Biological Reference Materials for Quality Control of Elemental Composition Analytical Data

Twelve biological-matrix, agricultural/food reference materials, Corn Stalk (Zea Mays) (NIST RM 8412), Corn Kernel (Zea Mays) (NIST RM 8413), Bovine Musele Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438) were developed. They were characterized with respect to elemental composition via two extensive international interlaboratory characterization campaigns providing 303 reference and informational concentration values for 34 elements (Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W, Zn) of nutritional, toxicological, and environmental significance. These products are available to the analytical community, for quality control of elemental composition analytical data, from the Standard Reference Materials Program, National Institute of Standards and Technology, Gaithersburg, MD, USA.     

Determination of copper, molybdenum and selenium in biological reference materials by inductively coupled plasma mass spectrometry

Summary In a contribution to the elemental characterization of 10 new reference materials, Bovine Muscle Powder (136), Corn Starch (162), Hard Red Spring Wheat Flour (165), Soft Winter Wheat Flour (166), Whole Milk Powder (183), Wheat Gluten (184), Corn Bran (186), Durum Wheat Flour (187), Whole Egg Powder (188) and Microcrystalline Cellulose (189), the total concentrations of Cu, Mo and Se were determined by the application of an analytical method based on isotope dilution inductively coupled plasma mass spectrometry. Cu and Mo contents were quantified by measurement of ⁶⁵Cu/⁶³Cu and ⁹⁷Mo/¹⁰⁰Mo isotopic ratios following spiking with ⁶⁵Cu and ⁹⁷Mo and digestion with nitric acid. Selenium was separated as hydrogen selenide from the matrix using sodium borohydride after spiking with ⁸²Se and acid digestion-dry ashing and quantified by measurement of the ⁸²Se/⁷⁸Se isotopic ratio. Comparison of these results with those from a variety of other methods and assessment of the procedures using certified reference materials indicated that the determinations of Cu, Mo and Se were performed without analytical bias.     

Summary of an interlaboratory characterization (certification) campaign to establish the elemental composition of a new series of agricultural/food reference materials

Summary Ten new Agricultural/Food Reference Materials (RMs) were characterized with respect to their elemental compositions via an interlaboratory characterization (certification) campaign. Chemical analyses were conducted in 73 cooperating laboratories applying 13 major classes of independently different analytical methods. A total of 213 best estimate values, and 65 informational values were obtained for Al, As, B, Ba, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Ti, V, W and Zn in the following RMs: Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415), Microcrystalline Cellulose (NIST RM 8416), Wheat Gluten (NIST RM 8418), Corn Starch (NIST RM 8432), Corn Bran (NIST RM 8433), Whole Milk Powder (NIST RM 8435), Durum Wheat Flour (NIST RM 8436), Hard Red Spring Wheat Flour (NIST RM 8437) and Soft Winter Wheat Flour (NIST RM 8438).     

Value assignment of nutrient concentrations in five standard reference materials and six reference materials

A number of food-matrix reference materials (RMs) are available from the National Institute of Standards and Technology (NIST) and from Agriculture Canada through NIST. Most of these materials were originally value-assigned for their elemental composition (major, minor, and trace elements), but no additional nutritional information was provided. Two of the materials were certified for selected organic constituents. Ten of these materials (Standard Reference Material [SRM] 1,563 Cholesterol and Fat-Soluble Vitamins in Coconut Oil [Natural and Fortified], SRM 1,566b Oyster Tissue, SRM 1,570a Spinach Leaves, SRM 1,974a Organics in Mussel Tissue (Mytilus edulis), RM 8,415 Whole Egg Powder, RM 8,418 Wheat Gluten, RM 8,432 Corn Starch, RM 8,433 Corn Bran, RM 8,435 Whole Milk Powder, and RM 8,436 Durum Wheat Flour) were recently distributed by NIST to 4 laboratories with expertise in food analysis for the measurement of proximates (solids, fat, protein, etc.), calories, and total dietary fiber, as appropriate. SRM 1846 Infant Formula was distributed as a quality control sample for the proximates and for analysis for individual fatty acids. Two of the materials (Whole Egg Powder and Whole Milk Powder) were distributed in an earlier interlaboratory comparison exercise in which they were analyzed for several vitamins. Value assignment of analyte concentrations in these 11 SRMs and RMs, based on analyses by the collaborating laboratories, is described in this paper. These materials are intended primarily for validation of analytical methods for the measurement of nutrients in foods of similar composition (based on AOAC INTERNATIONAL's fat-protein-carbohydrate triangle). They may also be used as "primary control materials" in the value assignment of in-house control materials of similar composition. The addition of proximate information for 10 existing reference materials means that RMs are now available from NIST with assigned values for proximates in 6 of the 9 sectors of the AOAC triangle. Five of these materials have values assigned for total dietary fiber-the first such information provided for materials available from NIST.     

