Simultaneous Multi-element Analysis Research Articles

Characteristics of Photodiode Arrays for Spectrochemical Measurements

A rather large number of spectrochemical studies and analyses can be greatly facilitated by the simultaneous measurement of spectral information over a range of wavelengths. Of particular importance and interest to analytical spectroscopists is the development of simultaneous multielement analysis systems. The development and implementation of such analyses have been hampered by a lack of convenient and versatile multichannel spectrochemical measurement systems. New detector subsystems based on modern electronic image sensors are helping to overcome this obstacle. One type of electronic image sensor is the self-scanning linear array of silicon photodiodes. These arrays are available with densities of 1024 photodiodes per in and in lengths of up to 1 in. They are packaged in conventional dual-in-line integrated circuit packages complete with the necessary scanning circuitry. These sensors have simple and inexpensive control and measurement circuitry, and superior blooming and lag performance when compared to most other electronic image sensors. In addition, the signal integrating capability of the arrays is a flexible and powerful asset for many spectrochemical measurements. These and other operational characteristics of photodiode arrays are emphasized in this study. In addition, the measurement capability of a computer coupled photodiode array spectrometer based on a 1024 element array which is capable of simultaneously measuring over 50 nm (500 Å) of continuous spectral information anywhere from 200 to 1000 nm is illustrated.

A systematic and rigorous statistical approach for establishing the accuracy of analytical results and its application to a comparison of alternative d

Previously established optimum operating conditions for simultaneous multi-element trace analysis of geological materials using a d.c. arc were applied

Introduction of Samples into a Microwave-Induced Argon Plasma using a Tungsten Filament and a High-Capacity Condenser

A high-capacity condenser (220, 000μF) was discharged through a filament (0.25 mm diam.), on which the sample was deposited, to heat the latter to 1600°C.The vaporized sample was carried by an argon flow into an electrodeless discharge (2450 MHz, 70-100 W) in a quartz capillary at atmospheric pressure. An addition of 2-10 mM potassium chloride to the sample solution enhanced the spectral line intensity of many elements and eliminated or supressed interference effects. The presence of potassium chloride was also favorable for the simultaneous multi-element analysis because various elements showed their maximum emission at the same spot along the discharge. The detection limits for Cu, Zn, As, Cd and Pb with 2-μl samples in the presence of 5 mM potassium chloride were 0.01-0.0003μg/ml, and the relative standard deviations were 6-14% at the 0.1μg/ml (1μg/ml for As) level.The method was successfully applied to the determination of Cu, Zn, As, Cd and Pb in hair.

Studies of an inductively-coupled high-frequency argon plasma for optical emisson spectrometry—II: Compromise conditions for simultaneous multielement analysis

This paper deals with the experimental selection of conditions under which a low-power inductively-coupled plasma (ICP) can be operated so as to achieve a good compromise for simultaneous multi-element analysis. With the experimental facilities employed by the authors such conditions were found at a power of 0·7 kW, a carrier gas flow of 1·31 min of argon, and an observation height of 15 mm. An outstanding detection power with detection limits below 1 ng ml for 27 out of 32 representative elements and satisfactory suppression of ionization interference effects were simultaneously achieved. Modifications of a previously described ultrasonic nebulizer led to a higher rate of sample injection into the plasma, an improved overall reliability of the sample introduction device, and better reproducibility of spectral-line intensities (1·0–1·2% at concentrations 100 times the detection limits for 15-s integrations). Details of the construction of the ultrasonic nebulizer and its performance are provided and a simple theoretical treatment of the dependence of the aerosol ejection rate on the carrier gas flow and the size of the fog chamber is presented. Possible interelement interferences in the ICP are broadly classified. From the optimization experiments and application studies general conclusions regarding the usefulness of the ICP for both the accurate determination of a few elements and general overall analysis comprising a large number of elements are drawn.

Automatic multi-sample simultaneous multi-element analysis with a h.f. plasma torch and direct reading spectrometer

The equipment described for automatic multi-sample simultaneous multielement analysis has been in everyday use for practical analysis for four years. Some important points in its design are discussed and reasons are advanced for using a high-powered, free-running oscillator to excite a plasma with two gas streams in addition to the stream carrying the sample aerosol. The frequently-used simple formulae for inductance, appropriate for long coils, were found inadequate; modified formulae, applicable to short coils, which agreed with experimental data, were used. Trace analysis and assay work can alike be performed with good accuracy and precision, and in a convenient way. Some typical results are given, with an indication of the versatility of the equipment.

