analyte levels in e-liquids and machine-generated EVP aerosols. Limits of detection (LODs) in the final 10-ml sample extract were 0.4 μg/ml for nicotine and 0.2 μg/ml for menthol. The method was used to analyze aerosol emissions of 141 EVPs associated with the 2019 EVALI outbreak; detectable levels of nicotine (2.19–59.5 mg/g of aerosol) and menthol (1.09–10.69 mg/g of aerosol) were observed in 28 and 11%, respectively, of the samples analyzed. Nicotine was not detected in any of the tetrahydrocannabinol (THC), cannabidiol (CBD), or oil-based products, while menthol (2.95 mg/g of aerosol) was only detected in one of these products (THC-labeled). The analytical method can be used to quantify nicotine and menthol concentrations in the e-liquids and aerosols from a range of EVPs, and these findings highlight a difference between e-cigarette and other vaping products.

Quadruple isotope dilution gas chromatography-mass spectrometry after simultaneous derivatization and spraying based fine droplet formation liquid phase microextraction method for the accurate and sensitive quantification of chloroquine phosphate in human serum, urine and saliva samples at trace levels

This study presents an accurate and precise analytical strategy for the determination of chloroquine phosphate at trace levels in human body fluids (urine, serum, and saliva). Simultaneous derivatization-spraying based fine droplet formation-liquid phase microextraction (SD-SFDF-LPME) method was used to derivatize and preconcentrate the analyte prior to gas chromatography-mass spectrometry (GC–MS) measurements. Acetic anhydride was employed as derivatizing agent in this study. After optimizing the SD-SFDF-LPME method, the limit of detection (LOD) and limit of quantitation (LOQ) were found to be 0.16 and 0.53 mg/kg, respectively. Quadruple isotope dilution (ID4) was coupled to the SD-SFDF-LPME method in order to alleviate matrix effects and promote accuracy/precision of the method. Chloroquine acetamide-d3 was firstly synthesized in our research laboratory and used as the isotopic analogue of the analyte in the ID4 experiments. Superior percent recovery results (99.4% – 101.0%) with low standard deviation values were obtained for the spiked samples. This validated the developed SD-SFDF-LPME-ID4-GC–MS method as highly accurate and precise for the determination of chloroquine phosphate at trace levels. In addition, the isotopic analogue of the analyte was obtained via the acetamide derivative of the analyte, which is an alternative to obtain isotopic analogues of organic compounds that are not accessible or commercially available.

The Association between Dietary Inflammatory Index and Sex Hormones among Men in the United States.

This study investigated the association between Dietary Inflammatory Index and sex hormones in a large, nationally representative adult male sample. We utilized data from the 2013-2014 and 2015-2016 National Health and Nutrition Examination Survey. Males aged ≥20 years who provided a 24-hour dietary intake history and underwent serum sex hormone testing were included in analysis. Weighted proportions and multivariable analysis controlling for age, race, energy, smoking status, education level, body mass index and time of venipuncture were used to evaluate the associations between Dietary Inflammatory Index and sex hormones. For 4,151 participants, Dietary Inflammatory Index ranged from -5.05 to 5.48. Mean±SD total testosterone was 419.30±176.27 ng/dl. Mean±SD total testosterone was lower among men in the highest tertile compared with men in the lowest tertile group (410.42±171.97 vs 422.71±175.69, p <0.001). A per unit increase in Dietary Inflammatory Index was related to 4.0% (95% CI 0.5-7.6) higher odds of testosterone deficiency. In the fully adjusted multivariable model, males in Dietary Inflammatory Index tertile 3 (the most pro-inflammatory) had 29.6% (3.1-63.0) higher odds of testosterone deficiency than those in tertile 1 (p trend=0.025). Interaction tests revealed no significant effect of body mass index on the association of Dietary Inflammatory Index with testosterone deficiency and all sex hormone parameters. Men adhering to a more pro-inflammatory diet appear to have a higher risk of testosterone deficiency, indicating the important role of diet in male reproductive health.

