Ensuring the reliability of stable isotope ratio data—beyond the principle of identical treatment

The need for inter-laboratory comparability is crucial to facilitate the globalisation of scientific networks and the development of international databases to support scientific and criminal investigations. This article considers what lessons can be learned from a series of inter-laboratory comparison exercises organised by the Forensic Isotope Ratio Mass Spectrometry (FIRMS) network in terms of reference materials (RMs), the management of data quality, and technical limitations. The results showed that within-laboratory precision (repeatability) was generally good but between-laboratory accuracy (reproducibility) called for improvements. This review considers how stable isotope laboratories can establish a system of quality control (QC) and quality assurance (QA), emphasising issues of repeatability and reproducibility. For results to be comparable between laboratories, measurements must be traceable to the international δ-scales and, because isotope ratio measurements are reported relative to standards, a key aspect is the correct selection, calibration, and use of international and in-house RMs. The authors identify four principles which promote good laboratory practice. The principle of identical treatment by which samples and RMs are processed in an identical manner and which incorporates three further principles; the principle of identical correction (by which necessary corrections are identified and evenly applied), the principle of identical scaling (by which data are shifted and stretched to the international δ-scales), and the principle of error detection by which QC and QA results are monitored and acted upon. To achieve both good repeatability and good reproducibility it is essential to obtain RMs with internationally agreed δ-values. These RMs will act as the basis for QC and can be used to calibrate further in-house QC RMs tailored to the activities of specific laboratories. In-house QA standards must also be developed to ensure that QC-based calibrations and corrections lead to accurate results for samples. The δ-values assigned to RMs must be recorded and reported with all data. Reference materials must be used to determine what corrections are necessary for measured data. Each analytical sequence of samples must include both QC and QA materials which are subject to identical treatment during measurement and data processing. Results for these materials must be plotted, monitored, and acted upon. Periodically international RMs should be analysed as an in-house proficiency test to demonstrate results are accurate.     

Carbonaceous species of TSP in urban and rural sites around coal-fired power stations in northwestern Greece

Total suspended particles from urban and rural locations around an industrial complex with four coal-fired power stations were collected for a period of 6 months (January-June 2001). Mass concentrations of TSP and carbonaceous species (TC, EC, OC and BC) were determined for seven sampling sites of the studied area. The contribution of TC mass to the total particle mass was similar for all sites with an average value of 12.36±1.27%. The fraction of elemental carbon (EC) was estimated between 32 and 46% of the total carbon (TC). The relationship between organic and elemental carbon showed the primary origin of organic carbon (direct emissions). The OC/BC ratio values were also considered in order to get information about the enrichment of aerosols in organic carbon. Four conditional categories out of the sampling site ‘collection were additionally extracted (“urban”, “rural”, “far” and “close” location to the power stations) and considered with respect to the values of the ratios OC/BC and OC/EC and the multiple correlation coefficients R² for the concentrations of OC, BC and EC. It has been found that in some cases the correlation coefficients rather than the ratios could inform on the type of site.     

Measurement of carbonaceous aerosols: validation of a thermal gravimetric method and its comparison with a thermal optical transmittance method

A high throughput thermal gravimetric method was developed to measure the carbonaceous aerosols and particulates collected on filters. Representative portions or the whole piece of a loaded or blank filter was sampled and conditioned at 105±5 °C for 4 h to drive away water moisture. The sample was then treated at 550±10 °C for 4 h. After each of the heat treatment steps, the sample was conditioned in a humidity and temperature-controlled cabinet for 12 h till constant weight. The weight of the filter before and after the heated treatment was measured and the weight difference between the treatment at 550 and 105 °C was calculated as the weight of the carbon containing substances (CCS). Reference chemical standards and certified reference materials SRM 1649a and 1650a were used to validate the method. CCS concentrations of real aerosol samples collected in the city of Hong Kong during the summer of 2001 were also measured, compared and correlated with the concentrations of total carbon (TC), elemental carbon (EC) and organic carbon (OC) of the samples determined using a thermal optical transmittance (TOT) method as specified in NIOSH method 5040. The weight of organic compounds in airborne particulate matters is usually estimated by multiplying the weight of TC, which is determined by thermal/thermal optical methods, by a factor of 1.2 or 1.4. To this end, a correction factor of approximately 1.6 was found to relate TC to the measured values of CCS in aerosol samples collected in the urban atmosphere of Hong Kong. The proposed procedure for measurement of CCS is simple, easy to follow and requires simple laboratory instrumentation. Typically, the analysis of more than 100 filter samples can be completed within three working days with minimal attention.     

