The use of split-sample design for performance evaluation of screening kits

Laboratory medicine is an important discipline in health care with its remarkable effect on risk assessment, diagnosis of health, and disease state. This accounts describes a newborn screening approach involving retest, recall, and follow-up procedures. This real life trial emphasizes the need for split-sample design evaluation of newly opened test kits. Quantitative measurements of phenylalanine and neonatal thyroid stimulating hormone (nTSH) were performed in two laboratories. After validation of the calibration in the laboratory that was using the industrially prepared screening kits for the first time, the same real newborn blood spot samples were analyzed for phenylalanine and nTSH measurements in both laboratories and the results obtained were compared non-parametrically, and examined by Deming regression and difference plots. There was no problem with the phenylalanine results: similar results were obtained for the same blood spot cards in both laboratories (P=0.496; bias estimation 0.13). However, the nTSH values were found to be significantly higher in the laboratory that used the nTSH kit for the first time. Although the validation of the calibration of the nTSH kit was valid with the manufactures control materials, spilt-sample results showed that there was a significant difference between the two laboratories (P=0.005; bias estimation 28.6). This study implies that acceptable comparability of split-sample design analysis is needed for testing the analytical performance of industrially prepared tests kits, and this can only be achieved with certified reference materials.Presented at the 8th Conference on Quality in the Spotlight, 17–18 March 2003, Antwerp, Belgium     

Hematological health-related intervals estimated using an indirect method in order to satisfy the accreditation standards

 The estimation of reference limits represents quite a taxing task for laboratories which frequently adopt the limits suggested by manufacturers or those reported in the literature. This practice does not meet the requirements of accreditation programs (i.e. Essential Criteria, Clinical Pathology Accreditation) that require laboratories to produce or check all their reference intervals. We collected 15 244 hematological results from females aged 0–99 years obtained by the Rovereto Hospital Laboratory and calculated the reference intervals, or to be more precise the health-related intervals, using an indirect method (based on all the inpatient and outpatient results). All the measurements were carried out using an automatic Coulter STK S analyzer, and the results were transferred to Verona by e-mail. The results for hemoglobin were: <1 year (n=154)=90–171 g/l; 2–8 years (n=619)=104–136 g/l; 9–14 years (n=322)=118–143 g/l; 15–44 years (n=6329)=106–144 g/l; 45–75 years (n=4893)=107–148 g/l; 75–99 years (n=2927)=90–153 g/l. The results appear different from the results currently used by Rovereto Hospital (120–160 g/l) but comparable to those reported in the literature with the exception of the subjects under 1 year and over 75 years, probably due to the excess of "diseased" subjects in these classes. The indirect method allows even small laboratories to produce or check their reference intervals for all age groups, increasing the clinical effectiveness of laboratory results and satisfying the accreditation standards. Received: 15 April 2000 · Accepted: 20 April 2000     

Electrical surface resistivity of conductive polymers - A non-Gaussian approach for determination of confidence intervals

Polyanilines doped with different acids (HCl, H₂SO₄ and dodecylbenzenesulfonic acid, DBSA) were prepared and their surface electrical conductivities were characterized in a four-probe device, connected to a real-time data acquisition board. Collected data were synchronized and conductivity calculations were performed. The conductive behavior of the polyanilines was investigated along the electrification time. This allowed for introduction of a non-Gaussian technique for determination of the confidence intervals of surface resistivity data. It is shown that the distribution of experimental surface resistivity data does not follow a normal probability distribution function (PDF). Thus, ordinary assumptions related to normal distribution of the experimental errors are wrong and must be corrected for proper determination of the confidence limits of measured resistivity values. It is shown here that confidence limits of resistivity values are asymmetrical and that distribution of experimental values can follow multimodal distributions.     

Non-parametric estimation of reference intervals in small non-Gaussian sample sets

This study aimed at validating common bootstrap algorithms for reference interval calculation.We simulated 1500 random sets of 50–120 results originating from eight different statistical distributions. In total, 97.5 percentile reference limits were estimated from bootstrapping 5000 replicates, with confidence limits obtained by: (a) normal, (b) from standard error, (c) bootstrap percentile (as in RefVal) (d) BCa, (e) basic, or (f) student methods. Reference interval estimates obtained with ordinary bootstrapping and confidence intervals by percentile method were accurate for distributions close to normality and devoid of outliers, but not for log-normal distributions with outliers. Outlier removal and transformation to normality improved reference interval estimation, and the basic method was superior in such cases. In conclusions, if the neighborhood of the relevant percentile contains non-normally distributed results, bootstrapping fails. The distribution of bootstrap estimates should be plotted, and a non-normal distribution should warrant transformation or outlier removal. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of niacin in infant formula by solid-phase extraction/liquid chromatography: peer-verified method performance-interlaboratory validation

