In-house Standards Research Articles

Making low concentration in-house pressed pellet trace element standards for carbonate rock analyses by WD-XRF

We describe a simple method for making in-house, low concentration (0–100ppm) pressed pellet standards for analyzing Ni, Cu, Mo, V and U in carbonate lithologies by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry. This method can easily be modified to include other elements of interest and to encompass a different range of concentrations. The purpose here was to circumvent the general lack of adequate geological certified reference materials (CRMs) having the necessary concentrations of the above five elements that are commonly used in paleoceanographic studies as proxies for changes in bioproductivity and paleoredox conditions in the water column and near the sediment–water interface. Standards were prepared by spiking 99.999% pure calcium carbonate powder with single element, inductively coupled plasma mass spectrometry (ICP-MS) standard stock solutions to yield final multi-element mixtures containing 0, 1, 2, 5, 10, 20, 50 and 100ppm of Ni, Cu, Mo, V and U, independently verified using acid digestion ICP-MS and PROTrace XRF trace element analyses. The level of in-house standard homogeneity was determined statistically using ANOVA tests (analyses of variance) on count rate data generated for each analyte from three surface transects (50×500μm) ablated on each standard using laser-ablation ICP-MS, demonstrating that all are statistically distinguishable and sufficiently homogenous for the intended purposes of larger spatial scale XRF measurements. The in-house standards were then used to refine preexisting XRF calibrations based on a broad suite of non-carbonate geological CRMs. The refined calibrations yield close agreement with ICP-MS and PROTrace XRF-derived values for the suite of in-house standards when analyzed repeatedly as ‘unknown samples’ by the XRF analytical protocol. The precision of sample preparation and analysis was assessed statistically by ANOVA tests on the results of repeated analyses of analyte concentrations for replicate XRF samples prepared from a representative carbonate sample, yielding reproducibility on the order of 1) <2.5% at the 50–100ppm level, 2) within ±5–10% or better at the 10–20ppm level, 3) within ±5–15% at the 5ppm level, and 4) ±10–55% at the 1–2ppm level which approaches analytical detection limits. Analytical detection limits and residual calibration backgrounds of the XRF protocol were constrained empirically by repeated analyses of ultrapure calcite blanks.

Laser ablation-inductively coupled plasma-mass spectrometry using a double-focusing sector field mass spectrometer of Mattauch–Herzog geometry and an array detector for the determination of platinum group metals and gold in NiS buttons obtained by fire assay of platiniferous ores

This paper explores the potential of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for the determination of Au, Ir, Pd, Pt, Rh and Ru in NiS buttons obtained by fire assay of platiniferous ores using a new type of ICP-MS instrument equipped with an array detector Mattauch–Herzog spectrometer. The method evaluated comprises the NiS fire assay of a representative amount of the ore sample (40–75 g), grinding of the NiS buttons subsequently obtained, pelleting of the resulting powders using polyethylene wax as a binder, and LA-ICP-MS analysis of the sample using in-house matrix-matched standards for calibration. The use of this new ICP-MS device proved very beneficial in this context, offering a remarkable level of precision (2–3% RSD for the most abundant analytes, Pt, Pd, Rh and Ru, and 6–11% RSD for Au and Ir) owing to its simultaneous capabilities and its extended linear range, which enabled an improved performance of the internal standard (61Ni). Moreover, the low level of argide-based interferences and the detection power of the instrument provided low limits of detection (10 ng g−1 level) even for those elements that could be potentially affected by ArNi+ and ArCu+ overlap in this particular matrix (Pd, Rh, Ru). The accuracy finally obtained (90% of results within 10% of the reference value, and 70% of results within 5%) is fit-for-purpose for this application. The resulting method can be thus considered very attractive as a faster and greener strategy for the control of these types of samples in the platinum group metal industry, circumventing the need for the cumbersome and environmentally unfriendly digestion procedures currently employed.