Effects of high-fat diet and Apoe deficiency on retinal structure and function in mice

To investigate the effects of a high-fat diet (HFD) and apolipoprotein E (Apoe) deficiency on retinal structure and function in mice. Apoe KO mice and wild-type C57BL/6J mice were given a low-fat diet (LFD) or a HFD for 32 weeks. Blood glucose, serum lipids, body weight and visceral fat weight were evaluated. Retinal sterol quantification was carried out by isotope dilution gas chromatography-mass spectrometry. The cholesterol metabolism related genes SCAP-SREBP expressions were detected by qRT-PCR. Retinal function was recorded using an electroretinogram. The thickness of each layer of the retina was measured by optical coherence tomography. Fundus fluorescein angiography was performed to detect retinal vasculature changes. Immunohistochemical staining was used to determine the expression of NF-κB, TNF-α and VEGFR2 in the retina among HFD, HFD Apoe−/−, LFD Apoe−/− and WT mice retinas. HFD feeding caused the mice to gain weight and develop hypercholesterinemia, while Apoe−/− abnormalities also affected blood lipid metabolism. Both HFD and Apoe deficiency elevated retinal cholesterol, especially in the HFD Apoe−/− mice. No up-regulated expression of SCAP-SREBP was observed as a negative regulator. Impaired retinal functions, thinning retinas and abnormal retinal vasculature were observed in the peripheral retinas of the HFD and Apoe−/− mice compared with those in the normal chow group, particularly in the HFD Apoe−/− mice. Moreover, the expression of NF-κB in the retinas of the HFD and Apoe−/− mice was increased, together with upregulated TNF-α mRNA levels and TNF-α expression in the layer of retinal ganglion cells of the peripheral retina. At the same time, the expression level of VEGFR2 was elevated in the intervention groups, most notably in HFD Apoe−/− mice. HFD or Apoe gene deletion had certain adverse effects on retinal function and structure, which were far below the combined factors and induced harm to the retina. Furthermore, HFD caused retinal ischemia and hypoxia. Additionally, Apoe abnormality increased susceptibility to ischemia. These changes upregulated NF-κB expression in ganglion cells and activated downstream TNF-α. Simultaneously, they activated VEGFR2, accelerating angiogenesis and vascular permeability. All of the aforementioned outcomes initiated inflammatory responses to trigger ganglion cell apoptosis and aggravate retinal neovascularization.

A sensitive determination method for trace bisphenol A in bottled water and wastewater samples: Binary solvent liquid phase microextraction-quadrupole isotope dilution-gas chromatography-mass spectrometry

A sensitive, accurate and precise methodology was established for the preconcentration and determination of bisphenol A in bottled water and wastewater samples at trace levels. A binary solvent liquid phase microextraction (BSLPME) method was optimized to extract bisphenol A before determination by gas chromatography-mass spectrometry (GC-MS). The type of binary solvent/disperser solvent, vortex period and mode of adding extraction and disperser solvent mixture to aqueous solution were determined by univariate optimization. Three significant parameters including volume of binary solvent, volume of dispersive solvent and ratio of binary solvent were optimized using Box-Behnken Design. Low limit of detection (0.30 ng/g) and limit of quantitation (0.99 ng/g) values were recorded for the BSLPME-GC-MS method. Hence, 173 times enhancement in the detection limit of the GC-MS system was achieved by the developed microextraction method. Quadrupole isotope dilution (ID4) strategy was used to augment the extraction method to achieve high accuracy and precision. When the developed BSLPME method was combined with the ID4 strategy, bottled water and wastewater samples spiked at approximately 200 ng/g recorded excellent recovery results of 100.3 ± 0.4% and 100.0 ± 0.5%, respectively. Therefore, accurate and precise determination of bisphenol A at trace levels was achieved by a low cost, rapid and green analytical method.

Quantitative analyses of essential fatty acids in cereals and green vegetables by isotope dilution-gas chromatography/mass spectrometry

An analytical method for the accurate determination of essential fatty acids in cereals and green vegetables is established based on isotope dilution-gas chromatography/mass spectrometry (ID-GC/MS). In this approach, 13C-labeled fatty acids were added as internal standards to the samples prior to the sample preparation. Repeatability and reproducibility for the analyses of the essential fatty acids extracted from homogenized cereals and green vegetables were examined to validate the ID-GC/MS method. The repeatability and reproducibility were within 2% relative standard deviation. The developed method provides higher-order measurement results with the relative expanded uncertainties of 1–2% and 2–4% for cereals and green vegetables, respectively. Based on the fatty acid measurements, the developed ID-GC/MS method can be used as a candidate reference method for the quantitation of essential fatty acids in cereals and green vegetables. The developed method was also applied to analyze several commercially available products including cereal and vegetable powders.

