NANOHUNTER
NANOHUNTER is the world's first benchtop total reflection X-ray fluorescence (TXRF) spectrometer that provides both trace-level elemental analysis and evaluation of the physical nature of the sample. Using a patented switchable wavelength and automated variable X-ray incidence angle excitation design, this instrument analyzes the full range of elements, from Al to U, in solids, liquids, and powders. It also provides chemical information as a function of analysis depth.With sensitivity on par with ICP-OES, the instrument provides part-per-billion (PPB) level detection limits for liquids. Direct measurement of makes this spectrometer suitable for replacing or supplementing traditional atomic spectroscopy methods.
Total reflection X-ray fluorescence is a specialized technique within the genre of X-ray fluorescence (XRF) spectrometry. In this method, an electron can be ejected from its atomic orbital by the absorption of a electromagnetic wave (photon) of sufficient energy. The energy of the photon (hν) must be greater than the energy with which the electron is bound to the nucleus of the atom. When an inner orbital electron is ejected from an atom, an electron from a higher energy level orbital will transfer into the vacant lower energy orbital. During this transition, a photon may be emitted from the atom. This fluorescent radiation is called the characteristic X-ray of the element. The energy of the emitted photon will be equal to the difference in energies between the two orbitals occupied by the electron making the transition. Due to the fact that the energy difference between two specific orbital shells for a given element is always the same (i.e., characteristic of a particular element), the photon emitted when an electron moves between these two levels will always have the same energy. Therefore, by determining the energy (wavelength) of the X-ray photons emitted by a particular element, it is possible to determine the identity of that element.For a particular energy (wavelength) of fluorescent radiation emitted by an element, the number of photons per unit time (generally referred to as peak intensity or count rate) is related to the amount of that analyte in the sample. The counting rates for all detectable elements within a sample are usually calculated by counting, for a set time, the number of photons that are detected for the various analytes characteristic X-ray energy lines. Therefore, by determining the energy of the X-ray peaks in a sample's spectrum, and by calculating the count rate of the various elemental peaks, it is possible to qualitatively establish the elemental composition of the sample and to quantitatively measure the concentration of these elements.
TXRF instruments are equipped with a high resolution energy dispersive type detection system, typically associated with energy dispersive spectroscopy (aka, EDS for electron microscopy) and energy dispersive X-ray fluorescence spectrometry (EDXRF). A solid state detector system converts each incoming X-ray into a sequence (train) of voltage signals of proportional amplitude. This is achieved through a three stage process.First, an X-ray irradiating the detector is converted into a charge by the ionization of atoms in a silicon detector under high bias voltage. Second, the resulting charge is converted into the voltage signal by a closely coupled field effect transistor (FET) pre-amplifier. The output from the preamplifier is a voltage "staircase ramp", where each X-ray appears as a voltage step. Each voltage step is proportional to the energy of a detected X-ray photon. Finally, these voltage steps are decomposed into a "pulse train" by a pulse processor. A multi-channel analyzer then sorts the pulses by amplitude (energy) to afford an output spectrum.
Total reflection X-ray fluorescence analysis (TXRF) is a unique special case of the energy-dispersive X-ray fluorescence (EDXRF) elemental analysis technique that uses grazing incidence X-ray excitation to dramatically enhance signal-to-noise (S/N) for high sensitivity trace determinations. With TXRF, background noise is virtually eliminated.
If a low divergent and nearly parallel X-ray beam impinges on the smooth surface of a flat reflector, with an angle smaller than the critical angle (φc), total reflection occurs. In this case, the X-ray beam only slightly penetrates into the reflector and most of the primary beam is reflected (total reflection). This leads to a dramatic reduction in spectral background due to scattering on the reflector. Together with the more efficient excitation due to the fact that the reflected beam contributes to excitation, leading to a doubling in the intensity of the fluorescence signal, the NANOHUNTER benchtop TXRF has trace-level detection limits for most elements.
