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PubMed2006

On the certification of cadmium at trace and ultratrace levels in standard reference materials using ID ICP-MS.

Analytical methods used for the isotope dilution inductively coupled plasma mass spectrometric (ID-ICP-MS) measurement of Cd at microg kg(-1) and sub-microg kg(-1) levels are described and applied to the certification of new dietary supplement, blood, and serum Standard Reference Materials (SRMs). The materials are: SRM 3240 Ephedra sinica Stapf Aerial Parts, SRM 3241 Ephedra sinica Stapf Native Extract, SRM 3243 Ephedra-Containing Solid Oral Dosage Form, SRM 3244 Ephedra-Containing Protein Powder, SRM 966 Toxic Metals in Bovine Blood, Level 1 (L1) and Level 2 (L2), and SRM 1598a Animal Serum. The concentration of Cd in the materials ranges from 120 microg kg(-1) down to 0.03 microg kg(-1). At these levels, the factors that most influence the accuracy of the ICP-MS data are the procedure blank and spectral and nonspectral interferences. Nonspectral interference, caused by the high concentration of dissolved solids in the matrices investigated, resulted in signal suppression. Matrix separation was used to enhance signal intensity and to reduce spectral interference for the accurate determination of Cd in SRM 1598a and SRM 3244. Chromatographic separation procedures using Chelex for SRM 1598a and anion exchange for SRM 3244 were optimized to achieve the desired separation characteristics without substantially increasing the procedure blank. Sensitivity for the determination of Cd in serum was additionally enhanced through the use of desolvation nebulization. We determined that separations were not required for the accurate ICP-MS determination of Cd in SRM 3240, SRM 3241, SRM 3243, and SRM 966 L2 under optimized analysis conditions. These samples were diluted to a minimum volume and introduced to the ICP-MS via low flow (40-100 microL/min) microconcentric nebulizers. SRM 966 L1 was also analyzed directly, but results were highly variable. The ID-ICP-MS sample preparation and ratio measurement protocols described here resulted in total expanded uncertainties of less than 1% for the determination of 90.85 microg kg(-1) Cd in SRM 3240, and less than 10% total expanded uncertainty for the determination of 0.0468 microg kg(-1) Cd in SRM 1598a.

Animals↗
PubMed2002

Establishment of a standard assay method for human thrombomodulin and determination of the activity of the Japanese reference standard.

This study was undertaken to establish a standard method for determination of the activity of human (h) thrombomodulin (TM). The reactions mainly consisted of formation of a h-TM and h-thrombin complex, activation of h-protein C by the complex and digestion of substrate by activated h-protein C. Linear time-dependent formation of p -nitroaniline from the substrate, S-2366, was observed up to 12 min during measurement of the activity of urinary h-TM (uh-TM) reference material by the standard method. Therefore, 10 minutes was established as the reaction time in the standard method. In the standard method, we defined the activity of h-TM forming 0.1 micromol of p -nitroaniline per min in the reaction as 1 JRS Unit. Recombinant h-TM (rh-TM) and uh-TM reference material gave rectilinear dose-response curves within a certain range of specific activities by their original methods in the standard method. The validity of the standard method was assessed based on the coefficients of variation (CV) obtained in the various measurements of h-TM. Intra-batch precision (CV) of h-thrombin and h-protein C was 2.90% and 6.57%, respectively, in the measurement of uh-TM activity. The intra-sample, inter-day, and inter-laboratory precision (CV) was 1.30%, 1.63% and 5.02%, respectively, in the measurement of the first Japanese reference standard for h-TM coded TJRS1. In these assays, the activity of the first Japanese standard was also determined and found to be 205 JRS units per ampoule. When the stability of the Japanese reference standard was assessed by measuring of the standard stored under various thermal conditions, the predicted loss of activity assuming monomolecular degradation according to the Arrhenius equation was less than 3.0% during 103 years at -20 degrees C. These results indicate that the standard method is appropriate for determination of the activity of h-TM and that the Japanese reference standard for h-TM, whose activity was determined here, can be stored at -20 degrees C for long periods without loss of activity.

Analysis of Variance↗
PubMedDate not supplied

Preparation of Standard Reference Material 2383 (Baby Food Composite) and use of an interlaboratory comparison exercise for value assignment of its nutrient concentrations.

