Average Relative Standard Deviation Values Research Articles

Generation of multiply charged ions from homogeneous MALDI microcrystals

The homogeneity of matrix assisted laser desorption/ionization (MALDI) microcrystals, laser fluence, and the proton affinity (PA) of matrices determine the generation of multiply charged ions. Here we adopt three structurally similar matrices, i.e. α-cyano-4-hydroxycinnamic acid (CHCA), 4-chloro-α-cyanocinnamic acid (Cl-CCA), and (E)-propyl α-cyano-4-hydroxyl cinnamylate (CHCA-C3) to examine the homogeneity of microcrystals by measuring the relative standard deviation (RSD) values of the matrices with the homogeneous sample preparation method, e.g. forced dried droplet (FDD). The average RSD values of CHCA, Cl-CCA, and CHCA-C3 matrices are ∼15%, ∼10%, and ∼20%, respectively. With the same CHCA matrix, we found the charge state of myoglobin ions can obtain more charges (+6) with the FDD method as compared to +5 charges obtained by the inhomogeneous sample preparation method, i.e. dried droplet (DD). The laser fluence also affects the generation of multiply charged ions. For instance, the maximum charge states of myoglobin and cytochrome c ions are +6 with CHCA and +4 with CHCA-C3 at threshold laser fluence and decreases at elevated laser fluence. The charge state of myoglobin ions with Cl-CCA matrix is +3 at threshold laser fluence and increases to the maximum charge state of +6 and eventually reduces to +5 with elevated laser fluence. Moreover, we found low PA value of matrix results in high charge state of analyte ions and vice versa. The matrix PA modulates the proton transfer reaction, leading to the formation of multiply charged ions. The homogeneous samples help control the charge states of ions and generate the multiply charged protein ions which can be used as potential mass calibration standards to search suitable protein samples at high m/z ratios with a MALDI time-of-flight mass spectrometer.

Direct Multielemental Trace Determinations in Plutonium Samples by Total Reflection X-ray Fluorescence Spectrometry Using a Very Small Sample Amount.

A simple, safe, and sensitive method for direct multielemental trace determinations in plutonium samples using total reflection X-ray fluorescence (TXRF) spectrometry has been developed. A very small volume (2 μL) of the sample solutions was deposited on TXRF supports after separation of the plutonium matrix from these solutions. Since the amount of the plutonium deposited on the supports was in the ng level only fixed on the supports and the specimen spots were not disturbed during the sample preparation, the samples could be analyzed directly without putting the instrument in a glovebox. This approach avoided a cumbersome operation of the instrument in a glovebox, which is normally utilized for Pu-based samples using other techniques. Similarly, the requirement of small amounts of the samples minimized the radiation dose to the operator as well as a cumbersome problem of management of radioactive analytical waste of plutonium samples. The samples were analyzed using the TXRF spectra of the specimens, concentration of the internal standard Se or Ga and predetermined sensitivity values. The elemental detection limits for the elements K-Sr varied from 1.06 to 0.09 ng. The elements K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Ba, Tl, and Pb were analyzed at μg/mL level. The analytical results of TXRF determinations showed average relative standard deviation (RSD) value of 4.5% (1σ, n = 3) and the TXRF determined results deviated from the expected values by 5.9% on average for samples prepared by adding multielements in plutonium solutions. Two real plutonium samples were also analyzed in similar manner. For the real plutonium sample solution the average RSD values of TXRF determinations were 10.6% (1σ, n = 3) for the elemental concentrations in the range of 0.2 to 61 μg/mL. These values are comparable with conventional trace element analytical techniques with added advantages mentioned above.

Cluster analysis of polymers using laser-induced breakdown spectroscopy with K-means

Laser-induced breakdown spectroscopy (LIBS) combined with K-means algorithm was employed to automatically differentiate industrial polymers under atmospheric conditions. The unsupervised learning algorithm K-means were utilized for the clustering of LIBS dataset measured from twenty kinds of industrial polymers. To prevent the interference from metallic elements, three atomic emission lines (C i 247.86 nm , H i 656.3 nm, and O i 777.3 nm) and one molecular line C–N (0, 0) 388.3 nm were used. The cluster analysis results were obtained through an iterative process. The Davies–Bouldin index was employed to determine the initial number of clusters. The average relative standard deviation values of characteristic spectral lines were used as the iterative criterion. With the proposed approach, the classification accuracy for twenty kinds of industrial polymers achieved 99.6%. The results demonstrated that this approach has great potential for industrial polymers recycling by LIBS.

