Isotope Dilution Mass Spectrometry Method Research Articles

Inspection of the Fragmentation Pathway for Thiamethoxam

Thiamethoxam is one of the main suspect in honeybee colony collapse disorder (CCD). Due to this reason, thiamethoxam including imidacloprid and clothianidin has been banned for two years in some Europe countries. The CCD phenomenon has also been reported in Korea. Regarding this issue and needs, a new project has started to develop the method for the quatitation of thiamethoxam using isotope dilution mass spectrometry (IDMS). In the process of optimization for the IDMS method with thiamethoxam and thiamethoxam-d3, we observed that the fragment peaks did not correspond to the fragmentation pathway as published elsewhere. Here, we proposed a candidate fragmentation pathway. To validate the proposed fragmentation pathway, another isotope analogue, thiamethoxam-d4, was introduced and the MS/MS spectra of both isotope analogues were compared. In addition, the MS/MS/MS spectra of thiamethoxam were inspected for more evidence of the candidate pathway. Those spectra indicated that the proposed fragmentation pathway could be used to assign the fragment peaks of thiamethoxam.

Development of high accuracy methods for the certification of calcium, iron, magnesium and potassium in human serum

High accuracy methods were developed for the measurements of calcium, potassium, iron and magnesium in human serum using standard addition and isotope dilution mass spectrometry methods. The results were comparable to those obtained by other national metrology institutes and designated institutes as demonstrated in an inter-laboratory comparison. The methods were then adopted for the assignment of reference values in a human serum material and the uncertainties associated with the certified values were obtained by combining the uncertainty components from the characterisation, homogeneity and long-term stability of the materials. The certified values are traceable to the International System of Units and the material can be used by the clinical testing laboratories to validate their methods or as a quality control material to improve the accuracy of their measurements.

Development of an apple juice certified reference material for cadmium, lead, total arsenic and arsenic species

In the development of the apple juice certified reference material, isotope dilution mass spectrometry method was used for the assignment of certified values and long-term stability study for cadmium and lead. For total arsenic, inorganic arsenic, as well as dimethylarsenic acid, standard addition method was used. The analytes were found to be homogenous and stable over a period of at least 4.5 months at storage temperature of −20°C (long-term stability). The certified mass fraction values were (0.220±0.011) mg/kg for cadmium, (0.245±0.014) mg/kg for lead, (0.185±0.015) mg/kg for total arsenic, (0.124±0.012) mg/kg for inorganic arsenic [As(III)+As(V)] and (0.0601±0.0052) mg/kg for DMAA. The recovery of the arsenic species was over 99%. This apple juice certified reference material can be used for method validation or as a quality control material by routine testing laboratories.

Comparison of standard addition and conventional isotope dilution mass spectrometry for the quantification of endogenous progesterone in milk

In this study, a standard addition–isotope dilution mass spectrometry (SA-IDMS) method for quantification of endogenous progesterone in milk has been described. The method validation results, linearity, limits of detection and quantification, recovery and uncertainty were fit for the purpose of assigning reference mass fractions to proficiency testing schemes. The developed technique was compared to the isotope dilution mass spectrometry (IDMS) method already existing in the laboratory. Analytical results of two milk samples were (1.377 ± 0.048) μg/kg and (4.457 ± 0.155) μg/kg by SA-ID-LC/MS method, while the results were (1.355 ± 0.019) μg/kg and (4.359 ± 0.059) μg/kg by ID-LC/MS, respectively. Since SA-IDMS was an effective quantitative method that overcame matrix effect, similar quantitative results from IDMS and SA-IDMS indicated that the quantification of progesterone in milk was barely influenced by matrix. Both IDMS and SA-IDMS could be used to assign reference mass fractions to progesterone in milk inter-laboratory proficiency testing schemes.

A universal SI-traceable isotope dilution mass spectrometry method for protein quantitation in a matrix by tandem mass tag technology.

