An interlaboratory study evaluating the interpretation of forensic glass evidence using refractive index measurements and elemental composition.

Seventeen laboratories participated in three interlaboratory exercises to assess the performance of refractive index, micro X-ray Fluorescence Spectroscopy (µXRF), and Laser Induced Breakdown Spectroscopy (LIBS) data for the forensic comparison of glass samples. Glass fragments from automotive windshields were distributed to the participating labs as blind samples and participants were asked to compare the glass samples (known vs. questioned) and report their findings as they would in casework. For samples that originated from the same source, the overall correct association rate was greater than 92% for each of the three techniques (refractive index, µXRF, and LIBS). For samples that originated from different vehicles, an overall correct exclusion rate of 82%, 96%, and 87% was observed for refractive index, µXRF, and LIBS, respectively. Special attention was given to the reporting language used by practitioners as well as the use of verbal scales and/or databases to assign a significance to the evidence. Wide variations in the reported conclusions exist between different laboratories, demonstrating a need for the standardization of the reporting language used by practitioners. Moreover, few labs used a verbal scale and/or a database to provide a weight to the evidence. It is recommended that forensic practitioners strive to incorporate the use of a verbal scale and/or a background database, if available, to provide a measure of significance to glass forensic evidence (i.e., the strength of an association or exclusion).

Calcium fluoride as a dominating matrix for quantitative analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS): A feasibility study.

Calcium fluoride formed by the reaction between ammonium bifluoride and calcium chloride was investigated as a dominating matrix for quantitative analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Transformation from a solid sample to the calcium fluoride-based matrix permitted quantitative analysis based on calibration standards made from elemental standards. A low abundance stable calcium isotope, i.e. 44Ca+, was monitored as the internal standard for quantitative analysis by LA-ICP-MS. Correlation coefficient factors for multiple elements were obtained with values over 0.999. The results for multiple elements in a certified reference material of soil (NIST SRM 2710a) agreed with the certified values in the range of expanded uncertainty, indicating the present method was valid for quantitation of elements in solid samples.

A comprehensive analysis of sialolith proteins and the clinical implications.

BACKGROUND: Sialolithiasis or salivary gland stones are associated with high clinical morbidity. The advances in the treatment of sialolithiasis has been limited, however, by our understanding of their composition. More specifically, there is little information regarding the formation and composition of the protein matrix, the role of mineralogical deposition, or the contributions of cell epithelium and secretions from the salivary glands. A better understanding of these stone characteristics could pave the way for future non-invasive treatment strategies. METHODS: Twenty-nine high-quality ductal stone samples were analyzed. The preparation included successive washings to avoid contamination from saliva and blood. The sialoliths were macerated in liquid nitrogen and the maceration was subjected to a sequential, four-step, protein extraction. The four fractions were pooled together, and a standardized aliquot was subjected to tandem liquid chromatography mass spectrometry (LCMS). The data output was subjected to a basic descriptive statistical analysis for parametric confirmation and a subsequent G.O.-KEGG data base functional analysis and classification for biological interpretation. RESULTS: The LC-MS output detected 6934 proteins, 824 of which were unique for individual stones. An example of our sialolith protein data is available via ProteomeXchange with the identifier PXD012422. More important, the sialoliths averaged 53% homology with bone-forming proteins that served as a standard comparison, which favorably compared with 62% homology identified among all sialolith sample proteins. The non-homologous protein fraction had a highly variable protein identity. The G.O.-KEGG functional analysis indicated that extracellular exosomes are a primary cellular component in sialolithiasis. Light and electron microscopy also confirmed the presence of exosomal-like features and the presence of intracellular microcrystals. CONCLUSION: Sialolith formation presents similarities with the hyperoxaluria that forms kidney stones, which suggests the possibility of a common origin. Further verification of a common origin could fundamentally change the way in which lithiasis is studied and treated.

Coal Discrimination Analysis Using Tandem Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

The contribution and impact of combined laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and laser-induced breakdown spectroscopy (LIBS) were evaluated for the discrimination analysis of different coal samples. This tandem approach allows simultaneous determination of major and minor elements (C, H, Si, Ca, Al, Mg, etc.) and trace elements (V, Ba, Pb, U, etc.) in the coal. The research focused on coal-classification strategies based on principle component analysis (PCA) combined with K-means clustering, partial least-squares discrimination analysis (PLS-DA), and support vector machine (SVM) for analytical performance. Correlation analyses performed from TOF mass and LIBS emission spectra from the coal samples showed that most major, minor, and trace element emissions had negative correlation with the volatile content. Suitable variables for the classification models were determined from these data. The individual TOF data, LIBS data, and combined data of TOF and LIBS as the inputs for different models were analyzed and compared. In all cases, the results obtained with the combined TOF and LIBS data were found to be superior to those obtained with the individual TOF or LIBS data. The nonlinear SVM model combined with TOF and LIBS data provided the best coal-classification performance, with a classification accuracy of up to 98%.