This paper reports the results of the interlaboratory peer validation study of AOAC Peer-Verified Method (PVM) 1:2,000 for the determination of niacin in infant formula by solid-phase extraction/liquid chromatography. We have used a Data Quality Objectives (DQO) approach to address not only method variability and robustness but also accuracy of data through the use of an appropriate reference material in conjunction with the interlaboratory validation study. Our DQO included the following: (1) statistical agreement of analytical results and quantitative recovery between 2 collaborating laboratories; (2) the repeatability relative standard deviation (RSDr) values and the HORRAT (Horwitz ratio) obtained (1.07), which satisfied the criteria of the Horwitz "limits of acceptability" at the analyte level present; (3) validation of lack of interference; and (4) accuracy agreement within assigned values for a certified reference material. National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1846 Infant Formula, with a certified value of 63.3 +/- 7.6 microg/g for niacin content, was used as a test material for collaborative study and accuracy assessment. Niacin values obtained by the originating laboratory were 59.7 +/- 4.0 microg/g (95% confidence interval [CI] = 1.4 microg/g with a relative standard deviation [RSD] of 6.7%) and by the peer laboratory were 56.6 +/- 6.6 microg/g (95% CI = 4.1 microg/g, with an RSD of 11.7%). Statistical evaluation using the means equivalence test showed that nicotinic acid values obtained by the peer laboratory were equivalent to those values obtained by the originating laboratory. Linear calibration curves and quantitative recovery were obtained. Integration of the PVM process with a readily available certified reference material gives the user confidence in the accuracy of the data generated by the method through traceability to the reference material used.     

Multielement determination of cadmium and lead in urine by simultaneous electrothermal atomic absorption spectrometry with an end-capped graphite tube.

A method for the multielement determination of cadmium and lead in urine is proposed by simultaneous electrothermal atomic absorption spectrometry (SIMAAS) with an end-capped transversely heated graphite atomizer (EC-THGA). The best conditions for cadmium and lead determination were obtained in the presence of NH4H2PO4 as a chemical modifier, using 500 degrees C and 1800 degrees C as the pyrolysis and atomization temperatures, respectively. Urine samples were diluted 1 + 4 directly in autosampler cups with a mixture of 0.125% (w/v) Triton X-100 + 2.5% (v/v) HNO3 + 0.31% (w/v) NH4H2PO4. The optimized heating program was carried out in 57 s, and the instrument calibration was done with aqueous reference solutions. The use of EC-THGA increased the sensitivity of cadmium and lead by 14% and 25%, respectively. The detection limits (n = 20, 3delta) were 0.03 microg L(-1) (0.36 pg) for cadmium and 0.57 microg L(-1) (6.8 pg) for lead. The performance of EC-THGA was acceptable up to 500 heating cycles. The reliability of the entire procedure was checked with the analysis of a lyophilized urine certified reference material. The found concentrations were in agreement with the recommended values (95% confidence level).     

On a resonance energy model based on expansion in terms of acyclic moments: Exact results

Summary The new concept of the resonance energy in conjugated hydrocarbons introduced by Jiang Y, Zhang H (1989) Theor Chim Acta 75:279 is further developed. This model is based on expansion of the -electron energy in terms of moments which are also equal to numbers of closed walks in a molecular graph. The reference system is established by counting only acyclic walks, i.e. those tracing only on acyclic subgraphs. Because acyclic walks could be counted only up to some finite length, the energy of the reference system has been evaluated by truncating higher terms in the expansion. In this paper a finite expression for the energy of the same reference system is derived, thus allowing its exact evaluation. The exact values differ significantly from the truncated ones. This difference, as well as the discrepancy between exact results and chemical experience, are discussed.     

