Preparation Of Reference Materials Research Articles

Preparation of Reference Material for Proficiency Test for Enumeration of Coliforms in Cheese Matrix

It is widely accepted that quantitative reference materials (RM), are indispensable tools for verification of the precision and accuracy of analytical measurements. The RM can be used by food microbiology laboratories, as part of their quality assurance programmes, to achieve their quality control. In Brazil, Anvisa RDC No. 12/01 specifies the enumeration of coliforms as one of the parameters for evaluating cheese quality. The aim of this study was to produce a quantitative RM for proficiency testing (PT) for use in the testing of enumeration of coliforms in cheese matrixes. A sample of an ultra-filtered cheese with a coliforms count of <3.0 MPN/g and a total n? of viable aerobes of 1.2 × 103 CFU/g was used as the matrix to produce the RM. The ultra-filtered cheese matrix was distributed in flasks, contaminated with a specific concentration of an Escherichia coli strain and submitted to freeze-drying. Sucrose was used as the cryo-protector. The RM produced was considered sufficiently homogeneous and stable at ≤ ?70?C during the entire study period (348 days). The material was also considered sufficiently stable at 4?C for six days, but instable at 30?C and 35?C for the same period. At ?20?C the RM was sufficiently stable for 161 days. It was concluded that the material showed all the necessary requirements for a quality RM to be used as PT items and could be transported to the laboratories taking part in a PT at up to 4?C for up to 6 days, since the results indicated maintenance of the cell concentrations during this period. This is the first study to describe a methodology for producing RM containing coliforms in a cheese matrix.

New matrix-free reference material for ethene in the form of optical fibres

Reference materials are indispensable in the quality control and quality assurance of analytical measurements. One novel approach to the generation of standard gaseous mixtures of toxic, reactive, volatile, labile, and malodorous substances involves thermal decomposition or rearrangement, under defined temperature conditions, of compounds immobilized, by chemical bonding, on the surface of an appropriate carrier to release specific amounts of a volatile compound. In this technique the type of support used to immobilize the compound is extremely important, because the amount of analyte released depends directly on the choice of material. In this paper we report the novel preparation of a matrix-free ethene standard in the form of glass fibres coated with a thin layer of aluminium, the surface of which is modified by reaction with a specific compound. As a result of thermal decomposition of this compound, gaseous ethene is formed. In this paper we present the results obtained from tests of stability and homogeneity, two properties of crucial importance in the preparation of reference materials, by comparison of a series of results obtained for randomly chosen samples of the reference material. Interlaboratory comparative studies resulted in determination of a reference value for the ethene formed after thermal decomposition of the surface compound ((2.12 ± 0.14) ng per fibre).

Development and validation of a methodology for uranium radiochronometry reference material preparation

The paper describes a methodology for a reference material preparation to be used for the determination of the production date (i.e. the time elapsed since the last chemical processing) of uranium materials based on the 230Th/234U radiochronometer. The reference material was prepared from highly enriched uranium by a complete separation of thorium decay products, thus zeroing the initial daughter nuclide concentration at known time. The complete elimination of thorium from the starting material was verified by gamma spectrometric measurements and by addition of a 232Th tracer to the material and its re-measurement in the final product after the separation. The validation of the methodology was carried out subsequently by comparing the ingrown daughter nuclide 230Th and the measured 230Th/234U ratio after recorded times following the last chemical separation with the calculated values obtained on the basis of their respective half-lives. The prepared reference material can be used as a quality control material for age determination of uranium in nuclear forensics and safeguards as well as for method validation.

