Probabilistic comparison and assessment of proficiency testing schemes and laboratories in the somatic cell count of raw milk

The somatic cell count (SCC) of milk is one of the main indicators of the udder health status of lactating mammals and is a hygiene criterion of raw milk used to manufacture dairy products. An increase in SCC is regarded as one of the primary indicators of inflammation of the mammary gland. Therefore, SCC is relevant in food legislation as well as in the payment of ex-farm raw milk and it has a major impact on farm management and breeding programs. Its determination is one of the most frequently performed analytical tests worldwide. Routine measurements of SCC are almost exclusively done using automated fluoro-opto-electronic counting. However, certified reference materials for SCC are lacking, and the microscopic reference method is not reliable because of serious inherent weaknesses. A reference system approach may help to largely overcome these deficiencies and help to assure equivalence in SCC worldwide. The approach is characterised as a positioning system fed by different types of information from various sources. A statistical approach for comparing proficiency tests (PTs) by assessing them using a quality index P _Q and assessing participating laboratories using a quality index P _L, both deriving from probabilities, is proposed. The basic assumption is that PT schemes are conducted according to recognised guidelines in order to compute performance characteristics, such as z-scores, repeatability and reproducibility standard deviations. Standard deviations are compared with the method validation data from the ISO method. Input quantities close to or smaller than the reference data of the method validation or the assigned value of the PT result in values for P _Q and P _L close to the maximum value. Evaluation examples of well-known PTs show the practicability of the proposed approach.     

Long-term external quality assessment program for CD4+ T-lymphocyte enumeration in Thailand

The accuracy and reliability of CD4+ T-lymphocyte enumeration are crucial for HIV healthcare management. Thailand’s CD4 external quality assessment (EQA) program was implemented in 2003. This program aims to improve the quality of CD4 testing by providing the quality control material, remedial action, and technical training. In this article, the overall longitudinal performance of the participating laboratories from 2003 to 2015 is reported. The EQA blood samples were sent to the participating laboratories in Thailand and other Southeast Asian (SEA) countries. The participants were requested to enumerate CD3+ and CD4+ T-lymphocytes. The trimmed mean, standard deviation (SD), coefficient of variation (CV), and standard deviation index (SDI) of both fraction and number were calculated from the returned data. Our result indicated a continuously increasing number of participants. The response rate of 72 trials was 98 %. The outlier rates for the fraction and number of CD4+ T-lymphocytes were 3.3 % and 3.4 %, respectively. The average CV of the fraction and number of CD4+ T-lymphocytes was 7.1 % and 9.4 %, respectively. In addition, the analysis of our current EQA trial no. 072 revealed that more than 98 % of participating laboratories had SDI values between ?2 and +2 for both fraction and number of CD3+ and CD4+ T-lymphocytes. In conclusion, the implementation of the CD4 EQA program in Thailand and other SEA countries has led to a reduction in the variability of the results of the CD4 count between laboratories and a continuous improvement in laboratory performance.     

Simultaneous quantification and qualification of synacthen in plasma

Tetracosactide (Synacthen), a synthetic analogue of adrenocorticotropic hormone (ACTH), can be used as a doping agent to increase the secretion of glucocorticoids by adrenal glands. The only published method for anti-doping control of this drug in plasma relies on purification by immunoaffinity chromatography and LC/MS/MS analysis. Its limit of detection is 300 pg/mL, which corresponds to the peak value observed 12 h after 1 mg Synacthen IM administration. We report here a more sensitive method based on preparation of plasma by cation exchange chromatography and solid-phase extraction and analysis by LC/MS/MS with positive-mode electrospray ionization using 7–38 ACTH as internal standard. Identification of Synacthen was performed using two product ions, m/z 671.5 and m/z 223.0, from the parent [M?+?5H]⁵⁺ ion, m/z 587.4. The recovery was estimated at 70%. A linear calibration curve was obtained from 25 to 600 pg/mL (R ²?>?0.99). The lower limit of detection was 8 pg/mL (S/N?>?3). The lower limit of quantification was 15 pg/mL (S/N?>?10; CV%?相似文献   