校园室内外大气PM2.5中的含碳气溶胶及室内源特征

分夏、冬季采集南昌大学前湖校区室外和3个不同室内环境中的PM2.5,测定有机碳(OC)和元素碳(EC),并分析室内、外碳气溶胶质量浓度及其分布特征;利用OC-EC关系式半定量分析室内排放源;结合室内、外二次有机碳(SOC)和SOC/OC的分布进一步讨论不同室内排放源的特征及对SOC的影响;对4个采样点的8个碳组分丰度特征比较分析,结果表明复印/打印机对室内OC的贡献高,8个碳组分的丰度分布特征与其它排放源具有较明显的差异。     

Optimisation of analytical procedures for the quantification of ionic and carbonaceous fractions in the atmospheric aerosol and applications to ambient samples

In the last decade, our research group set up and optimised analytical techniques for the characterisation of the major components of atmospheric aerosol (i.e. secondary inorganic ions and carbonaceous material) and source markers (e.g. levoglucosan, carbonates). In this study, we present a complete overview on the most problematic aspects that can be encountered during the quantification of the two main components of aerosol, i.e. the ionic and carbonaceous fractions. More in detail, different liquid chromatographic approaches were set up for main ions and anhydrosugars determination. Quality assurance procedures (i.e. tests on data reliability) were applied during the set-up phase and they are presented in this work. As regards the carbonaceous component characterisation, two evolved gas analysis techniques were set up and applied: the thermogravimetric technique coupled to the Fourier transformed infrared spectroscopy (TGA/FTIR) and the thermal–optical transmittance method (TOT). A suitable protocol for organic and elemental carbon separation was set up for the TGA/FTIR system and a comparison with the results obtained by the TOT method was carried out. Studies on the impact of filter load, field blanks, and sample composition on OC/EC quantification by the TOT method were performed. Moreover, approaches for carbonate carbon quantification on different kinds of filters were developed. It was demonstrated that this approach allows to reach the ionic balance in samples impacted by carbonate compounds. The optimised methods have been applied for the analysis of thousands of PM filters allowing the obtainment of reliable results.     

Development of metrological models for internal standard single-point and multi-point calibrations for the assessment of tear gas weapons compliance with legislation

Tear gases are the most widely used non-lethal weapons, both by security forces and by the general public. The pepper spray, whose active agent is capsaicin, is the only self-defence aerosol allowed in Portugal, where capsaicin concentration must be below 5 g/100 mL. The cost-effective evaluation of the compliance of self-defence weapons with legislation involves the use of two measurement procedures with increasing quantitative capability. Samples are first assessed by preliminary measurement procedure based on single-point GC–MS calibration. Whenever the measurement uncertainty from this assessment makes evaluation inconclusive, the evaluation of sample compliance using multi-point GC–MS calibration is performed. Metrological models including sound criteria for the evaluation of sample compliance with legislation were developed for both measurement procedures. Such models include the evaluation of the impact of instrumental performance, calibration model, sample dilution and standards preparation on measurement uncertainty. The relative expanded uncertainty, in the studied range (capsaicin 3–7 g/100 mL), of measurements supported in single-point calibrations ranged from 10 to 22% and the ones supported on multi-point calibrations from 8 to 12% depending on capsaicin concentration and daily GC–MS repeatability. Measurements are fit for the intended use since they present a relative expanded uncertainty smaller than a target value of 30, or 15%, for measurements supported in single- or multi-point calibrations, respectively.     

大气气溶胶中有机碳和元素碳监测方法的进展

本文主要介绍和评述了近10年来大气气溶胶中的有机碳和元素碳的采样和分析技术的进展,引用参考文献41篇。     

Production of aerosols by optical catapulting: Imaging,performance parameters and laser-induced plasma sampling rate

Optical catapulting (OC) is a sampling and manipulation method that has been extensively studied in applications ranging from single cells in heterogeneous tissue samples to analysis of explosive residues in human fingerprints. Specifically, analysis of the catapulted material by means of laser-induced breakdown spectroscopy (LIBS) offers a promising approach for the inspection of solid particulate matter. In this work, we focus our attention in the experimental parameters to be optimized for a proper aerosol generation while increasing the particle density in the focal region sampled by LIBS. For this purpose we use shadowgraphy visualization as a diagnostic tool. Shadowgraphic images were acquired for studying the evolution and dynamics of solid aerosols produced by OC. Aluminum silicate particles (0.2–8 μm) were ejected from the substrate using a Q-switched Nd:YAG laser at 1064 nm, while time-resolved images recorded the propagation of the generated aerosol. For LIBS analysis and shadowgraphy visualization, a Q-switched Nd:YAG laser at 1064 nm and 532 nm was employed, respectively. Several parameters such as the time delay between pulses and the effect of laser fluence on the aerosol production have been also investigated. After optimization, the particle density in the sampling focal volume increases while improving the aerosol sampling rate till ca. 90%.     