Isotope dilution mass spectrometry (IDMS), an important metrological method, is widely used for absolute quantification of peptides and proteins. IDMS employs an isotope-labeled peptide or protein as an internal standard although the use of a protein provides improved accuracy. Generally, the isotope-labeled protein is obtained by stable isotope labeling by amino acids in cell culture (SILAC) technology. However, SILAC is expensive, laborious, and time-consuming. To overcome these drawbacks, a novel universal SI-traceable IDMS method for absolute quantification of proteins in a matrix is described with human transferrin (hTRF). The hTRF and a human serum sample were labeled with different tandem mass tags (TMTs). After mixing the TMT-labeled hTRF and serum sample together followed by digestion, the peptides were separated by nano-liquid chromatography and analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Using the signature peptides, we calculated the ratios of reporter ions from the TMT-labeled peptides which, in turn, allowed determination of the mass fraction of hTRF. The recovery ranged from 97% to 105% with a CV of 3.9%. The LOD and LOQ were 1.71 × 10(-5) g/g and 5.69 × 10(-5) g/g of hTRF in human serum, respectively, and the relative expanded uncertainty was 4.7% with a mass fraction of 2.08 mg/g. For comparison, an enzyme-linked immunosorbent assay (ELISA) method for hTRF yielded a mass fraction of 2.03 mg/g. This method provides a starting point for establishing IDMS technology to accurately determine the mass fractions of protein biomarkers in a matrix with traceability to SI units. This technology should support the development of a metrological method useful for quantification of a wide variety of proteins.

Isotopic dilution analysis using ICP/AES: application to uranium samples and comparison to MC ICP/MS measurements

An ICP/AES owning a high resolving power is able to measure the isotopic shift in emission atomic lines for heavy elements such as uranium. 235U and 238U are therefore clearly separated and identified. Using this phenomenon, the transposition of isotopic dilution mass spectrometry method to the ICP/AES instrument allows to quantify, with accuracy and precision, the 235U content of a solution. The method, named IDAES, is the first that combine isotope dilution method and ICP/AES measurements. In order to demonstrate the validity of the IDAES method, an IDMS protocol using a MC ICP/MS instrument, is also applied to determine the amount content of 235U of the sample.

Development of a cosmetic cream certified reference material: Certification of lead, mercury and arsenic mass fractions in cosmetic cream

This paper describes the development of a cosmetic cream certified reference material containing lead, mercury and arsenic. High accuracy exact matching isotope dilution mass spectrometry or standard addition method was used for the assignment of certified values and long-term stability study. A multiple spiking approach was employed to simplify the analytical procedure. The metal contents were found to be homogenous and stable for a period of 14 days at 46°C (short-term stability) and over a period of at least 6 months at ambient temperature (long-term stability). A metrological approach was used to consider potential biases to achieve appropriate accuracy for the certified mass fraction values. The expanded relative uncertainties at 95% confidence level for lead (26.14mg/kg±0.76mg/kg), mercury (2.956mg/kg±0.092mg/kg) and arsenic (5.25mg/kg±0.28mg/kg) were 2.90%, 3.11% and 5.38%, respectively.

Preparation and characterisation of certified reference materials for furazolidone and nitrofurazone metabolites in prawn

Nitrofuran residues in food, particularly intensively farmed prawns, were identified as an important trade and health issue. No certified reference materials were available to allow laboratories to demonstrate satisfactory performance of their analytical methods. Freeze-dried prawn reference materials MX012A and MX012B were prepared at the National Measurement Institute, Australia, from blank and contaminated prawn tissue. A high-accuracy, exact-matching isotope dilution mass spectrometry method was developed for the analysis of two nitrofuran metabolites in the prawn materials. Residues were extracted by acid hydrolysis and derivatisation with 2-nitrobenzaldehyde, extracts were purified by liquid–liquid extraction followed by solid-phase extraction, and instrumental analysis was by ultra-high-pressure liquid chromatography with electrospray tandem mass spectrometry (UHPLC-ESI-MSMS). The method was used to certify the reference materials for mass fraction of 3-amino-2-oxazolidinone (AOZ) and semicarbazide (SEM), including the preparation of detailed measurement uncertainty budgets. MX012A contains AOZ at (137.5 ± 8.5) ng/g of freeze-dried material, and MX012B contains AOZ at (30.2 ± 1.8) ng/g and SEM (fortified) at (70.3 ± 3.1) ng/g. When reconstituted as directed on the certificate, the materials contain AOZ at (20.6 ± 1.3) ng/g and (4.53 ± 0.27) ng/g (MX012A and MX012B, respectively) and SEM at (10.5 ± 0.5) ng/g (MX012B). The individual components contributing to the measurement uncertainty estimates were the mass fractions assigned to calibration standards, gravimetric mass measurements, precision of the analytical method, reproducibility, long-term storage stability of the material at −20 °C, stability of the material during transportation, and potential bias due to extraction efficiency of the incurred analyte and matrix interference.