Comparison of multianalyte proficiency test results by sum of ranking differences, principal component analysis, and hierarchical cluster analysis

Sum of ranking differences (SRD) was applied for comparing multianalyte results obtained by several analytical methods used in one or in different laboratories, i.e., for ranking the overall performances of the methods (or laboratories) in simultaneous determination of the same set of analytes. The data sets for testing of the SRD applicability contained the results reported during one of the proficiency tests (PTs) organized by EU Reference Laboratory for Polycyclic Aromatic Hydrocarbons (EU-RL-PAH). In this way, the SRD was also tested as a discriminant method alternative to existing average performance scores used to compare mutlianalyte PT results. SRD should be used along with the z scores—the most commonly used PT performance statistics. SRD was further developed to handle the same rankings (ties) among laboratories. Two benchmark concentration series were selected as reference: (a) the assigned PAH concentrations (determined precisely beforehand by the EU-RL-PAH) and (b) the averages of all individual PAH concentrations determined by each laboratory. Ranking relative to the assigned values and also to the average (or median) values pointed to the laboratories with the most extreme results, as well as revealed groups of laboratories with similar overall performances. SRD reveals differences between methods or laboratories even if classical test(s) cannot. The ranking was validated using comparison of ranks by random numbers (a randomization test) and using seven folds cross-validation, which highlighted the similarities among the (methods used in) laboratories. Principal component analysis and hierarchical cluster analysis justified the findings based on SRD ranking/grouping. If the PAH-concentrations are row-scaled, (i.e., z scores are analyzed as input for ranking) SRD can still be used for checking the normality of errors. Moreover, cross-validation of SRD on z scores groups the laboratories similarly. The SRD technique is general in nature, i.e., it can be applied to any experimental problem in which multianalyte results obtained either by several analytical procedures, analysts, instruments, or laboratories need to be compared.

Microbial Transformation of Curcumin to Its Derivatives with a Novel <Emphasis Type="Italic">Pichia kudriavzevii</Emphasis> ZJPH0802 Strain

Curcumin, a polyphenolic compound, has shown a wide range of pharmacological activities and has been widely used as a food additive. However, the clinical use of curcumin is limited to some extent because of its poor water solubility and low bioavailability. To overcome these problems, many approaches have been attempted and structural modification of curcumin by microbial transformation has been proven to be an alternative. In this study, we isolated a novel yeast strain Pichia kudriavzevii ZJPH0802 from a soil sample, which is capable of converting curcumin to its derivatives. The transformed products by this strain were evaluated by HPLC, (+) electrospray ionization (ESI)-MSⁿ, and ¹H nuclear magnetic resonance methods. Compared with controls, two new peaks of the transformed broth appeared at retention times of 26 min (I) and 62 min (II) by HPLC analysis. The two transformed products were then further identified by (+) ESI-MSⁿ. The spectrum showed that compound I had an accurate [M+H+NH₃]⁺ ion at m/z 392, [M+H]⁺ ion at m/z 375, [M+H–H₂O]⁺ ion at m/z 357, and (+) ESI-MS³ spectrum showed that ion at m/z 357 could further form fragment ions at m/z 339, 177, and 163; compound II had an accurate [M+H]⁺ ion at m/z 373, [M+H–H₂O]⁺ ion at m/z 355, and (+) ESI-MS³ spectrum showed that ion at m/z 355 could further form fragment ions at m/z 219, 179, 177, 163, and 137. These two transformed products thereby were confirmed as hexahydrocurcumin (I) and tetrahydrocurcumin (II).     