Elemental Analysis of Asphaltenes Using Simultaneous Laser-Induced Breakdown Spectroscopy (LIBS)-Laser Ablation Inductively Coupled Plasma Optical Emission Spectrometry (LA-ICP-OES).

Laser-induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) were used simultaneously for the elemental analysis of asphaltene samples using minimum sample pretreatment in combination with low laser energy to reduce the amount of removed particles and avoid carbon deposits in the ablation cell. Quantitative analyses of S, Ni, and V were accomplished with LA-ICP-OES using external calibration with the C line as internal standard. The aromatic/paraffinic nature of the asphaltenes was also obtained throughout the H/C ratio using LIBS and partial least square regression model. The results showed very good agreement (±10%) between the concentration obtained by LA-ICP-OES and microwave-assisted acid digestion values.

Elemental imaging of heterogeneous inorganic archaeological samples by means of simultaneous laser induced breakdown spectroscopy and laser ablation inductively coupled plasma mass spectrometry measurements.

Multilayered fragments of murals were used to evaluate the usefulness of two laser-based instrumental methods: laser induced breakdown spectroscopy (LIBS) and laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) for elemental imaging of unique historic samples. Simultaneous LA/LIBS measurements with the use of 266nm Nd:YAG laser were performed on cross-sections of mediaeval Nubian objects with specific blue painting layers including either Egyptian blue (CaCuSi4O10) or lapis lazuli (Na8-10Al6Si6O24S2-4). A combined use of both laser-based methods allowed for clear distinguishing of blue pigments based on visual imaging of a chemical composition of heterogeneous archaeological inorganic samples. The identification of the pigments was confirmed with Raman spectroscopy.

Solid matrix transformation and tracer addition using molten ammonium bifluoride salt as a sample preparation method for laser ablation inductively coupled plasma mass spectrometry.

Solid sampling and analysis methods, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), are challenged by matrix effects and calibration difficulties. Matrix-matched standards for external calibration are seldom available and it is difficult to distribute spikes evenly into a solid matrix as internal standards. While isotopic ratios of the same element can be measured to high precision, matrix-dependent effects in the sampling and analysis process frustrate accurate quantification and elemental ratio determinations. Here we introduce a potentially general solid matrix transformation approach entailing chemical reactions in molten ammonium bifluoride (ABF) salt that enables the introduction of spikes as tracers or internal standards. Proof of principle experiments show that the decomposition of uranium ore in sealed PFA fluoropolymer vials at 230 °C yields, after cooling, new solids suitable for direct solid sampling by LA. When spikes are included in the molten salt reaction, subsequent LA-ICP-MS sampling at several spots indicate that the spikes are evenly distributed, and that U-235 tracer dramatically improves reproducibility in U-238 analysis. Precisions improved from 17% relative standard deviation for U-238 signals to 0.1% for the ratio of sample U-238 to spiked U-235, a factor of over two orders of magnitude. These results introduce the concept of solid matrix transformation (SMT) using ABF, and provide proof of principle for a new method of incorporating internal standards into a solid for LA-ICP-MS. This new approach, SMT-LA-ICP-MS, provides opportunities to improve calibration and quantification in solids based analysis. Looking forward, tracer addition to transformed solids opens up LA-based methods to analytical methodologies such as standard addition, isotope dilution, preparation of matrix-matched solid standards, external calibration, and monitoring instrument drift against external calibration standards.

Analysis of Plant Leaves Using Laser Ablation Inductively Coupled Plasma Optical Emission Spectrometry: Use of Carbon to Compensate for Matrix Effects.

Direct solid sampling by laser ablation into an inductively coupled plasma synchronous vertical dual view optical emission spectroscope (LA-SVDV-ICP-OES) was used for the elemental analysis of nutrient elements Ca, B, Mn, Mg, K, and Zn and essential (non-metallic) elements P and S in plant materials. The samples were mixed with paraffin as a binder, an approach that provides better cohesion of the particles in the pellets in addition to supplying carbon to serve as an internal standard (atomic line C I 193.027 nm) as a way to compensate for matrix effects, and/or variations in the ablation process. Precision was in the range of 1-8% relative standard deviation (RSD) with limit of detection in the range of 0.4-1 mg/kg-1 and 25-640 mg/kg-1 for metallic and non-metallic elements, respectively.

Laser-Ablation Sampling for Accurate Analysis of Sulfur in Edible Salts.