Determination of 4 polycyclic aromatic hydrocarbons in spicy strips by vacuum concentration coupled with isotope dilution gas chromatography-mass spectrometry

A method based on isotope internal standard dilution was established for the determination of four polycyclic aromatic hydrocarbons(PAH4) including chrysene, benzo [a] anthracene, benzo [b] fluoranthene and benzo [a] pyrene in spicy strips sold in the markets. The hot strips were homogenized and the target compounds were extracted with n-hexane, concentrated in vacuum, saponified and purified by solid phase extraction column, then the pretreated samples were separated by DB-EUPAH column(20 m×0. 18 mm, 0. 14 μm), detected by gas chromatography-mass spectrometry(GC-MS)and quantified by internal standard of isotope. The recoveries of PAH4 in different concentration levels of hot noodles were 91. 0%-103. 5%, and the relative standard deviation(RSD)was 1. 89%-6. 73%(n=6). The detection limit was 0. 30 μg/kg and the quantitative limit was 1. 0 μg/kg. The content of PAH4(sum) in 27 collected samples ranged from 1. 35 μg/kg to 11. 44 μg/kg, and the detection rate was 100%. With less solvent consumption, good purification effect and blank control, the method is simple, rapid and accurate and meets the detecting requirements of PAH4 in hot strips.

A method for measuring glycerol-blanked triglyceride concentrations by using gas chromatography-isotope dilution mass spectrometry.

Serum triglyceride concentrations are measured as total glycerides content in many Western countries. In Japan, glycerol-blanked triglycerides (TG-GB) are measured to identify postprandial hypertriglyceridaemia and to minimize the influence of glycerol formulation on serum triglyceride values. However, TG-GB measurements have not been standardized. Therefore, we developed an efficient quantification system for total glycerides and free glycerol that allows the calculation of TG-GB concentrations. We measured total glycerides and free glycerol in human serum by using gas chromatography-isotope dilution mass spectrometry and compared its performance to the reference method of the US Centers for Disease Control and Prevention (CDC). Our practical method of total glycerides and free glycerol quantification achieved excellent precision for both within-run and among-run coefficients of variation (<1.5% and <2.7%, respectively), with an average recovery of 99.8% for free glycerol. However, we noted an average %bias of -0.26% for total glycerides and -3.15% for free glycerol between our TG-GB method and the CDC reference method. This practical method of total glycerides and free glycerol quantification enables traceability assessment of TG-GB measurements. Differences between the output values of TG-GB and the CDC reference method might result from the differences in free glycerol values.

METHOD VALIDATION FOR ORGANOCHLORINE INSECTICIDES DETERMINATION IN GINSENG BY USING ISOTOPE-DILUTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY (ID-GC-MS)

Organochlorine insecticides are still exploited among the most prominent pesticides for plant protection purposes. Known for having hazardous to humans and persistent in the environment properties, it is necessary to build an accurate method for detecting organochlorine insecticides in food and environmental substances. Isotope-dilution gas chromatography-mass spectrometry (ID-GC-MS) is a versatile coupling measurement system and high order method that combines both selectivity, sensitivity and high accuracy. The present paper aims at showing the methodology of the organochlorine insecticides (alpha-HCH and gamma-HCH) determination in ginseng by using ID-GC-MS. The described method covered sample preparation using an organic solvent (hexane) extraction, followed by florisil cleaning-up. After the reconstitution of the solvent base, the measurement was conducted by using ID-GC-MS in the optimal instrument parameter. Using the determined optimal conditions, the parameters such as sensitivity, linearity, precision, and accuracy were studied for validation of the ID-GC–MS method. The limit of detection and the limit of quantitation of the instrument were 0.5 ng/g and 2.0 ng/g for both analytes. The method showed linearity with the correlation coefficient of 0.999 for both alpha-HCH and gamma-HCH over the concentration range of 1‒300 ng/g. The precision ranged from 3.0 to 3.7% and 2.4 to 3.3% for alpha-HCH and gamma-HCH, respectively. The mean recoveries for alpha-HCH and gamma-HCH were found at 98.0 and 95.6%, respectively. Following method validation, the measurement uncertainty of the alpha-HCH and gamma-HCH determination was evaluated according to EURACHEM GUM guide at a 95 % confidence level (k = 2). The expanded uncertainty in the measurement of alpha-HCH and gamma-HCH was 5.4% and 8.2%, respectively. All these parameters demonstrate the high sensitivity of the offered method and the success of the described method in the determination of alpha-HCH and gamma-HCH in ginseng sample.