The preparation of the recently released Standard Reference Material (SRM) 2383 Baby Food Composite and the process used for value assignment of nutrient concentrations are reported. SRM 2383 can be used as a control material when assigning values to in-house control materials and when validating analytical methods for measuring proximates, vitamins, and minerals in baby food and similar matrixes. The SRM was prepared as a commercial baby food would be prepared, with the same ingredients. The Certificate of Analysis for SRM 2383 provides assigned values for concentrations of proximates, vitamins, and minerals for which product labeling is required by the Nutrition Labeling and Education Act of 1990. These assigned values were based on measurements by the National Institute of Standards and Technology (NIST) and/or collaborating laboratories. Assignment of analyte concentrations based solely on analyses by collaborating laboratories is described in this paper. Certified values are provided for retinol, tocopherols, and several carotenoids including total beta-carotene; the certification of and methodology used for measurement of these analytes is discussed in a companion paper (this issue, page 288). Reference values are provided for solids, ash, fat, nitrogen, protein, carbohydrate, calories, vitamin B1, vitamin B2, vitamin B6, niacin, biotin, calcium, phosphorus, magnesium, manganese, iron, zinc, copper, sodium, potassium, and chloride. Reference values for additional carotenoids are reported in the companion paper (this issue, page 288). Information values are provided for iodine, selenium, molybdenum, vitamin D, vitamin B12, folic acid, pantothenic acid, choline, inositol, sugars, total dietary fiber, and 3 classes of fats.

Carbohydrates↗
PubMed1995

Comparison of eight microcomputer dietary analysis programs with the USDA Nutrient Data Base for Standard Reference.

OBJECTIVE: To compare the general operating features and nutrient databases of eight microcomputer dietary analysis programs. DESIGN: A 3-day food record with 73 food items was entered into each program by the authors. The general operating features of the program were summarized and evaluated. The nutrient database was evaluated by comparing the nutrient analysis output with the 1993 US Department of Agriculture (USDA) Nutrient Data Base for Standard Reference (NDB), full version, release 10, for microcomputers. RESULTS: The programs varied in cost, number of foods and nutrients in the database, use of non-USDA data, and inputting of data for missing values. We also found differences in the quality of user manuals and help screens, ease of food entry and averaging of 3-day nutrient intake, speed of analyzing and printing results, quality and number of print/export options, and overall ease of learning and using the program. All but one of the programs were within 15% of the USDA NDB for energy, protein, total fat, and total carbohydrates. However, there was some difference in the number of other nutrients and food components varying more than 15% from the USDA NDB. These differences occurred because of variations in the number of food items included in each programs' database and the number of missing nutrient values in the database. APPLICATIONS: Our results demonstrate the importance of carefully choosing a microcomputer dietary analysis program that is suitable to the user's specific and predetermined needs.

Databases, Factual↗
PubMed1975

Development of standard reference materials for air quality measurement.

The National Bureau of Standards is engaged in a continuing program involving gaseous Standard Reference Materials for air pollution measurements. Preparation of such materials requires definition of the stability, homogeneity, and accuracy of the samples. This information is obtained by long term studies of the gas systems, by development of absolute methods of analysis, and by analysis of large numbers of samples prepared in bulk. The results of studies, extending over several years, of low concentration of carbon monoxide in nitrogen and nitric oxide in nitrogen are reported. Over one thousand samples of these materials have been analyzed and the stability with time and the within-batch homogeneity have been characterized. Accuracy is achieved by use of gravimetric standards and with dynamic dilution systems. Accuracy attainable by either method is described. The use of permeation tubes of sulfur dioxide and nitrogen dioxide is necessary in some situations because of the reactivity of the gases. Data covering the stability and accuracy of these devices has been collected over a period of several years.

Air Pollutants↗
PubMed2004

Polybrominated diphenyl ether congeners and toxaphene in selected marine standard reference materials.