Surfactant/oil/water system for the determination of selenium in eggs by graphite furnace atomic absorption spectrometry

An oil-in-water formulation has been optimized to determine trace levels of selenium in whole hen eggs by graphite furnace atomic absorption spectrometry. This method is simpler and requires fewer reagents when compared with other sample pre-treatment procedures. Graphite furnace atomic absorption spectrometric (GF AAS) measurement was carried out using standard addition calibration and Pd as a modifier. The precision, expressed as relative standard deviation, was better than 5% and the limit of detection was 1 µg L^− 1. The validation of the method was performed against a standard reference material Whole Egg Powder (RM 8415), and the measured Se corresponded to 95.2% of the certified value. The method was used for the determination of the Se level in eggs from hens treated with Se dietary supplements. Inorganic and organic Se sources were added to hen feed. The Se content of eggs was higher when hens were fed with organic Se compared to the other treatments. The proposed method, including sample emulsification for subsequent Se determination by GF AAS has proved to be sensitive, reproducible, simple and economical.     

Selenomethionine content of candidate reference materials

Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography–isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L^–1 hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH₃Se group to form volatile CH₃SeCN. Addition of isotopically enriched ⁷⁴Semet to an analytical sample enables estimation of the naturally occurring protein-bound ⁸⁰Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 μg Se_total g^–1. Commercial selenium yeast tablets are labeled as containing an elevated level of “organic selenium”, usually as Semet. The sample we investigated contained 210 μg Se_total g^–1 sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153±21 μg Se_Semet g^–1; n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine. Received: 13 December 2000 / Revised: 5 March 2001 / Accepted: 12 March 2001     

Characterization (certification) of Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415) and Whole Milk powder (NIST RM 8435) Reference Materials for essential and toxic major, minor and trace element constituents

Summary Bovine Muscle Powder (NIST RM 8414), Whole Egg Powder (NIST RM 8415) and Whole Milk Powder (NIST RM 8435) Reference Materials were characterized for essential and toxic major, minor and trace element composition in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods yielded best estimate concentration values for 27, 23 and 21 elements, and informational concentration values for 5, 4 and 9 elements, respectively, in RM's 8414, 8415 and 8435. These Reference Materials are intended for analytical quality control of element determinations on meat, egg and milk-based products as well as agricultural/food materials with related matrices.Contribution no. 92–147 from Centre for Land and Biological Resources Research     

Selenomethionine content of candidate reference materials.

Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography-isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L(-1) hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH3Se group to form volatile CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample enables estimation of the naturally occurring protein-bound 80Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 microg Se(total g(-1). Commercial selenium yeast tablets are labeled as containing an elevated level of "organic selenium", usually as Semet. The sample we investigated contained 210 microg Se(total) g(-1) sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153 +/- 21 microg Se(semet) g(-1); n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine.     