Diagnosis of Gestational Diabetes Mellitus with Point-of-Care Methods for Glucose versus Hospital Laboratory Method Using Isotope Dilution Gas Chromatography-Mass Spectrometry as Reference.

Background In Sweden, both glucose analyzers in accredited laboratories and point-of-care glucose devices are used for gestational diabetes mellitus (GDM) diagnosis. The aim of this study was to compare the diagnostic performance of the HemoCue Glucose 201+ (HC201+) and RT (HC201RT) systems with that of the hospital central laboratory hexokinase method (CL) based on lyophilized citrate tubes, using the isotope dilution gas chromatography-mass spectrometry (ID GC-MS) as reference. Methods A 75 g oral glucose tolerance test was performed on 135 women screened positive for GDM. Diagnosis was based on the World Health Organization 2013 diagnostic thresholds for fasting (n = 135), 1 h (n = 135), 1 h (n = 135), 1 h (Results Significantly more women were diagnosed with GDM by HC201+ (80%) and CL (80%) than with the reference (65%, P < 0.001) based on fasting and/or 2 h thresholds, whereas the percentage diagnosed by HC201RT (60%) did not differ significantly from the reference. In Bland-Altman analysis, a positive bias was observed for HC201+ (4.2%) and CL (6.1%) and a negative bias for HC201RT (−1.8%). In the surveillance error grid, 95.9% of the HC201+ values were in the no-risk zone as compared to 98.1% for HC201RT and 97.5% for CL. Conclusions A substantial positive bias was found for CL measurements resulting in overdiagnosis of GDM. Our findings suggest better performance of HC201RT than HC201+ in GDM diagnosis. The results may have possible implications for GDM diagnosis in Sweden and require further elucidation.

Magnetic C60 nanospheres based solid-phase extraction coupled with isotope dilution gas chromatography–mass spectrometry method for the determination of sixteen polycyclic aromatic hydrocarbons in Chinese herbal medicines

C60-based magnetic nanospheres were synthesized by coating Fe3O4 nanospheres with silica, then modifying with 3-aminopropyltriethoxysilane as a linker and a C60 fullerene stationary phase. The morphologies, magnetic properties, infrared absorption and carbon content of magnetic nanospheres were studied by TEM, VSM, FTIR and carbon and sulfur analyzer. The magnetic nanospheres were employed for the magnetic solid-phase extraction (MSPE) of 16 polycyclic aromatic hydrocarbons (PAHs) in nine Chinese herbal medicines. The analyses were conducted by isotope dilution gas chromatography–mass spectrometry. The main parameters influencing the extraction, including extraction solvent, adsorbent amount, and extraction time were optimized. Method validation showed that the limit of detection (LOD) was 0.02–0.11 µg/kg, and the limit of quantification (LOQ) was 0.07–0.36 µg/kg. The spiked recoveries rates for 16 PAHs in white peony root were 84.7–107.2%. The relative standard deviation (RSD) was 1.7–8.4%. The established method was further used for the determination 16 PAHs in nine Chinese herbal medicines. Total content of 16 PAHs varied from 73.6 µg/kg (fructus lycii) to 2172.6 µg/kg (astragalus root). The results indicate that the pollution of PAHs in Chinese herbal medicines is serious. The established method can effective detect PAHs contamination in Chinese herbal medicines.

Performance of StatSensor Point-of-Care Device for Measuring Creatinine in Patients With Chronic Kidney Disease and Postkidney Transplantation.

