Continuum Source Atomic Absorption Spectrometer Research Articles

Observation, identification and correction of structured molecular background by means of continuum source AAS—determination of selenium and arsenic in human urine

A high-resolution continuum source atomic absorption spectrometer based on a xenon short-arc lamp, a transversely heated graphite furnace module with longitudinal Zeeman option, a double echelle monochromator and a linear array CCD detector was developed. The system allows the investigation and clarification of background correction problems in conventional AAS caused by atomic and molecular interferences during the atomization of samples with complex matrices. As an example, the determination of selenium at 196.026 nm and arsenic at 193.696 nm in undiluted human urine samples is demonstrated. The two species NO and PO responsible for the spectral interferences were identified and successfully corrected for by means of a mathematical correction algorithm. From measurements of human urine reference materials (Lyphochek Urine Metals Control Level 1 No. 69011 and No. 69041; Bio-Rad, Anaheim, CA, USA), it was found that the analytical performance of this method is comparable to that of line source AA systems. For Se the determined element concentrations of 59 ± 3 and 79 ± 4 µg l−1, respectively, correspond well with the certified values of 61 ± 12 and 73 ± 14 µg l−1, and for the LOD and the reproducibility values of 38 pg in the matrix and 3.5% were obtained, respectively. In the case of As, only NaCl and PO produced molecular structures and were corrected for. Again the measured concentration of 168 ± 6 µg l−1 lies in the acceptable range of 154 ± 31 µg l−1 given for the reference sample (Lyphochek Urine Metals Control Level 2 No. 69012; Bio-Rad) and the LOD was found to be 25 pg in presence of the undiluted human urine matrix.

Measurements on the Zeeman-splitting of analytical lines by means of a continuum source graphite furnace atomic absorption spectrometer with a linear charge coupled device array

A spectrometer for time-resolved high-resolution spectroscopic measurements of line splittings in inverse Zeeman effect corrected atomic absorption spectrometry is presented. The system consists of a continuum source, a longitudinal Zeeman-THGA module, a high-resolution double echelle monochromator, and a linear CCD array. Splitting patterns of atomic lines in a magnetic field have been determined and are compared with theory. The continuum source atomic absorption spectrometer can be used for the investigation of spectra interferences in Zeeman corrected AA spectrometry. As an example, the background overcompensation at the cadmium 228.8 nm line in the presence of a Mg(NO 3) 2 +NH 4H 2PO 4 mixture is examined.

Continuum-source graphite-furnace atomic absorption spectrometry with photodiode array detection

A recently developed graphite-furnace continuum-source atomic absorption spectrometer is described and evaluated. For single-element determinations, the system provides detection limits equal to or better than those reported for commercial hollow cathode lamp instruments employing Zeeman background correction at wavelengths as low as 213 nm (Zn). Furthermore, using a fixed atomization cycle and constant detector parameters, simultaneous multielement determinations can be performed for metals having absorption lines falling within a 10 nm spectral window. Detection limits in this case are within a factor of 2 of those reported for single-element determinations. For most metals, detection limits are at least a factor of 2 times better than those previously reported for continuum-source atomic absorption spectrometers. The limiting source of noise for the system is detector readout noise at wavelengths below 240 nm, and signal shot noise at wavelengths above 250 nm.

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%.

Continuum source atomic absorption spectrometry in an air-acetylene flame with improved detection limits

A continuum source atomic absorption spectrometer with flame atomization and photodiode array detection is described. High-resolution atomic absorption spectra spanning a spectral window of 9 nm are obtained using a 5-s integration period. As many as 11 elements can be detected in a single spectrum. The improved light-gathering power of the system results in detection limits similar to those observed with conventional line source systems at wavelengths as low as 223 nm. For example, detection limits of 2 ng/mL are observed for Cd (228 nm), Mn (279 nm), and Ag (328 nm)

Signal to noise ratios for continuum source atomic absorption spectrometry using a linear photodiode array to monitor sub-nanometre wavelength intervals

