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PubMed1995

Standard reference materials and data quality assurance: the lesson from the analysis of trace elements.

The problem of having accurate and precise analytical data of the concentrations of trace elements and compounds in bioclinical studies is of fundamental importance. This can be conveniently faced if appropriate standard reference materials, with known concentrations of the analyte object of study, are available. This paper reviews the present situation of these standard materials in the field of trace element analysis in biological specimens. The most important requirements in the preparation and in the application of these materials are presented and discussed.

Evaluation Studies as Topic↗
PubMed2000

Determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid in a urine-based standard reference material by isotope-dilution liquid chromatography-mass spectrometry with electrospray ionization.

A new method is presented for the determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid (THC-9-COOH) in urine-based standard reference materials (SRMs) for marijuana metabolite. This method is based on isotope-dilution liquid chromatography-mass spectrometry (LC-MS) using electrospray for ionization (ESI). An isotopically labeled compound, 5',11-nor-delta9-THC-9-carboxylic acid-d3, was used as an internal standard. Solid-phase extraction (SPE) was used to prepare samples for LC-MS analyses. LC was performed on a C18 column with an isocratic mobile phase consisting of 0.05 M of ammonium acetate in methanol/water (75:25). Electrospray ionization in the negative ion mode was used to monitor the [M-H]- ions at m/z 343 and 346 for THC-9-COOH and its labeled internal standard, respectively. Samples of SRM 1507b (THC-9-COOH in freeze-dried urine) were prepared and measured on three separate sets. The within-set coefficients of variation ranged from 0.32% to 2.77%. The correlation coefficients of the regression lines were 0.999 to 1.000. The detection limit for THC-9-COOH with this method is estimated to be 5 pg/mL. This method compared well with the gas chromatography-mass spectrometry method used for certification, and results were within the certified values of THC-9-COOH for SRM 1507b.

Chromatography, Liquid↗
PubMed1996

Standard reference materials and data quality assurance in the biomedical analysis of trace elements.

Accurate and precise analytical data of the concentrations of bio-analytes in bioclinical studies are of fundamental importance. Quality assurance procedures should always be performed to check the overall analytical work. This can be conveniently performed if appropriate standard reference materials with known concentrations of the analyte object of study are available. This paper underlines the key points related to the production and use of biological standard materials for trace element analysis. In particular, the present situation in the field of trace element determination in human biological fluids and the related problems are illustrated. The considerations given in this work may contribute to the preparation of the new biomarker standard materials.

Biomarkers↗
PubMed2001

Development of isotope dilution cold vapor inductively coupled plasma mass spectrometry and its application to the certification of mercury in NIST standard reference materials.

An isotope dilution cold vapor inductively coupled plasma mass spectrometry (ID-CV-ICPMS) method featuring gaseous introduction of mercury via tin chloride reduction has been developed and applied to the quantification and certification of mercury in various NIST standard reference materials: SRM 966 Toxic Metals in Bovine Blood (30 ng x mL(-1)); SRM 1641d Mercury in Water (1.6 microg x mL(-1)); and SRM 1946 Lake Superior Fish Tissue (436 ng x g(-1)). Complementary mercury data were generated for SRMs and NIST quality control standards using cold vapor atomic absorption spectroscopy (CVAAS). Certification results for the determination of mercury in SRM 1641d using two independent methods (ID-CV-ICPMS and CVAAS) showed a degree of agreement of 0.3% between the methods. Gaseous introduction of mercury into the ICPMS resulted in a single isotope sensitivity of 2 x 10(6) counts x s(-1)/ng x g(-1) for 201Hg and significantly reduced the memory and washout effects traditionally encountered in solution nebulization ICPMS. Figures of merit for isotope ratio accuracy and precision were evaluated at dwell times of 10, 20, 40, 80, and 160 ms using SRM 3133 Mercury Spectrometric Solution. The optimum dwell time of 80 ms yielded a measured 201Hg/202Hg isotope ratio within 0.13% of the theoretical natural value and a measurement precision of 0.34%, on the basis of three replicate injections of SRM 3133.

Animals↗
PubMed2000

Exclusion of deep venous thrombosis with D-dimer testing--comparison of 13 D-dimer methods in 99 outpatients suspected of deep venous thrombosis using venography as reference standard.