Background:The StatSensor is a point-of-care device which measures creatinine in capillary whole blood. Previous studies reported an underestimation of the creatinine measurements at high creatinine concentrations and were performed in the prestandardization era for creatinine.Objective:This accuracy-based study evaluates the use of this device in kidney-transplanted patients and those with chronic kidney disease (CKD).Design:Cross-sectional diagnostic accuracy study.Setting:Nephrology outpatient clinic in an urban tertiary center.Participants:Adults with CKD or a functioning kidney transplant.Measurements:Duplicate StatSensor creatinine measurements were performed on capillary whole blood samples collected by direct fingerstick and SAFE-T-FILL collection device. Results were compared with simultaneous venous blood sampling for serum and plasma creatinine measured by an enzymatic method on the Roche Integra 400 mainframe analyzer with traceability to the ID-GC-MS (isotope dilution gas chromatography mass spectrometry) reference method.Methods:Deming regression, Pearson correlation coefficient, and Bland-Altman analysis were used to assess accuracy and comparability between capillary whole blood measured by StatSensor and plasma creatinine measured by routine analyzer with traceability to the reference method. Estimated glomerular filtration (eGFR) rates were calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and concordance with Kidney Disease Improving Global Outcomes (KDIGO) CKD stage classification was evaluated.Results:There were 60 participants (mean age = 61.9 ± 15.0 years, 55% men, 33% transplant, mean plasma creatinine = 137 ± 59 µmol/L). Bland-Altman analysis indicated a positive mean bias of 12.7 µmol/L between StatSensor fingerstick creatinine measurement and plasma creatinine. Comparison of eGFR (CKD-EPI) calculated from the StatSensor fingerstick creatinine versus plasma creatinine showed misclassification across all KDIGO CKD stages. Postanalytical correction of the bias did not improve misclassifications. The use of mean of duplicate StatSensor creatinine results did not improve performance compared with the use of singlet results.Limitations:Single center, limited participant numbers.Conclusions:The results of our study suggest that the limiting characteristics of the StatSensor device are not only bias, but also imprecision. The level of imprecision observed may influence clinical decision-making and limit the usefulness of StatSensor as a CKD screening tool. If choosing to utilize it for either screening for or monitoring CKD, it is essential that clinicians understand the limitations of point-of-care devices and apply this knowledge to test interpretation.

First Indonesian proficiency testing using reference value from isotope dilution mass spectrometry method for benzoic acid, methyl paraben, and n-butyl paraben in sweet soy sauce

Research Center for Chemistry-Indonesian Institute of Sciences (RCChem-LIPI) has successfully organized proficiency testing (PT) for the determination of benzoic acid, methyl paraben, and n-butyl paraben in sweet soy sauce. This is the first PT in Indonesia that uses reference values derived from a primary method gas chromatography–isotope dilution mass spectrometry method. Twenty participants from four economies registered in this PT. This paper presents the procedures in the preparation of the PT samples, the homogeneity and stability checks, as well as in the determination of the assigned values. The test samples were a candidate certified reference material prepared in accordance with ISO 17034 and ISO Guide 35. The performance evaluation of participants’ results was conducted in accordance with ISO 13528 by using the PROLab™ software. This paper also discusses the approaches taken in the calculation of the performance’s scores which were set according to the criterion required in homogeneity check, stability check, and limit of uncertainty.

Asymmetric dimethylation and citrullination of proteinic arginine and homoarginine synthesis in human Helicobacter pylori infection.