A basic measurement model for reference material preparation

The basic model \( x_{\text{CRM}} = x_{\text{char}} + \delta x_{\text{bb}} + \delta x_{\text{sts}} + \delta x_{\text{lts}} \) in the ISO Guide 35 for the evaluation of uncertainty is reviewed. In the basic model, the authors of the Guide assume that the homogeneity and stability studies are designed in such a way that the values of the error terms are zero, but their uncertainties are not. Based on their assumption, it is shown that the basic model in the Guide requires output quantity xCRM to be employed as input quantities to define δxbb, δxsts, and δxlts, which results in circular reasoning on the value of CRM. In order to revise the basic model in the Guide, a proposed basic model Y = X is derived from the general model Y = X(1 + b′T) in the Guide as the special case of T = 0. The uncertainty evaluation for the proposed model is discussed. It is shown that it is not necessary to evaluate the uncertainty due to the between-bottle inhomogeneity ubb separately, when a single method is employed in the characterization. The ubb is shown to be one of the uncertainty components of the certified value xchar, because xchar is the mean value of at least 10 bottles.

Multi‐Elemental Analysis of ATHO‐G Rhyolitic Glass (MPI‐DING Reference Material) by Femtosecond and Nanosecond LA‐ICP‐MS: Evidence for Significant Heterogeneity of B, V, Zn, Mo, Sn, Sb, Cs, W, Pt and Pb at the Millimetre Scale

This paper reports on the application of variants of LA‐ICP‐MS – including infrared femtosecond laser ablation (fs‐LA) inductively coupled plasma‐quadrupole mass spectrometry (ICP‐QMS) and nanosecond laser ablation (ns‐LA) coupled with single‐collector sector‐field (SF‐) ICP‐MS – to the in situ determination of trace elements in different splits of the reference material (RM) ATHO‐G (MPI‐DING). Analyses of the materials performed by fs‐ and ns‐LA‐ICP‐MS demonstrated the efficiency of the techniques with typical accuracy at a level of ≤ ± 20%. One ‘anomalous’ split, however, displayed a significant discrepancy from the reference concentrations for B, V, Zn, Mo, Sn, Sb, Cs, W and Pb. Three‐ to six‐fold enrichment of V, Mo, Cs and Pt relative to the reference contents in this split is likely to have been due to direct contact of the silicate melt with Pt crucible walls and ceramics. Boron, Zn, Sn, Sb, W and Pb depletion relative to the reference concentrations is probably due to siderophile element adsorption by the Pt walls and/or related to the formation of volatile‐depleted compositional cords during the preparation process. Our results imply that additional precautions should be taken against volatile/siderophile element heterogeneity in marginal/surface layers (≤ 10 mm) during the preparation of RMs by the fusion technique.

Preparation of an in-house reference material containing fumonisins in Thai rice and matrix extension of the analytical method for Japanese rice.

Mycotoxin contamination in rice is less reported, compared to that in wheat or maize, however, some Fusarium fungi occasionally infect rice in the paddy field. Fumonisins are mycotoxins mainly produced by Fusarium verticillioides, which often ruins maize. Rice adherent fungus Gibberella fujikuroi is taxonomically near to F. verticillioides, and there are sporadic reports of fumonisin contamination in rice from Asia, Europe and the United States. Therefore, there exists the potential risk of fumonisin contamination in rice as well as the need for the validated analytical method for fumonisins in rice. Although both natural and spiked reference materials are available for some Fusarium mycotoxins in matrices of wheat and maize, there are no reference materials for Fusarium mycotoxins in rice. In this study, we have developed a method for the preparation of a reference material containing fumonisins in Thai rice. A ShakeMaster grinding machine was used for the preparation of a mixed material of blank Thai rice and F. verticillioides-infected Thai rice. The homogeneity of the mixed material was confirmed by one-way analysis of variance, which led this material to serve as an in-house reference material. Using this reference material, several procedures to extract fumonisins from Thai rice were compared. Accordingly, we proved the applicability of an effective extraction procedure for the determination of fumonisins in Japanese rice.

