Assad S. Al-Ammar

Elimination of boron memory effect in inductively coupled plasma-mass spectrometry by ammonia gas injection into the spray chamber during analysis

Abstract Injection of 10–20 ml/min of ammonia gas into an inductively coupled plasma-mass spectrometry (ICP-MS) spray chamber during boron determination eliminates the memory effect of a 1 μg/ml B solution within a 2-min washing time. Ammonia gas injection also reduces the boron blank by a factor of four and enhances the sensitivity by 33–90%. Boron detection limits are improved from 12 and 14 to 3 and 4 ng/ml, respectively, for two ICP-MS instruments. Trace boron concentrations in certified reference materials agree well using ammonia gas injection.

Elimination of boron memory effect in inductively coupled plasma-mass spectrometry by addition of ammonia

Boron memory effect in inductively coupled plasma-mass spectrometry is characterized theoretically and verified experimentally. The boron memory effect originates from the tendency of boron to volatilize as boric acid from the sample solution layer that covers the inside surface of the spray chamber. The skimmer, the sampler, the ion lenses, the quadrupole and other components of the mass spectrometer are not responsible for the memory effect at trace boron concentration levels. A technique to eliminate the memory effect is proposed and tested. Ammonia gas is used to convert the boron from the volatile boric acid form to the non-volatile ammonium borate. Ammonia is introduced by injecting a small volume of ammonia solution simultaneously with the sample solution. Addition of ammonia is effective in completely eliminating the boron memory effect and reducing boron signals to blank levels instantaneously (within 20 s) in a conventional concentric nebulizer-double pass spray chamber arrangement.

Feasibility of using beryllium as internal reference to reduce non-spectroscopic carbon species matrix effect in the inductively coupled plasma–mass spectrometry (ICP-MS) determination of boron in biological samples

Abstract The mechanism by which carbon matrix species cause non-spectroscopic matrix interference on boron (B) and beryllium (Be) during the determination of B in biological samples is investigated. The study indicates that, unlike other matrix species such as Ca and Na that cause non-spectroscopic matrix interference only through space charge effect, carbon species manifest non-spectroscopic interference by two mechanisms. The minor non-spectroscopic interference of carbon is through space charge effect. However, the major non-spectroscopic effect of carbon is by a charge transfer mechanism from C + -species to B and Be atoms in the central channel of the plasma discharge. The large difference in the magnitude of the carbon charge transfer non-spectroscopic matrix interference between Be and B makes Be unsuitable as an internal reference for B in solutions containing more than 1500 μg/ml dissolved organic carbon (DOC). This DOC content is approximately half the DOC usually present in the final sample solution for B determination in biological samples. However, Be still acts as a perfect internal reference to B in solution containing matrix elements that exert their non-spectroscopic interference effect through space charge mechanism (such as Na, K, Ca, etc.).

Improving boron isotope ratio measurement precision with quadrupole inductively coupled plasma-mass spectrometry

A method was developed to improve the precision of inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for the determination of boron isotope ratios (11B/10B) in various environmental materials including seawater. This approach is based on the common analyte internal standardization (CAIS) chemometric algorithm. The sample solution obtained after digestion is spiked with lithium, and both 7Li/6Li and 11B/10B values are measured using long-counting periods (20 min). The CAIS algorithm corrects the measured 11B/10B values for (a) statistical fluctuations resulting from short-term noise; (b) drift in 11B-to-10B ratio as a result of long-term deviation in instrumental parameters likely to occur during long counting times; (c) change in 11B-to-10B ratio caused by variation in matrix elements concentrations; and (d) drift in mass bias correction factor. Comparing boron isotopic ratios in seawater measured by conventional and the new isotope ratio methods validates the procedure. A synthetic isotopic mixture of boron SRM 951 and enriched 10B SRM 952 also was examined. The CAIS method provided a measured boron isotopic ratio precision of 0.05% R.S.D. while eliminating 5.1% matrix concentration error and 0.25% instrumental drift error.

Correction for non-spectroscopic matrix effects in inductively coupled plasma-atomic emission spectroscopy by internal standardization using spectral lines of the same analyte

Abstract The common analyte internal standardization (CAIS) technique was extended to correct for non-spectroscopic matrix effects in inductively coupled plasma-atomic emission spectroscopy (ICP-AES) measurements. The technique is based on simultaneous measurement of two different spectral lines of the same analyte. A matrix correction factor is then estimated from its linear correlation with the ratio of intensities of these two measured lines. Experimental tests with four elements (Ba, La, Mg, and Mn) in three matrices (NaCl, H 2 SO 4 , HNO 3 ) demonstrate a significant decrease (from 3 to 22 times) of the matrix effect after correction.