Evaluation of Coregulation as a Governance Option To Manage Aflatoxin Risk in Texas Maize

Coregulation as a form of risk management relies upon a government-private partnership in regulation using government-backed codes of practice or action plans. In Texas, implementation of coregulation to manage aflatoxin risk has been practiced since 2011 and operates under the program title One Sample Strategy (OSS). Aflatoxin-contaminated cereals and oilseeds that contain greater than 20 μg/kg of the toxin (B1, B2, G1, and G2) are adulterated as defined by the Texas Commercial Feed Rules and regulated by the Texas Feed and Fertilizer Control Service of the Office of the Texas State Chemist. The present study was intended to evaluate the implementation and effectiveness of the coregulation program for 3 years based on selected evaluation criteria aiming to improve aflatoxin risk management and thus reduce market and food safety risk in Texas. In 2013, 124 analysts qualified to participate in the program at 23 grain elevators. During the 2013 harvest, use of control samples to ensure testing accuracy revealed that the average relative standard deviation among all participants was 14.5%. In 2014 and 2015, 129 and 151 analysts, respectively, qualified to measure aflatoxin, and the average relative standard deviation values for the working control across the 29 and 30 participating firms were 16.2 and 13.7%, respectively. All firms demonstrated the capability to grind maize to the OSS-prescribed particle size (70% passing through a 20-mesh sieve) in all 3 years. The Texas Feed and Fertilizer Control Service verified testing accuracy of OSS participants analyzing 612, 693, and 482 retained samples in 2013, 2014, and 2015, respectively. Results were plotted in an operating curve to depict type I and type II errors. The implementation of the OSS built upon a quality system-based code of practice successfully managed aflatoxin risk in Texas by using coregulation as a governance option.

Effects of variability sources on analysis of the composition of large ancient metal objects

The restoration of the Resurrection Pulpit, which is conserved in the church of San Lorenzo in Florence (Italy), was the occasion for an in-depth study of one of the most famous works created by Donatello (1386–1466) in his last years. The project aimed at contributing to the understanding of the creative process through identification and comparison of the compositions of the metal alloys used to cast the different parts of the Resurrection Pulpit. Prior to any concentration comparison, a realistic estimation of the uncertainty associated to each value was established. Indeed, the objective of the present work is to evaluate this uncertainty and its dependence on the potential sources, including sampling, subsampling, chemical attack, measurement and heterogeneity (depth (Z) and surface location (X/Y)). Finally, an optimized procedure for the determination of the concentrations of major and minor components of the metal alloy is proposed. With this purpose, several samples were taken and analyzed by means of ICP-OES and ICP-MS (inductively coupled plasma-optical emission spectroscopy/mass spectrometry). The maximum dispersions in terms of relative standard deviation (RSD) obtained by following the proposed procedure are for Cu <3%, for Pb <12% and for Sn <12%, and the average RSD values, being slightly lower, are for Cu <1.5%, for Pb <10% and for Sn <11%. These dispersions for all three elements are mainly introduced by large X/Y distances between the sampling points.

Speciation of selenium and tellurium in milk by hydride generation atomic fluorescence spectrometry

A simple, fast and highly sensitive method has been developed for the differentiation of Se and Te into their (IV) and (VI) oxidation states in milk samples by HG-AFS. This procedure involves a previous leaching of milk slurries by sonication with aqua regia for 10 min. Se(IV) and Te(IV) were determined by analysis of the samples without a pre-reduction step; being total Se and Te determined after reduction with KBr. The method provides limit of detection values (LOD) of 0.012 and 0.023 ng ml−1 for Se(IV) and Te(IV) respectively. Average relative standard deviation values of 10.5%, 3.9%, 12% and 12.5% were found for the determination of Se(IV), Se(VI), Te(IV) and Te(VI) in milk samples containing Se from 11.1 to 32.2 ng g−1 and Te from 1.1 to 10 ng g−1. Recovery experiments made on actual samples spiked with Se(IV), Se(VI), Te(IV) and Te(VI) evidenced that the sonication with aqua regia does not modify the oxidation state of the elements considered.

