A multicommutated flow system was designed and evaluated for the determination of selenium by hydride generation atomic absorption spectrometry (HG-AAS). It was applied to the determination of total selenium in samples of cow's milk (fluid and powder) and infant formulae. Linearity was satisfactory in the range up to 27.5 mg L À1 (h ¼ 0.082 C + 0.0033, h ¼ peak-height, absorbance, C ¼ concentration in mg L À1 , r 2 ¼ 0.999). Detection (3s) and quantification (10s) limits in solution were LD ¼ 0.08 mg L À1 and LQ ¼ 0.27 mg L À1 , corresponding to LD ¼ 3.2 mg kg À1 and LQ ¼ 10.8 mg kg À1 in solid samples, and to LD ¼ 0.8 mg L À1 , LQ ¼ 2.7 mg L À1 in fluid milk samples. Trueness was verified by analysis (n ¼ 5) of two reference materials (NIST 1549, Non-fat Milk Powder and NIST 1846 Infant Formula). At the 95% significance level, results were statistically equivalent to the certified values. Instrumental precision (s r (%), n ¼ 5) was in the range 1.4% to 11.7%, analytical precision (s r (%), n ¼ 5) being 4.2 and 9.3% respectively for the determination of the above mentioned reference materials. The sampling frequency of the system was 160 hour À1 .
A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l(-1) for arsenic and selenium, respectively; sampling frequency was 120 samples h(-1) for arsenic and 160 samples h(-1) for selenium. Linear ranges found were 1.54-10 μg l(-1) (R = 0.999) for arsenic and 0.27-27 μg l(-1) (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95-116%. Analytical precision (s ( r ) (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.
An on-line preconcentration system for the simultaneous determination of Copper (Cu) and manganese (Mn) in water samples was developed and coupled to a microwave-induced plasma optical emission spectrometer (MIP OES). The flow injection system was designed with a minicolumn packed with sisal fiber (Agave sisalana). A multivariate experimental design was performed to evaluate the influence of pH, preconcentration time, and eluent concentration. Optimal conditions for sample preparation were pH 5.5, preconcentration time was 90 s, and HCl 0.5 mol L−1 was the eluent. The main figures of merit were detection limits 3.7 and 9.0 µg L−1 for Cu and Mn, respectively. Precision was expressed as a relative standard deviation better than 10%. Accuracy was evaluated via spiked recovery assays with recoveries between 75–125%. The enrichment factor was 30 for both analytes. These results were adequate for water samples analysis for monitoring purposes. The preconcentration system was coupled and synchronized with the MIP OES nebulizer to allow simultaneous determination of Cu and Mn as a novel sample introduction strategy. The sampling rate was 20 samples/h. Sisal fiber resulted an economical biosorbent for trace element preconcentration without extra derivatization steps and with an awfully time of use without replacement complying with the principles of green analytical methods.
Biorsorbents can be used to pack minicolumns for the preconcentration of trace elements and thus improve the detection limits of some techniques. A biosorbent is efficient when presents binding sites as carbonyls, amines, and carboxylic groups, among others. Thus, natural materials as the sisal fiber (Agave sisalana) may be a good candidate. Sisal fiber demonstrated good performance for Cu preconcentration when it was impregnated with alizarine fluorine blue (AFB). However, very good results were reported for the first time by our group with this column, without the use of additional reagents for both, Mn and Cu determinations in water samples by using microwave plasma atomic emission spectroscopy (MP AES). In this paper a comparison of the sisal fiber preparation with and without impregnation with AFB is presented and discussed in terms of the figures of merit, including precision, trueness, limits of detection and quantification. In addition to that, the number of determinations without the need of replacement of the solid phase was evaluated. Results demonstrated that the impregnation of sisal fiber with AFB does not leads to an improvement in the analytical performance. Analytical Greenness Metric Approach (AGREE) was used to evaluate the greenness of both methods and results obtained were similar. Despite this, the method without impregnation of the fiber has some remarkable advantages, that contributes to Green Analytical Chemistry (GAC), related to the lifetime of the sorbent, not considered in the AGREE tool.
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