Polybrominated diphenyl ether (PBDE) congeners and components of the complex mixture toxaphene are stable in the environment and readily bioaccumulated into wildlife and human tissues. PBDEs are presently used in large quantities worldwide as flame retardants in textiles, furniture, computer equipment, and cables. Toxaphene is a complex mixture of chlorinated bornanes and bornenes that was the most heavily used pesticide in the United States until it was banned in 1982; however, some countries continue to use toxaphene. The National Institute of Standards and Technology has quantified PBDE congeners and toxaphene in several available Standard Reference Materials (SRMs) using methods of gas chromatography with electron impact mass spectrometry (GC-EI-MS) and GC negative chemical ionization (NCI) MS, respectively. SRM 1588a Organics in Cod Liver Oil and SRM 1945 Organics in Whale Blubber were examined for PBDE congeners 47, 99, 100, 153, and 154, total toxaphene, and toxaphene congeners 26, 50, and 62. SRM 1946 Lake Superior Fish Tissue was also examined for total toxaphene and toxaphene congeners. The sum of the PBDE congeners (mean, (1 SD) wet basis) for SRM 1945 was 150 ng g(-1) (7 ng g(-1)). The concentration of PBDE 47 in SRM 1588a was 82.7 ng g(-1) (2.8 ng g(-1)). Other PBDEs were detected in SRM 1588a but were not quantified due their low levels. The total toxaphene (wet mass basis) was 1,210 ng g(-1) (127 ng g(-1)), 1,960 ng g(-1) (133 ng g(-1)), and 3,980 ng g(-1) (248 ng g(-1)) in SRMs 1945, 1946, and 1588a, respectively. The values for PBDEs and toxaphene determined in the SRMs, while not certified, indicate that the SRMs will be suitable control materials for PBDE and toxaphene analyses.

Adipose Tissue↗
PubMed1984

[Standardization of cholera vaccine and preparation of a national reference standard].

The antigenic potency of the proposed national reference preparations in comparison with that of the corresponding international reference preparations was studied by means of the active protection test in mice. The antigenic potency of the proposed national reference preparations for Inaba and Ogawa was found to be the same or even greater than the antigenic potency of the international reference preparations for cholera vaccine. A high level of antigenic activity was observed during comparison of a production lot of cholera divaccine with the international reference preparation and the national reference preparation in parallel tests. The proposed national reference preparations for Inaba and Ogawa may be used for evaluating the antigenic potency of the lot of cholera vaccine produced in Bulgaria as the standard preparation.

Animals↗
PubMed2007

Quantitative 2D HSQC NMR determination of polymer structures by selecting suitable internal standard references.

A new analytical method based on the 2D HSQC NMR sequence is presented, which can be applied for quantitative structural determination of complicated polymers. The influence of T1 and T2 relaxations, off-resonance effects, coupling constants and homonuclear couplings are discussed. It was found that the T2 values measured on polymeric samples with the conventional HSQC-CPMG sequence could not be used to correct the errors caused by T2 relaxations during the polarization transfer delay. A unique way of selecting the proper internal standard reference signal(s) is therefore proposed to eliminate the major errors caused by T2 relaxations, resonance offsets, coupling constant deviations and homonuclear couplings. Two polymer samples, a cellulose triacetate and an acetylated lignin, have been used to illustrate the principles. The methodology developed in this work is robust to instrument miss-setting and it can find wide-spread applications in areas where a quantitative analysis of structurally complicated polymers is necessary.

Acetylation↗
PubMed2006

Simultaneous analysis of oxygenated and nitrated polycyclic aromatic hydrocarbons on standard reference material 1649a (urban dust) and on natural ambient air samples by gas chromatography-mass spectrometry with negative ion chemical ionisation.

This study deals with the development of a routine analytical method using gas chromatography-mass spectrometry with negative ion chemical ionisation (GC/NICI-MS) for the determination of 17 nitrated polycyclic aromatic hydrocarbons (NPAHs) and 9 oxygenated polycyclic aromatic hydrocarbons (OPAHs) present at low concentrations in the atmosphere. This method includes a liquid chromatography purification procedure on solid-phase extraction (SPE) cartridge. Application of this analytical procedure has been performed on standard reference material (SRM 1649a: urban dust), giving results in good agreement with the few data available in the literature. The analytical method was also applied on ambient air samples (on both gas and particulate phases) from the French POVA program (POllution des Vallées Alpines). NPAHs concentrations observed for a rural site during the Winter period are about 0.2-100.0pgm(-3) in the particulate phase and about 0.0-20.0pgm(-3) in the gas phase. OPAHs present concentrations 10-100 times higher (0.1-2.0ngm(-3) and 0.0-1.4ngm(-3) for the particulate and the gas phases, respectively). These preliminary results show a good correlation between the characteristics of the sampling site and the compound origins (primary or secondary).