Improving isotope ratio precision in inductivelycoupled plasma quadrupole mass spectrometry by common analyte internal standardization

The common analyte internal standardization (CAIS) chemometric technique is extended to improve isotope ratio precision obtained by inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS). A correction function for isotope ratio measurement is derived from a relationship of mass sensitivity as a function of element mass after considering the degree of ionization and isotopic abundance. An analyte isotope ratio correction factor can be determined by simultaneously measuring several internal reference isotopic ratios and the analyte. The CAIS approach corrects for isotopic mass bias and isotope ratio variation with sample matrix concentration. Isotope ratio precision is improved from about 0.4 to 0.05%, because long-counting times allow correcting mass bias and isotope ratio drift during extended data-acquisition periods. Isotope ratio accuracy is improved from 0.2 to 0.02%.

Correction for non-spectroscopic matrix effects in inductively coupled plasma-mass spectrometry by common analyte internal standardization

Abstract The Common Analyte Internal Standardization (CAIS) chemometric technique is extended to correct for non-spectroscopic matrix effects in inductively coupled plasma-mass spectrometry (ICP-MS). The approach is based on using an internal reference element to correct for the matrix effect. Unlike the conventional internal reference method, the CAIS technique allows for the analyte to behave differently from the internal reference under the influence of the matrix. With the CAIS technique a single internal reference element is sufficient to correct for all the analytes. Experimental tests with 13 analytes in four different matrices using different ICP-MS instruments demonstrate that the CAIS is efficient and general for matrix effect correction. Not only is the corrected concentration more accurate, but the precision is significantly better. The capability of CAIS to correct for the effect of a mixture of two matrices was also established experimentally, and 20–30% matrix suppression was eliminated. Furthermore, the developed technique was used as a simple diagnostic quality assurance procedure to evaluate the performance of the mass spectrometer.

Simultaneous sample preconcentration and matrix removal using field-flow fractionation coupled to inductively coupled plasma mass spectrometry ☆

Abstract An on-channel sample preconcentration-matrix removal arrangement, based on coupling field-flow fractionation (FFF) to inductively coupled plasma mass spectrometry (ICP-MS), has been constructed for on-line sample pretreatment ICP-MS trace element determination. A commercial FFF system is modified to incorporate an on-channel preconcentration procedure allowing injection of up to 50 ml of sample, which could be preconcentrated by 50–1400 fold. A high molecular weight complexing agent added to the sample forms strong complexes with the measured trace analytes but not with the sample matrix. When the sample-complexing agent mixture is introduced to the FFF unit, the uncomplexed matrix element is removed by permeation through a membrane that separates the FFF sample compartment. The trace analytes remain in the FFF channel, because their high molecular weight complexes do not permeate through the membrane. Preconcentration and matrix elimination occur simultaneously. The matrix-free, preconcentrated sample is introduced directly to the ICP-MS nebulizer. The method was tested using 10-ml sample aliquots that contain As, Cd, Cu, Mo, Pb, Re, Sn, Te, Tl, Y, Zn and Zr analytes and 5000 mg l −1 Ca or Na matrices and ethylene imine polymer complexing agent. Copper and Re isotopic ratio values in reference standards also were determined after preconcentration and matrix element removal.

Inelastic collisional deactivation in plasma-related non-spectroscopic matrix interferences in inductively coupled plasma atomic emission spectrometry

Abstract Inelastic collisional deactivation of the analyte excited state is demonstrated as a dominant cause for non-spectroscopic matrix interference in inductively coupled plasma atomic emission spectrometry (ICP-AES) for commonly used plasma operating conditions in routine analysis. A mathematical simulation of the inelastic collisional model was examined. Comparison between the theoretical model and experimental results using atomic and ionic lines of the analytes Zn, Ba, Mg, Mn and Sr validates the inelastic collisional deactivation model as a dominant cause for non-spectroscopic matrix effect. Matrices evaluated were NH 4 Cl, NH 4 SCN, (NH 4 ) 2 SO 4 , and H 2 SO 4 to represent difficult-to-ionize matrices (DIE) and NaCl and CaCl 2 to represent easy-to-ionize element matrices (EIE).

Correction for volatility differences between organic sample analytes and standards in organic solutions analyzed by inductively coupled plasma-atomic emission and mass spectrometry

A novel technique was developed to correct for the error in inductively coupled plasma atomic emission and mass spectrometric measurements arising from a difference in volatility between the sample analyte compounds and standards. The technique is based on the measurement of the analyte signal at two spray-chamber temperatures. A volatility correction factor is then estimated from a linear correlation between the reciprocal of a correction factor and the relative change in intensity resulting from measurements at two spray-chamber temperatures. Tests with organosilicon and organochlorine compounds demonstrate a significant decrease (from 2 to 30 times) in error after correction. The technique requires no prior knowledge of the chemical structure of the analyte.