James D. Winefordner

Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry, LIBS, a future super star

The “super stars” of analytical atomic spectrometry are electrothermal atomization-atomic absorption spectrometry (ETA-AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). Many other atomic spectrometric methods have been used to determine levels of elements present in solid, liquid and gaseous samples, but in most cases these other methods are inferior to the big three super star methods. The other atomic methods include glow discharge emission, absorption and mass spectrometric methods, laser excited fluorescence emission and ionization methods, and flame and microwave plasma emission and mass spectrometric methods. These “lesser” methods will be compared to the “super star” methods based on a number of figures of merit, including detection power, selectivity, multi-element capability, cost, applications, and “age” of the methods. The “age” of the method will be determined by a modification of the well-known Laitinen “Seven Ages of an Analytical Method” (H.A. Laitinen, Anal. Chem., 1973, 45, 2305). Calculations will show that certain methods are capable of single atom detection, including several atomic absorption methods, as well as laser atomic ionization and fluorescence methods. The comparison of methods will indicate why the “super stars” of atomic spectrometric methods will continue to retain their status and what must be done for the lesser atomic methods to approach “super star” status. Certainly most of the lesser atomic spectrometric methods will have a limited place in the analytical arena. Because of the wide current interest and research activity, special emphasis will be placed on the technique of laser induced breakdown spectrometry (LIBS). Its current status and future developments will therefore be reviewed.

Raman spectroscopy in bioanalysis.

Recent advances in instrument design have allowed researchers to use smaller, more efficient components in designing Raman spectrometers. Advances in instrumentation have increased the performance of Raman instruments and increased their usage in bioanalysis. This paper reviews recent improvements in instrument design and discusses several applications of Raman spectroscopy to diagnosis in biology, chemistry and medicine.

Laser induced breakdown spectroscopy as a tool for discrimination of glass for forensic applications

Materials analysis and characterization can provide important information as evidence in legal proceedings. The potential of laser induced breakdown spectroscopy (LIBS) for the discrimination of glass fragments for forensic applications is presented here. The proposed method is based on the fact that glass materials can be characterized by their unique spectral fingerprint. Taking advantage of the multielement detection capability and minimal to no sample preparation of LIBS, we compared glass spectra from car windows using linear and rank correlation methods. Linear correlation combined with the use of a spectral mask, which eliminates some high-intensity emission lines from the major elements present in glass, provides effective identification and discrimination at a 95% confidence level.

Surface Enhanced Raman Spectrometry on Silver Hydrosols Studied by Flow Injection Analysis

Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm−1 with an Ar+ laser at 514.5 nm.

Colloid filtration: A novel substrate preparation method for surface-enhanced Raman spectroscopy

Abstract A new method for preparing a monodisperse layer of metal colloid particles is presented. Metal colloid particles are filtered onto the surface of an aluminum oxide capillary pore surface capture membrane using both vacuum and syringe filtration devices. Scanning electron microscope (SEM) images reveal that the metal particles can be deposited with very little aggregation. Electronic absorption spectra show that the concentration of particles on the surface can be controlled by varying the silver colloid solution concentration. The linear dynamic range of absorbance of particles on the surface is demonstrated to be at least one order of magnitude. Surface-enhanced Raman (SER) activity is observed for the compound 9-aminoacridine (AA) at 514.5 nm using a filtered silver colloid solution. The SER activity of AA is observed to be related to the degree of colloid aggregation on the surface. Surfaces with no aggregation have no SER activity at this wavelength. The syringe colloid filtration technique is a fast, inexpensive method for producing surfaces with a highly controlled metal particle geometry, extremely useful for comparisons between theoretical and experimental results. These surfaces are also ideal for theoretical substrate design.

Determination of F, Cl, and Br in Solid Organic Compounds by Laser-Induced Plasma Spectroscopy

The feasibility of using laser-induced plasma spectroscopy (LIPS) as a rapid and simple method to analyze fluorine, chlorine, and bromine in solid organic compounds was investigated. A Nd:YAG laser at 1064 nm with pulse energy of 100 mJ was used to produce the plasma. This method presents many advantages for the determination of halogens in organic compounds, including very simple sample preparation and near-real-time analysis. Solid organic compounds were measured in air and helium atmospheres. Carbon in organic compounds was chosen as the internal standard for the measurement of F, Cl, and Br. Linear responses for these elements were obtained for both atmospheres. However, the sensitivity was much higher and the background noise was much lower in the helium atmosphere.

The use of rigid ethanolic solutions for the phosphorimetric investigation of organic compounds of pharmacological interest

Abstract Phosphorescence excitation and emission spectral peaks, lifetimes, working curves and limits of detection of 22 organic compounds of pharmacological importance in rigid (77°K) ethanolic solution are given. Ethanol can be easily prepared in a high degree of purity, and most drugs are much more soluble in ethanol than in most solvents previously used for phosphorimetric studies. The possible application of phosphorimetry to the trace analysis of drugs in biological fluids is discussed.

Measurement of the free atom fraction of 22 elements in an acetylene-air flame

Abstract The ratio of the free atom concentration and the total concentration of an element in a fuel-rich premixed acetylene-air flame is measured experimentally for 22 elements. The atom concentration is derived from the integrated absorption measured with a continuous source; the total concentration of an element is calculated from the flow rates of solution and flame gases. Because copper is found to be completely atomized, this element is proposed as a standard of reference for the acetylene-air flame.

Species Differentiation of a Diverse Suite of Bacillus Spores by Mass Spectrometry-Based Protein Profiling

ABSTRACT In this study, we demonstrate the versatility of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOFMS) protein profiling for the species differentiation of a diverse suite of Bacillus spores. MALDI-TOFMS protein profiles of 11 different strains of Bacillus spores, encompassing nine different species, were evaluated. Bacillus species selected for MALDI-TOFMS analysis represented the spore-forming bacterial diversity of typical class 100K clean room spacecraft assembly facilities. A one-step sample treatment and MALDI-TOFMS preparation were used to minimize the sample preparation time. A library of MALDI-TOFMS spectra was created from these nine Bacillus species, the most diverse protein profiling study of the genus reported to date. Linear correlation analysis was used to successfully differentiate the MALDI-TOFMS protein profiles from all strains evaluated in this study. The MALDI-TOFMS protein profiles were compared with 16S rDNA sequences for their bacterial systematics and molecular phylogenetic affiliations. The MALDI-TOFMS profiles were found to be complementary to the 16S rDNA analysis. Proteomic studies of Bacillus subtilis 168 were pursued to identify proteins represented by the biomarker peaks in the MALDI-TOFMS spectrum. Four small, acid-soluble proteins (A, B, C, and D), one DNA binding protein, hypothetical protein ymf J, and four proteins associated with the spore coat and spore coat formation (coat JB, coat F, coat T, and spoIVA) were identified. The ability to visualize higher-molecular-mass coat proteins (10 to 25 kDa) as well as smaller proteins (<10 kDa) with MALDI-TOFMS profiling is critical for the complete and effective species differentiation of the Bacillus genus.

A New, simple atom reservoir for atomic fluorescence spectrometry

Abstract The disadvantages of flames as atomizers are summarized, and a new, simple and efficient means of atomization of samples is proposed. The solution on a platinum loop is vaporized by electrical heating into an argon stream. Limits of detection were 10-14 g for cadmium, 10-8 g for mercury, and 10-7 g for gallium. Linear calibration graphs were obtained over 3 or 4 orders of magnitude. Of the various sheathing gases studied, argon was most efficient. The method is relatively insensitive to matrix effects.