In a direct assay comparison we evaluated the diagnostic performance of 10 novel D-Dimer assays for the exclusion of deep venous thrombosis (DVT). In addition, 3 conventional ELISA D-Dimer assays were included as reference tests. The study was performed in 99 consecutive outpatients referred to the emergency department for clinical suspicion of DVT. Venography was used as reference standard and demonstrated the presence of DVT in 50 patients (6 patients with isolated distal DVT and 44 patients with proximal DVT). The qualitative D-Dimer assays Minutex and SimpliRED and the quantitative BC DD showed overall sensitivities (for proximal and distal DVT) of only 80-83% with specificities that ranged from 87 to 94%. Overall sensitivity was 94% for the qualitative INSTANT I.A. and 98% for the quantitative Turbiquant at a cut-off level equal to the detection limit. Using different cut-off levels a sensitivity of 100% for proximal DVT and for proximal as well as distal DVT could be obtained for NycoCard, IL DD, Liatest, Tinaquant and VIDAS D-Dimer assays with specificities that ranged from 31% (NycoCard) to 71% (VIDAS) for proximal DVT and from 12% (NycoCard) to 47% (IL DD) for overall DVT. At a cut-off level equal to the upper limit of the reference range only Tinaquant and VIDAS showed a sensitivity of 100% for proximal as well as for distal DVT with a specificity of 39% and 41% respectively. The results of this study suggest that the VIDAS and Tinaquant D-Dimer assays have the highest sensitivity for the exclusion of DVT in outpatients. In outpatients that have a low or moderate pretest probability for DVT, these tests may be used in management studies where anticoagulation is withheld on the basis of D-Dimer testing alone.

Adult↗
PubMed2006

Development of a NIST standard reference material containing thirty volatile organic compounds at 5 nmol/mol in nitrogen.

Primary gravimetric gas cylinder standards containing 30 volatile organic compounds (VOCs) in nitrogen were prepared using a procedure previously developed to prepare gas mixture cylinder standards of VOCs at the 5 nmol/mol level. This set of primary standards was intercompared to existing gas cylinder standards, containing as many as 19 of the 30 volatile organics present in these new primaries, using gas chromatography with a hydrogen flame ionization detector coupled with cryogenic preconcentration. The linear regression analysis showed excellent agreement among the standards for each compound. Similar mixtures containing many of these compounds in treated aluminum gas cylinders have been evaluated over time and have shown stability for as much as 10 years. The development of these 30-component primary standards led to the preparation and certification of a reissue of Standard Reference Material (SRM) 1804 at the nominal amount-of-substance fraction of 5 nmol/mol for each analyte. A lot of 20 cylinders containing the mixture was prepared at NIST following previously demonstrated protocols for preparation of the cylinders. Each cylinder was analyzed against one cylinder from the lot, designated as the "lot standard," for each of the 30 compounds. As a result of the uncertainty analysis, the data showed that rather than declaring the lot homogeneous with a much higher uncertainty, each cylinder could be individually certified. The expanded uncertainty limits ranged from 1.5 to 10% for 28 of the 30 analytes, with two of the analytes having uncertainties as high as 19% in those SRM cylinders certified. Due to stability issues and some high uncertainties for a few analytes in 2 of the samples, 18 of the 20 candidate SRM samples were certified. These volatile organic gas mixtures represent the most complex gas SRMs developed at NIST.

Journal Article↗
PubMed1992

Comparison of six microcomputer dietary analysis systems with the USDA Nutrient Data Base for Standard Reference.

We compared the general operating features and nutrient databases of six microcomputer dietary analysis systems. A 3-day food record with 73 food items was entered into each program; nutrient averages were compared with the US Department of Agriculture Nutrient Data Base for Standard Reference (USDA NDB), full version, release 9, for microcomputers. The six programs were found to vary widely in cost, number of foods and nutrients in the database, use of non-USDA data and imputation of data for missing values, number of print/export options, time to analyze the 3-day food record, and overall ease of use. Although all of the microcomputer dietary analysis systems were within 7% of the USDA NDB for energy, protein, total fat, and total carbohydrates, the proportion of other nutrients varying more than 15% from the USDA NDB varied considerably between programs. Variance among programs for 3-day food record nutrient values occurred because of differences in the number of food items included in the database (leading to varying degrees of substitution), the recency of the nutrient data (whether or not the most recent USDA releases had been incorporated), and the number of missing values (the degree to which non-USDA sources or estimated calculations were used to fill in the blanks from the USDA standard). Our results demonstrate that it is important for each dietitian to carefully choose a microcomputer dietary analysis system that is suitable to specific and predetermined needs.