Production of highly-enriched 134Ba for a reference material for isotope dilution mass spectrometry measurements

Isotope dilution mass spectrometry (IDMS) is an analytical technique capable of providing accurate and precise quantitation of trace isotope abundance and assay providing measurement uncertainties below 1 %. To achieve these low uncertainties, the IDMS method ideally utilizes chemically pure “spike” solutions that consist of a single highly enriched isotope that is well-characterized relating to the abundance of companion isotopes and concentration in solution. To address a current demand for accurate 137Cs/137Ba ratio measurements for “age” determination of radioactive 137Cs sources, Idaho National Laboratory (INL) is producing enriched 134Ba isotopes that are tobe used for IDMS spikes to accurately determine 137Ba accumulation from the decay of 137Cs. The final objective of this work it to provide a homogenous set of reference materials that the National Institute of Standards and Technology can certify as standard reference materials used for IDMS. The process that was developed at INL for the separation and isolation of Ba isotopes, chemical purification of the isotopes in solution, and the encapsulation of the materials will be described.

S1 certification of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in a candidate certified reference material (organochlorine pesticides in tea) by isotope dilution gas chromatography-mass spectrometry.

This paper presents the certification of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in a candidate tea certified reference material (code: GLHK-11-03) according to the requirements of the ISO Guide 30 series. Certification of GLHK-11-03 was based on an analytical method purposely developed for the accurate measurement of the mass fraction of the target analytes in the material. An isotope dilution mass spectrometry (IDMS) method involving determination by (i) gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS) and (ii) gas chromatography-electron ionization-high-resolution mass spectrometry (GC-EI-HRMS) techniques was employed. The performance of the described method was demonstrated through participation in the key comparison CCQM-K95 "Mid-Polarity Analytes in Food Matrix: Mid-Polarity Pesticides in Tea" organized by the Consultative Committee for Amount of Substance-Metrology in Chemistry in 2012, where the study material was the same as the certified reference material (CRM). The values reported by using the developed method were in good agreement with the key comparison reference value (KCRV) assigned for beta-endosulfan (727 ± 14μgkg(-1)) and endosulfan sulfate (505 ± 11μgkg(-1)), where the degree of equivalence (DoE) values were 0.41 and 0.40, respectively. The certified values of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in dry mass fraction in GLHK-11-03 were 350, 730, and 502μgkg(-1), respectively, and the respective expanded uncertainties, due to sample inhomogeneity, long-term and short-term stability, and variability in the characterization procedure, were 27μgkg(-1) (7.8%), 48μgkg(-1) (6.6%), and 33μgkg(-1) (6.6%).

The quantification of human chorionic gonadotropin by two isotope dilution mass spectrometry methods

Two isotope dilution mass spectrometry (IDMS) methods were established and compared for absolute quantification of the mass fraction of an important clinical diagnostic marker, i.e. human chorionic gonadotropin (hCG), by employing hydrolysis and enzymatic digestion. In the first method, after hydrolysis of the protein, amino acids were separated by high-performance liquid chromatography (HPLC) and then detected by tandem mass spectrometry (MS) with multiple reaction monitoring (MRM) for phenylalanine, proline, valine and the internal standards (13C9-phenylalanine, 13C5-proline and 13C5-valine). In the second method, after enzyme digestion, the signature peptide (VLQGVLPALPQVVCNYR, m/z = 964 → 1036) and the internal standard (d10-VLQGVL*PALPQVVCNYR, m/z = 970 → 1317) were separated by HPLC, and then detected by MS with MRM. By optimizing the key factors of hydrolysis and enzymatic digestion, the mass fractions of hCG detected by these two methods are consistent. The mass fraction of hCG by hydrolysis is 0.6150 g g−1 (expanded uncertainty = 0.016 g g−1, k = 2), the mass fraction of hCG by enzyme digestion is 0.5810 g g−1 (expanded uncertainty = 0.072 g g−1, k = 2), and the weighted average mass fraction is 0.6126 g g−1 (expanded uncertainty = 0.016 g g−1, k = 2). This study would benefit the absolute quantification of clinical marker proteins, and underpin the development of relative certified reference materials of clinical diagnostic markers to ensure the accuracy, comparability and traceability of medical laboratory testing.

