Analytical Capabilities of a Grand Spectrometer in Analysis of Solutions Using Inductively Coupled Plasma

It has been shown that Grand spectrometers based on a hybrid assembly of BLPP-2000 photodetector arrays produced by VMK-Optoelektronika can be used for atomic emission spectral analysis of solutions using inductively coupled plasma atomic emission spectroscopy (ICP-AES). For the prototype of a Grand-ICP spectrometer consisting of a Grand spectrometer, RF plasma generator, and RF (radio frequency) power supply the following analytical characteristics were determined: element detection limit, long-term stability linear ranges of calibration graphs for several elements, and optimal operating parameters of the RF generator. The linear concentration range of analyte elements is 105 when using a single analytical line of the element. The long-term stability is less than 2% in 6 h without using an internal standard. The detection limits are comparable to those of modern ICP spectrometers with an axial plasma view and lie in a range of sub-microgram per liter. It has been found that the effect of superposition of the spectral lines of the plasma background, for example, OH molecular lines or others, on the analyte lines can be eliminated by subtracting the blank sample spectrum from the analyte spectrum using Atom software. The analytical characteristics of the spectrometer allow the use of the device both for developing new ICP-based systems and for restoring the performance of defective ICP spectrometers.

At present, the most popular method of the elemental analysis of solutions is inductively coupled plasma atomic emission spectrometry (ICP-AES) owing to its advantages such as detection limits (DLs) of elements below 1 μg/L, high excitation temperature of elements, low matrix effects, and high time and spatial stability of plasma [1]. Experience shows that when operating spectral ICP-AES complexes in analytical laboratories, the durability of the ICP source often exceeds the durability of the spectrometer. For replacement of a defective spectrometer, it is possible use the domestic Grand spectrometer, the spectra in which are recorded by hybrid assemblies of photodetector arrays [2].
The purpose of this work is to estimate the capabilities of a Grand spectrometer with an ICP source for the analysis of solutions. The spectra are recorded by a MAES analyzer with a hybrid assembly of 14 BLPP-2000 photodetector arrays.
To obtain the argon inductively coupled plasma, we used the radio-frequency (RF) generator from a Quantima GBC Scientific Equipment spectrometer (Australia) operating at a frequency of 40.68 MHz. The RF generator is of the "C" class, in which a 3CX1500D triode is used, the same as in Varian ICR spectrometers. An ICP-MS Elan 6500 power source was used to power the GBC RF generator. To protect against RF radiation, plasma light, and harmful combustion products, a special box tripod was made, which contained the RF generator, inductor, quartz burner holder, ML175005 burner, and sample injection system consisting of an ML180021 spray chamber, TR-50-A1 pneumatic nebulizer, and Gilson Minipulse 2 peristaltic pump. The plasma was ignited by a high-voltage spark introduced into the intermediate burner gas flow. The cold "tail" of the plasma was removed from the optical path by an shear gas. The spectra were recorded on a Grand spectrometer with a nonclassical diffraction grating of 2400 lines/mm. The detector was a MAES analyzer, consisting of 14 BLPP-2000 crystals with high quantum efficiency in the ultraviolet and visible spectral ranges [2]. The spectrometer makes it possible to record the entire spectrum simultaneously in the wavelength range of 190-350 nm with an exposure time of 2 ms. An axial view of the plasma with a horizontally positioned plasma torch was used in the measurements.
The main parameters of the ICP generator and the Grand multichannel spectrometer are given below: Processing the obtained spectra included the subtraction of the blank sample spectrum from the analyte spectrum (Fig. 1). As a result, the analyte spectrum without molecular bands or other components of the plasma background is obtained, which greatly facilitates the choice of the analytical line at low analyte contents in the sample and the plotting of calibration graphs. In addition to the subtraction of the spectrum, the Atom program makes it possible to correct interelement effects, superposition, and much more. Figure 2 shows examples of calibration graphs for determining Cd, Ni, Mn, and Zn in solutions with concentrations from 8 μg/L to 50 mg/L. The solutions containing 50, 5.0, 1.0, 0.2, 0.04, and 0.008 mg/L of the element to be determined were prepared by diluting with deionized water with a resistivity of 18 MΩ cm. As a rule, the most intense lines free of spectral noise were chosen as analytical ones. The linear dynamic range of the calibration dependence when using one spectral line of the element is 10 5 .
The long-term stability of the analytical signal measured periodically every 2.5 min with the spectrum integration time of 10 s for 6 h without stopping the sample spraying system and turning off the plasma and without using the internal standard is less than 2% (Fig. 3), which is comparable to modern ICP spectrometers.
Spectral resolution, pm 10 Detector stabilization temperature, °C 2 0 Thus, an experimental prototype of the Grand spectrometer was designed with a hybrid assembly of the BLPP-2000 photodetector arrays and an ICP source, and its analytical capabilities were estimated. The linear dynamic range of the calibration dependence for determining a series of elements is 10 5 when using one analytical line and the long-term stability is less than 2% in 6 h without using an internal standard. The detection limits are not inferior to similar characteristics for modern ICP spectrometers and lie in a range of sub-microgram per liter. The obtained analytical characteristics of the spectrometer make it possible to use it both to design a new ICP complex and to restore the performance of defective ICP spectrometers.