Proficiency testing schemes for polytechnic students: an educational project in The Netherlands

In the August 1999 issue of Accreditation and Quality Assurance reference was made to proficiency testing schemes organised for students at polytechnics in The Netherlands. The present paper describes in more detail this educational project which aims at increasing students' awareness of quality assurance and quality control (QA/QC) at polytechnics. The project has to be seen in relation to other regular activities to educate and train students and to prepare them for working in an analytical laboratory. This combined effort should result in well-educated and well-trained students with the right attitude to analytical work and to QA/QC. The project was organised under the auspices of the Working Group "Quality Assurance in Laboratory Education" (KILO).     

Comparison of two different approaches to calibrate an energy-dispersive x-ray fluorescence spectrometer for the analysis of aerosol-loaded filters

The quantitative analysis of aerosol loaded filters by x-ray fluorescence spectroscopy implies the use of calibration curves obtained from synthetic standards. Two preparation methods to obtain these calibration samples are described and compared, showing that matrix and enhancement effects are neglible for membranous filters and that both calibrations lead to acceptable results. Calibration standards produced via an aerosol generator always lead to a greater sensitivity compared to the standard produced with droplets. The filters resist the conditions of replicated measurements.     

Mercury in atmospheric aerosols: A preliminary case study for the city of Krakow,Poland

The level of contamination by mercury associated with airborne particulate matter in Krakow was determined. Samples of PM10 were collected on quartz filters using low-volume samplers. The total particulate mercury (TPM) concentrations in collected samples were determined by mercury analyser MA-3000 (Nippon Instruments Corporation). The reported results include also data on the carbonaceous aerosol and inorganic ions concentrations during the reported sampling campaign. The average concentration of the Total Particulate Mercury (TPM) in Krakow (Poland) was 0.22 ng·m⁻³ (during the period from 22 February to 2 March) and 0.49 ng·m⁻³ (on 3 March). A marked correlation between TPM and elemental carbon (EC) as well as with Cl^– was found. No significant association of the TPM with NO₃^– and SO₄^2– could be shown. The dry deposition flux of mercury was calculated as an average over the sampling period and was 47.3 ng·m⁻²·d⁻¹.     

Carbonaceous components in atmospheric aerosol: measurement procedures and characterization

Carbonaceous material in the particulate matter was measured in Rome urban area. The carbonaceous material constitutes a significant component of total aerosol mass (30-40%) and it is composed by two main fractions, elemental carbon (EC) and organic carbon (OC). EC is essentially a primary pollutant emitted directly from incomplete combustion processes whereas OC has both primary and secondary origin. A chemical OC investigation has been carried out in order to determine the nalkanes, the n-alkanoic acids, the polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs by means an HRGC-MS procedure. A different seasonal distribution of these compound classes attributed to photochemical radical activity (n-alkanes and PAH decrease in spring- and summertime) and to biogenic plant emission (n-alkanoic acid increase in summertime) has been evidenced.     

Comparison of two different approaches to calibrate an energy-dispersive x-ray fluorescence spectrometer for the analysis of aerosol-loaded filters

The quantitative analysis of aerosol loaded filters by x-ray fluorescence spectroscopy implies the use of calibration curves obtained from synthetic standards. Two preparation methods to obtain these calibration samples are described and compared, showing that matrix and enhancement effects are neglible for membranous filters and that both calibrations lead to acceptable results. Calibration standards produced via an aerosol generator always lead to a greater sensitivity compared to the standard produced with droplets. The filters resist the conditions of replicated measurements.     

The establishment of quality systems in veterinary diagnostic testing laboratories in developing countries: experiences with the FAO/IAEA External Quality Assurance Programme

Quality systems, established to internationally accepted standards, are one mechanism that can assist in evaluations of the sustainability of technology transfer, the proficiency of the user, and the reliability and comparability of data generated, resulting in potential enhancement of laboratory credibility. The means of interpreting existing standards and implementing quality systems in developing country veterinary diagnostic laboratories has become a significant adjunct to the technology transfer element within the Food and Agriculture/ International Atomic Energy Agency, FAO/IAEA programme. The FAO/IAEA External Quality Assurance Programme (EQAP) is given as an example for an initial step towards enhancing the “quality” culture in developing country veterinary laboratories. In 1995 the EQAP began as an effort to assure that test results emanating from laboratories using FAO/IAEA ELISA kits for animal disease diagnosis are valid. For this purpose 15 international external quality-assurance rounds have been performed to date for a variety of animal diseases e.g. Rinderpest, brucellosis, trypanosomosis, and foot-and-mouth disease (FMD). Results indicate that the EQAP is a valuable tool in the assessment of both the results provided by, and use of the ELISA kits provided through, the joint FAO/IAEA programme. Furthermore EQAP can assist laboratory diagnosticians to enhance quality control/quality assurance (QC/QA) procedures for conducting FAO/IAEA ELISAs and to advise on the implementation of similar QC/QA procedures in other laboratory activities. Based on the experiences made during the implementation of the EQAP a proposal for establishing a quality system standard was ratified through the World Organization for Animal Health (OIE) general conference in May 2000. The OIE Standard On Management And Technical Requirements For Laboratories Conducting Tests For Infectious Animal Diseases is based on ISO 17025 and provides a clear formula for establishing quality systems in veterinary diagnostic laboratories world-wide.     