Characterization of a wheat flour reference material (ARC/CL) for twelve elements

Summary An ARC/CL coded wheat flour reference material (ARC/CL RM) with established recommended concentration values for 12 elements [1,2] was further characterized for P, K and Cr contents by means of an intercomparison study. Minor corrections were made to earlier recommended values in accordance with new results obtained. Fifteen laboratories using a total of 11 methods based on six entirely different analytical principles participated in the intercomparison study. The medians and standard deviations were calculated for the results of the intercomparison study. After rejecting as outliers values falling outside the median ± sd, the present recommended values were obtained by recalculating the median and 95% confidence limits. Recommended values were established for the major elements Ca, K, Mg, P, the minor elements Cu, Fe, Mn, Zn, and the trace elements Mo, Cr, Ni and Se. The relative standard deviations for the 95% confidence limits of the medians were lower than 10% for major and minor elements, 11% for Mo and 18% for Cr. All of the recommended concentration values fell into category A, having a high degree of confidence. The present RM, with its 16 recommended concentrations, is of value for use in nutritional, food composition and contaminant monitoring studies.     

Characterization of a potato reference material for major, minor and trace elements

Summary A potato reference material (RM) was prepared for the analytical quality control program to be employed by the Sub-network on Trace Elements in Food of the FAO European Co-operative Network on Trace Elements. Approximately 50 kg of commercially available potato granules prepared from baked, mashed and roller-dried potatoes, containing 2.8% ash and 3 mg/kg added butylhydroxyanisole was purchased. The granules were carefully homogenised in large glass cylinders followed by division into 50 g portions into numbered acid-washed bottles. The bottled material was tested for homogeneity by taking ten bottles throughout the bottling line and determining by validated atomic absorption spectrometric methods 1.0 g samples for seven mineral elements. Homogeneity for Mg, Ca, Zn, Fe, Mo, Ni and Cd was better than 5%. An international network on experienced, high-quality reference laboratories was established to conduct an interlaboratory comparison study on the determination of 14 mineral elements in the RM. A total of seven methods based on independent analytical principles were employed by the reference laboratories. After excluding outlying analytical results, the criteria defined by the IAEA were used for classification of the overall medians obtained through the interlaboratory comparison study. The relative standard deviations for the 95% confidence limits of the medians were as follows: P=4.2%, K=0.7%, Na=4.7%, Ca=5.5%, Mg=2.4%, Fe=9.3%, Mn=4.0%, Zn=3.6%, Cu=4.7%, Mo=23%, Ni=22%, Cr=19%, Pb=11% and Cd=4.6%. With the exception of Cr, all of the recommended concentration values obtained for the above indicated elements fell into category A, i.e. values recommended with a high degree of confidence according to the classification criteria of the IAEA. The present RM is the only certified potato RM currently available for mineral elements.

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Charakterisierung eines Kartoffel-Referenzmaterials für Haupt-, Neben- und Spurenelemente

     

直接进样-电感耦合等离子体质谱法测定特殊医用配方食品中铬、钼和硒

本文采用1%四甲基氢氧化铵溶液溶解样品,单氦碰撞池模式直接分析特殊医用配方食品中的铬、钼和硒。研究表明:铬、钼和硒在质量浓度2.0~50.0μg/L范围内呈良好的线性关系,铬、钼、硒的检出限分别为0.012、0.009和0.009mg/kg;加标回收率在94%~117%之间,相对标准偏差在1.47%~5.78%之间。本方法对NIST 1849a和FAPAS T07216QC标准物质中铬、钼和硒的测定值与参考值相符。该方法操作简单、快速,适合特殊医用配方食品中铬、钼和硒的同时测定。     

Characterization of ARC/CL wheat flour and potato powder reference materials for content of total dietary fiber

Summary ARC/CL wheat flour and potato powder reference materials (RMs) prepared by the Central Laboratory of the Agricultural Research Centre of Finland, earlier specified for contents of essential and toxic trace elements, were characterized for contents of total dietary fiber (TDF). Recommended concentration values established were obtained on the basis of an interlaboratory comparison study conducted involving 10 reference laboratories recognized for their reliability in TDF determinations. The recommended TDF contents established were based on an enzymatic-gravimetric method employed by the participating laboratories to determine TDF or water insoluble (WIS) and water soluble (WS) DF which were then added up to obtain TDF. After exclusion of outliers the recommended concentration values were expressed as the medians ±95% confidence limits of the average values by the participating laboratories. The coefficient of variation obtained for the recommended concentration range of TDF was within 7% for both RMs.     

