Abstract:
Rapid sample introduction when using flow injection analysis (FIA) as a sample introduction method to an inductively coupled plasma (ICP) emission spectrometer necessitates that the problem of the large dead volume of the typical spray chamber used in the nebulization and sample transport system of an ICP source be dealt with. The long equilibration times of conventional ICP spray chambers tend to cause poor wash-out with carry-over between sample peaks. A literature survey indicated that a simple reduction of spray chamber volume, without modification of the basic design was associated with poor spray chamber performance and appearance of volatilization type interferences. A promising avenue identified in the literature study to designing a small, yet effective spray chamber was to incorporate centrifugal principles in the spray chamber design. Of a variety of reduced volume spray chambers designed and evaluated, one which made use of a tangential aerosol outlet proved to have desirable characteristics for use in an FIA-ICP interface. The outlet placement was important for the success of the centrifugal approach. This mini-volume spray chamber had a volume of one-tenth that of the commercial chamber, thereby providing more rapid equilibration times with an aerosol displacement time of less than 1 s. The mini-chamber conditioned the aerosol effectively, and showed less volatilization interference than the large commercial chamber. The small volume chamber, when used with FIA sample introduction allowed excellent peak resolution to be obtained at sample injection rates as fast as 320 per hour when determining boron. Using a 300-micro litre injected sample volume, carry-over from a 25 mg.2. -1 boron standard to a 2,5 mg.2.-l boron standard following immediately thereafter was 3% for the mini-chamber as compared to 15% carry-over for the conventional spray chamber. A further advantage of the small chamber was that dispersion ratios close to unity were obtained, so that little sensitivity loss occurred through using the FIA sample introduction mode. The relationship between FIA peak height and concentration was linear, which made calibration a relatively simple procedure. The FIA-ICP method was also evaluated for the determination of calcium, magnesium, manganese and strontium