Databases, Factual↗
PubMed1979

The T-lymphocyte as a diploid reference standard for flow cytometry.

T-lymphocytes prepared from the peripheral blood of normal individuals exhibit uniform postmitotic DNA contents that are constant from individual to individual when fixed in ethanol and stained with mithramycin, or when fixed in formalin and stained with acriflavine-Feulgen and analyzed by flow microfluorometry. T-lymphocytes fixed by either method are stable on storage for several months. These cells are suitable for use as an external diploid reference standard for flow cytometric detection of cells with abnormalities in postmitotic content exceeding 5% of diploid reference. Cells with abnormalities in postmitotic DNA content of less than 5% can be detected in mixtures containing both normal and malignant cells by multiparameter analysis.

DNA↗
PubMed1988

Direct absorptiometric quantitation in high-performance liquid chromatography in the absence of concomitant reference standards.

A method for absorptiometric quantification in high-performance liquid chromatography that utilizes the known molar absorption coefficients of the individual components of a mixture of analytes to enable a series of determinations to be carried out without the concomitant use of reference standards is described. An equation is derived that describes the dependence of the molar amount of a defined analyte on the parameters influencing the detector response and on the peak area of the analyte in the chromatogram. The equation can be used for the direct calculation of the molar amount of individual analytes in a well resolved mixture. A method for the analysis of two analytes, the peaks of which totally overlap but which differ by their molar absorption coefficients, is also described. The validity of the equations and the applicability of the proposed method was examined in the analysis of 5-(2-dimethylaminoethoxy)-7-oxo-7H-benzo[c]fluorene hydrochloride (benflurone) and its metabolites. Some examples of the application of this approach are considered.

Chemical Phenomena↗
PubMed2006

Population-based reference standards for cardiovascular fitness among U.S. adults: NHANES 1999-2000 and 2001-2002.

PURPOSE: To provide reference standards for cardiovascular fitness levels, using population-based estimates of estimated maximal oxygen uptake (VO2max) from a diverse sample of U.S. adults. METHODS: Analysis of data from adults (20-49 yr) who completed a submaximal exercise test in the National Health and Nutrition Examination Survey 1999-2000 and 2001-2002. Estimated VO2max was categorized as low (<20th percentile), moderate (between 20th and 59th percentiles), or high (> or =60th percentile) fitness using age- and sex-specific cut-points. RESULTS: There were 1978 subjects, roughly 29% Mexican-American, 20% non-Hispanic black, and 51% non-Hispanic white. Using population-based sample weights, this was equivalent to 54,078,766 persons with mean (+/- SE) age, 34.4 +/- 0.3 yr; body mass index (BMI), 27.0 +/- 0.2 kg x m(-2); and estimated VO2max, 40.4 +/- 0.3 mL x min(-1) x kg(-1). There was a significant association between race and fitness level and between race and fitness level by sex (P < 0.0001). Low fitness was highest among non-Hispanic blacks (percentage (95% confidence interval): 32%, (26-38%)) compared with Mexican-Americans (22% (18-27%)) and non-Hispanic whites (18% (15-21%)), particularly among females, where 35% (28-42%) non-Hispanic black women had low fitness compared with 22% (16.3-27.4%) Mexican-American and 18% (13.7-22.4%) non-Hispanic white women. CONCLUSIONS: Non-Hispanic black adults have the highest percentage of low cardiovascular fitness among major race groups in the United States. On a population basis, over one third of non-Hispanic black women have low cardiovascular fitness, suggesting this group in particular may be at increased health risk due to poor fitness.

Adult↗
PubMedDate not supplied

Extension of AOAC Official Method 996.01 to the analysis of Standard Reference Material (SRM) 1846 and infant formulas.