Preparation of reference materials for the determination of RoHS-relevant flame retardants in styrenic polymers

Reference materials for the analysis of polybrominated diphenyl ethers, polybrominated biphenyls and other common brominated flame retardants (FR) in styrenic polymers were prepared to suit the demands of actual restriction of the use of certain hazardous substances in electrical and electronic equipment analytics. Three methods of preparation were employed, viz. pellet forming, dissolution/vaporisation and extrusion, whereby extrusion proved to be the most suitable method. For extrusion, three procedures of pre-mixing were investigated: the polymers were either mixed with FR powder, FR solutions or FR concentrates that were taken from waste industrial polymers. The latter procedure proved to be most appropriate in terms of analyte concentration, predictability and recovery. The homogeneity of the samples, as well as the chemical and thermal long-term stabilities, was investigated. The result was an optimised method to prepare a suitable reference material for laboratory use.

Method Development for Analysis of Urban Dust Using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry to Detect the Possible Presence of World Trade Center Dust Constituents

The collapse of the World Trade Center Towers on September 11, 2001, sent dust and debris across much of Manhattan and in the surrounding areas. Indoor and outdoor dust samples were collected and characterized by U.S. Geological Survey (USGS) scientists using scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS). From this characterization, the U.S. Environmental Protection Agency and USGS developed a particulate screening method to determine the presence of residual World Trade Center dust in the indoor environment using slag wool as a primary "signature". The method describes a procedure that includes splitting, ashing, and sieving of collected dust From one split, a 10 mg/mL dust/isopropanol suspension was prepared and 10-30 microL aliquots of the suspension placed on an SEM substrate. Analyses were performed using SEM/EDS manual point counting for slag wool fibers. Poisson regression was used to identify some of the sources of uncertainty, which are directly related to the small number of fibers present on each sample stub. Preliminary results indicate that the procedure is promising for screening urban background dust for the presence of WTC dust. Consistent sample preparation of reference materials and samples must be performed by each laboratory wishing to use this method to obtain meaningful and accurate results.

Preparation of reference material for organochlorine pesticides in a herbal matrix

The development of reference material for four organochlorine pesticides, namely hexachlorobenzene and three isomers of hexachlorocyclohexane (alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane and gamma-hexachlorocyclohexane), in a ginseng root sample is presented. Raw materials (Panax ginseng) were purchased from a local market and confirmed to contain certain levels of incurred organochlorine pesticide residues by a validated gas chromatography-mass selective detection method. A total of more than 300 bottles each containing 25 g of samples were prepared after the materials had been freeze-dried, milled and thoroughly mixed. The homogeneity and stability of samples from randomly selected bottles were verified and the reference values were characterized using a highly precise isotope dilution gas chromatography-mass spectrometry (ID-GCMS) method that was recently developed by our laboratory. The purity of standard organochlorine chemicals was determined against certified reference materials to establish the accuracy of the ID-GCMS analysis. The concentrations (+/- expanded uncertainty) of hexachlorobenzene, alpha-hexachlorocyclohexane, beta-hexachlorocyclohexane and gamma-hexachlorocyclohexane in the reference material were 0.198 +/- 0.015, 0.450 +/- 0.022, 0.213 +/- 0.011 and 0.370 +/- 0.032 mg kg(-1), respectively. A portion (70 bottles) of the samples was also used in a proficiency testing (PT) scheme for assessing the testing capabilities of field laboratories. The consensus mean values of the PT obtained from the 70 participants were on the same order but deviated by -2.7 to -14.1% from those of the assigned reference values. Because of the wide spread of participants' data (relative standard deviation ranging from 44 to 56%), the PT results were not included in the calculation of the assigned values of the reference materials. The materials served as suitable reference materials to ascertain the quality control and validation processes for the determination of organochlorine pesticides in herbal matrices.