Air Pollutants↗
PubMed1978

Characterization of an antiserum used in a radioimmunoassay for arginine-vasopressin: implications for reference standards.

The region of the arginine-vasopressin (AVP) molecule critical for binding to the effective antibodies in a RIA has been localized to the vicinity of the Phe3 position by using the cross-reaction in the assay between AVP and a number of its structural analogs. Binding seems to be almost independent of any direct contributions from components of the tripeptide tail of AVP. Using this RIA it was found that disequilibrium conditions of incubation produce a 5-fold increase in assay sensitivity over equilibrium conditions. Amino acid analysis revealed that three synthetic peptide preparations used as reference standards comprised only 70-80% of their weight as peptide and this finding points up the need to correct such reference standards for their peptide content. The ratio of rat vasopressor activity to RIA activity of these three preparations as well as of a natural AVP preparation, however, approximated unity. Results obtained comparing measurements of AVP in rat neural lobes by RIA and rat vasopressor assay show a correlation between RIA and bioassay of 0.9406, a slope of 1.086, and an intercept of 20 mU, suggesting good agreement for AVP determined by these two assay systems.

Animals↗
PubMed2003

Determination of polychlorinated biphenyl congeners and chlorinated pesticides in a fish tissue standard reference material.

The concentrations of a wide range of polychlorinated biphenyl congeners (PCBs) and chlorinated pesticides in a fish tissue Standard Reference Material (SRM) have been determined using multiple methods of analysis. This material, SRM 1946, Lake Superior Fish Tissue, was recently issued by the National Institute of Standards and Technology (NIST) and complements a suite of marine environmental natural-matrix SRMs that are currently available from NIST for the determination of organic contaminants such as aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), PCBs, and chlorinated pesticides. SRM 1946 is a fresh tissue homogenate (frozen) prepared from filleted adult lake trout (Salvelinus namaycush namaycush) collected from the Apostle Islands region of Lake Superior. SRM 1946 has certified and reference concentrations for PCB congeners, including the three non- ortho PCB congeners, and chlorinated pesticides. Certified concentrations are available for 30 PCB congeners and 15 chlorinated pesticides. Reference concentrations are available for 12 PCB congeners and 2 chlorinated pesticides. In addition, SRM 1946 is characterized for additional chemical constituents and properties: fatty acids, extractable fat, methylmercury, total mercury, selected trace elements, proximates, and caloric content. The characterization of chlorinated compounds is described in this paper with an emphasis on the approach used for the certification of the concentrations of PCB congeners and chlorinated pesticides. The PCB congener and chlorinated pesticide data are also compared to concentrations in other marine natural-matrix reference materials available from NIST (fish oil, mussel tissue, whale blubber, and a second fresh frozen fish tissue homogenate prepared from filleted adult lake trout collected from Lake Michigan) and from other organizations such as the National Research Council Canada (ground whole carp), the International Atomic Energy Agency (fish homogenate), and the European Commission Joint Research Centre [fish oils (cod and mackerel) and mussel tissue].

Animals↗
PubMed2003

Filling the AOAC triangle with food-matrix standard reference materials.