Determination of 16 phthalate acid esters in infant formula by gas chromatography-tandem mass spectrometry

A method was established for the determination of 16 phthalate acid esters (PAEs) in infant formula by gas chromatography-tandem mass spectrometry (GC-MS/MS). PAEs in infant formula samples were homogenized by deionized water, extracted with acetonitrile, and purified by a solid-phase extraction (SPE) method using primary secondary amine (PSA) sorbents. The separation was performed on a DB-5 MS UI (30 m×0.25 mm×0.25 μm) capillary column. Effects of different elution solvents on alumina/PSA and PSA SPE columns were investigated. Fair recoveries of 16 PAEs were achieved on the PSA column upon elution by mixed n-hexane-acetone (60:40, v/v). All the 16 PAEs were quantified by matrix-matched isotopic-dilution mass spectrometry (IDMS); the 16 PAEs showed linear relationships in the concentration range of 0.01-2.0 mg/kg with linear coefficients (R2) greater than 0.9996. The limits of detection (LODs) and quantification (LOQs) were in the range of 0.15-2.5 μg/kg and 0.50-8.33 μg/kg, respectively. The recoveries of the 16 PAEs, obtained using the IDMS method, were 96.1%-104.0% with relative standard deviations (RSDs) lower than 3.3% (n=5). These results established the method described here as sensitive and precise for the simultaneous determination of 16 PAEs in infant formula, even at trace concentrations.

Quantification of viral proteins of the avian H7 subtype of influenza virus: an isotope dilution mass spectrometry method applicable for producing more rapid vaccines in the case of an influenza pandemic.

Vaccination is the most effective means to prevent influenza and its serious complications. Influenza viral strains undergo rapid mutations of the surface proteins hemagglutinin (HA) and neuraminidase (NA) requiring vaccines to be frequently updated to include current circulating strains. It is nearly impossible to predict which strains will be circulating in the next influenza season. It is, therefore, imperative that the process of producing a vaccine be streamlined and as swift as possible. We have developed an isotope dilution mass spectrometry (IDMS) method to quantify HA and NA in H7N7, H7N2, and H7N9 influenza. The IDMS method involves enzymatic digestion of viral proteins and the specific detection of evolutionarily conserved target peptides. The four target peptides that were initially chosen for analysis of the HA protein of H7N2 and H7N7 subtypes were conserved and available for analysis of the H7N9 subtype that circulated in China in the spring of 2013. Thus, rapid response to the potential pandemic was realized. Quantification of a protein is performed by employing multiple peptides to ensure that the enzymatic digestion of the protein is efficient in the region of the target peptides, verify the accuracy of the measurement, and provide flexibility in the case of amino acid changes among newly emerging strains. The IDMS method is an accurate, sensitive, and selective method to quantify the amount of HA and NA antigens in primary liquid standards, crude allantoic fluid, purified virus samples, and final vaccine presentations.

Development and validation of a liquid chromatography isotope dilution mass spectrometry method for the reliable quantification of alkylphenols in environmental water samples by isotope pattern deconvolution

We present here a new measurement method for the rapid extraction and accurate quantification of technical nonylphenol (NP) and 4-t-octylphenol (OP) in complex matrix water samples by UHPLC-ESI-MS/MS. The extraction of both compounds is achieved in 30min by means of hollow fiber liquid phase microextraction (HF-LPME) using 1-octanol as acceptor phase, which provides an enrichment (preconcentration) factor of 800. On the other hand we have developed a quantification method based on isotope dilution mass spectrometry (IDMS) and singly 13C1-labeled compounds. To this end the minimal labeled 13C1-4-(3,6-dimethyl-3-heptyl)-phenol and 13C1-t-octylphenol isomers were synthesized, which coelute with the natural compounds and allows the compensation of the matrix effect. The quantification was carried out by using isotope pattern deconvolution (IPD), which permits to obtain the concentration of both compounds without the need to build any calibration graph, reducing the total analysis time. The combination of both extraction and determination techniques have allowed to validate for the first time a HF-LPME methodology at the required levels by legislation achieving limits of quantification of 0.1ngmL−1 and recoveries within 97–109%. Due to the low cost of HF-LPME and total time consumption, this methodology is ready for implementation in routine analytical laboratories.