Elaboration of Four Olive Oil Certified Reference Materials: InterOleo-CRM 2006 Certification Study

The study for the elaboration and certification of four olive oil reference materials covering all the physical–chemical characteristics, defined in Commission Regulation (EC) 1989/2003, is reported herein. The different steps of the process, preparation of reference materials, homogeneity and stability studies, and characterization study have been carried out for 14 laboratories from five European countries. The certificate of analysis for these certified reference materials (CRMs) provide assigned values for concentrations of more than 50 parameters or characteristics of olive oils in compliance with the European legislation about the labeling of food products. The certified values and its corresponding uncertainties were obtained applying robust statistics to the raw data provided by the laboratories taking part in the interlaboratory study. The certificate is valid for a maximum period of 18 months from the elaboration date. These four CRMs are intended for use as a primary material for quality control and for validation of analytical methods for measurements in authentication and adulteration problems of olive oils.

Stability Studies of Principal Illicit Drugs in Oral Fluid: Preparation of Reference Materials for External Quality Assessment Schemes

Data on the stability of drugs of abuse in oral fluid are needed to define the optimal transportation and storage conditions when this biological fluid has to be used for off-site screening and confirmation analyses, as well as in the preparation of reference material for external quality assessment schemes. The short-term and long-term stability of opiates, cocaine, amphetamines, and methylenedioxy derivatives in unstimulated oral fluid was evaluated in different storage conditions, with and without the addition of citrate buffer and sodium azide. Short-term stability was evaluated at 25 degrees C and 37 degrees C for up to 7 days. Long-term stability was evaluated at different time intervals for up to 2 months at 4 degrees C and -20 degrees C. The effect of three different freezing and thawing cycles was also studied. No significant loss of amphetamines and methylenedioxy derivatives, morphine, codeine, and benzoylecgonine was observed under any of the investigated conditions. Conversely, hydrolysis of the ester bonds of cocaine and 6-MAM, leading to the formation of benzoylecgonine and morphine, respectively, was observed under all the applied conditions when oral fluid was not buffered and preserved. The addition of citrate buffer (pH, 4) and sodium azide (0.1%) to oral fluid prevented their degradation during up to 7 days of storage at 25 degrees C and 37 degrees C and up to 2 months at 4 degrees C and -20 degrees C. The stability of the principal illicit drugs spiked in buffered and stabilized oral fluid is adequate for transportation of collected samples at ambient temperature and for shipment and storage of reference materials for external quality assessment schemes.

Preparation of reference materials for rice kernels

In order to execute a performance test of electronic moisture meters for rough rice, rice kernels with different moisture contents must be produced to serve as standard reference materials. Standard operational procedures for the preparation of reference material were proposed in this study. Rewetted materials were prepared by mixing grain kernels with water uniformly. Dried materials were produced by drying samples with hot air. After a holding period of 3 days, grains at various locations in the sample containers were sampled at different storage periods. The moisture content of the sample was then measured by the oven method. The homogeneity of the samples was tested by the analysis of variance (ANOVA) technique. The stability of sample moisture was evaluated by a linear regression equation. These results indicated that the variation of moisture content was low. The moisture content had no relationship with the stored period and indicated the uniformity and stability of the reference materials for rice kernels. The variability within a subgroup and between subgroups was monitored by a quality control technique. Results indicated that the variability of moisture content of samples is within acceptable limits. The test of homogeneity and long-term stability by statistical techniques of this study can serve as an evaluation technique for biological reference materials.

Studies on N-Terminal Glycation of Peptides in Hypoallergenic Infant Formulas: Quantification of α-N-(2-Furoylmethyl) Amino Acids