Evaluation of a multiresidue method for measuring fourteen chemical groups of pesticides in water by use of LC-MS-MS

European Council Directive 98/83/EC on the quality of water intended for human consumption brought a new challenge for water-quality control routine laboratories, mainly on pesticides analysis. Under the guidelines of ISO/IEC 17025:2005, a multiresidue method was developed, validated, implemented in routine, and studied with real samples during a one-year period. The proposed method enables routine laboratories to handle a large number of samples, since 28 pesticides of 14 different chemical groups can be quantitated in a single procedure. The method comprises a solid-phase extraction step and subsequent analysis by liquid chromatography-mass spectrometry (LC-MS-MS). The accuracy was established on the basis of participation in interlaboratory proficiency tests, with encouraging results (majority |z-score| <2), and the precision was consistently analysed over one year. The limits of quantitation (below 0.050 μg L⁻¹) are in agreement with the enforced threshold value for pesticides of 0.10 μg L⁻¹. Overall method performance is suitable for routine use according to accreditation rules, taking into account the data collected over one year. Figure Simultaneous SPE extraction system for high thoughput analysis Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Notes: IAREN is an accredited laboratory under the ISO/IEC 17025:2005 for 165 analytical determinations and part of the NORMAN Network of Reference laboratories for monitoring of emerging environmental pollutants in the European Union. This work was presented (podium presentation) at the 12th Symposium on Sampling and Handling of the International Association of Environmental Analytical Chemistry (IAEAC), Zaragoza, 2006.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

Thermodynamic description of phases in the neodymium-barium-copper-oxygen system

The available experimental data were used to construct thermodynamic models of Nd-Ba-Cu-O system phases. The coordinates of the nonvariant points of this system were determined, and the phase diagram for the Nd_{1 + x} Ba_{2 ? x} Cu₃O_{6 + z} (x = 10^?4) compound was calculated.     

Identification of possible technical problems in determination of the major inorganic constituents of brown-rice flour by evaluating proficiency test results

To support skill upgrading in analysis of inorganic constituents of environmental and food samples, the National Metrology Institute of Japan (NMIJ) and the National Food Research Institute (NFRI) have organized a proficiency test (PT) of determination of Mn, Fe, Cu, Zn, As, and Cd in brown-rice flour based on the international standard (ISO/IEC 17043:2010). One hundred and thirty-three sets of reports were assessed by use of the E _n -number and z-score approaches in accordance with ISO/IEC 17043 and the international harmonized protocol for PT. The PT results and analytical procedures, reported in detail, were reviewed, and possible technical reasons for questionable or unsatisfactory results are discussed.

Using <Emphasis Type="Italic">ex situ</Emphasis> X-ray powder diffraction at synchrotron radiation to follow changes in the phase composition of perovskite-like strontium cobaltites

Precision X-ray diffraction at synchrotron radiation was used to reveal the separation of perovskite-like oxides SrCo_0.8-x Fe_0.2Nb _x O_3-z (x = 0.2 and 0.3) into two phases of a similar structure identical to initial perovskite structure, but having different unit cell parameters and supposedly different oxygen deficiency. The structural transformation is accompanied by oxygen outlet from the structure. The study of oxygen atoms intercalation from air into the oxygen-deficient structure showed that the structural changes are reversible: heating to 400°C in air restores the initial state of samples.     

The Stability of Detonation Nanodiamond Hydrosols in the Presence of Salts and Surfactants

The regions of stability and coagulation of hydrosols of oxidized detonation nanodiamonds in the presence of inorganic salts and surfactants of different types have been determined. Concentration C_c of inorganic salts corresponding to the onset of the growth of aggregates in a hydrosol dramatically decreases with an increase in coagulating ion charge z: C_c ~ z^?5.3. Anionic and nonionic surfactants stabilize dispersions of nanodiamonds, while additives of cationic and zwitterionic surfactants cause coagulation. The study of the coagulating effect of alkylpyridinium chlorides has shown that the coagulation threshold halves upon elongation of the hydrocarbon chain in a surfactant molecule by a СН₂ group.     