NANOHUNTER dramatically improves on the conventional TXRF approach by combining patented dual wavelength excitation, together with fully automated optics, in a design that allows the X-ray incidence angle to be varied and/or optimized. The analytical benefits of this innovative design represent a substantial leap forward in atomic spectroscopy. Of special significance is that the system can address analysis for the full range of samples, including bulk solids, liquids, powders, and thin films.
NANOHUNTER's ability to automatically measure samples with different angles (φ) of incident X-ray excitation allows not only the determination of elemental concentrations but also how the elements are distributed relative to some substrate or bulk modulus. For the materials scientist involved in nanotechnology research, this ability allows the physical nature of surface layers to be characterized as particles on a surface, a homogenous thin film, or as something in between.
NANOHUNTER bests conventional XRF by providing high sensitivity across the periodic table, exceeding the performance of any general purpose laboratory XRF instrument ever offered commercially—and in a compact design that needs no cooling, uses no consumables, and runs on standard wall power.
Sensitivity of the NANOHUNTER is comparable to ICP-OES instruments, but with numerous advantages. It also offers detection limits that are, for many elements, more than an order-of-magnitude lower than achievable with conventional wavelength dispersive X-ray fluorescence (WDXRF) spectroscopy. Relative to ICPOES, the advantage of TXRF is in the minimal level of sample preparation required. Liquid samples, like contaminated wastewater, for example, require only a few simple steps that do not require a wet laboratory.
The NANOHUNTER benchtop TXRF spectrometer effortlessly performs trace element analysis of liquids without the labor and web lab requirements associated with the conventional ICP-OES approach. Analysis is just six simple steps: 1) measure out a sample, 2) add an internal standard, 3) mix, 4) extract an aliquot, 5) dispense onto a slide, and 6) dry and analyze.
NANOHUNTER is the perfect tool for trace element analysis of organic materials. An example of this application was recently published: Koichiro Kodama, et al. ChemBioChem, 8, 232-238 (2007): "The recovered Ras protein (82 mg, 3 mL) was lyophilized and dissolved in nitric acid (2 M, 5 mL). A known amount of cobalt ion (10 ppm) was mixed as an internal standard. This sample was spotted on a filter (shown, top image), dried under a heat lamp, and subjected to XRF analysis (shown, bottom image) using Mo Kα radiation (17.5 keV). The amount of palladium and copper ions was estimated by measuring peak areas against the Co Kα peak at 6.93 keV, assuming that the ratio of the Pd Lα, Co Kα, and Cu Kα peak areas are 1:27.5:39 when they are at the same concentration. The lower detection limit is 0.004 ppm (60 nM; copper)."
The ability of the NANOHUNTER to accept relative large samples makes the instrument ideal for the direct, non-destructive measurement of inorganic materials. From glass and silicon wafers to soils and pharmaceuticals, NANOHUNTER sensitivity and flexibility are unequaled.
NANOHUNTER has many other uses where other analytical methods—and their associated sample preparation requirements—are cumbersome, time consuming, or prone to error.
By employing a unique switchable wavelength and automated variable X-ray incidence angle excitation design, this instrument analyzes the full range of elements, from Al to U, without compromising sensitivity for lighter elements. It can also provide structural information about a surface profile by varying the angle of the beam incidence, allowing homogeneous films to be distinguished from particles. Designed for the analysis of contamination on, or diffusion into, advanced materials and thin films, the system can also be used for quantitative and qualitative trace elemental analysis of solids, liquids, and powders.
The Rigaku NANOHUNTER was specifically designed to offer comprehensive trace element and materials characterization analysis capabilities to a broader range of research disciplines, and in more diverse analytical settings, than was possible with previous technology. Whether for geologists, chemists, biochemists, biologists, materials scientists and engineers, non-destructive trace element analysis is attainable, with minimal to no sample preparation, for applications that span from metalloprotein research to environmental assessment and semiconductor wafer metrology.