To obtain information about the extent of the early Maillard reaction between the N-termini of peptides and lactose, alpha-N-(2-furoylmethyl) amino acids (FMAAs) were quantified together with epsilon-N-(2-furoylmethyl)lysine (furosine) in acid hydrolyzates of hypoallergenic infant formulas, conventional infant formulas, and human milk samples using RP-HPLC with UV-detection. FMAAs are formed during acid hydrolysis of peptide-bound N-terminal Amadori products (APs), and furosine is formed from the Amadori products of peptide-bound lysine. Unambiguous identification was achieved by means of LC/MS and UV-spectroscopy using independently prepared reference material. The extent of acid-induced conversion of APs to FMAAs was studied by RP-HPLC with chemiluminescent nitrogen detection (CLND). Depending on the corresponding alpha-N-lactulosyl amino acid, between 6.0% and 18.1% of FMAAs were formed during hydrolysis for 23 h at 110 degrees C in 8 N HCl. From epsilon-N-lactulosyllysine, 50% furosine is formed under these conditions. Whereas furosine was detectable in all assayed samples, five different FMAAs, alpha-FM-Lys, alpha-FM-Ala, alpha-FM-Val, alpha-FM-Ile, and alpha-FM-Leu, were exclusively detected in acid hydrolyzates of hypoallergenic infant formulas in amounts ranging from 35 to 396 mumol/100 g protein. Taking the conversion factors into account, modification of N-terminal amino acids in peptides by reducing carbohydrates was between 0.3% and 8.4%. This has to be considered within the discussion concerning the nutritional quality of peptide-containing foods.

Mussel Reference Material Preparation Proposal as a Quality Assurance Tool for Brazilian Seashore Biomonitoring

Analytical measurement results may affect economical, political and environmental protection decisions. Therefore, there is a growing demand for quality assurance of such results. The use of certified reference materials, CRMs, is a simple and efficient way to validate analytical methods and to keep them under control. However, CRMs are expensive and usually obtained abroad, which makes their use prohibitive for a large number of Brazilian chemical laboratories. This paper presents a proposal for the preparation of a mussel reference material using the Perna perna species. This material will be used in biomonitoring studies of the Brazilian Seashore. The various aspects of the preparation such as sampling, processing, physical and chemical characterization are presented. Preliminary results for the concentration of elements such as As, Br, Co, Cr, Fe, K, Na, Se and Zn determined by INAA and Cd and Hg determined by AAS, are also presented.

Stability studies of amphetamine and ephedrine derivatives in urine

Knowledge of the stability of drugs in biological specimens is a critical consideration for the interpretation of analytical results. Identification of proper storage conditions has been a matter of concern for most toxicology laboratories (both clinical and forensic), and the stability of drugs of abuse has been extensively studied. This concern should be extended to other areas of analytical chemistry like antidoping control. In this work, the stability of ephedrine derivatives (ephedrine, norephedrine, methylephedrine, pseudoephedrine, and norpseudoephedrine), and amphetamine derivatives (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), and 3,4-methylenedioxymethamphetamine (MDMA)) in urine has been studied. Spiked urine samples were prepared for stability testing. Urine samples were quantified by GC/NPD or GC/MS. The homogeneity of each batch of sample was verified before starting the stability study. The stability of analytes was evaluated in sterilized and non-sterilized urine samples at different storage conditions. For long-term stability testing, analyte concentration in urine stored at 4 degrees C and -20 degrees C was determined at different time intervals for 24 months for sterile urine samples, and for 6 months for non-sterile samples. For short-term stability testing, analyte concentration was evaluated in liquid urine stored at 37 degrees C for 7 days. The effect of repeated freezing (at -20 degrees C) and thawing (at room temperature) was also studied in sterile urine for up to three cycles. No significant loss of the analytes under study was observed at any of the investigated conditions. These results show the feasibility of preparing reference materials containing ephedrine and amphetamine derivatives to be used for quality control purposes.