Determination of As, Cd, Cr, and Hg in SRM 2584 (trace elements in indoor dust) by high-resolution inductively coupled plasma mass spectrometry

Standard reference material (SRM) 2584 (Trace Elements in Indoor Dust) was developed as a reference standard for evaluating field methods and for validating laboratory and reference methods for the assessment of lead contamination and exposure. In addition to lead, the toxic trace elements As, Cd, Cr, and Hg, at approximately 17, 10, 140, and 5 microg g(-1), respectively, have been certified in the SRM. These four analytes were successfully determined by use of high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Isobaric interferences at masses of As and Cr were resolved by using the high resolution mode (nominal 8000) and the medium resolution mode (nominal 3000), respectively, of the instrument. The effects of a significant drift in analyte sensitivity in the course of measurement were rectified by use of internal standardization, single spike standard addition, and an optimized analysis sequence. The results were compared with those obtained by instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). The results for the quality control, SRM 2704 (Buffalo River Sediment), were in good agreement with the certified values, indicated by the uncertainty intervals of the measured values overlapping the certified intervals at 95% confidence level.     

Uncertainty limits for certified values of standard reference materials

Summary Uncertainty limits usually employ the 95% confidence limits and should include allowances for the uncertainty of known sources of systematic errors of the measurements. But in many cases, when an interlaboratory comparison study is used for certification purposes of standard reference materials, only the 95% confidence limits are considered and given as the uncertainty limit. In this work, we shall show the results as the number of mean values (n) reported vary and only the 95% confidence limits are considered, using as an example the intercomparison study on IAEA/SL-3/lake sediment sample. And finally, we shall compare the results if only the 95% confidence limits are considered with those of the standard deviation and propose when n is large that the standard deviation should be employed instead of the 95% confidence limits as the uncertainty limits, if the other systematic and random errors are not included.     

Validation of the CALUX bioassay for PCDD/F analyses in human blood plasma and comparison with GC-HRMS

Following the dioxin crisis of 1999, several studies were conducted to assess the impact of this crisis on the dioxin body burden in the Belgian population. The Scientific Institute of Public Health identified a population from whom plasma samples were available and from whom, during the follow up survey, plasma samples were obtained in 2000. In total, 496 samples were collected for GC-HRMS and CALUX analyses to verify statistical assessment conclusions. This study was seen as an opportunity to validate the CALUX bioassay for biological sample analysis and to compare toxic equivalency (TEQ) values obtained by the reference GC-HRMS technique and by the screening method. This article focuses on the validation results of the CALUX bioassay for the analyses of the dioxin fractions of blood plasma. The sample preparation is based on a liquid–liquid extraction, followed by an acid silica in series with an activated carbon clean-up. A good recovery (82%) and reproducibility (coefficient of variation less than 25%) were found for this method. Based on 341 plasma samples, a significant correlation was established between the bioassay and chemical method (R = 0.64). However, a proportional systematic error was observed when the results obtained with the CALUX bioassay were regressed with the results from the GC-HRMS analyses. The limit of quantification (LOQ) used to calculate TEQ values from the GC-HRMS determinations, the use of the relative potency values instead of the toxic equivalent factor and the potential of CALUX bioassay to measure all compounds with affinity for the AhR may partly explain this proportional systematic error. Nevertheless, the present results suggest that the CALUX bioassay could be a promising valid screening method for human blood plasma analyses.     

Limits of detection and decision. Part 1

Extensive Monte Carlo studies of instrumental limits of detection were performed on a simple univariate chemical measurement system having homoscedastic, Gaussian measurement noise and using ordinary least squares (OLS) processing of tens of millions of independent calibration curve data sets. It was found that prediction interval-based experimental detection limits were significantly negatively biased, in both the net response domain and the chemical content domain, resulting in substantially higher rates of false negatives than specified via customary critical t values. The diagnostic fix for the bias problem provided clear proof that hypothesis-based detection limits need not be unique, even as distributions of random variates, if the alternate hypothesis is non-unique. It was also demonstrated that hypothesis-based decision and detection limits have finite support that does not include the region near zero analyte content, so that both have finite moments and finite confidence intervals.     

Precision in differential field-flow fractionation: a chemometric study

In the present paper, the capabilities of differential field-flow fractionation, i. e., the determination of an incremental quantity of a colloidal species, e. g., an uptake adsorbed mass, determined by the joint use of two independent FFF measurements, over a species and the same modified species respectively, are considered. The different error types, those related to the retention time determinations and those coming from the operating parameter fluctuations were considered. The different components were computed with reference to SdFFF determinations of bare polystyrene (PS) submicronic particles and the same PS particles covered by IgG. Comparison was made between theoretically computed precision and experiments. The error coming from the experimental measurement of retention times was identified to be the main source of errors. Accordingly, it was possible to make explicit the detection limits and the confidence intervals of the adsorbed mass uptake, as a function of experimental quantities such as the retention ratio, the detector calibration ratio, the injected quantity, the baseline noise, and the void time relative error. An experimentally determined and theoretically foreseen dependence of both the experimental detection and confidence limits (approximately +/- 10(-17) g) on the square root of the injected concentration, for constant injected volume, was found.     