Evaluation of matrix effect in isotope dilution mass spectrometry based on quantitative analysis of chloramphenicol residues in milk powder

In the present study, we developed a comprehensive strategy to evaluate matrix effect (ME) and its impact on the results of isotope dilution mass spectrometry (IDMS) in analysis of chloramphenicol (CAP) residues in milk powder. Stable isotope-labeled internal standards do not always compensate ME, which brings the variation of the ratio (the peak area of analyte/the peak area of isotope). In our investigation, impact factors of this variation were studied in the extraction solution of milk powder using three mass spectrometers coupled with different ion source designs, and deuterium-labeled chloramphenicol (D5-CAP) was used as the internal standard. ME from mobile phases, sample solvents, pre-treatment methods, sample origins and instruments was evaluated, and its impact on the results of IDMS was assessed using the IDMS correction factor (θ). Our data showed that the impact of ME of mobile phase on the correction factor was significantly greater than that of sample solvent. Significant ion suppression and enhancement effects were observed in different pre-treated sample solutions. The IDMS correction factor in liquid–liquid extraction (LLE) and molecular imprinted polymer (MIP) extract with different instruments was greater or less 1.0, and the IDMS correction factor in hydrophilic lipophilic balance (HLB) and mix-mode cation exchange (MCX) extract with different instruments was all close to 1.0. To the instrument coupled with different ion source design, the impact of ME on IDMS quantitative results was significantly different, exhibiting a large deviation of 11.5%. Taken together, appropriate chromatographic conditions, pre-treatment methods and instruments were crucial to overcome ME and obtain reliable results, when IDMS methods were used in the quantitative analysis of trace target in complex sample matrix.

Determination of GHB and its precursors (GBL and 1,4-BD) in dietary supplements through the synthesis of their isotopologues and analysis by GC–MS method

Gamma-hydroxybutyric acid (GHB) and its “pro-drugs”, gamma-butyrolactone (GBL) and 1,4 butanediol (1,4-BD), are drugs of abuse with depressant effects on the central nervous system. Many analytical methods have been proposed for the quantitative determination of these compounds mainly in biological matrices but only few have been addressed to dietary supplements and foods. Facile synthesis of the GBL and 1,4-BD isotopologues are available by “one pot” Ru-catalyzed homogeneous deuteration of dicarboxylic acids. In this work we propose a new method for determination of GHB, GBL and 1,4-BD in commercially available dietary supplements, based on isotope dilution mass spectrometry (ID-MS). The procedure involves a simple extraction of sample with acidic acetonitrile and direct analysis by GC–ID-MS method without any purification or derivatization. Indeed, the proposed method takes advantage of the complete conversion of GHB (free acid or its salts) to GBL, allowing the quantification of GHB and its pro-drugs. Five levels for each calibration curve have been prepared by diluting working solutions of the analytes to obtain concentrations ranging from 1 to 20mg/mL. The validation procedures have shown an accuracy between 88% and 99% and a precision between 7.3% and 2.9% of each analyte in the sample matrix. Positive ions chemical ionization (PICI) have been employed to preserve the information on molecular ions and to improve specificity and sensitivity of quantitative determination.

Utilizing isotope dilution-matrix-assisted laser desorption ionization-time of flight mass spectrometry as a reference procedure for the radioimmunoassay of serum thyroxine

BackgroundThe thyroid hormone, thyroxine (T4), is a tyrosine-based hormone produced by the thyroid gland, which is essential in regulating a number of biological processes, including growth, neurodevelopment, carbohydrate metabolism, oxygen consumption and protein synthesis. Data on human thyroid hormone metabolism were gathered since the middle of the 1970s mainly by the use of radioactive iodinated (125I or 131I) hormones. MethodsWe describe an isotope dilution-matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) method for the simultaneous determination of endogenous thyroid hormone and its 13C6-labeled analogue in serum. The 13C6-thyroxine (13C6-T4) was used as an internal standard; T4 and its isotopically labeled analogue were measured in the selected reaction monitoring mode for the transitions from m/z 777.8 to 732.1 and from m/z 784.2 to 738.1, respectively. ResultsSerum samples were prepared and concentrated by a solid-phase extraction chromatography method. The recovery rate was measured by 125I-T4 and can be up to 82.8±2.8%. The detection limit and linear range for T4 were 5ng/ml and 5–400ng/ml, respectively. The correlation coefficient (R2) between radioimmunoassay (RIA) and isotope dilution-MALDI-TOF MS for detection of serum T4 was 0.982. ConclusionThis assay has a good relationship against a commercial RIA and the isotope dilution-mass spectrometry method and may serve as a reference method for quantitative analysis of T4.