Final report of the pilot study CCQM-P110-B1: A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 µmol/mol by Fourier transform infrared spectroscopy (FT-IR)

This pilot study compares the performance of participants in analyzing gas mixtures of nitrogen dioxide in nitrogen by comparison with in-house gravimetric standards using Fourier transformed infrared spectroscopy (FT-IR). In this study the same gas mixtures were used as in the key comparison CCQM-K74, which was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol. In the comparison CCQM-K74 most of the participants used chemiluminescence, with a small number using UV absorption or FT-IR spectroscopy, and thus it is of interest to improve understanding of the comparative performance of these techniques because they do not exhibit any cross-sensitivity to nitric acid (HNO3), which was known to be present in the mixtures used for the comparison.The results of this pilot study indicate good consistency and a level of agreement similar to that reported in the comparison CCQM-K74, demonstrating that FT-IR can be operated as a comparison method when calibrated with appropriate gas standards and can achieve similar measurement uncertainties to chemiluminescence and UV absorption techniques.An additional pilot study, CCQM-P110-B2, was conducted on the same gas mixtures in parallel with this pilot study. The second study addressed FT-IR spectroscopy when used to measure the gas mixtures with respect to reference spectra. The results of this second study will be reported elsewhere.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM-GAWG.

Antitrophoblast antibodies are associated with recurrent miscarriages

To investigate whether antitrophoblast antibodies are associated with unexplained recurrent miscarriages, we used choriocarcinoma cells JEG-3, since these cells are negative for class I and II antigens, but they do express HLA-G, resembling an antigen expression of endovascular and interstitial trophoblasts. Case-control study. Academic research center. One hundred ninety-four patients with two or more consecutive, idiopathic recurrent miscarriages (RM; <20 weeks of gestation) were compared with 110 controls with normal pregnancies and without pregnancy complications. Anti-JEG-3 reactivities were measured by using flow cytometry and comparisons with two in-house standards antibody samples of low and high reactivity. Anti-JEG-3 reactivities above the 95% confidence interval of controls were defined as positive. Sera of RM patients reacted significantly stronger with JEG-3 cells than that of controls. In addition, RM patients significantly more often had positive anti-JEG-3 reactivities (17.5%) than controls 5%. This difference was markedly increased with a subgroup of 80 RM patients who had three or more miscarriages, as 27 of these women (34%) were anti-JEG-3 positive. Antitrophoblast antibodies show significantly more mean channel shift reactivities, and positive reactivities are significantly more prevalent in RM patients as compared with controls. Such antibodies may be involved in mechanisms affecting pregnancies.

An International Collaboration To Standardize HIV-2 Viral Load Assays: Results from the 2009 ACHI E V 2E Quality Control Study

Accurate HIV-2 plasma viral load quantification is crucial for adequate HIV-2 patient management and for the proper conduct of clinical trials and international cohort collaborations. This study compared the homogeneity of HIV-2 RNA quantification when using HIV-2 assays from ACHI(E)V(2E) study sites and either in-house PCR calibration standards or common viral load standards supplied to all collaborators. Each of the 12 participating laboratories quantified blinded HIV-2 samples, using its own HIV-2 viral load assay and standard as well as centrally validated and distributed common HIV-2 group A and B standards (http://www.hiv.lanl.gov/content/sequence/HelpDocs/subtypes-more.html). Aliquots of HIV-2 group A and B strains, each at 2 theoretical concentrations (2.7 and 3.7 log(10) copies/ml), were tested. Intralaboratory, interlaboratory, and overall variances of quantification results obtained with both standards were compared using F tests. For HIV-2 group A quantifications, overall and interlaboratory and/or intralaboratory variances were significantly lower when using the common standard than when using in-house standards at the concentration levels of 2.7 log(10) copies/ml and 3.7 log(10) copies/ml, respectively. For HIV-2 group B, a high heterogeneity was observed and the variances did not differ according to the type of standard used. In this international collaboration, the use of a common standard improved the homogeneity of HIV-2 group A RNA quantification only. The diversity of HIV-2 group B, particularly in PCR primer-binding regions, may explain the heterogeneity in quantification of this strain. Development of a validated HIV-2 viral load assay that accurately quantifies distinct circulating strains is needed.

Carbon and oxygen isotope analysis of small carbonate samples (20 to 100 µg) with a GasBench II preparation device