Analysis of boron in biological reference materials using prompt gamma activation analysis

Summary A prompt gamma activation analysis facility has been constructed on the ST1 horizontal beam port at the HANARO research reactor, KAERI in 2003. The detector system consists of a high-purity Ge detector surrounded by BGO/NaI(Tl) scintillators as an annulus type to reject the Compton scattered photons. Detection sensitivity for boron was obtained from the prompt gamma-ray spectra of boric acid, B(OH)₃, containing 0.1-65 μg boron. The net peak for the calculation of the boron concentration was obtained by eliminating the sodium 472 keV peak, involved in the boron 478 keV peak. The biological samples used are NIST SRMs such as Peach Leaves, Apple Leaves, Tomato Leaves, Spinach Leaves, Total Diet, Typical Diet, Oyster Tissue and Corn Bran, etc. The measured values for high boron concentration showed up to a 3% of the relative, but in a low concentration below 5 ppm, present values were higher than the certified ones.     

Characterization (certification) of Corn Bran (NIST RM 8433), Corn Starch (NIST RM 8432) and Microcrystalline Cellulose (NIST RM 8416) Reference Materials for essential and toxic major, minor and trace elemental constituents

Summary Corn Bran (NIST RM 8433), Corn Starch (NIST RM 8432) and Microcrystalline Cellulose (NIST RM 8416) Reference Materials were characterized for essential and toxic major, minor and trace elemental composition in an interlaboratory cooperative characterization campaign. Extensive application of widely varied analytical methods by analysts in cooperating laboratories yielded 10–29 best estimate and 1–16 informational concentration values for each of these materials. Two materials, Corn Starch and Microcrystalline Cellulose, contain particularly low levels of trace elements. These reference materials are intended for analytical quality control of elemental determinations in corn and plant products as well as other agricultural/food materials with related matrices.Contribution No. 92–146 from Centre for Land and Biological Resources Research     

Determination of lithium in biological samples by inductively coupled plasma mass spectrometry

Lithium was determined in human serum by inductively coupled plasma mass spectrometry. Sample preparation was kept to the minimum: serum samples were diluted and beryllium was added as internal standard. Special attention was given to the choice of the internal standard and to the occurrence of memory effects. To test the accuracy of the method several biological reference materials were analysed, namely a “Second-Generation” Biological Reference Material (Freeze-Dried Human Serum) (University of Ghent), Human Serum SRM 909, Whole Egg Powder SRM 1845 and Mixed Human Diet SRM 1548 (National Institute of Standards and Technology). The results were compared with those obtained by other techniques. For the “second-generation” reference freeze-dried human serum a mean lithium concentration of 15.10 ng g^?1 with a standard deviation of 0.54 ng g^?1 dry weight was found. Analyses on serum samples from healthy individuals yielded lithium concentrations ranging from 0.22 to 0.97 μg l^?1.     

Multi-element trace determinations in pure alkaline earth fluoride powders by high-resolution ICP-MS using wet-chemical sample preparation and laser ablation

Four alternative analytical procedures for the determination of ten important trace impurities (Mg, Cr, Fe, Cu, Zn, Sr, Zr, Cd, Ba, and Pb) in pure alkaline earth fluoride powders were applied using high-resolution inductively coupled plasma mass spectrometry (ICP-MS). Two procedures are based on a wet-chemical microwave digestion with boric acid and quantification by the standard addition technique and isotope dilution mass spectrometry (IDMS), respectively. In addition, analyses are also performed by laser ablation as a direct solid sampling technique applying matrix-matched external calibration as well as isotope dilution of the powdered sample. For most elements good agreement between the different methods is found. Detection limits for laser ablation vary between 0.05 ng g^–1 for Zr and 20 ng g^–1 for Mg. They are about one to two orders of magnitude lower than those of the wet-chemical procedures, which is mainly due to the high dilution factor during the sample preparation step. Advantages and restrictions of the different analytical procedures are discussed with respect to their routine applicability. Due to its relatively high accuracy, low detection limits, and time-efficiency LA-ICP-IDMS is the preferred choice if no standard reference materials are available.     