Uranium isotope dilution mass spectrometry using NBL certified reference materials as spikes

The isotope dilution mass spectrometry method of analysis is used to determine the elemental uranium contents in a wide variety of uranium bearing materials. The method is based on the mass spectrometric analysis of a mixture prepared by diluting the sample to be analyzed with a spike of distinctly different isotopic composition to that of the sample. In this work, a beginning is made to identify suitable candidates among the multitude of certified reference materials (CRMs) available at the New Brunswick Laboratory to supplant the use of 233U which remains now as the preferred spike nuclide. The results of the study presented here identify CRM 112-A (of normal isotopic composition) and CRM 115 (depleted uranium composition) as suitable candidates to replace 233U as spike material for determining uranium in high enriched uranium materials, and CRM 116 (235U mass fraction of >90 %) for determining uranium in materials of low enrichment.

Simultaneous Quantification of Steroids in Rat Intratesticular Fluid by HPLC—Isotope Dilution Tandem Mass Spectrometry

An isotope dilution mass spectrometry method has been developed for the simultaneous measurement of picolinoyl derivatives of testosterone (T), dihydrotestosterone (DHT), 17β-estradiol (E(2)), and 5α-androstan-3α,17β-diol (3α-diol) in rat intratesticular fluid. The method uses reversed-phase high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. Following derivatization of 10-μL samples of testicular fluid with picolinoyl chloride hydrochloride, the samples were purified by solid phase extraction before analysis. The accuracy of the method was satisfactory for the 4 analytes at 3 concentrations, and both inter- and intraday reproducibility were satisfactory for T, DHT, and E(2). Measurements of intratesticular T concentrations in a group of 8 untreated adult rats by this method correlated well with measurements of the same samples by radioimmunoassay. As in men, there was considerable rat-to-rat variability in T concentration, despite the fact that the rats were inbred. Although its levels were more than an order of magnitude lower than those of T, DHT was measured reliably in all 8 intratesticular fluid samples. DHT concentration also varied from rat to rat and was highly correlated with T levels. The levels of E(2) and 3α-diol also were measurable. The availability of a sensitive method by which to measure steroids accurately and rapidly in the small volumes of intratesticular fluid obtainable from individual rats will make it possible to examine the effects, over time, of such perturbations as hormone and drug administration and environmental toxicant exposures on the intratesticular hormonal environment of exposed individual males and thereby to begin to understand differences in response between individuals.

A Method for the Routine Determination of Methylmercury in Marine Tissue by GC Isotope Dilution-ICP-MS

Currently, there is no legal limit for methyl mercury (MeHg) in food; thus, no standardized method for the determination of MeHg in seafood exists within the European jurisdiction. In anticipation of a future legislative limit an inductively coupled plasma isotope dilution mass spectrometry (GC-ICP-ID-MS) method was developed in collaboration with the European Standardization Organization (CEN). The method comprises spiking the tissue sample with Me201Hg, followed by decomposition with tetramethylammonium hydroxide, pH adjustment and derivatization with sodium tetraethylborate, and finally organic extraction of the derivatized MeHg in a hexane phase. Subsequently, the sample is analyzed via GC-ICP-MS and the result calculated using the ID equation. The working range of the method was 0.0005-1.321 mg/kg MeHg in marine tissue, with an internal reproducibility (RSD) of 12-1%. The method was validated based on statistical measures, such as the z-scores, using the commercially available reference materials from National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1566b, NIST SRM 2977 and National Research Council of Canada (NRCC) TORT 2, NRCC, DORM 3, NRCC DOLT 4, and European Reference Material (ERM) CE 464. Z-scores for all standard reference materials, except for NIST SRM 1566b, were better than 11.51. The wide range of marine tissues used during the validation ensures that the method will be applicable for measuring of MeHg in seafood matrixes of all kinds.