There is currently no official method for the analysis of fatty acids (including trans fatty acids) in infant formulas. AOAC Official Method 996.01 for Fat Analysis in Cereal Products was extended to the analysis of milk-based infant formula Standard Reference Material (SRM)1846 to determine its applicability for use with infant formulas. Following the analysis of SRM 1846, 2 infant formulas, one milk-based liquid and one soy-based powdered infant formula, were analyzed for total fatty acid composition. Fatty acid methyl esters were prepared and analyzed by gas chromatography. The results of the analysis of SRM 1846 show that the mean analyzed values were highly reproducible as indicated by low coefficients of variation (CV). The CVs were <5% for the major fatty acids. Mean analyzed values for individual fatty acids in SRM 1846 were within +/- 1 standard deviation of the certificate values. The analyzed value for total fat as triglycerides (26.27 +/- 0.25%) agreed well with the certificate value (27.1 +/- 0.59%). Analyses of infant formulas showed that the concentrations of linoleic acid and fat meet the requirements for such formulas.

Animals↗
PubMed1986

Relation of structure to function for the U. S. reference standard endotoxin after exposure to 60Co radiation.

The structure and function of the highly purified U.S. reference standard endotoxin (RSE) were studied after exposure to ionizing radiation from a 60Co source. With increasing doses of radiation, the trilaminar ribbon-like structure of untreated endotoxin exhibited focal swelling, after which only spherical particles were seen by electron microscopy. These morphological changes were paralleled by the respective loss of O-side chain repeating units and pieces of the R-core from the lipopolysaccharide molecules, as demonstrated by electrophoresis. The biologic function of the irradiated endotoxin was assessed with a variety of tests. At higher doses of radiation, a direct relation was observed between the degradation of the molecular and supramolecular structure and the loss of biologic function. At lower doses of radiation, however, there was variability among the functional assays in their rate of change with progressive irradiation of the RSE. The results suggest that the carbohydrate moiety plays an important role both in determining the supramolecular structure and in modulating certain biologic activities of bacterial endotoxins.

Animals↗
PubMed1996

Growth curves in untreated Ullrich-Turner syndrome: French reference standards 1-22 years.

UNLABELLED: In this retrospective study spanning 22 years, 167 untreated females with Ullrich-Turner syndrome were identified and their case records followed throughout their growth period. Information on total and segmental height and weight was retrieved from the case records and used to plot growth curves. Centiles from birth to adulthood were calculated which showed that the normal pubertal growth spurt was absent. Compared with normal French reference standards, the adult total height deficit was about 21 cm and the adult upper body height deficit was about 15 cm. CONCLUSION: Reference curves for untreated Ullrich-Turner syndrome are provided, which should form a basis for assessing the impact of growth-promoting treatment in this disorder.

Adolescent↗
PubMed1978

Toward the development of a standard reference cholera antitoxin.

The need for a reference cholera antitoxin to serve as a standard for the calibration of cholera enterotoxin and toxoid as well as for measurement of the antitoxin response in animals and patients was recognized by the NIH Cholera Advisory Committee, NIAID, DHEW, USA. Two cholera antitoxins have been used for several years as provisional references, but neither was considered to embody all of the properties of an ideal standard. Accordingly, a lot of cholera antitoxin was prepared by immunization of goats with a formalinized, highly purified cholera toxin adsorbed on aluminum phosphate adjuvant. Booster injections were given at 8, 16 and 24 weeks. Plasma samples obtained from the 25 to 27 week bleedings were converted to serum, pooled, and freeze-dried. This serum possessed both high and constant toxin neutralizing activity in rabbit skin, rabbit ileal segment, mice, Y-1 adrenal cells and Chinese hamster ovary cells, and had high avidity by the rabbit skin assay. Hemagglutination tests gave identical values. It was shown to be highly specific by gel diffusion, but flocculation was relatively poor. On the basis of specificity, high avidity and toxin-neutralizing capacity this goat antitoxin (NIH Lot 1) was considered superior to previous provisional standards and is proposed as a satisfactory standard reference reagent.

Antibodies, Bacterial↗
PubMed2003

Determination of polycyclic aromatic hydrocarbons with molecular weight 300 and 302 in environmental-matrix standard reference materials by gas chromatography/mass spectrometry.