Pollution characteristics of atmospheric fine particles and their secondary components in the atmosphere of Shenzhen in summer and in winter

Two field measurements for atmospheric fine particles were conducted in Baoan district of Shenzhen during the summer and winter in 2004. Totally 30 sets of 24 h samples were collected, and then the mass concentrations and chemical compositions were determined. The seasonal varia- tions and secondary pollution characteristics of fine particles during the sampling periods were dis-cussed with meteorological factors. The results show that seasonal variations of atmospheric particles are significant in Shenzhen. The average mass concentrations of PM2.5 and PM10 in summer were 35 μg·m-3 and 57 μg·m-3, respectively, and those in winter were 99 μg·m-3 and 135 μg·m-3, respec-tively. The concentrations of both PM2.5 and PM10 in winter increased 184% and 137%, respectively, compared to those in summer. PM2.5 accounted for 61% and 75% of PM10 in summer and in winter, respectively, indicating severe fine particle pollution in Shenzhen. During the summer and winter sampling periods, the mean OC/EC ratios were 3.4 and 1.6, respectively. The estimated secondary organic carbon (SOC) averagely accounted for 56% and 6% of the total OC in summer and in winter, respectively, which implies a major contribution of SOC to OC in summer. During the continuous high temperature period in summer, both the concentrations and fractions of secondary aerosol compo-nents in PM2.5 were highly elevated, suggesting severe secondary pollution again. The prevailing wind was from South China Sea in summer, and the air quality was good. The prevailing wind in winter was from Mainland China to the north, and the polluted air mass led to poor air quality.     

Metrology in laboratory medicine – Reference measurement systems

 The medical laboratory must provide results of measurements that are comparable over space and time in order to aid medical diagnosis and therapy. Thus, metrological traceability, preferably to the SI, is necessary. The task is formidable due to the many disciplines involved, the high production rate, short request-to-report time, small sample volumes, microheterogeneity of many analytes, and complex matrices. The prerequisite reference measurement systems include definition of measurand, unit of measurement (when applicable), consecutive levels of measurement procedures and calibrators in a calibration hierarchy, international organizations, reference measurement laboratories, dedicated manufacturers, written standards and guides for the medical laboratory, production of reference materials, internal and external quality control schemes, and increasingly accreditation. The present availability of reference measurement procedures and primary calibrators is shown to be insufficient to obtain international comparability of all types of quantity in laboratory medicine. Received: 19 April 2000 / Accepted: 3 July 2000     

Separation and quantification of imidazoles in atmospheric particles using LC–Orbitrap‐MS

A method using ultra‐high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol particles. The aqueous particle extract was used without further enrichment or sample clean‐up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25 nM) and good intraday and interday repeatability (<1.6 and <6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10 µg m^?3. The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4‐imidazolecarboxaldehyde and 4‐methyl‐5‐imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples.     

Some practical examples of method validation in the analytical laboratory

Method validation is a key element in both the elaboration of reference methods and the assessment of a laboratory's competence in producing reliable analytical data. Hence, the scope of the term method validation is wide, especially if one bears in mind that there is or at least should be a close relation between validation, calibration and quality control QA/QC. Moreover, validation should include more than the instrumental step only since the whole cycle from sampling to the final analytical result is important in the assessment of the validity of an analytical result. In this article validation is put in the context of the process of producing chemical information. Two cases are presented in more detail: the development of a European standard for chlorophenols and its validation by a full scale collaborative trial, and the intralaboratory validation of a method for ethylenethiourea using alternative analytical techniques.     

Establishing a quality assurance plan for nucleic acid-based diagnostic laboratories: from planning to implementation

Nucleic acid-based technologies have opened new perspectives in diagnosis, prognosis, and treatment in clinical medicine. To maintain patient confidence in this rapidly expanding field and to provide the highest standard of analysis, strict laboratory quality assurance procedures must be followed. While impressive break-through are taking place in this field, the need for an appropriate and suitable quality assurance (QA) plan for nucleic acid-based diagnostic laboratories must be a top priority. In this study, we developed a systematic QA plan for this kind of diagnostic laboratories that would enable us to assure the highest quality standards of their services. We focus on those labs that would like to start introducing a quality system for the first time and discuss the most appropriate ways to pave the way to implement a QA plan from the beginning. This QA plan is suitable for any nucleic acid-based techniques laboratory regardless of the field or services provided.