We evaluated the performance of laser ablation analysis techniques such as laser-induced breakdown spectroscopy (LIBS), laser ablation inductively coupled optical emission spectrometry (LA-ICP-OES), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), in comparison with that of ICP-OES using aqueous solutions for the quantification of sulfur (S) in edible salts from different geographical origins. We found that the laser ablation based sampling techniques were not influenced by loss of S, which was observed in ICP-OES with aqueous solutions for a certain salt upon their dissolution in aqueous solutions, originating from the formation of volatile species and precipitates upon their dilution in water. Although detection of S using direct laser sampling with LA-ICP-MS has well-known isobaric and polyatomic interferences, LIBS and LA-ICP-OES showed good accuracy in the detection of S for all salts. LIBS also provided the ability to identify the dominant chemical form in which S is present in salts. Correlation between S and oxygen, observed in LIBS spectra, provided chemical information about the presence of S2- or [Formula: see text], which are associated with the origin and quality of edible salts.

A study on the in vitro percutaneous absorption of silver nanoparticles in combination with aluminum chloride, methyl paraben or di-n-butyl phthalate.

Some reports indicate that the silver released from dermally applied products containing silver nanoparticles (AgNP) (e.g. wound dressings or cosmetics) can penetrate the skin, particularly if damaged. AgNP were also shown to have cytotoxic and genotoxic activity. In the present study percutaneous absorption of AgNP of two different nominal sizes (Ag15nm or Ag45nm by STEM) and surface modification, i.e. citrate or PEG stabilized nanoparticles, in combination with cosmetic ingredients, i.e. aluminum chloride (AlCl3), methyl paraben (MPB), or di-n-butyl phthalate (DBPH) was assessed using in vitro model based on dermatomed pig skin. The inductively coupled plasma mass spectrometry (ICP-MS) measurements after 24h in receptor fluid indicated low, but detectable silver absorption and no statistically significant differences in the penetration between the 4 types of AgNP studied at 47, 470 or 750µg/ml. Similarly, no significant differences were observed for silver penetration when the AgNP were used in combinations with AlCl3 (500µM), MPB (1250µM) or DBPH (35µM). The measured highest amount of Ag that penetrated was 0.45ng/cm2 (0.365-0.974ng/cm2) for PEG stabilized Ag15nm+MPB.

Liquid sampling-atmospheric pressure glow discharge as a secondary excitation source for laser ablation-generated aerosols: parametric dependence and robustness to particle loading.

Liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma is being developed as a secondary vaporization-excitation source for the optical emission analysis of laser ablation (LA)-generated particle populations. The practicalities of this coupling are evaluated by determining the influence of source parameters on the emission response and the plasma's robustness upon LA introduction of easily ionized elements (EIEs). The influence of discharge current (45-70 mA), LA carrier gas flow rate (0.1-0.8 L min(-1)), and electrode separation distance (0.5-3.5 mm) was studied by measuring Cu emission lines after ablation of a brass sample. Best emission responses were observed for high-discharge currents, low He carrier gas flow rates, and relatively small (<1.5 mm) electrode gaps. Plasma robustness and spectroscopic matrix effects were studied by monitoring Mg(II) : Mg(I) intensity ratios and N2-derived plasma rotational temperatures after the ablation of Sr- and Ca-containing pellets. Plasma robustness investigations showed that the plasma is not appreciably affected by the particle loadings, with the microplasma being slightly more ionizing in the case of Ca introduction. In neither case did the concentration of the concomitant element change the robustness values, implying a high level of robustness. Introduction of the LA particles results in slight increases in the rotational temperatures (∼10% relative), with Ca-containing particles having a greater effect than Sr-containing particles. The observed variation of 9% in the plasma rotational temperature is in the same order of magnitude as the short-term reproducibility determined by the proposed LA-LS-APGD system. The determined rotational temperatures ranged from 1047 to 1212 K upon introducing various amounts of Ca and Sr. The relative immunity to LA particle-induced matrix effects is attributed to the relatively long residence times and high power densities (>10 W mm(-3)) of the LS-APGD microplasma.

Laser ablation in analytical chemistry.

In 2002, we wrote an Analytical Chemistry feature article describing the Physics of Laser Ablation in Microchemical Analysis. In line with the theme of the 2002 article, this manuscript discusses current issues in fundamental research, applications based on detecting photons at the ablation site (LIBS and LAMIS) and by collecting particles for excitation in a secondary source (ICP), and directions for the technology.

Carbon isotope separation and molecular formation in laser-induced plasmas by laser ablation molecular isotopic spectrometry.