Dear Editor, Since the pioneering work by Emiliani and Shackleton, the carbon and oxygen stable isotopes of carbonates have been of major importance in geological and environmental sciences.[1-8] Palaeoceanographic and terrestrial climate research (e.g. on secondary cave carbonates or lacustrine sediments) routinely make use of the δ13C and δ18O of carbonates as climate proxies.[9-12] Online sample preparation and continuous-flow isotope ratio mass spectrometry (IRMS) with multi-loop injection procedures are now widely applied analytical techniques, because they allow precise and accurate measurements at high sample throughput.[13] The samples sizes used in analytical systems for carbonates described in the literature are generally larger than ca. 50 µg, with an external precision of ca. 0.05–0.10‰.[14, 15] Unfortunately, sample size is often a limiting factor in studies of many climate records (lacustrine sediments, speleothems, foraminifera) when sampling for individual sediment layers to obtain sub-annual to seasonal information.[16, 17] Reliable, accurate, and fast analysis of samples as small as possible is desired for ultra-high-resolution sampling for palaeoclimate investigations, but also for other geological applications, such as investigations of traces of carbonates in silicate rocks.[9, 18-20] Fiebig and co-workers described a method for the precise measurement of carbonate samples in the range 10 to 30 µg for the GasBench II, the same device as we describe in this communication.[21] However, their method requires a modification of the hardware and the use of liquid nitrogen, which increases the costs and the complexity of the measurements. In this letter we describe the improvements in analytical performance possible by simply reducing the size of sample vials from 12 to 4.5 mL and show that precise and accurate measurements on samples as small as 20 µg of carbonate are possible. For the experiments described below we employ the ThermoFinnigan (Bremen, Germany, now Thermo Fisher Scientific) GasBench II, equipped with a CTC autosampler (CTC Analytics AG, Zwingen, Switzerland), and coupled to a ConFlow IV interface and a Delta V Plus mass spectrometer (both Thermo Fisher Scientific) at the ETH Zurich (Zurich, Switzerland). The system setup is essentially the same as used in an earlier study.[13] Instead of the 12 mL exetainers normally used, we load micro-samples (7–150 µg) of carbonate into 4.5 mL round-bottomed borosilicate vials (Labco, High Wycombe, UK, part No. 948 W), capped with Labco butyl rubber septa.[13] Samples were weighed using a Mettler Toledo MT5 FACT microbalance (reproducibility 0.8 µg; Leicester, UK). The exetainers were flushed for 240 s on a model 222XL autosampler (Gilson™, Middleton, WI, USA), with helium grade 5.0 (99.999% He) at a flow rate of 55 mL/min, corresponding to a flushing volume of 220 mL. The smaller 4.5 mL exetainers allow the reduction of helium consumption compared with the 12 mL vials, as no air contamination was observed during our experiments (Fig. 1). Eight-one exetainers (including 18 in-house standards (powdered Carrara marble, MS2) are subsequently heated to 72 ± 0.1 °C in the aluminium block of the autosampler and acid-digested following standard procedures.[13] The heating period of the autosampler heating block is somewhat longer for short vials, due to the air in the heating block below the vials. If small vial runs are planned for an extended period of time, metal cylinders placed below the vials can be used to circumvent the problem.

An evaluation of the use of yttrium and beryllium as internal standards in inductively coupled plasma emission spectrometry for untreated aqueous solutions in presence of high concentrations of organic solvents and matrices

Non-spectral interferences are known to affect the robustness and precision of inductively coupled plasma-emission spectrometry (ICP-AES), especially in the case where the ICP-AES instrumentation includes conventional nebulization systems and the samples should not be pre-treated or are specially prepared as in-house working standards. Under these circumstances, yttrium ionic lines and a beryllium atomic line may be evaluated as internal standards (ISs). In this study, the working standards were prepared with the addition of several reagents that are known to affect the plasma's robustness in a set of series of multi-element standard solutions. In the applied methodology, conventional equipment (a cross-flow pneumatic nebulizer and a double-pass, Scott-type spray chamber) was used and the operating parameters of ICP-AES were adjusted to produce a robust plasma. A sum of 39 analytical lines of 19 elements (Ag, Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, Mg, Mn, Ni, Pb, Tl and Zn) were studied. The studied organic substances were solvents such as dioxane and formic acid and also glucose and sucrose at various concentration levels. The overall sensitivity changes and the accuracy of the method were used as quantitative criteria to evaluate the effect of the presence of the above mentioned substances. The results are useful for the analysis of many kinds of untreated samples, as well as for the analysis of eluents from separation procedures in hyphenated ICP-AES methodologies.