Determination of As, Cd, Cr, and Hg in SRM 2584 (Trace Elements in Indoor Dust) by high-resolution inductively coupled plasma mass spectrometry

Standard reference material (SRM) 2584 (Trace Elements in Indoor Dust) was developed as a reference standard for evaluating field methods and for validating laboratory and reference methods for the assessment of lead contamination and exposure. In addition to lead, the toxic trace elements As, Cd, Cr, and Hg, at approximately 17, 10, 140, and 5 μg g^–1, respectively, have been certified in the SRM. These four analytes were successfully determined by use of high-resolution inductively coupled plasma mass spectrometry (HR-ICP–MS). Isobaric interferences at masses of As and Cr were resolved by using the high resolution mode (nominal 8000) and the medium resolution mode (nominal 3000), respectively, of the instrument. The effects of a significant drift in analyte sensitivity in the course of measurement were rectified by use of internal standardization, single spike standard addition, and an optimized analysis sequence. The results were compared with those obtained by instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP–MS). The results for the quality control, SRM 2704 (Buffalo River Sediment), were in good agreement with the certified values, indicated by the uncertainty intervals of the measured values overlapping the certified intervals at 95% confidence level.     

A comprehensive profile of DNA copy number variations in a Korean population: identification of copy number invariant regions among Koreans

To examine copy number variations among the Korean population, we compared individual genomes with the Korean reference genome assembly using the publicly available Korean HapMap SNP 50 k chip data from 90 individuals. Korean individuals exhibited 123 copy number variation regions (CNVRs) covering 27.2 mb, equivalent to 1.0% of the genome in the copy number variation (CNV) analysis using the combined criteria of P value (P < 0.01) and standard deviation of copy numbers (SD ≥ 0.25) among study subjects. In contrast, when compared to the Affymetrix reference genome assembly from multiple ethnic groups, considerably more CNVRs (n = 643) were detected in larger proportions (5.0%) of the genome covering 135.1 mb even by more stringent criteria (P < 0.001 and SD ≥ 0.25), reflecting ethnic diversity of structural variations between Korean and other populations. Some CNVRs were validated by the quantitative multiplex PCR of short fluorescent fragment (QMPSF) method, and then copy number invariant regions were detected among the study subjects. These copy number invariant regions would be used as good internal controls for further CNV studies. Lastly, we demonstrated that the CNV information could stratify even a single ethnic population with a proper reference genome assembly from multiple heterogeneous populations.     

圆盘膜萃取-气相色谱-质谱法同时测定水中16种酞酸酯类化合物

提出了气相色谱-质谱法同时测定水中16种酞酸酯类化合物(PAEs)的方法。采用自制圆盘萃取装置、无塑料制品接触试验程序进行水样富集,对圆盘膜片选择、过膜压力、洗脱剂种类与用量等进行考察;对仪器工作条件离子源温度、升温速率、进样口温度和不同时间段监测离子及增益等进行了探讨。16种PAEs的质量浓度分别在一定的范围内与峰面积呈线性关系,检出限(3S/N)在0.17～2.45μg.L-1之间。以空白蒸馏水为基底,在3个浓度水平下做加标回收试验,回收率在79.8%～104%之间,相对标准偏差(n=6)在1.1%～9.4%之间。     

An atlas of forecasted molecular data. 2. Vibration frequencies of main-group and transition-metal neutral gas-phase diatomic molecules in the ground state

This atlas of diatomic-molecular vibration frequencies parallels the previously offered Atlas of Internuclear Separations. The Atlas was produced by mining the data from Huber and Herzberg and training neural network software to forecast new data. New protocols were employed with the powerful software, which was originally designed for forecasting the financial markets. The Atlas presents 1920 additional vibration frequencies for use until critical tables are available to fill the needs more precisely. The precision of the predictions is characterized by the average fractional 1% confidence limit, that is, 10.66%. The accuracies of the predictions are determined in two ways. First, 221 of the 224 Huber and Herzberg data values used for training and validation fall within the prediction confidence limits or fall outside by less than 10% of the Huber and Herzberg values, and 181 values agree (within the limits). Second, 87 of 101 comparison data values, consisting of literature data and some additional Huber and Herzberg values, fall within the prediction confidence limits or fall outside by less than half the prediction values, and 44 of the 101 values agree (within the limits).