Analysis

While perhaps the most extensive such timeline to date, it is surely not complete. Sources for further information have been provided.

Figure 1: Sir Lsaac Newton.
1666: Isaac Newton (1642–1727) (Figure 1) shows that the white light from the sun could be dispersed into a continuous series of colors. He coined the word "spectrum." His apparatus, an aperture to define a light beam, a lens, a prism, and a screen, was the first spectroscope. He suggested that light was composed of minute corpuscles (particles) moving at high speed.

1678: Dutch mathematician and physicist Christian Huygens (1629–1695) proposes the wave theory of light.

1729: French mathematician and scientist Pierre Bougeur (1698–1758) notes that the amount of light passing through a liquid sample decreases with increasing sample thickness.

The term spectral engine is not new and is normally intended to indicate the integration of optics and electronics to form a single measurement package. In the system described in this column, the term is extended to include the close-coupling of the measurement system to the sample via nonimaging optics.

Emil W. Ciurczak

The last column closed with an in and out calculation challenge. To reiterate: We consider an EI source sensitivity specified as 1 × 10–7 C/µg of methyl stearate introduced into the source (this is a reasonable number for instruments of moderate performance). Detail-oriented readers immediately ask about the time associated with that sample introduction. Is it 1 s? 10 s? 100 s?

Over the past 30 years, X-ray fluorescence (XRF) has become the elemental technique of choice for the determination of parts-per-million to percentage concentration levels in many solid materials including metals, ores, rocks, glasses, powders, plastics, ceramics, and foodstuffs (1). The principles of XRF spectrometry are well-documented in the literature (2). A sample is irradiated with a beam of high-energy X-rays. As the excited electrons in the sample fall back to a ground state, they emit X-rays that are characteristic of those elements present in the sample. The individual X-ray wavelengths are then separated and measured via a system of crystals, optics, and detectors. Elemental concentrations in unknown samples are quantified by comparing the X-ray intensities against known calibration standards.

Recently, there has been great interest in a variety of novel ultrafast coherent anti-Stokes Raman scattering (CARS) methods that utilize broadband lasers (1–3), often involving narrowband probe pulses (4–6), chirped pulses (7,8), or fiber-broadened pulses (9–11) to obtain broadband vibrational information from molecules. With the variation of single-pulse, broadband, multiplex CARS microscopy discussed here, broad bandwidth spectra are acquired rapidly during the microscope scan and the spatially variant compositions of samples composed of multiple components are readily determined.

The 33rd Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) will be held at Disney's Contemporary Resort, Lake Buena Vista, Florida, from September 24 to September 28, 2006. Taking advantage of the unique entertainment opportunities available at the Walt Disney World Resort, the FACSS will hold its Wednesday evening event at the Adventurers Club at Walt Disney World's Pleasure Island. In addition, conferees can purchase specially priced Disney Meeting and Convention tickets for the theme parks when they register.

Plenary Lectures

Two technical papers recognized as significant early contributions in the discussion of the limitations of analytical accuracy and uncertainty include those by Horwitz of the U.S. FDA (1,2). For this next series of articles, we will be discussing both the topic and the approaches to this topic taken by the classic papers just referenced. The determination and understanding of analytical error is often approached using interlaboratory collaborative studies. We have previously delved into that subject in "Chemometrics in Spectroscopy" with a multipart column series (3–8).

Howard Mark

David W. Ball
There is a form of spectroscopy known as photoacoustic spectroscopy. As with many forms of spectroscopy, its name is descriptive. The prefix "photo" makes sense for a form of spectroscopy, but "acoustic"? Doesn't that mean "relating to sound"? Is there really a form of spectroscopy that uses sound?

Yes, there is.

Figure 1: Number of articles published using the key phrase "photoacoustic spectroscopy" since the early 1970s.

In spectrochemical analysis, we wish to convert measured spectral line intensities to concentration of the elements present in the sample. This is the process known as calibration. For a linear calibration, this function takes the general form y = mx + b:

C i = A 0 + A 1 I i [1]

where C i is the concentration of element i and I i is the measured spectral line intensity. (Note: This measured intensity may be either total or net intensity, that is, peak minus background.)

Here we wish to address one important aspect of this calibration process, the correction of interelement effects. In general, there are two types of interelement interferences, spectral line overlaps and so-called matrix effects.

Line Overlap Correction

The 55th Annual Denver X-Ray Conference on Applications of X-Ray Analysis, sponsored by the International Centre for Diffraction Data (ICDD), will be held from August 7 to August 11, 2006, at the Denver Marriott Tech Center Hotel in Denver, Colorado. In addition to the conference events, the beautiful Mile High City offers something for everyone: sporting events; great dining; a collection of museums, galleries, and shopping; and more.

The Denver X-Ray Conference (DXC) is the world's leading forum for scientists in the field of X-ray materials analysis. The conference provides sessions on training, education, and applications that will appeal to both newcomers in the field and those with many years of experience. Another exciting part of the DXC is the presence of leading manufacturers of X-ray equipment, who will be exhibiting their latest devices and answering technical questions.