An international collaborative study to establish the WHO 1st international standard for alpha‐1‐antitrypsin

The aim was to establish the 1st International Standard (IS) for alpha-1-antitrypsin (AAT) to standardise potency assignment of therapeutic products, calibrated in moles and mg active AAT in line with product labelling practice. Assigning total protein and antigen values to the IS was also investigated. The active concentration of four candidate AAT preparations was determined in an international collaborative study by inhibition of trypsin (calibrated by active-site titration). Total protein and antigen content were determined for each candidate using local methods and in-house standards, and a common AAT preparation. The total protein content of the IS was also determined by amino acid analysis. Potency determination of recombinant and transgenic materials against the IS was investigated in a follow-up study. Data analysis for potency determination indicated no statistical difference between any of the candidates, or between the results for recombinant and plasma-derived products. Total protein content of the IS determined by amino acid analysis was consistent with the potency value. The variability in the total protein and antigen results for the other candidates was reduced when the data were recalculated relative to the IS. Candidate C (05/162) was established by the WHO Expert Committee on Biological Standardization (ECBS) in 2006 as the WHO 1st IS for AAT with a potency of 243 nmoles (12·4 mg) active inhibitor per ampoule. In 2008, ECBS approved the IS for potency determination of recombinant material and assigned a total protein and antigen value of 12·4 mg.

GRENVILLE SKARN TITANITE: POTENTIAL REFERENCE MATERIAL FOR SIMS U-Th-Pb ANALYSIS

We have investigated the homogeneity, chemical composition, structure, degree of radiation damage, and post-formation evolution of titanite crystals from skarns of the Grenville Province of the Canadian Shield using SHRIMP, TIMS, Raman and PL spectroscopy, EBSD, and EPMA–WDS. These results are used to assess the potential of the titanite as Reference Material (RM) for micro-analytical U–Th–Pb age dating. The SHRIMP data show that these megacrysts (5–31g) have concordant U–Pb isotope systematics, 60 to 500 ppm U, 120 to 1200 ppm Th, 206 Pb/ 204 Pb between 500 and 2500, ages of ~1 Ga, and excellent homogeneity at the scale of the analytical volume of the ion probe. The ID–TIMS titanite data for OLT1, OLT2 and TCB show that these crystals are essentially concordant. Data for OLT1 and OLT2 show slight scatter ( i.e. , in excess of that expected from the uncertainty in an individual analysis). For OLT1, one of seven analyses shows Pb loss or, possibly, a younger period of growth. Crystals OLT1 and OLT2 have respective TIMS concordia ages of 1014.8 ± 2.0 Ma (2σ, n = 6, MSWD = 1.8) and 998.0 ± 4.5 Ma (2σ, n = 3, MSWD = 3.3) for domains that have not lost Pb. The TIMS analyses of TCB are tightly clustered and give a concordia age of 1018.1 ± 1.7 Ma (2σ, n = 4, MSWD = 0.92). Raman and PL spectra show a low to moderate degree of accumulated radiation-induced damage in the Grenville Skarn Titanite crystals and uniform internal distributions of this damage. The EDSB contrast images indicate little or no crystallographic misorientation. The EMPA–WDS data show that the outer 50–100 μm of the OLT1 and TCB crystals are enriched in Al and F, and depleted in Fe and Nb, when compared with the interior. In spite of the variation in composition and degree of radiation damage amongst samples, there are no identifiable matrix effects in our SHRIMP data. Some Grenville skarn titanite (GST) crystals have potential as RM for micro-analytical U–Th–Pb age dating. Crystal TCB has excellent homogeneity of U–Th–Pb isotopic composition. Crystals OLT1 and OLT2 have minor TIMS age heterogeneity. However, this heterogeneity is smaller than that of the Khan titanite, our current in-house titanite standard. Careful selection of analysis areas during SIMS, and of chips for TIMS analysis, allows high-quality isotopic data to be obtained from these large crystals of titanite.

An online method combining a Gasbench II with continuous flow isotope ratio mass spectrometry to determine the content and isotopic compositions of minor amounts of carbonate in silicate rocks