Interactions of Proteins with the Acidic Components of the Electrolyte Solution and Their Role in the Performance of Separations by CZE

This paper reports the results of a study performed to investigate the dependence of the performance of protein separation by capillary zone electrophoresis (CZE) on the anionic component of the electrolyte solutions consisting of 20 mM N,N,N′,N′-tetramethyl-1,3-butanediamine (TMBD) titrated to either pH 4.0 or pH 6.5 with either a monoprotic or a polyprotic acid. With the exception of hydrochloric acid, the acids were selected among those commonly used as the constituents of the solutions employed for protein analysis by either HPLC or CZE. TMBD was chosen for its effectiveness at preventing the interactions of proteins with the inner wall of bare fused-silica capillaries. The performance of separations was evaluated using four basic model proteins having pI value and molecular mass ranging from 9.5 to 11.0 and from 12,400 to 25,000 Da, respectively. It is shown that the different acids used as the components of the background electrolyte solutions, all containing the same concentration of TMBD, affect to different extents both migration time and peak shape of the tested proteins. The performance displayed by the BGE containing phosphate ions is enhanced using TMBD in combination with diethylenetriamine, an aliphatic vicinal triamine having effective buffering capacity at pH 4.0 and capability at minimizing protein–capillary wall interactions. The reported experimental evidences are discussed based on the possible interactions that the phosphate ions are known to establish with both the protein molecules and the surface of bare fused-silica capillaries.     

Death kinetics of <Emphasis Type="Italic">Escherichia coli</Emphasis> in goat milk and <Emphasis Type="Italic">Bacillus licheniformis</Emphasis> in cloudberry jam treated by ohmic heating

The influence of ohmic heating on the death kinetic parameters of Escherichia coli ATCC® 25922 in goat milk and spores of Bacillus licheniformis ATCC® 14580 in cloudberry jam was investigated and compared with that of conventional heating. Ohmic treatment of goat milk shortened the decimal reduction time D in comparison with the D values obtained at conventional treatment. Similarly, the z value, increase of temperature required for a ten-fold reduction of D, was also lower at ohmic treatment. The death kinetics of Bacillus licheniformis ATCC® 14580 spores in cloudberry jam was also studied employing both types of heat treatment. Similar conclusions were obtained for the D values as in the case of goat milk. However, the differences between the z values obtained for ohmic and conventional heating were not significant.     

LC-MS Quantitative Determination of Atropine and Scopolamine in the Floral Nectar of Datura Species

The present study aimed at determining selected alkaloid components in the nectar of Datura species, to elucidate whether the alkaloid content of the floral nectar can lead to intoxication. A simple and rapid liquid chromatography coupled with electrospray mass spectrometry analysis was developed for the quantitative determination of atropine and scopolamine, the main toxic alkaloids of the Datura species. This method allowed the direct coupling of an electrospray mass selective detector to the LC system. Under these conditions, atropine and scopolamine were well separated from other components and detected with mass spectrometry (mass selective detector). Simultaneous determination of atropine and scopolamine was performed with gradient elution on an Ascentis Express C₁₈ (Supelco) reversed-phase column based on a new fused core particle design. Liquid chromatography coupled with electrospray mass spectrometry was used in positive ion mode. Atropine and scopolamine produced protonated species at m/z 290 and 304 (which are also the base peaks). Our data confirmed that the alkaloid characteristics for the vegetative and reproductive parts of the Datura plants may also occur in the nectar secreted by the flowers. In Datura species with large flowers and high nectar amounts, the alkaloid content increases proportionately and thus the nectar may be a potential source of intoxication.     

Isomorphism in the KTaWO<Subscript>6</Subscript>-RbTaWO<Subscript>6</Subscript>-CsTaWO<Subscript>6</Subscript> system

Synthetic procedures have been developed and compounds of composition K _x Rb _y Cs _z TaWO₆ (x + y + z = 1) have been obtained. Their structure has been investigated by X-ray diffractometry. It has been shown that a continuous series of solid solutions is formed in the ternary system under study. Thermal decomposition of A^ITaWO₆ compounds (A^I = K, Rb, Cs) has been investigated by high-temperature X-ray diffractometry.     