Development of a radiochemical neutron activation analysis procedure for determination of rhenium in biological and environmental samples at ultratrace level

Summary Radiochemical neutron activation procedures using liquid-liquid extraction with tetraphenylarsonium chloride in chloroform from 1M HCl and solid extraction with ALIQUAT 336 incorporated in a polyacrylonitrile binding matrix from 0.1M HCl were developed for accurate determination of rhenium in biological and environmental samples at the sub-ng ^. g^-1 level. Concentrations of Re in the range of 0.1 to 2.4 ng ^. g^-1 were determined in several botanical reference materials (RM), while in a RM of road dust a value of ~10 ng ^. g^-1 was found. Significantly elevated values of Re, up to 90 ng ^. g^-1 were found in seaweed (brown algae). Results for Re in the brown algae Fucus vesiculosus in which elevated ⁹⁹Tc values had previously been determined suggested possible competition between Re and Tc in the accumulation process.     

Determination of arsenic in food and dietary supplement standard reference materials by neutron activation analysis

Arsenic was measured in food and dietary supplement standard reference materials by neutron activation analysis for the purpose of assigning certified or reference As mass fractions and to assess material homogeneity. Instrumental neutron activation analysis was used to value assign As in candidate SRM 3532 Calcium Dietary Supplement and candidate SRM 3262 Hypericum perforatum (St. John’s Wort) Aerial Parts down to about 100 μg/kg. Values were also determined for two additional candidate St. John’s Wort SRMs with As mass fractions <100 μg/kg. The presence of significant amounts of ²⁴Na and ⁸²Br limited the reproducibility of the method below 100 μg/kg. For measurement of lower As mass fractions, a radiochemical neutron activation analysis method with extraction of As³⁺ into diethyl-dithiocarbamate in chloroform and detection limits down to 0.1 μg/kg. As was used to value-assign As mass fractions for SRM 3280 Multivitamin/Multielement Tablets and for candidate SRM 3233 Fortified Breakfast Cereal, and at <10 μg/kg in candidate SRM 1845a Whole Egg Powder.     

Quantification of five neonicotinoids in human urine by modified QuEChERS with isotope dilution mass spectrometry: a preliminary study for the development of certified reference material

ABSTRACT

A study for the quantification method of neonicotinoid pesticides (Neos) in human urine that aims to develop the certified reference material (CRM) in the future was carried out. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method based on dispersive solid phase extraction (d-SPE) with isotope dilution mass spectrometry (IDMS) was evaluated for the quantification of five Neos (acetamiprid, dinotefuran, imidacloprid, thiacloprid and thiamethoxam) in human urine control by optimisation of the extraction solvent, and the type and amount of d-SPE material. Two types of human urine controls (sample A and B) containing 5 μg/kg and/or 25 μg/kg of Neos were prepared and employed for this study. The results of spike test using sample A (2 mL) obtained by modified QuEChERS method with acetone extraction (10 mL) and d-SPE using a strong cation exchanger (silica gel modified with benzenesulphonic acid phase, SCX) 500 mg were as follows: 97.8%–103.1% for 5 μg/kg and 97.2%–102.7% for 25 μg/kg (described as percentage by the quantification results of IDMS relative to the spiked amount of pesticides). These results were comparable to those by SPE cartridge method using SCX functionalised hydrophilic styrene divinylbenzene (PCX). The repeatabilities of the analyses, represented as relative standard deviations, were also comparable for spike level 5 μg/kg and 25 μg/kg of Neos: 0.1%–7.2% for modified QuEChERS with IDMS and 0.2%–5.6% for PCX cartridge method. The results of spike test using sample B for a spike level 5 μg/kg were 96.0%–100.6%. These results indicate that modified QuEChERS method with IDMS can be used for the development of certified reference material and has the potential to use for the quantification of Neos in real human urine.     

The determination of boron in rocks by deuteron activation analysis

The determination of boron in rocks by charged particle activation using the¹⁰B(d, n)¹¹C reaction is studied. A sample holder that allows reproducible irradiation of powdered samples is developed.¹¹C is separated as¹¹CO₂. For boron concentrations between 2.35 and 25.2 μg·g⁻¹, the standard deviations ranges from 7.1 to 22.8%. The results for USGS reference silicate rocks and Moroccan phosphate rock are compared to those obtained by other techniques.     