Well-characterized reference materials are needed by laboratories in the food testing and nutrition communities to facilitate compliance with nutritional labeling laws, to provide traceability for food exports needed for acceptance in many foreign markets, and to improve the accuracy of nutrition information that is provided to assist consumers in making sound dietary choices. As a result of the enactment of the Nutrition Labeling and Education Act of 1990 and the Infant Formula Act of 1980, the National Institute of Standards and Technology (NIST) has developed a suite of food-matrix Standard Reference Materials (SRMs) characterized for nutrient concentrations. These include SRM 1544 Fatty Acids and Cholesterol in a Frozen Diet Composite, SRM 1546 Meat Homogenate, SRM 1548a Typical Diet, SRM 1566b Oyster Tissue, SRM 1846 Infant Formula, SRM 1946 Lake Superior Fish Tissue, SRM 2383 Baby Food Composite, SRM 2384 Baking Chocolate, SRM 2385 Spinach, and SRM 2387 Peanut Butter. Many of these materials were developed at the request of the food industry to populate a nine-sectored fat-protein-carbohydrate triangle developed by AOAC International. With the completion of SRM 2387, SRMs representing each sector of the triangle are now available. These food-matrix reference materials are intended primarily for validation of analytical methods for the measurement of proximates, fatty acids, vitamins, minerals, and so on in foods of similar composition. They may also be used as "primary control materials" in the value-assignment of in-house, secondary, control materials to confirm accuracy as well as to establish traceability to NIST.

Food Analysis↗
PubMed1992

Comparison of various detection methods for periodontopathic bacteria: can culture be considered the primary reference standard?

The development of diagnostic tests for a periodontal infection raises the issue as to what the appropriate reference standard, or "gold standard," should be for the evaluation of a new test. The present research was initiated to compare the ability of several detection methods, i.e., a serial dilution anaerobic culture and/or microscopic procedure, a DNA probe procedure, and immunological reagents using both an enzyme-linked immunosorbent assay and an indirect immunofluorescence assay to detect Treponema denticola, Porphyromonas gingivalis, Bacteroides forsythus, and Actinobacillus actinomycetemcomitans in subgingival plaque samples taken from 204 periodontally diseased tooth sites. The prevalence of the four monitored species varied as a function of both the species and the detection method. Spirochetes were present in 99% of the plaques, whereas A. actinomycetemcomitans was detected at the lowest frequency. The culture method yielded the lowest prevalence values for the three cultivable species. This raised the question as to which results, those obtained by culture or those obtained by the DNA probes and the immunological reagents, were the most reliable. This issue was addressed by looking at the prevalence profile of the monitored organisms, as determined by all the detection methods. If the species was detected by three or four of the detection methods, then it was considered present, whereas if it was absent by three or four of the detection methods, then it was considered absent. This approach showed the DNA probes and immunological reagents to be significantly superior (P less than 0.05) to the culture approach for the detection of P. gingivalis, A. actinomycetemcomitans, and B. forsythus and to be comparable to the microscopic approach in the detection of T. denticola.

Aggregatibacter actinomycetemcomitans↗
PubMed2003

Comparison of the complete mtDNA genome sequences of human cell lines--HL-60 and GM10742A--from individuals with pro-myelocytic leukemia and leber hereditary optic neuropathy, respectively, and the inclusion of HL-60 in the NIST human mitochondrial DNA standard reference material--SRM 2392-I.

Forensic and clinical laboratories benefit from DNA standard reference materials (SRMs) that provide the quality control and assurance that their results from sequencing unknown samples are correct. Therefore, the mitochondrial DNA (mtDNA) genome of HL-60, a promyelocytic leukemia cell line, has been completely sequenced by four laboratories and will be available to the forensic and medical communities in the spring of 2003; it will be called National Institute of Standards and Technology (NIST) SRM 2392-I. NIST human mtDNA SRM 2392 will continue to be available and includes the DNA from two apparently healthy individuals. Both SRM 2392 and 2392-I contain all the information (e.g. the sequences of 58 unique primer sets) needed to use these SRMs as positive controls for the amplification and sequencing any DNA. Compared to the templates in SRM 2392, the HL-60 mtDNA in SRM 2392-I has two tRNA differences and more polymorphisms resulting in amino acid changes. Four of these HL-60 mtDNA polymorphisms have been associated with Leber Hereditary Optic Neuropathy (LHON), one as an intermediate mutation and three as secondary mutations. The mtDNA from a cell line (GM10742A) from an individual with LHON was also completely sequenced for comparison and contained some of the same LHON mutations. The combination of these particular LHON associated mutations is also found in phylogenetic haplogroup J and its subset, J2, and may only be indicative that HL-60 belongs to haplogroup J, one of nine haplogroups that characterize Caucasian individuals of European descent or may mean that haplogroup J is more prone to LHON. Both these mtDNA SRMs will provide enhanced quality control in forensic identification, medical diagnosis, and single nucleotide polymorphism detection.