Ion Isolation in a Linear Ion Trap Using Dual Resonance Frequencies

Ion isolation in a linear ion trap is demonstrated using dual resonance frequencies, which are applied simultaneously. One frequency is used to eject ions of a broad m/z range higher in m/z than the target ion, and the second frequency is set to eject a range of ions lower in m/z. The combination of the two thus results in ion isolation. Despite the simplicity of the method, even ions of low intensity may be isolated since signal attenuation is less than an order of magnitude in most cases. The performance of dual frequency isolation is demonstrated by isolating individual isotopes of brominated compounds.

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X-ray spectroscopy of lanthanum manganites: Nature of doping holes,correlation effects,and orbital ordering

The Mn3s X-ray photoelectron spectra of manganites were studied. It was shown that for the formal valence of manganese from 3+ to 3.3+, the doping holes are O2p in character; as the valence of manganese increases further, the Mn3d states acquire holes. For La_0.7Sr_0.3MnO₃, the Mn3p-3d resonance spectra provided information about the occupied and unoccupied Mn3d states, and the correlation energy U = 6.7 eV was determined experimentally. An analysis of X-ray dichroism on the L absorption spectra of three-dimensional La_7/8Sr_1/8MnO₃ showed that the cooperative Jahn Teller distortion of the orthorhombic phase at 240 K was related to (x ² ? z ²)/(y ² ? z ²) type orbital ordering.     

Preparation of in-house reference material of benzylpenicillin in milk and results of a Brazilian proficiency testing scheme

Two milk test materials containing benzylpenicillin and a benzylpenicillin-free material were prepared and used for the operation of a Brazilian proficiency testing (PT) scheme according to the requirements of ISO/IEC 17043. The PT scheme was designed to include laboratories in charge of confirmatory analysis as well as screening analysis. Sets of sample vials, benzylpenicillin-free and spiked items containing 0.2 g of lyophilized milk, were distributed to each participant. Of 20 participants who reported screening data, 18 accomplished satisfying results, providing evidence of the capability of Brazilian laboratories to produce reliable qualitative information. The assigned value (robust average calculated from 6 results) and its uncertainty were (8.28 ± 0.52) μg/L. Participants’ performance was evaluated using z-scores. A small number of participants were able to report quantitative benzylpenicillin results, and consequently care should be taken in the interpretation of the laboratory’s performance, considering the statistical nature of z-scores. Long-term stability testing on remaining PT items showed that a stable benzylpenicillin quality control material was produced and can be used for internal quality control or validation purposes.     

Interpretation of interlaboratory comparison results to evaluate laboratory proficiency

Guidelines are given for the evaluation of proficiency test (PT) results in order to increase the effectivity of PT participation. For better understanding, some statistical background is given along with some examples to show the effects of the choices made by the PT provider. The calculation method of the assigned value and the selection of the standard deviation both affect the z-score that is used by the participating laboratory to judge the quality of its performance in the PT. Therefore, the participating laboratory is advised to use the PT results with care and, if necessary, to recalculate the z-scores. Finally, advice is given on how not to follow up bad PT results along with some valuable steps that could be part of an effective follow-up procedure.     

Mechanochemical synthesis of colloidal silver bromide particles in the NaBr–AgNO<Subscript>3</Subscript>–NaNO<Subscript>3</Subscript> system

X-ray diffraction and thermal analyses, electron microscopy, and dynamic light scattering have been employed to study silver bromide nanoparticles obtained by the mechanochemical exchange reaction NaBr + AgNO₃ + zNaNO₃ = (z + 1)NaNO₃ + AgBr in sodium nitrate matrix (diluent and side reaction product) at z = z₁ = 8.06 and z = z₂ = 4.31. AgBr nanoparticles have been obtained in the free form by dissolving the matrix in water, and their activity in the photodegradation of methylene blue dye has been studied.