http://www.sciencedirect.com/science/article/pii/000927978390087X

http://www.sciencedirect.com/science/article/pii/000927978390087X

https://link.springer.com/article/10.1023%2FA%3A1009255012328?LI=true

 Hi Hakim, it didn't solve my question. SDDC method is method of interest.

Hi Adrij, SDDC method involves complex formation of arsenic with SDDC reagent. 

Nitric acid added will not hinder the formation of volatile arsenic (arsine), here are some examples of how others perform the test.

Most of the methods mentioned are using distillation to minimize interference from other metal ions, lead acetate cotton wool was applied to absorb any hydrogen sulfide generated (as lead sulfide). The only thing you need to take note is add sufficient and preferably slightly excess of reducing agent (zinc, tin chloride and iodide solution). 

As I mentioned before, nitric acid added will make sure arsenic always stay in ionic state. The concentration of nitric acid in metals standard solution normally stays around 10% v/v, practically this value shouldn't affect the reduction of arsenic in this case. 

In the methods attached, they choose sodium hydroxide solution to dissolve their arsenic standard because of solubility of As2O3 is higher in alkaline solution. However the 2nd document attached also mentioned to add sulfuric acid after dissolution of arsenic. 

Hope this answered your question. Feel free to message me if you still have other query, but it might take days before I check the message again. 

http://eusalt.com/sites/www.eusalt.com/files/page-documents/EuSalt%20AS011-2005%20Arsenic%20-%20Silver%20Diethyldithiocarbamate%20Photometric%20Method.pdf

https://nepis.epa.gov/Exe/ZyNET.exe/91013LXA.txt?ZyActionD=ZyDocument&Client=EPA&Index=1976%20Thru%201980&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&UseQField=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5CZYFILES%5CINDEX%20DATA%5C76THRU80%5CTXT%5C00000022%5C91013LXA.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=2

Thanks Yan.

Hi Yan, a new question. I am treating As contaminated water, so for using SDDC method, not using NaOH solution & salt other than you mentioned, will it be correct?

Suggest me with necessary links.

Thanks & best wishes.

Hi Adrij, I'm sorry if I interpret it wrongly, are you saying would it be accurate if you are not using sodium hydroxide and other salts mentioned in the references I suggested to you ? 

Actually sodium hydroxide was used to dissolve As2O3 during arsenic stock solution preparation. If you are using other arsenic compound, check their solubility in different solvents. It's not necessary to use sodium hydroxide every time. 

I take it the salt you mentioned is lead acetate. Lead acetate was used to remove any sulfide generated during distillation process, which later cause colour interference. If you are not using sulfuric acid, or you are very sure that your sample won't generate any sulfide when heated, or you are not using distillation for isolation of arsenic, you may exclude lead acetate from your analysis. 

Actually you can buy arsenic standard solution from other well known chemical supplier, e.g Perkin Elmer, Merck, Agilent etc. As for sample analysis, if you face interference in this method, either you try to remove those interfering elements, or you may try molybdenum blue method or atomic spectroscopy. 

Hope this helps. 

Hello Yan, I hope confused you by not telling the area of interest. I am going to take a project on arsenic treatment of water. So the method (not yet decided) will treat an influent water, after which I need to measure the residual arsenic concentration. So it is basically arsenic in water type solution. Thats what I am asking. Actually I am using sodium arsenate & sodium arsenite salts. 

Hope I made clear my points to you.

Thanks.

Hi Adrij, you can use any arsenic salt for your solution preparation, just look out for their solubility in different solvents as some of them is more soluble in alkaline solution or acidic solution. 

Sodium arsenate and arsenite are soluble in water so you can dissolve them solely in water. But for preservation wise you can acidify your solution with acids if you intent to store it for a long time. If you will dispose it after each time analysis, you can ignore addition of acids. 

As for methods, you can use SDDC method if you want to. Is it standard method IS: 2088 - 1983 you are referring to ? Spectrophotometric method can be quite fast and cheap but prone to a lot of interference, e.g sample colour, metals present in sample, organic material present in sample etc.

If you are looking for a more reliable method, most of the lab using atomic spectroscopy, AAS and ICP are the common instruments for metal analysis. 

To determine which method you want to select, the thing you need to know is how low is the level of arsenic you want it to be. Rough estimation are listed as below: 

As < 10ppm - Spectrophotometric method 

                    - AAS   

As < 0.1ppm - ICP-OES 

                      - HGAAS 

As < 1ppb - ICP-MS 

There are some spectrophotometric methods that are quite sensitive but most of them are easily interfered by elements present in your sample, thus other treatments are required (e.g. distillation, precipitation etc).

Thanks Yan, I got your points. Yes the SDDC method will be used. 

I attended a demo presentation of Palintest/Wagtech arsenator device which measures As 2-100ppb in about 20 min. But the error was there in every test, showing 0, 24 ppb against 10 ppb, 73 against 50, 95+ against 100. You see this field test kit are only useful if there has to be a rough estimation. But for supplying treated water, this pathway don't work. Thats how I concentrated on SDDC method. [As] < 10 ppb is desired.

Thanks again for your valuable findings.

I agree with Dr.Jie