A comparative investigation of some analytical performance characteristics of an inductively-coupled radio frequency plasma and a capacitively-coupled microwave plasma for solution analysis by emission spectrometry

This paper reports results of an inter-laboratory investigation involving standardized experiments performed with standard measuring equipment to establish unambiguously the differences in analytical performance of an inductively-coupled radio frequency plasma (ICP) and a capacitively-coupled microwave plasma (CMP) for simultaneous multi-element analysis (SMEA) of solutions. The authors compared a laboratory-built, prototype ICP and a standard commercial CMP. The analytical characteristics covered were the following: (i) detection limits, (ii) matrix effects produced by cesium sulfate, cadmium sulfate, and di-amnioniumhydrogenphosphate, (iii) sensitivities, and (iv) precision. These characteristics were evaluated for 14 spectral lines of 12 representative elements. The results were corrected for differences in the performance (aerosol injection rate into the plasma) of the nebulizers used with the two excitation sources and for differences in transmission factor, optical conductance and photomultiplier responsivity between the two “identical” measuring equipments. It was definitively established that in all respects the ICP (investigated here) is superior to the CMP (considered here) as an excitation source for SMEA of solutions.

Simultaneous Multielement Quantitative Spectrochemical Analysis Using a DC Arc Source and a Computer Coupled Photodiode Array Spectrometer

Abstract Self scanning linear arrays of silicon photodiodes have been utilized as multichannel detectors in a variety of spectrochemical measurements (1,2,3,4). These arrays have densities of 1000 photodiodes per inch and can be thought of as completely solid state single line image sensors. In some earlier work (3) a spectrometer based on this detector was utilized for qualitative dc arc spectrochemical analysis. In this note we report on the utilization of an improved computer coupled photodiode array spectrometer system for simultaneous multielement quantitative analysis with a dc arc source.

Inductively coupled plasma-optical emission analytical spectrometry

A compact inductively coupled plasma-optical emission system for the trace determination of metallic elements in solution is described. Theoretical considerations are presented to determine operating parameters that agree well with the empirically determined values. The aerosol desolvation system commonly used with this type of source has been eliminated, and pneumatic nebulization is employed in place of the more elaborate ultrasonic method. Some characteristics of the plasma are reported. Detection limits are in the range 0.1-- 10 ng/ml for most elements studied. The present facility is readily adaptable to simultaneous multi-element trace analysis. (auth)

Application of Inductively-Coupled Plasma Excitation Sources to the Determination of Trace Metals in Microliter Volumes of Biological Fluids

Abstract The inductively coupled plasma is a promising excitation source for the simultaneous multielement determination of trace (nanogram per milliliter) elements in biological fluids. As little as 25 µl of sample fluid (whole blood, serum, or plasma) has been used, with essentially no sample preparation. This technique offers significant advantages over other methods requiring considerable sample handling that may greatly increase the danger of contamination or loss of trace constituents. The precision of the method is typically ±3 to 5%. Because this is an emission spectroscopic technique, a multichannel direct-reading spectrometer allows simultaneous multielement analyses to be made on microliter samples.

The application of cathodic sputtering to the production of atomic vapours in atomic fluorescence spectroscopy

Cathodic sputtering is used as a source of atomic vapour for the chemical analysis of metals and alloys by atomic fluorescence spectroscopy. The sputtered vapour is produced in a Pyrex glow-discharge chamber which is suitable for the rapid interchange of flat, metallic samples. The discharge operates with a water-cooled cathode specimen and a flow-through gas control system. Linear calibration curves are obtained for the determination of nickel, chromium, copper, manganese and silicon in some iron-base alloy standards. For nickel, chromium and copper, detection limits are of the order of 20 ppm in the iron, and for manganese and silicon about 70 and 400 ppm respectively. The reproducibility of the fluorescence measurements is about ±1%. The system can be readily adapted to provide simultaneous multi-element analysis.

