Guarang

Sorry but your proposed approach won't work for a sample such as this. Indirect detection methods have a narrow working range, low sensitivity or both. It won't work with a sample such as seawater except for the major ions. Definitely not for minor ions such as sulfate or phosphate.

Dear Dr Harri,

Following papers will help you out. Please find attachments.

Regrds,

Robin

:)

Papers

Dear Dr. Harri.

The methods from Dr. Joshi are adequate. You also can use atomic absorbance for Metal ions and ICP for non-metal ones. Also UV-VIS with colored reagents to chelate the species is very useful.

Should be used ion chromatography better, and eleminate sulphate ion before injected sample

Dear Robin, Sebastián, Arnau and Wanna. Thank you very much for the guidance you provided. I found the paper by Wilson et al. especially helpful. I think I will try out a combination of UV and electrochemical detection using the conditions described in that paper. Probably ECD would be very sensitive if used in optimised conditions.

Ion chromatography with conductivity detection would be the best and easiest way.

A thermo dionex column CS12 will separate Na+, NH4+, K+, Mg++, Ca++ and Sr++ in around 13 min; for halides, sulphate, phosphate, nitrate and nitrite you could use thermo dionex AG4 in a similar time.

Thanks for the excellent information, Eric. The only problem is that we don´t have a conductivity detector in our laboratory. Therefore I´d like to examine use of ECD and UV. If anyone has experience in applying ECD in this context, please let me know.

You won't have luck with any of these detectors for the alkali metals and alkaline earth metals in a sea water sample although the halides can be detected via ECD and will probably provide the necessary sensitivity with a silver electrode. Indirect detection via vacancy chromatography is possible via UV or FLD butthis methodology has 10-50x worse detection limits than suppressed mode detection using conductivity detection. Detection of these ions in sea water is challenging even with suppressed conductivity detection so using indirect techniques with inferior detection limits isn't going to work.

Dear Chris. Thank you very much for further information. I wonder if it is feasible to analyse also other anions such as phosphate or sulphate with ECD? We are currently using an ESA Coulochem II potentiostat equipped with a Thermo Scientific Dionex high-sensitivity analytical cell 5011A. We have found the cell very useful also in electrochemical oxidation of neurotoxins with subsequent detection with FLD. I hope it is ok to contact you if/when we have further questions relating to ECD with the 5011A.

A reference is provided for help. The method works for seawater as sample.

Iodide and bromide (HPLC-UV). Analytical Chemistry, Volume 64, pp. 1484-1489, Year 1992.

Still another paper for iodide (HPLC-DAD). The method is proposed for iodide in table salt, but should also work for seawater. Detection could be done at 266 nm, if DAD is not available.

Food Chemistry, Volume 124, pp. 1741-1746, Year 2011.

Harri

Unfortunately, phosphate and sulfate are very stable in these oxidized forms so reduction or further oxidation are both rather difficult. I'm not aware of any ECD detection methods for these anions.

You can do it using LC equipped with monolithic column modified with latex. Positive or negative charge on the surface ( depending on he latex) will be able to retain cations or anions.

Dear Krishna, Chris and Ashraf - thank you very much for further info and references. This has been a very helpful discussion and paves a good way to our method testing.

You can use different fluorescence probe for sulphate,phosphate,nitrate etc. Which is difficult to analyse otherwise..

Guarang

Sorry but your proposed approach won't work for a sample such as this. Indirect detection methods have a narrow working range, low sensitivity or both. It won't work with a sample such as seawater except for the major ions. Definitely not for minor ions such as sulfate or phosphate.

I agree with Chris that indirect detection methods in HPLC mode for anions in sea water. Just wondered if capillary electrophoresis with acetonitrile stacking might have a chance with indirect UV detection. Alternatively, tetracationic ionic liquid reagent could be test in CE-MS or LC-MS mode to improve detectability of phosphate (utilizing the complexation characteristics of ionic liquid with multiple positive charge). Alternatively HPLC with suppressed conductivity would be possible.

A sensor package for the simultaneous determination of nanomolar concentrations of nitrite, nitrate, and ammonia in seawater by fluorescence detection

Robert T Masserini Jr.Corresponding author contact information,

Kent A Fanning1

University of South Florida, Department of Marine Science, 140 7th Ave. South, St. Petersburg, FL 33701, USA

http://dx.doi.org/10.1016/S0304-4203(99)00088-2

Marine Chemistry

Volume 68, Issue 4, February 2000, Pages 323–333

for detection of nitrite,nitrate and ammonia

for phosphate

Microchim Acta (2008) 161: 1–39

DOI 10.1007/s00604-007-0897-6

Printed in The Netherlands

Review

Fluorescent probes for microdetermination of inorganic

phosphates and biophosphates

Christian Spangler, Michael Schaeferling, Otto S. Wolfbeis

Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Regensburg, Germany

Received 4 July 2007; Accepted 30 October 2007; Published online 20 December 2007

#

Springer-Verlag 2007

PVC matrix membrane sensor for fluorescent determination of phosphate Original Research Article

Talanta, Volume 70, Issue 1, 15 August 2006, Pages 32-36

Xucong Lin, Xiaoping Wu, Zenghong Xie, Kwok-Yin Wong

why not put an ion exchange column into your HPLC apparatus and detec by UV-VIS or preferredly PDA

Kai,

The reason is quite simple: most of the analytes of interest do not absorb in the UV or the visible.

I would like to share with after your fruitful discussion....The problem that i'm facing to handle the Ion Chromatograph ICS 5000 is....I am trying to get the major anoins (Cl, SO4, Br, NO3, PO4) concentration of estuary water with high salinity. I am facing the memory problem effect , especially for Cl and SO4, because these are main two ions present in sea water. That's why, I use to run after diluting it by milli-q water. This time I am unable to get the right value of other anions like F, No3 etc.

Can you people suggest me to recover this problem.

Could you let me know what column and column dimention you are using?

Sure...right now, i am using the ASRS_4mm for the anions..

What sepation column are you using?

AS7(4*250mm)

What injection mode are you using (full loop or partial loop injection)?

Full loop injection

Carryover problems associated with injecting samples that contain a wide range of analyte concentrations are usually associated with problems with the fluid path sweepout. What I would try first is to inspect all fluid connections between the injection valve and the detector cell and make sure that the tubing ends are square, the tubing surface is defect free and that the tubes are properly set by sliding the ferrules back a bit prior to resetting each fitting and pushing the tube against the fitting while tightening the bolt. It's helpful to have a magnifying glass or an inspection microscope to determine whether or not there are defects in the tubing cut. If you are cutting the tubes yourself, you should be using the Upchurch tubing cutter in a rotary motion to score the tubing and then snap the scored tubing. This technique won't always produce a clean tubing surface but it guarantees that the tubing will be at a 90° angle. As such, you should always inspect the tubing cut even when using this cutting technique. Never just push the tubing cutter blade through the tube as this will produce a beveled cut, producing an unswept volume that causes carryover issues. Make sure that you inspect the injection loop as part of this process.