A radioreagent method of analysis of boron in sub-microgram range

A radioreagent method for the determination of boron in submicrogram range is described. This method is based on the reaction of boric acid with hydrofluoric acid labeled with¹⁸F and the measurement of the activity of the product, HBF ₄ ^* , which is isolated by complexation with methylene blue and extraction with 1,2-dichloroethane. The 0.51 Mev gamma ray activity resulting from¹⁸F of an aliquot of the extract is found to be proportional to the amount of boron in the sample. It was found that at least 0.1 μg of boron can be measured by this method with an accuracy of about 5% error. The short-lived nature of¹⁸F makes it necessary that the analysis be performed as soon as the isotope is available. The sample to be analyzed should be freed from hydrofluoric acid as well as other species which form precipitate or complexes with Hf. The method was applied successfully to the analysis of one of the Netional Bureau of Standards reference samples.     

An inter-calibration campaign using various selected Pu spike isotopic reference materials

In nuclear safeguards, precise and accurate isotopic analyses are needed for two major elements from the nuclear fuel cycle: uranium and plutonium. This can be achieved by Isotope Dilution Mass Spectrometry (IDMS), which is one of the most reliable analytical techniques for the determination of plutonium amount content to a high level of accuracy. In order to achieve reliable isotope measurements isotopic reference materials with certified amount of plutonium and isotopic composition are required. At the Institute for Reference Materials and Measurements (IRMM) various plutonium spike reference materials for isotopes ²³⁹Pu, ²⁴⁰Pu, ²⁴²Pu and ²⁴⁴Pu are available. This enabled the setup of an inter-calibration campaign inter-linking selected plutonium spikes on a metrological basis applying state-of-the-art measurement procedures. The aim of this campaign is threefold: firstly to perform measurements on selected plutonium spike isotopic reference materials for quality control purposes, secondly to verify the amount content and the isotopic composition of the recently produced IRMM-1027m large sized dried (LSD) spikes and thirdly to demonstrate IRMM’s measurement capabilities for plutonium analysis via external quality tools. The obtained results using various spike isotopic reference materials will be presented and discussed in this paper. The measurement uncertainties of the IDMS results were calculated according to the guide to the expression of uncertainty in measurement (GUM).     

Spectrophotometric determination of trace and ultratrace levels of boron in silicon and chlorosilane samples

Summary Spectrophotometric methods for the determination of boron in the low g/g and ng/g range in high-purity silicon and dichloro- and trichlorosilanes were investigated in detail. The procedures established involve dissolution of silicon samples and the hydrolyzed products of chlorosilane samples in hydrofluoric acid-containing reagents followed by evaporation of the silicon matrix as H₂SiF₆. The boron retained in the treated sample solution was then determined by a spectrophotometric method using carminic acid as a chromatic reagent. Special effort has been paid to the control of the analytical blank and reproducible determination of boron. The results indicate that addition of mannitol and proper control of the evaporation process are effective in preventing volatilization of boron during the evaporation of silicon matrix and can thus attain high recovery of boron and reproducible analysis. Through meticulous control of the analytical blank and experimental conditions, the limit of detection for boron determination with the established method can be as low as ng/g levels. Application of the methods to the determination of boron in various stages of purification of silicon and trichlorosilane as well as in borophosphosilicate film was conducted.     

Precise determination of boron in titanium by inductively coupled plasma mass spectrometry

A method was developed for the determination of boron in titanium by inductively coupled plasma mass spectrometry (ICP-MS). A commercially available PTFE sample introduction system, leading to the desired low detection limits for boron, was used. The method is suitable for the determination of boron concentrations down to about 1 μg g^?1 in the solid material. The influence of the internal standard on the precision was studied and beryllium was selected as the internal standard. For the titanium analysed (BCR reference material 090), the ICP-MS result agreed with those obtained using other techniques. Several bars of titanium reference material were supplied and a study of the homogeneity of boron in this material was made. Using analysis of variance on the results obtained for the different bars, the homogeneity of boron in the reference material could be estimated to be better than 2.1%.