An online method using continuous flow isotope ratio mass spectrometry (CF-IRMS) interfaced with a Gasbench II device was established to analyze carbon and oxygen isotopic compositions and to estimate the content of minor amounts of carbonate in silicate rocks. The mixtures of standard materials and high-purity quartz are firstly used to calibrate different quantities of carbonate in silicates. The results suggest that the accuracy and precision of the online analysis are both better than those obtained using an offline method. There is a positive correlation between the carbonate weight and the Mass44 ion beam intensity (or peak area). When the weight of carbonate in the mixtures is greater than 70 microg (equal to approximately 1800 mV Mass44 ion beam intensity), the delta(13)C and delta(18)O values of samples usually have accuracy and precision of +/-0.1 per thousand and +/-0.2 per thousand (1sigma), respectively. If the weight is less than 70 microg, some limitations (e.g., not perfectly linear) are encountered that significantly reduce the accuracy and precision. The measured delta(18)O values are systematically lower than the true values by -0.3 to -0.7 per thousand; the lower the carbonate content, the lower the measured delta(18)O value. For samples with lower carbonate content, the required phosphoric acid doses are higher and more oxygen isotope exchanges with the water in the phosphoric acid. To guarantee accurate results with high precision, multiple analyses of in-house standards and an artificial MERCK sample with delta(13)C values from -35.58 to 1.61 per thousand and delta(18)O from 6.04 to 18.96 per thousand were analyzed simultaneously with the unknown sample. This enables correction of the measured raw data for the natural sample based on multiple-point normalization. The results indicate that the method can be successfully applied to a range of natural rocks.

Correction of multi-collector-ICP-MS instrumental biases in high-precision uranium–thorium chronology

We present a method for the calibration of in-house thorium isotope standards for use in U–Th chronology, along with an assessment of instrumental biases on the Nu Plasma multi-collector inductively-coupled-plasma mass spectrometer. Uranium and thorium mass fractionation is found to be very strongly coupled, with no evidence of differences in mass bias behaviour. Both Th-isotope and U–Th fractionation are most closely approximated by a linear-law fractionation model. Any deviations from linear law are at the sub-permil level. We also investigate potential biases introduced by intensity-dependant, and ion-beam-path dependant variations in ion-counter response. At count rates <∼350,000 counts per second, intensity-dependant gain variation can be accounted for entirely by dead-time, while beam-path differences can cause gain variation of up to ∼0.8% for different Th isotopes. If this beam-path bias is to be adequately corrected, ion-counter measurements of Th-isotope ratios must be made with reference to bracketing Th-isotope standards measured in the same configuration.

A WHO Reference Reagent for the Serum Transferrin Receptor (sTfR): international collaborative study to evaluate a recombinant soluble transferrin receptor preparation

The usefulness of serum transferrin receptor (sTfR) as a marker of iron deficiency is limited by lack of standardization of commercial immunoassays for sTfR. An international collaborative study was performed to evaluate a lyophilized preparation of recombinant soluble transferrin receptor (rsTfR) for its suitability to serve as a World Health Organization (WHO) Reference Reagent to standardize immunoassays for sTfR. The concentration of pure rsTfR was determined from the A(280 nm) using the adjusted theoretical extinction coefficient and molecular weight calculated from its sequence, before dilution and lyophilization in a sTfR-depleted serum matrix. Six manufacturers and a health protection laboratory assayed the candidate Reference Reagent, coded 07/202, along with three lyophilized serum samples, using commercial assays for sTfR. Dose-response plots demonstrated acceptable overall parallelism between 07/202, manufacturers' in-house standards, and serum samples. However, there was poor agreement on the estimated (r)sTfR content of 07/202 and serum samples. Expressing the sTfR content of the serum samples relative to 07/202 markedly improved agreement between methods. Use of 07/202 would reduce inter-method variability. The preparation was established as the 1st WHO Reference Reagent for sTfR with assigned free rsTfR monomer values of 21.7 mg/L and 303 nmol/L (0.5 mL reconstitution).

Quality of Online Chat Reference Answers Differ between Local and Consortium Library Staff: Providing Consortium Staff with More Local Information Can Mitigate these Differences

