Clifton P. Calloway

Simultaneous determination of the Lanthanides by tungsten coil atomic emission spectrometry

The fourteen Lanthanides are determined by tungsten coil atomic emission spectrometry. Twenty-five microlitre sample aliquots are placed directly on the coil. A simple constant current power source carefully dries the sample prior to analysis. During this dry step, the voltage is monitored to prevent over heating. This allows for shorter atomization programs, while improving sensitivity and coil lifetime. During the 5 s high temperature atomization step, the emission signals for as many as seven Lanthanides are determined simultaneously in the same 55 nm spectral window. The analytical figures of merit for all 14 natural Lanthanides are reported and compared with nitrous oxide flame atomic emission spectrometry. Tungsten coil atomic emission concentration detection limits are in the range 0.8 (Yb) to 600 (Pr) µg l−1, and are lower than those for the flame in most cases. The absolute detection limits are near or below the ng level: significantly lower than the flame detection limits due to the smaller sample volume required. A three-fold improvement in detection limit may be realized by combining the signals for multiple emission lines for a single element. The method is applied to the determination of seven Lanthanides in a soil sample acquired from the National Institute of Standards and Technology. After a simple acid extraction, the measured values agree with the reported values with 95% confidence in all cases but one, Yb. Finally, a conditioning program for new tungsten coils enhances reproducibility and maximizes the emission signal.

Standard Dilution Analysis

Standard dilution analysis (SDA) is a novel calibration method that may be applied to most instrumental techniques that will accept liquid samples and are capable of monitoring two wavelengths simultaneously. It combines the traditional methods of standard additions and internal standards. Therefore, it simultaneously corrects for matrix effects and for fluctuations due to changes in sample size, orientation, or instrumental parameters. SDA requires only 200 s per sample with inductively coupled plasma optical emission spectrometry (ICP OES). Neither the preparation of a series of standard solutions nor the construction of a universal calibration graph is required. The analysis is performed by combining two solutions in a single container: the first containing 50% sample and 50% standard mixture; the second containing 50% sample and 50% solvent. Data are collected in real time as the first solution is diluted by the second one. The results are used to prepare a plot of the analyte-to-internal standard signal ratio on the y-axis versus the inverse of the internal standard concentration on the x-axis. The analyte concentration in the sample is determined from the ratio of the slope and intercept of that plot. The method has been applied to the determination of FD&C dye Blue No. 1 in mouthwash by molecular absorption spectrometry and to the determination of eight metals in mouthwash, wine, cola, nitric acid, and water by ICP OES. Both the accuracy and precision for SDA are better than those observed for the external calibration, standard additions, and internal standard methods using ICP OES.

Double tungsten coil atomic emission spectrometry: signal enhancement and a new gas phase temperature probe

A new double atomizer arrangement for tungsten coil atomic emission spectrometry is described. Two small constant current power supplies, a Czerny–Turner spectrograph, and a charge coupled device (CCD) detector are used to determine refractory elements in water samples. The analytical figures of merit for Ba, Sr, Ti, and V are reported and compared with the single coil arrangement. The use of two atomizers provides more energy for the atomization and excitation of the analytes and consequently improves sensitivity. Addition of a second coil improves limits of detection for refractory elements by a factor of 40 (V) and 5 (Ti). Using 25 µl sample volumes, the limit of detection for V is 10 µg l−1 at the 437.9 nm emission line, and 400 µg l−1 for the 399.9 nm Ti emission line. Vanadium is determined in a polluted water certified reference material, and the results agree with the certified value (250 mg l−1) at the 95% confidence level. For Ba and Sr, which emit strongly with a single coil, the double coil detection limits are improved by less than a factor of two: 0.007 µg l−1Ba and 0.4 µg l−1Sr. Emission signals for Ag, Cu and Sn are observed for the fist time with a tungsten coil atomic emission spectrometry (WCAES) system. A new method to determine the gas phase temperature by atomic emission spectrometry is also presented. Emission intensities for Dy (418.7 and 421.1 nm) and Eu (462.7 and 466.2 nm) are used to calculate Boltzmann temperatures for both the single and double coil arrangements. Temperature values calculated by this method agree with the traditional optical two-line absorption method using Sn (284.0 and 286.3 nm).

Direct Determination of Cadmium in Urine by Electrothermal Vaporizer–Inductively Coupled Plasma Analysis Using a Tungsten Coil Vaporizer

Since their introduction, tungsten coils (W-coils) have been used as electrothermal atomizers in atomic absorption spectrometry, atomic emission spectrometry (AES), and atomic fluorescence spectrometry, and as electrothermal vaporizers (ETV) for the inductively coupled plasma (ICP).1 The power requirements to reach vaporization temperatures in the 3300 K range are minimal (150 W), and the devices do not require water cooling. The W-coil is therefore an ideal vaporizer for portable spectrometers, and it is easily attached to standard ICP instrumentation. An array of clinical, biological, and environmental sample types has been analyzed using W-coil devices.2 Complicated sample matrices usually require special calibration techniques such as the standard addition method or the use of matrix-matched standard solutions. While matrix modifiers have been used to some extent with W-coil devices, the mechanisms of action of the modifiers are not well understood, and the technique is not as successful as it is with the graphite furnace.3 This work reports the analysis of urine samples after simple aqueous dilution by W-coil ETV-ICP-AES. The combination of the internal standard and standard addition methods provides accurate and precise data without the need for matrix modifiers or acid digestion.

Determination of Silicone in Breast Tissue by Graphite Furnace Continuum Source Atomic Absorption Spectrometry

A method has been developed for the determination of silicone in breast tissue samples using a graphite furnace continuum source atomic absorption spectrometer. Silicone was measured as Si present in a heptane extract of the dried tissue samples. Thirty tissue samples were examined from 16 women having silicone gel-filled breast implants. Concentrations of Si in the dried tissue samples ranged from below the method detection limit of 3 ppm, to 6%.

Evaluation of a continuum source tungsten coil atomic absorption spectrometer: a study of Zn behavior

The performance of a tungsten coil atomizer atomic absorption spectrometer with a D2 lamp continuum source, a Czerny-Turner monochromator, and a charge coupled device detector was evaluated for the determination of Zn. The main attractive characteristics of the instrument are its simplicity and the relative low cost of the atomizer. In spite of a poor limit of detection (40 µg L-1, 3 blank standard deviation/slope), Zn was accurately determined in one water and one urine certified reference standards. The recovery in water was 106% and in urine the obtained result is in the acceptable certified range.

Atomic absorption spectrometry with a flame emission source

Abstract An atomic absorption spectrometer with flame atomization and a flame emission light source is described. The light source is prepared by aspirating a solution containing a high concentration of analyte into the emission flame. Two different source flames (air/acetylene and nitrous oxide/acetylene) have been evaluated, with the N2O flame providing better signal to noise ratios (S/N) in most cases. Source S/N values as high as 5900 (Cr) have been observed. Experimental parameters have been optimized for nine test elements to give limits of detection obtained with this system that are in some cases as good as those obtained with the traditional hollow cathode lamp source; for example, Cu (4 ng ml ), Mn (3 ng ml ) and Ni (5 ng ml ). Linear dynamic ranges typically span 2–3 orders of magnitude. This system offers an inexpensive emission source with the ability to quickly change the setup to accommodate different analytes.