Journal Article↗
PubMed2000

Diagnostic performance of biopsy-based methods for determination of Helicobacter pylori infection without a reference standard.

Endoscopic biopsy-based tests are considered to be the reference method for diagnosing Helicobacter pylori infection and monitoring antibiotic treatment, but unbiased data on their diagnostic performance is lacking. In this study we evaluated the diagnostic performance of culture, histology and rapid urease testing of antral biopsies separately and in combination. Antral biopsies were taken from consecutive patients undergoing upper gastrointestinal endoscopies at a single center between January 1995 and May 1997. The biopsies were examined for culture, histology, and CLOtest. The diagnostic performance, i.e., the sensitivity and specificity of the tests was estimated with 7 non-linear equations in 7 unknowns. To determine sources of heterogeneity that may have biased the results, data were stratified for age, gender, and whether they were taken before or after anti-Helicobacter antibiotic treatment. During the study period 631 patients underwent 869 upper gastrointestinal endoscopies. In 122 (14%) of the antral specimens the test results of culture, histology and CLOtest differed. Based on the nonlinear regression techniques we estimated that in 347 tests (40%) H. pylori infection was present. Overall sensitivity, specificity, positive and negative predictive value for each test were as follows: culture 91.4%, 96.3%, 94.2%, 94.4%, respectively; histology 90.3%, 97.8%, 96.4%, 93.8%, respectively; CLOtest 94.9%, 96.7%, 95.0%, 96.6%, respectively. In combination, the three tests provided the definitive diagnosis, either non-infected or infected, in 862 out of the 869 tests. Sensitivity of gastric antral histology was 64.9% (95% CI: 38-86) in females who did and 84.5% (95% CI: 77-90) in females who did not have had recent antibiotic therapy to cure the infection. Approximately 5-10% of H. pylori infected patients, were mis-diagnosed with a single biopsy-based test taken from the gastric antrum. Only a combination of bacterial culture, histological examination and the CLOtest represents an appropriate reference standard for research purposes to identify infected patients.

Adult↗
PubMed1979

Body water compartments with human aging using fat-free mass as the reference standard.

Forty-five healthy men and women aged 16-39 and 59-89 yr were studied for total body water (TBW) and extracellular water (ECW); intracellular water (ICW) was calculated as the difference (ICW = TBW - ECW). An independent measurement of total body fat by inert gas uptake provided a value (+/- 2%) for fat-free mass (FFB is wt minus body fat). Results agreed with observations by others that TBW and ICW are lower in the aged and lower in women, whether expressed as absolute volumes or per unit of weight, surface area, or height. However, with FFB as the reference standard very different aging trends appeared. TBW/FFB remained constant to our oldest measured subjects (704 +/- 7 ml/kg). ICW/FFB was slightly lower at advanced age, but the 4-5% decrease for each sex was within statistical variability. With age ECW increased slightly and its proportion within the fat-free body (ECW/FFB) was significantly higher. Based upon FFB, the distribution, proportions, and aging trends of body water compartments were similar for men, women, and male rats. Although its potential limitations must be appreciated, the FFB appears widely useful as a reference standard. The stability of ICW volume and of fat-free mass in aging man does not support the hypothesis that cellular mass is lost by healthy mammals with age.

Adipose Tissue↗
PubMed2001

The development and certification of Standard Reference Materials (SRMs) to assess and ensure accurate measurement of Pb in the environment.

The National Institute of Standards and Technology (NIST) has had a major quality-assurance role in the federal effort to reduce lead poisoning of children in the United States through its mission of ensuring the accuracy of chemical measurements. NIST certifies reference materials (standard reference materials--SRMs) that are used to benchmark measurements by secondary and field methods of analysis--to ensure that decisions of great health and economic impact are soundly based on good measurement science. Over the past 10 years, in cooperation with the US Environmental Protection Agency (EPA), US Department of Housing and Urban Development (HUD), and the United States Geological Survey (USGS), NIST has prepared and certified SRMs for lead content in soil, indoor dust, and paint. The role of these materials in meeting regulatory and abatement needs is described and their certified values are summarized.

Dust↗