SENSITIVE DETERMINATION OF IRON IN DRINKING WATER, MINERAL WATER, GROUNDWATER, AND SPRING WATER USING RAPID PHOTOMETRIC TESTS
The quality of drinking water is regulated by a variety of quality requirements, defi ned; for example, in the form of limits specifi ed by EU Council Directive 98/83 [1]. The decisive principles behind the defi nition of the limits – besides health-hazard aspects – also include sensory and technical reasons [2].
One example for the defi nitions described above is that of iron. The EU Council Directive 98/83 (version of 3 November 1998) classifi es iron as an indicator parameter, i.e. in the concentrations present in drinking water, iron does not have a health- damaging effect [3]. The WHO classifi es iron as follows: “Not of health concern at levels found in drinking water” [4]. Raised concentrations of iron, however, result in the formation of iron hydroxide products, which in turn form deposits in the water-pipe system and to the brown discoloration of the water coming out of the tap [5].
To safeguard the supply of clear and colorless water, country- specifi c limits have been set for drinking water. The limit for iron set e.g. by the EU directive is 0.2 mg/L Fe [3], while the US environmental agency, the EPA, specifi es a limit for the concentration of iron of 0.3 mg/l [6].
Regarding the prevention of the formation of iron deposits in the water-pipe system, the German Technical and Scientifi c Association for Gas and Water (DVGW) recommends that a limit of 0.02 mg/L should not be exceeded [7].
As a measure to ensure that the specifi ed limits and recommendations are complied with, drinking water is in many cases subjected to a treatment step in which the iron present in the water is precipitated. This method virtually eliminates any iron content, reducing the iron concentration to a level in the lower ppb range [7].
IET March / April 2017
www.envirotech-online.com Fig. 1: Drinking water
Analytical Methods
The accurate determination of such low concentrations requires a highly sensitive analytical method. Conventional procedures that enable quantifi cation down to the trace range include fl ame atomic absorption spectroscopy (fl ame AAS, F-AAS) and also optical emission spectrometry with inductively coupled plasma (ICP-OES). Depending on the dosage volume the measuring range of the F-AAS method according to DIN EN ISO 38406-32 is 0.002–0.020 mg/L Fe. The limit of quantifi cation (LOQ) for the ICP-OES method according to DIN EN ISO 11885 lies at 0.002 mg/L Fe [8,9]. Measured according to the ICH Q2 standard, the ICP-MS method used at Merck achieves an LOQ of 0.0007 mg/L Fe.
Analysis of iron using analytical test kits (rapid photometric methods)
When it comes to obtaining a swift, sensitive result without having to make a high investment in instruments, rapid photometric methods offer a practical alternative.
Test kits are generally characterized by their easy handling and speed of the procedure. The choice of the type of method depends on the specifi c area of application, the measuring range, and the accuracy of the measurement to be achieved. In the case of iron, the user can choose between two sensitive photometric methods.
The determination of iron using the 1,10-phenanthroline method according to APHA 3500-Fe B and DIN 38406-1 enables photometric measurement down to a level of 0.01 mg/L, which is entirely suffi cient for many samples [10].
In the case that iron is to be measured with a far greater degree of sensitivity, the user can select the triazine method. In this method, all iron ions are reduced to iron(II) ions. These then react in a thioglycolate-buffered medium containing a triazine derivative to produce a red-violet complex, which is subsequently determined photometrically [11]. When using a 100-mm cell and the Prove 600 UV-VIS spectrometer from the Spectroquant®
In the case of drinking water, such low concentrations are, due
to the treatment stage and the by nature low content of iron in groundwater, not infrequently encountered.
For this reason, the user should give preference to the more sensitive triazine method in this case. Merck offers this method in the form of Spectroquant®
Iron Test, Cat. No. 114761, which
has an overall measuring range of 0.0025-5.00 mg/L Fe. Used in conjunction with the corresponding Spectroquant®
photometers,
in which the method is already pre-programmed, the time- consuming procedure for the calculation of a calibration curve can be fully omitted.
Fig. 2: Spectroquant®
Prove 600
Sample preparation and performance of the measurement with Spectroquant®
Iron Test 114761
Very few steps are required for preparing the sample and the actual measurement of the iron content. Samples must fi rst be acidifi ed with nitric acid to stabilize the iron, while carbonic acid-containing samples must also be fi rst degassed in an ultrasound bath.
Prove
product range, iron concentrations as low as 0.0025 mg/L can be measured.
For the sensitive measurements in the 100-mm cell in the 0.0025 – 0.500 mg/L Fe measuring range, fi rst 20 mL of the sample solution is pipetted into a suitable reaction vessel, after which 12 drops of the Fe-1 reagent are added. After a reaction time of 3 minutes, the solution is transferred to the 100-mm cell and measured in the photometer.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84
