iCE™ 3500 AAS Atomic Absorption Spectrometer

Segmented flow sample introduction systems are a very helpful tool to increase the productivity in your laboratory. Such devices work with a valve system that enables fast uptake of the sample to the plasma, and minimize the wash out times between different samples. Therefore, the time required for analysis can be shortened considerably. An example for such a system is the sprint valve system available on the Thermo Scientific iCAP 7600 ICP-OES (https://www.thermofisher.com/order/catalog/product/842320076121).

Slurry nebulization is more commonly used in environmental testing applications. In principle, slurry nebulization can be used for pharmaceutical testing and there have been studies done on this. Obviously particle size is a key factor here - the smaller the particles the better. However, it is also worth pointing out that the method preferred by USP is microwave digestion.

The parameters BEC, LOD, and LOQ are frequently used to describe the detection capabilities of an analytical instrument. The acronym BEC abbreviates the parameter blank equivalent concentration. This value refers to the “apparent concentration”, and is composed of the contamination level in the blank, any residual interference signal, and the instrument background (from the detection system). The parameter instrumental detection limit (IDL, often referred to as Limit of Detection, LOD) is defined as the limit of detection that can be achieved by the instrument used. This amount is typically defined as a quantity that gives a distinguishable signal in the detection system. The common definition for the IDL is based upon the standard deviation (LOD = 3.3 x standard deviation of the regression line of calibration curve) of a blank sample measured in the beginning of a calibration curve, or a minimum signal to noise ratio of 3:1. Both parameters, BEC and IDL are automatically calculated by Thermo Scientific Qtegra Intelligent Scientific Data Solution (ISDS) platform software (https://www.thermofisher.com/order/catalog/product/IQLAAEGABSFAOVMBCZ). In contrast, on the IDL, the parameter method detection limit (MDL) includes the extent of all dilution steps carried out during the sample preparation. The MDL is typically based upon a blank solution that has been prepared according to the preparation procedure that is being used to prepare all the samples. In situations where there is no sample preparation or if the preparation involves a single dilution step, MDLs might be calculated based on the standard deviation of a low level standard. MDL concentrations are always more conservative than IDL concentrations.

If samples are in solid form, the dilution incurred will be dictated by the digestion procedure being used to prepare the sample for analysis. If samples are being analyzed in their native form or after simple dilution, there may be more flexibility in the dilution factor used during preparation. Regardless of the sample's original form, the sample matrix must contain a tolerable level of dissolved solids prior to introducing it into the instrument. If an ICP-MS is being used for analysis, the sample matrix should contain 0.2% TDS or, if no special configuration for the sample introduction system is used (e.g., utilizing AGD).

Internal standards are used in many applications to correct for potential drifts in instrumental sensitivity over time or changes in the sample matrix. The selection of a suitable internal standard should include the following aspects: - The internal standard should have a first ionization potential similar to the analyte, and should have a similar mass as the analyte.
- The internal standard must not be part of the sample.
- It should not generate or be affected by spectral interferences.
- It should be at a low and uniform (preferably zero) concentration in all samples.

Although ICP-MS is a technique considered by some to be relatively robust with respect to matrix effects, in reality, matrix effects do commonly exist and the use of internal standards is standard practice. Internal standards also help account for changes in the transport efficiency of the sample through aerosol.