The importance of L-arginine (Arg) and relatives, including L-homoarginine (hArg) and asymmetric dimethylarginine (ADMA), in humans infected with Helicobacter pylori (Hp) is little understood. ADMA is produced by asymmetric dimethylation of the guanidine group of Arg residues in certain proteins and is released by proteolysis. High concentrations of circulating free ADMA are considered a risk factor for morbidity and mortality in adults. This risk is considered to arise from the inhibition of the synthesis of nitric oxide (NO), which is a potent vasodilator and inhibitor of platelet aggregation. In the present study, we quantified by stable isotope dilution gas chromatography-mass spectrometry (GC-MS) the concentration of free (f) and total (t) ADMA, Arg, hArg, lysine (Lys) and the sum of citrulline (Cit) and ornithine (Orn) (6M HCl, 20h, 110°C) in serum samples of apparently healthy elderly subjects (n = 27; age, 31-105years) who were tested for Hp infection. Nine subjects (5 males, 4 females) were found to be Hp seropositive (Hp+) and 18 subjects (8 males, 9 females) were found to be Hp seronegative (Hp‒). Proteinic (p) concentrations were determined by difference. fADMA (0.493 ± 0.068 vs 0.466 ± 0.081µM, P = 0.382), pADMA (113 ± 73 vs 76 ± 59nM, P = 0.169) and tADMA (0.606 ± 0.126 vs 0.543 ± 0.121µM, P = 0.280) serum concentrations were found not to differ between the Hp+ and Hp- subjects. Serum concentrations of fArg (162 ± 30 vs 177 ± 36µM, P = 0.471), fhArg (1.600 ± 0.638 vs 1.831 ± 0.742µM, P = 0.554), and fLys (388 ± 170 vs 395 ± 149µM, P = 0.700) also did not differ statistically between Hp+ and Hp- subjects. tArg (12.4 ± 1.49 vs 13.0 ± 1.33mM, P = 0.190), tLys (23.0 ± 2.65 vs. 23.9 ± 2.66mM, P = 0.456) and tCit + Orn (2.53 ± 0.76 vs 2.63 ± 0.85mM, P = 0.817) did not differ between Hp+and Hp‒ subjects as well. phArg concentration was close to the limit of quantitation of the method (Hp+: 30 ± 210nM; Hp-: 42 ± 205nM), suggesting that hArg is virtually absent in serum proteins of the investigated subjects. pCit + Orn did not differ between infected and non-infected subjects. Our study suggests that Hp infection is not associated with elevated asymmetric dimethylation and citrullination of Arg proteins present in the serum or with the hArg synthesis from free Arg in elderly subjects. However, asymmetric Arg dimethylation was found to correlate inversely with Arg citrullination in Hp- (r2 = 0.408, P = 0.004) but not in Hp+ (r2 = 0.065, P = 0.506), with Arg citrullination decreasing and Arg asymmetric dimethylation increasing with subjects' age.

Determination of fatty acid contents in infant formula by isotope dilution-gas chromatography/mass spectrometry

An isotope dilution-gas chromatography/mass spectrometry (ID-GC/MS) method was developed as a candidate reference method for the accurate determination of the amount of fatty acids in infant formula. 13C- or 2H-labeled fatty acids were used as internal standards to correct for recovery and instrument sensitivity during sample preparation and MS measurements, respectively. The developed ID-GC/MS method was validated based on the repeatability and reproducibility of selected fatty acid analyses. For fatty acid measurements in a homogenized infant formula, the repeatability and the reproducibility were <2.0% and <3.0%, respectively. In addition, the developed method provided relative expanded uncertainties of 1%−6% for analyses of target fatty acids indicating a higher-order metrological quality. The developed method was successfully applied to evaluate the fatty acid contents of five commercial infant formulas and to determine the stability of homogenized infant formula under different storage conditions.

Isotope dilution gas chromatography - mass spectrometry for the development of certified reference material of ethyl carbamate in hydroalcoholic matrix

Ethyl carbamate (EC) is a toxic organic contaminant naturally present in some foods and alcoholic beverages. In order to improve the reliability of EC analysis, certified reference materials (CRM) can be used by the laboratories for quality control and for validation and standardization of analytical methods. This paper presents the development of a CRM of EC in hydroalcoholic matrix. This matrix is comprised by a 43% (v/v) aqueous ethanol solution that simulates distilled alcoholic beverages, which generally have alcoholic degree between 35% and 50%. An isotope dilution gas chromatography–mass spectrometry (ID GC–MS) method was developed, validated and employed to attribute the property value and to carry out the appropriate CRM studies, according to ISO Guide 35. Hydroalcoholic matrix was preferred instead of some distilled beverage because in the natural matrix there are EC precursors, which reacting with ethanol enable EC formation, even along storage under appropriate conditions. The applicability of the developed ID GC–MS method was evaluated by testing 26 samples of whisky, vodka, tequila, pisco, rum and the Brazilian cachaça. No interference was observed showing that it can be employed for EC quality control in distilled beverages. According to the analysis of variance, the CRM was considered homogeneous and stable at (4 ± 2) °C for at least three years. The EC concentration is (149.2 ± 5.7) ng/g.