A 500-Channel Silicon-Target Vidicon Tube as a Photodetector for Atomic Absorption Spectrometry

Abstract The suitability of a vidicon TV tube as a detector for atomic absorption spectrometry (AA) was investigated. The spectral response was seen to be adequate throughout the range 217.0-313.8 nm. The instrument was then used as a detector in determining several elements by flame AA, and the results compared favorably with those obtained by a conventional detection system. The system should thus be feasible for simultaneous multielement analysis.

Studies of flame and plasma torch emission for simultaneous multi-element analysis—I: Preliminary investigations

The need for rapid and relatively simple techniques for simultaneous multi-element analysis of solutions focusses attention on emission techniques using a high-temperature flame, a radio-frequency plasma torch or a plasma jet. This paper deals with the premixed nitrous oxide-acetylene flame and the inductively-coupled argon plasma torch as excitation sources for trace analysis of solutions. Experimental facilities encompass various commercially available burners (including a burner for a gas-shielded flame), an improved plasma torch using a new type of HF generator (52 MHz, 2 kW) and a new arrangement of an ultrasonic nebulizer, less conventional accessory optics, a medium monochromator (1-m Czemy-Turner), and a double-beam, dual-channel arrangement using two monochromators. Detection limits of representative elements were determined in both sources and the conditions favourable for simultaneous multi-element trace analysis were investigated. In many instances, detection limits lower than those published previously were attained. With the plasma torch, the ng ml region—and for many elements even the sub- ng ml region—is easily accessible. The paper includes a discussion of some fundamentals of detection limits. This is to connect the present approach, which stems basically from emission spectrographic analysis, more smoothly with common usage in flame spectrometrio analysis.

Simultaneous multielement analysis using sequentially excited atomic fluorescence radiation—II: An improved instrument for simultaneous analysis

An improved instrument for simultaneous multielement analysis is described. The instrument has been used for the simultaneous determination of Ag, Cu, Fe and Mg with an air-acetylene flame.

Simultaneous multielement analysis using sequentially excited atomic fluorescence radiation

Atomic fluorescence radiation has properties which simplify instrumentation problems for simultaneous multielement analysis. An instrument for simultaneous analysis, containing a rotating filter wheel and a single photomultiplier-amplifier system, and using pulse modulated hollow cathode lamps is briefly described. The instrument has been used for the simultaneous determination of Ag, Cu, Fe and Mg with an air-hydrogen flame.

The application of new techniques to simultaneous multi-element analysis

Abstract

Determination of trace elements in zinc by isotope dilution spark source mass spectrometry

The applicability of the isotope dilution technique in spark source mass spectrometry has been investigated for the determination of Pb, Cu, Cd, Ag, Tl, and Sn in zinc metal. In the procedure developed, a solution of the zinc is spiked with known amounts of stable isotopes of the elements to be determined, and the elements are electrodeposited onto gold wires that subsequently serve as electrodes for the mass spectrographic isotopic analysis. Chemical operations, including isothermal distillation of reagents, dissolution of the zinc, and the electro-deposition step are conducted in a closed system to minimize contamination. The results of the analysis of two NBS zinc standard reference materials include determinations ranging from 11 ppm (11 μg g ) for Pb to as low as 0.02 ppm (20 ng g ) for Sn. It is concluded that this method is of general utility for simultaneous multi-element trace analysis and is especially applicable in providing much needed standardization in spark source mass spectrometry.

Multi-element analysis by means of atomic absorption with a time-resolved spark as primary light source

The use of a time-resolved spark as primary light source for multi-element atomic absorption analysis has been investigated. The elements of interest were introduced into the spark by a solution technique using rotating graphite disk electrodes. Time resolution of the spark radiation was achieved with a rotating disk in front of the slit. The following factors influencing the absorption, namely, time, concentration of solution in the spark, speed of rotation of the disk electrode, and the inductance in the spark circuit were investigated in order to choose optimum parameters. The maximum sensitivities obtained for the four elements copper, calcium, magnesium, and zinc compared favourably with those obtained with hollow cathode lamps as primary sources. Owing to the relatively poor reproducibility of the spark emission the reproducibility of the absorption measurements is not good. A sample of plant material was analysed using this technique and the advantages of the method, namely, simultaneous multi-element analysis and the simplicity of altering the atomic absorption working range by variation of spark parameters, are illustrated.