Non-chromatographic speciation analysis of arsenic and antimony in milk hydride generation atomic fluorescence spectrometry

A rapid, high sensitivity method has been developed for the determination of As(III), As(V), Sb(III) and Sb(V) in milk samples by using hydride generation atomic fluorescence spectrometry. The method is based on the leaching of As and Sb from milk through the sonication of samples with aqua regia followed by direct determination of the corresponding hydrides both before and after reduction with KI. It was confirmed by recovery experiments on spiked commercially available samples that neither the reduced nor the oxidized forms of the elements under study or mixtures of the two oxidation states were modified by the room temperature sample treatment with aqua regia. The methodologies developed provided 3 σ limit of detection values of 8.1, 10.3, 5.4 and 7.7 ng l −1 for As(III), As(V), Sb(III) and Sb(V) in the diluted samples. Average relative standard deviation values of 5.7, 5.5, 8.2 and 4.7% were found for determination of As(III), As(V), Sb(III) and Sb(V) in commercially available samples of different composition and origin containing from 3.5 to 13.6 ng g −1 total As and from 4.9 to 11.8 ng g −1 total Sb, it being confirmed that As(V) and Sb(V) are the main species present in the samples analyzed (62±5 and 73±5%, respectively). The time required to determine As and Sb species in milk involves 10 min sonication and 30 min prereduction but these steps can be carried out for several sample simultaneously. Additionally the fluorescence measurement step involves less than 20 min for three replicates of all the four measurements required. So, in less than 2 h it is possible to determine the content of As(III), As(V), Sb(III) and Sb(V) in four samples.

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH4 in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7ngl−1 for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2ngg−1 As, from 3.1±0.2 to 11.6±0.4ngg−1 Sb, from 10.7±0.5 to 25.5±0.4ngg−1 Se, from 0.9±0.2 to 9.4±0.6ngg−1 Te and from 11.5±0.1 to 27.7±0.4ngg−1 Bi.

Simultaneous Determination of the Predominant Hyperforins and Hypericins in St. John's Wort (Hypericum perforatum L.) by Liquid Chromatography

Hypericin and hyperforin are believed to be among the active constituents in common St. John's wort (Hypericum perforatum L.). Presently, dietary supplements are generally standardized to contain specified levels of hypericin and hyperforin, and the related compounds, pseudohypericin and adhyperforin. A rapid method was developed for simultaneous determination of these 4 active constituents by liquid chromatography (LC). A 1 g portion of dried, finely ground leaf/flower sample is extracted with 20 mL methanol for 2 h. A 0.6 mL aliquot of the crude extract is combined with 5.4 mL acetonitrile-methanol (9 + 1) and passed through a mixed solid-phase cleanup column. The eluate is examined by LC for hyperforin, adhyperforin, hypericin, and pseudohypericin on a Hypersil reversed-phase column by using simultaneous ultraviolet (284 nm) and fluorescence detection (excitation, 470 nm; emission, 590 nm). The compounds are easily separated isocratically within 8 min with a mobile phase of acetonitrile-aqueous 0.1 M triethylammonium acetate (8 + 2). Average recoveries of hyperforin and adhyperforin were 101.9 and 98.4%, respectively, for 3 sample mixtures containing concentrations ranging from approximately 0.2 to 1.5% combined hyperforins per gram dry weight. Average relative standard deviation (RSD) values for hyperforin and adhyperforin for all 3 mixtures were 18.9 and 18.0%, respectively. Average recoveries of hypericin and pseudohypericin were 88.6 and 93.3% respectively, from 3 sample mixtures containing concentrations ranging from approximately 0.2 to 0.4% combined hypericins per gram dry weight. Average RSD values for hypericin and pseudohypericin for all 3 mixtures were 3.8 and 4.2%, respectively.

A Rapid Method for the Determination of Trace Element Impurities in Silicons Oils by ICP-MS After Microwave-Assisted Digestion

A microwave-assisted digestion procedure has been developed for the treatment of silicone oil samples. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentration level of 40 trace element impurities, like Li, Na, Mg, Al, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Sr, Rb, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Ba, La, Ce, Nd, Hf, W, Au, Pb, Hg, Th, Bi and U in these samples, having obtained average relative standard deviation values of 9.6%. The methodology developed has been tested by recovery studies on different natural samples spiked with known amounts of Mg, Cr, Mn, Fe, Zn and Pb at concentration levels of 10, 0.5, 5, 5, 10 and 1 μg g−1 and recovery percentage values varies from 97 to 105 %.