The development and initial evaluation of a pulsed continuum source atomic absorption spectrometer using a linear photodiode array and weak pulsing of the source is discussed. A 256-pixel array, mounted in a high-dispersion monochromator, was used to monitor a narrow interval (0.4–0.8 nm) around the wavelength of interest, resulting in rapid (<10 ms) readout times. Experimental results confirmed the readout noise limitation of the array. The minimisation of readout lag, quantisation noise and relative analogue-to-digital (A/D) converter noise resulted in a readout noise limit that was twice the manufacturer's specifications. Pixel averaging, in conjunction with a large entrance slit width, reduced the absorbance noise. With flame atomisation, use of a linear photodiode array resulted in a factor of 3.9–6.2 improvement in the signal to noise ratio of five elements (zinc, cadmium, nickel, cobalt and iron) in comparison with photomultiplier tube detection. Lamp pulsing resulted in a 50% increase in integrated intensity and was limited by the power rating of the power supply. The combined effect of a pulsed source and photodiode array detection improved the signal to noise ratios by factors ranging from 5.8 to 8.5.

Continuum source atomic absorption spectrometry in a graphite furnace with photodiode array detection.

A graphite furnace continuum source atomic absorption spectrometer using a photodiode array detector is described that provides high-resolution wavelength versus absorbance spectra over a 2.5-nm range for a single atomization step. The multiwavelength detection power allows the simultaneous determination of several elements, reduces problems caused by spectral interferences, and automatically corrects for nonzero background absorbance. Each spectrum is acquired in 0.33 s, and several successive spectra can be obtained during a single run. Three-dimensional wavelength-absorbance-furnace temperature spectra can be obtained by using ramped heating steps to provide a rough separation of elements in a mixture. Limits of detection calculated for 19 elements range from 0.1 pg for magnesium to 700 pg for arsenic. The sampling precision was found to be better than 10% relative standard deviation in all cases, with the precision for a single atomization being greatly increased when multiple absorption lines for a single element are observed in the spectrum. The error found for the measurement of the iron concentration in an NBS standard bronze was 8.5%, with the calculated concentration agreeing with the certified concentration within 95% confidence limits.

High-resolution continuum source atomic absorption spectrometry in an air-acetylene flame with photodiode array detection

A high-resolution continuum source atomic absorption spectrometer using a photodiode array detector and flame atomisation is described which provides wavelength versus absorbance spectra over a 2.5-nm spectral range. The multi-wavelength detection power allows the simultaneous determination of several elements, reduces problems caused by spectral interferences and automatically corrects for non-zero background absorbance. Each spectrum is acquired in 33 ms and many successive spectra can be averaged to improve the signal to noise ratios. Limits of detection calculated for nine elements range from 0.03 mg l–1 for magnesium to 10 mg l–1 for nickel.

High-Resolution continuum-source atomic absorption spectrometry in an inductively coupled plasma with photodiode array detection

Atomic absorption spectrometry (AAS) is a well established technique using flames and graphite furnaces. An inductively coupled plasma (ICP), however, is an attractive alternative atom/ion reservoir. A high-resolution continuum-source atomic absorption spectrometer with a photodiode array detector and an ICP as the atomization/ionization reservoir is described. Multi-wavelength capability permits the simultaneous determination of several elements by their atomic and/or ionic transitions. Each acquired spectrum is averaged for 10 s to improve the signal-to-noise ratios. Detection limits are calculated for 14 elements and compared with literature values.

Time-Resolved Electrothermal Atomic Absorption Spectra

A wavelength-modulated continuum source atomic absorption spectrometer is used to obtain time-resolved atomic absorption spectra (absorbance vs wavelength) using an electrothermal atomizer. Absorbance spectra are acquired at a rate of 56 Hz during atomization. The operator may choose any portion of the atomization time period to be examined as well as the number of absorbance profiles to be averaged. This time-resolved spectral information facilitates the positive identification of spectral interferences as well as providing for detailed inspection of both analyte and background absorption signals. Several interferences are examined.