Laser ablation molecular isotopic spectrometry (LAMIS) recently was reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. This research utilized the LAMIS approach to study C2 molecular formation from laser ablation of carbon isotopic samples in a neon gas environment at 0.1 MPa. The isotopic shift for the Swan system of the C2 Δν = 1 band was chosen for carbon isotope analysis. Temporal and spatial resolved measurements of (12)C2, (12)C(13)C, and (13)C2 show that C2 forms from recombination reactions in the plasma. A theoretical simulation was used to determine the temperature from the molecular bands and to extract the isotopic ratio of (12)C/(13)C derived from (12)C2, (12)C(13)C, and (13)C2. Our data show that the ratio of (12)C/(13)C varies with time after the laser pulse and with distance above the sample. (12)C/(13)C deviates from the nominal ratio (2:1) at early times and closest to the sample surface. These measurements provide understanding of the chemical processes in the laser plasma and analytical improvement using LAMIS.

Analysis and classification of heterogeneous kidney stones using laser-induced breakdown spectroscopy (LIBS).

Kidney stones were analyzed using laser-induced breakdown spectroscopy (LIBS), utilizing a high resolution multi-channel charge-coupled device (CCD) spectrometer and a nanosecond-pulse Nd : YAG laser. The kidney stones were also characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques for comparative analysis. It was found that the ratio of hydrogen (H) to carbon (C) was an important indicator of organic compounds such as uric acid. Advantages of LIBS, especially with regards to amount of sample required and sample preparation as well as the ability to carry out elemental analysis and classification of kidney stones simultaneously, over other analytical techniques such as XRD and XRF are discussed. The common minor elements detected in the kidney stones include P, S, Si, Ti, and Zn. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of broadband LIBS spectra were employed for classifying different types of kidney stones. The results are beneficial in understanding kidney stone formation processes, which can lead to preventive therapeutic strategies and treatment methods for urological patients.

Metal particles produced by laser ablation for ICP-MS measurements.

Pulsed laser ablation (266nm) was used to generate metal particles of Zn and Al alloys using femtosecond (150fs) and nanosecond (4ns) laser pulses with identical fluences of 50Jcm(-2). Characterization of particles and correlation with inductively coupled plasma mass spectrometer (ICP-MS) performance was investigated. Particles produced by nanosecond laser ablation were mainly primary particles with irregular shape and hard agglomerates (without internal voids). Particles produced by femtosecond laser ablation consisted of spherical primary particles and soft agglomerates formed from numerous small particles. Examination of the craters by white light interferometric microscopy showed that there is a rim of material surrounding the craters formed after nanosecond laser ablation. The determination of the crater volume by white light interferometric microscopy, considering the rim of material surrounding ablation craters, revealed that the volume ratio (fs/ns) of the craters on the selected samples was approximately 9 (Zn), 7 (NIST627 alloy) and 5 (NIST1711 alloy) times more ablated mass with femtosecond pulsed ablation compared to nanosecond pulsed ablation. In addition, an increase of Al concentration from 0 to 5% in Zn base alloys caused a large increase in the diameter of the particles, up to 65% while using nanosecond laser pulses. When the ablated particles were carried in argon into an ICP-MS, the Zn and Al signals intensities were greater by factors of approximately 50 and approximately 12 for fs versus ns ablation. Femtosecond pulsed ablation also reduced temporal fluctuations in the (66)Zn transient signal by a factor of 10 compared to nanosecond laser pulses.

Glass particles produced by laser ablation for ICP-MS measurements.

Pulsed laser ablation (266nm) was used to generate glass particles from two sets of standard reference materials using femtosecond (150fs) and nanosecond (4ns) laser pulses with identical fluences of 50Jcm(-2). Scanning electron microscopy (SEM) images of the collected particles revealed that there are more and larger agglomerations of particles produced by nanosecond laser ablation. In contrast to the earlier findings for metal alloy samples, no correlation between the concentration of major elements and the median particle size was found. When the current data on glass were compared with the metal alloy data, there were clear differences in terms of particle size, crater depth, heat affected zone, and ICP-MS response. For example, glass particles were larger than metal alloy particles, the craters in glass were less deep than craters in metal alloys, and damage to the sample was less pronounced in glass compared to metal alloy samples. The femtosecond laser generated more intense ICP-MS signals compared to nanosecond laser ablation for both types of samples, although glass sample behavior was more similar between ns- and fs-laser ablation than for metal alloys.

Laser ablation in analytical chemistry-a review.

Laser ablation is becoming a dominant technology for direct solid sampling in analytical chemistry. Laser ablation refers to the process in which an intense burst of energy delivered by a short laser pulse is used to sample (remove a portion of) a material. The advantages of laser ablation chemical analysis include direct characterization of solids, no chemical procedures for dissolution, reduced risk of contamination or sample loss, analysis of very small samples not separable for solution analysis, and determination of spatial distributions of elemental composition. This review describes recent research to understand and utilize laser ablation for direct solid sampling, with emphasis on sample introduction to an inductively coupled plasma (ICP). Current research related to contemporary experimental systems, calibration and optimization, and fractionation is discussed, with a summary of applications in several areas.