A Review of:&#x0D; Meert, D.L., &amp; Given, L.M. (2009). Measuring quality in chat reference consortia: A comparative analysis of responses to users’ queries.” College &amp; Research Libraries, 70(1), 71-84.&#x0D; &#x0D; Objective – To evaluate the quality of answers from a 24/7 online chat reference service by comparing the responses given by local and consortia library staff using in-house reference standards, and by assessing whether or not the questions were answered in real time.&#x0D; &#x0D; Design – Comparative analysis of online chat reference transcripts.&#x0D; &#x0D; Setting – Large academic library in Alberta, Canada.&#x0D; &#x0D; Subjects – A total of online chat reference transcripts from the first year of consortium service were analyzed for this study. Of these, 252 were answered by local library staff and 226 from consortia (non-local) library staff.&#x0D; &#x0D; Methods – A stratified random sample of 1,402 transcripts were collected from the first year of consortium service (beginning of October to end of April). This method was then applied monthly, resulting in a sample size of 478 transcripts. In the first part of the study, responses were coded within the transcripts with a “yes” or “no” label to determine if they met the standards set by the local university library’s reference management. Reference transaction standards included questions regarding whether or not correct information or instructions were given and if not, whether the user was referred to an authoritative source for the correct information. The second part of the study coded transcripts with a “yes” or “no” designation as to whether the user received an answer from the staff member in “real time” and if not, was further analyzed to determine why the user did not receive a real-time response. Each transcript was coded as reflecting one of four “question categories” that included library user information, request for instruction, request for academic information, and miscellaneous/non-library questions. &#x0D; &#x0D; Main Results – When all question types were integrated, analysis revealed that local library staff met reference transaction standards 94% of the time. Consortia staff met these same standards 82% of the time. The groups showed the most significant differences when separated into the question categories. Local library staff met the standards for “Library User Information” questions 97% of the time, while consortia staff met the standards only 76% of the time. “Request for Instruction” questions were answered with 97% success by local library staff and with 84% success by consortia. Local library staff met the “Request for Academic Information” standards 90% of the time while consortia staff met these standards 87% of the time. For “Miscellaneous Non-Library Information” questions, 93% of local and 83% of consortia staff met the reference transaction standards. For the second part of the study, 89% of local library staff answered the questions in real time, as opposed to only 69% of non-local staff. The three most common reasons for not answering in real time (known as deferment categories) included not knowing the answer (48% local; 40% consortia), technical difficulty (26% local; 16% consortia), and information not being available (15% local; 31% consortia).&#x0D; &#x0D; Conclusion – The results of this research reveal that there are differences in the quality of answers between local and non-local staff when taking part in an online chat reference consortium, although these discrepancies vary depending on the type of question. Providing non-local librarians with the information they need to answer questions accurately and in real time can mitigate these differences.

Validation of an immunoturbidimetric method for determination of porcine serum C-reactive protein

Measurement of porcine C-reactive protein (CRP) in serum is an important tool for monitoring health and welfare in pigs. In this study, an immunoturbidimetric method from Olympus System Reagent (OSR 6147) used to measure human CRP in serum that employ a human traceable calibrator has been evaluated in porcine serum samples. Intra- and inter-assay imprecision were lower than that obtained with the porcine-specific commercially available ELISA. The expected difference in serum CRP between healthy and non-healthy pigs was detected. CRP values measured by the immunoturbidimetric method showed a good correlation with those obtained by ELISA, although differences in absolute CRP values were observed. When an in-house porcine standard was used a better agreement was obtained. In conclusion, the immunoturbidimetric method of Olympus can be used with porcine samples. The easier use of this method should facilitate the implementation of CRP serum determination for diagnostic and prognostic purposes in swine medicine. The results emphasize the need to establish species-specific standard and methods to decrease inter-laboratory discrepancies.

10Be and 26Al measurements at the Zurich 6MV Tandem AMS facility

The setups for the 10 Be and 26 Al AMS measurements at the Zurich 6 MV EN Tandem AMS facility are presented and data analysis procedures for both radionuclides are discussed. Performance parameters of the system are shown. In-house AMS standards are compared to commercially available AMS standards.

Viability of in-house datamarting approaches for population genetics analysis of SNP genotypes

BackgroundDatabases containing very large amounts of SNP (Single Nucleotide Polymorphism) data are now freely available for researchers interested in medical and/or population genetics applications. While many of these SNP repositories have implemented data retrieval tools for general-purpose mining, these alone cannot cover the broad spectrum of needs of most medical and population genetics studies.ResultsTo address this limitation, we have built in-house customized data marts from the raw data provided by the largest public databases. In particular, for population genetics analysis based on genotypes we have built a set of data processing scripts that deal with raw data coming from the major SNP variation databases (e.g. HapMap, Perlegen), stripping them into single genotypes and then grouping them into populations, then merged with additional complementary descriptive information extracted from dbSNP. This allows not only in-house standardization and normalization of the genotyping data retrieved from different repositories, but also the calculation of statistical indices from simple allele frequency estimates to more elaborate genetic differentiation tests within populations, together with the ability to combine population samples from different databases.ConclusionThe present study demonstrates the viability of implementing scripts for handling extensive datasets of SNP genotypes with low computational costs, dealing with certain complex issues that arise from the divergent nature and configuration of the most popular SNP repositories. The information contained in these databases can also be enriched with additional information obtained from other complementary databases, in order to build a dedicated data mart. Updating the data structure is straightforward, as well as permitting easy implementation of new external data and the computation of supplementary statistical indices of interest.