Stability studies of testosterone and epitestosterone glucuronides in urine

The stability of testosterone glucuronide (TG), epitestosterone glucuronide (EG) and the T/E ratio in urine has been studied. Samples were analyzed by gas chromatography coupled to mass spectrometry (GC/MS). Urine samples were submitted to a solid-liquid cleanup followed by extraction of unconjugated testosterone (T) and epitestosterone (E) with tert-butyl methyl ether (free fraction). The remaining aqueous phase was hydrolyzed with beta-glucuronidase and extracted at alkaline pH with n-pentane. Analytes were analyzed by GC/MS as their enol-trimethylsilyl (TMS) derivatives. The urine for stability testing was obtained from an excretion study after the administration of T to healthy volunteers. The homogeneity of the sample was verified before starting the stability study. The stability of TG and EG was evaluated at different storage conditions. For long-term stability testing, analyte concentration in urine stored at 4 degrees C and -20 degrees C was determined at different time intervals for 22 months. For short-term stability testing, analyte concentration was evaluated in urine stored at 37 degrees C for 3 and 7 days. The effect of repeated freezing (at -20 degrees C) and thawing (at room temperature) was studied for up to three cycles. Data obtained in this work demonstrated the stability of TG, EG and the T/E ratio in sterilized urine samples stored at 4 and -20 degrees C for 22 months and after going through repeated freeze/thaw cycles. Decreases in concentration were observed after 7 days of storage at 37 degrees C due to the partial cleavage of the glucuronide conjugates; however, the T/E ratio was not affected. These results show the feasibility of preparing reference materials containing TG and EG to be used for quality control purposes.

Feasibility study of preparation and certification of reference materials for nitrogen dioxide and sulfur dioxide in diffusive samplers

This paper presents the results of a feasability study for the preparation and certification of reference materials (RMs) for nitrogen dioxide (NO(2)) and sulfur dioxide (SO(2)) in diffusive samplers. RMs for NO(2) were prepared by exposure to gas mixtures in a chamber while the RMs for SO(2) were prepared by liquid spiking. Certification of RMs for NO(2) was found feasible with a certified uncertainty of 5.8% and a proposed shelf life of 5 years. The uncertainty was calculated with contribution from the homogeneity of preparation, stability and transport of the CRMs and from an external verification of the certified value. To reach 5.8% of uncertainty, the contribution of the differences between the results of analysis by ion chromatography and colorimetry must be eliminated. It is proposed to solve this by pre-extracting the samplers with water before analysis. The results of this study indicate that the samplers are stable for at least two years before and after exposure when stored in a refrigerator. By contrast, the certification of RMs for SO(2) was found to not be feasible due to instability problems. This instability was attributed to reaction of sulfate on the walls of the samplers. Alternatively, the preparation of RMs by simultaneous exposure to SO(2) and NO(2) has been tested. Satisfying homogeneities has been reached both for NO(2) and SO(2).

Preparation of Reference Material 8504, Transformer Oil.

A new reference material (RM), RM 8504, has been prepared for use as a diluent oil with Aroclors in transformer oil Standard Reference Materials (SRMs) 3075 to 3080 and SRM 3090 when developing and validating methods for the determination of polychlorinated biphenyls (PCBs) as Aroclors in transformer oil or similar matrices. SRMs 3075-3080 and SRM 3090 consist of individual Aroclors in the same transformer oil that was used to prepare RM 8504. A unit of RM 8504 consists of one bottle containing approximately 100 mL of transformer oil. No additional constituents have been added to the oil.

Teaching reference material preparation: the PHARE-country experience

The paper presents an overview about the outcome of two hands-on courses on environmental reference material production organised by the European Commission’s Environment Institute within the context of its PHARE-AQUACON activities. Two plant reference materials, i.e. TP-28 (black tea) and TP-29 (mallow) were prepared and characterised by the course participants. Data on homogeneity and information values about the contents of inorganic and organic pollutants are presented. Furthermore, information about the AQUACON-Project are given, too.

Mat Control: a new laboratory for the preparation of reference materials at the University of Barcelona, Spain

With the aim of responding to the growing demand for quality control materials (QCMs) in Spain for routine analysis and use in proficiency testing schemes, a research group of the Analytical Chemistry Department of the University of Barcelona built up a fully equipped laboratory for preparing reference materials. This article discusses the background of the group, the design and description of the laboratory, the production and working plan, as well as a summary of the results obtained from the activities of the laboratory Mat Control since its creation in 2001.