**4.2 Results and discussion**

434 Macro to Nano Spectroscopy

Buffer solution, 0.1 mol L*−*1 NH4+ /NH3 at pH: 8.5, was used to produce analytical signal in the FIA system. Salicylic acid was provided from Merck (Darmstadt, Germany). Standard salicylic acid solutions were prepared daily by dissolving the appropriate amount of salicylic acid in an ethanol:water mixture (30 : 70). The reagent carrier solution was

Fluorescence measurements for the batch experiments were performed with an SPF-500 model spectrofluorometer (American Instrument Co, Jessup, USA) using 1 cm quartz cells. Instrument excitation and emission slits were fixed at 10 nm. The light source was a 150 W Xenon lamp (American Instrument Co, Jessup, USA). Excitation and emission wavelengths were set at 299 nm and 409 nm, respectively. An eight-channel ISMATEC IPC peristaltic pump (Z¨urich, Switzerland), 0.75 mm i.d. PFTE tubing, was used to propel the samples and reagent solutions. Samples were injected into the carrier stream by a Rheodyne injection valve provided with a 20 μL loop. A Varian 2070 spectrofluorometer (Tokyo, Japan) using a 15 μL flow cell was used for the on-line measurements of analytical signals. Instrument excitation and emission slits were set at 20 nm. The light source was an ozoneless 75 W Xenon lamp (Tokyo, Japan). A strip chart recorder was attached to the instrument. Cationexchange resin, sodium form of A650 W (100–200 mesh), was provided by the BioRad Labs (Hercules, CA, USA). The cation-exchange resin minicolumn (6 cm long, 2 mm i.d) was

pH measurements were carried out using a Jenway digital pH-meter model 3040 (Essex, England). An ATI UNICAM 929 model AAS (Cambridge, UK) flame atomic absorption spectrophotometer with a deuterium-lamp background correction was used for the determination of iron in reference to the FIA method. The measuring conditions were as follows: UNICAM hollow cathode lamp, 10 cm 1-slot burner, air–acetylene flame (fuel gas flow-rate of 1.50 L min*−*1), 0.2 nm spectral bandwidth, and 7 mm burner height. The wavelength and the lamp current of iron were 248 nm and 5 mA, respectively. The flow injection manifold was similar to that proposed in our previous study (Isildak et al., 1999). Peristaltic pump was used to transport the reagent carrier solution through the system. The sample was injected using an injection loop (20 μL). The reagent carrier solution and the sample were allowed to mix in the flow stream and in the mini-column. The decrease in the fluorescence intensity of the salicylic acid as a function of Fe(III) concentration was measured in the flow cell using 299 nm for excitation and 409 nm for emission. Water samples were obtained from different places of the river, sea and thermal spring in Samsun, Turkey. They were filtered through a 0.45 μm Millipore Filter (Millford, MA, USA). Water samples were split into two portions: one part was directly injected into the FIA system for the determination of iron(III). Before the analysis of the other part, 1 mL of H2O2 (10 mass %) was added to a 9 mL sample solution for complete oxidation of iron(II) to iron(III). Then, 20μL of this solution were injected into the system for the determination of total iron, as in

A 0.10 g sample of the certified metal alloy (Zn/Al/Cu 43XZ3F) was dissolved in 12 mL of concentrated HCl + HNO3 (3 : 1) in a 100 mL beaker. The mixture was heated on a hot plate nearly to dryness; 5 mL of HNO3 were added to complete the dissolution, and the solution was diluted to 100 mL with deionized water, filtered and transferred quantitatively to a 1000 mL volumetric flask and filled up to the volume with deionized water. The volume of 10 mL

+ /NH3 buffer solution (90:10)

composed of 2*×*10*−*6 mol L*−*1 salicylic acid and 0.1 mol L*−*1 NH4

at pH 8.5.

prepared in our laboratory.

the procedure described above.

Fig. 6 shows the fluorescence emission spectra of 5*×*10*−*5 mol L*−*1 salicylic acid in a buffer solution at pH 8.5 before and after the reaction with 1*×*10*−*5 mol L*−*1 iron(II) and iron(III), respectively, in batch experiments. As can be seen, the intensity of salicylic acid fluorescence decreased significantly in the presence of iron(III). From these spectra, the emission wavelength chosen for the FIA measurement was 409 nm, using 299 nm for the fluorescence excitation.

Fig. 6. Emission spectrum of 5*×*10*−*5 M salicylic acid in batch experiment (in the absence and presence of 1*×*10*−*5 M Fe(III) and 1*×*10*−*5 M Fe(II) ions): a) salicylic acid, b) salicylic acid + Fe(II), c) salicylic acid + Fe(III).