Use of a common standard improves the performance of liquid chromatography-tandem mass spectrometry methods for serum 25-hydroxyvitamin-D

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is becoming increasingly popular for measuring 25-hydroxyvitamin-D (25-OH-D). Results submitted to the International Quality Assessment Scheme (DEQAS) have shown poor interlaboratory agreement. We investigated whether the use of a common standard would reduce interlaboratory imprecision. A commercial standard and two controls were distributed with the DEQAS samples in January 2008. Participants were asked to calculate the results of samples and controls using their usual standard and the commercial standard. A method questionnaire was also distributed. Use of a common standard reduced the mean interlaboratory imprecision (coefficient of variation [CV]) for total 25-OH-D from 16.4% (in-house standards) to 10.4% (common standard). For 25-OH-D(3) and 25-OH-D(2), the mean CVs were reduced from 16.7% and 21.1% to 8.5% and 12.6%, respectively. Mean values obtained for total 25-OH-D using the common standard were higher by 6.1%. Use of a common standard improved agreement among laboratories using LC-MS/MS methods for 25-OH-D. This suggests that problems with assay standardization contribute to interlaboratory imprecision. This may be related to the nature of the matrix used for working standards or errors in the calibration of stock standard solutions of 25-OH-D. Some participants used a gravimetric method, others UV spectrophotometry, to establish the concentration of stock solutions. Among the latter group there was uncertainty over the molar absorption coefficient of 25-OH-D solutions. We conclude that LC-MS/MS is not yet sufficiently robust to become the reference method for 25-OH-D and that gas chromatography-mass spectrometry might be a more suitable candidate.

Measuring Quality in Chat Reference Consortia: A Comparative Analysis of Responses to Users’ Queries

Academic libraries have experienced growing demand for 24/7 access to resources and services. Despite the challenges and costs of chat reference service and consortia, many libraries are finding the demand for these services worth the cost. One key challenge is providing and measuring quality of service, particularly in a consortia setting. This study explores the quality of service provided in one academic library participating in a 24/7 chat reference consortium, by assessing transcripts of chat sessions using in-house reference quality standards. Findings point to both similarities and differences between chat interactions of local librarians versus consortia staff.

Measuring Quality in Chat Reference Consortia: A Comparative Analysis of Responses to Users' Queries

Academic libraries have experienced growing demand for 24/7 access to resources and services. Despite the challenges and costs of chat reference service and consortia, many libraries are finding the demand for these services worth the cost. One key challenge is providing and measuring quality of service, particularly in a consortia setting. This study explores the quality of service provided in one academic library participating in a 24/7 chat reference consortium, by assessing transcripts of chat sessions using in-house reference quality standards. Findings point to both similarities and differences between chat interactions of local librarians versus consortia staff.

Significant improvements in the analysis of perfluorinated compounds in water and fish: Results from an interlaboratory method evaluation study

The 2nd international interlaboratory study (ILS) on perfluorinated compounds (PFCs) in environmental samples was organized to assess the performance of 21 North American and European laboratories on the analysis of PFCs in water and fish. A study protocol was provided to assess accuracy, precision, matrix effects and to study the use of in-house standards. The participants used shared native and mass-labelled standards that were provided for this study to quantify the PFC concentrations in the samples. Matrix effects in the determination of PFCs can be considerable and can decrease the sensitivity, the accuracy and internal standard recoveries. Therefore, two quantification methods were evaluated by all laboratories: standard addition quantification (SAQ) and solvent-based calibration curve quantification (SBCCQ; using mass-labelled internal standards (IS)). The between laboratory reproducibility (i.e. coefficient of variance) was smaller for the SBCCQ results (except for PFBS and PFHxS for which no mass-labelled analogues were available) compared to those obtained by the SAQ method. The within laboratory precision of individual laboratories is good (mean for all PFCs in water 12% and 6.8% in fish). The good performance is partially attributable to the use of well-defined native- and mass-labelled standards. Therefore, the SBCCQ method is recommended. The results show that analytical methods for PFCs in water and fish have improved considerably. Critical steps identified in this study are (i) the use of well-defined native standards for quantification, (ii) the use of mass-labelled internal standards (preferably one for each target compound) and (iii) minimization of matrix effects by a better clean up.