An analytical approach based on gas chromatography/ mass spectrometry (GC/MS) is presented for the measurement of polycyclic aromatic hydrocarbons with molecular weight (MW) 300 and 302 in environmental samples. Three different GC stationary phases [5% and 50% phenyl methylpolysiloxane and dimethyl (50% liquid crystalline) polysiloxane] were compared, and retention indexes (RI) are given for 23 individual MW 302 isomers. Identification of MW 300 and 302 isomers in four environmental-matrix Standard Reference Materials (SRMs) (SRM 1597, coal tar extract; SRM 1648 and SRM 1649a, air particulate matter; and SRM 1941, marine sediment) was based on the comparison of RI data and mass spectra from authentic standards. Dibenzo[a,l]pyrene, which is of considerable interest because of its high carcinogenicity, was identified and quantified in the four environmental-matrix SRMs. A total of 23 isomers of MW 302 and four isomers of MW 300 were quantified in four different environmental-matrix SRMs, and the results are compared to previously reported results based on liquid chromatography with fluorescence detection.

Environmental Pollutants↗
PubMed1994

Quantitation of epsilon-amino group using amino acids as reference standards by trinitrobenzene sulfonic acid. A simple spectrophotometric method for the estimation of hapten to carrier protein ratio.

A simple, sensitive and direct spectrophotometric method is presented for the determination of epsilon-amino groups of L-lysine present in carrier proteins, using the free amino acids L-lysine and L-glutamic acid as reference standards, and 2,4,6-trinitrobenzene 1-sulfonic acid (TNBS) reagent. The amount of epsilon-amino group present in the carrier protein after coupling with hapten is directly quantitated using the standard curve generated by the difference in absorbance observed with L-lysine and L-glutamic acid after their reaction with TNBS reagent. Spectral analysis of L-lysine and L-glutamic acid (27.36 nmol) derivatives of TNBS at 335 nm showed that TNP-L-lysine had twice the absorbance of TNP-L-glutamic acid, since TNBS reagent interacts equally with the alpha-amino and epsilon-amino groups present in L-lysine and the alpha-amino group of L-glutamic acid, respectively. The relationship between absorbance and concentration of epsilon-amino groups (up to 16 micrograms/ml) was found to be linear. The number of epsilon-amino groups of lysine present in carrier proteins such as BSA, HSA, thyroglobulin and the enzyme, horseradish peroxidase, were analyzed by the present method and were found to be similar to the reported values. Various carrier protein-hapten conjugates (protein-mycotoxin/vitamin/steroid hormone conjugates) were made and analyzed by the method developed in order to determine their mole to mole ratio.

Antigens↗
PubMed1995

Assignment of weight-based antibody units to a human antipneumococcal standard reference serum, lot 89-S.

A human reference serum pool, lot 89-S, has been developed for use in quantitating concentrations of antibody to Streptococcus pneumoniae. Weight-based units have been assigned to antibodies to 11 pneumococcal polysaccharide (PnPs) serotypes (1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F) by using enzyme-linked immunosorbent assay methodology and a human standard reference serum, USNRP IS 1644. The experimentally derived assignments for anti-PnPs antibodies of the immunoglobulin G (IgG), IgM, and IgA isotypes in lot 89-S correlate well to the separately determined immunoglobulin assignment. These assignments for this antipneumococcal standard serum were used to quantitate IgG, IgM, and IgA isotype levels and the total immunoglobulin level in pediatric samples from a pneumococcal conjugate vaccine trial. The data indicate that these assignments may be used to assess levels of antibody to PnPs serotypes in human serum.

Adult↗
PubMed2001

Short tandem repeat profiling provides an international reference standard for human cell lines.

Cross-contamination between cell lines is a longstanding and frequent cause of scientific misrepresentation. Estimates from national testing services indicate that up to 36% of cell lines are of a different origin or species to that claimed. To test a standard method of cell line authentication, 253 human cell lines from banks and research institutes worldwide were analyzed by short tandem repeat profiling. The short tandem repeat profile is a simple numerical code that is reproducible between laboratories, is inexpensive, and can provide an international reference standard for every cell line. If DNA profiling of cell lines is accepted and demanded internationally, scientific misrepresentation because of cross-contamination can be largely eliminated.

Cell Line↗