In-Line Sample Preparation

Frequently Asked Questions
• What is the In-line Sample Preparation Module (ILSPM)?
• What are the benefits of using an In-line Sample Preparation Module?
• What methods can be run by using an ILSPM?
• Can I use the same module for running CN distillations and TN & TP digestions?
• Does the unit require any special hook-up?
• Do you have any data showing that the in-line methods work?
• Do the In-Line Prep Modules handle sludges or solids?
• What's the principle of the in-line total nitrogen digestion?
• What's the principle of the in-line total phosphorus digestion?
• What's the principle of the in-line cyanide distillation?
• What's the principle of the in-line total recoverable phenolics?
• What's the principle of the in-line surfactants?
What is the In-line Sample Preparation Module (ILSPM)?
The ILSPM is an option of the QuikChem FIA+ System platform. These modules are capable of in-line distillations, digestions and solvent extractions.
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What are the benefits of using an In-line Sample Preparation Module?
• Automates distillations, digestions and solvent extractions
• Significantly improves productivity
• Reduces consumption of sample preparation reagents
• Closed preparation system reduces exposure to corrosive and toxic reagents
• Increases accuracy and precision with controlled system conditions
• Provides simple operation - just place the sample in the automatic sampler and start the run
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What methods can be run by using an ILSPM?
• Total nitrogen
• Total phosphorus
• Cyanide
• Phenolics
• Surfactants
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Can I use the same module for running CN distillations and TN & TP digestions?
The same module can be used for digesting TN and TP separately. All the other modules are customized to prepare samples for a specific analysis.
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Does the unit require any special hook-up?
The installation of the module is very simple. The entire setup can be done in about 20 minutes. It's recommended having a dedicated channel for the in-line methods in order to avoid daily setup.
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Do you have any data showing that the in-line methods work?
Yes. All QuikChem methods contain method support data.
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Do the In-Line Prep Modules handle sludges or solids?
The in-line modules are intended for liquid samples only.
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What's the principle of the in-line total nitrogen digestion?
Nitrogen compounds are oxidized in-line to nitrate using alkaline persulfate/UV digestion. Oxidation of nitrogen-containing compounds to nitrate is achieved at 90°C with additional energy supplied by UV light. The digestion occurs prior to the injection valve. Results for wastewater samples with settleable solids may be up to 20% low when compared with a rigorous off-line digestion. If effluent samples are acid preserved, in-line digestion results will match manual off-line digestion. Results for the samples without settleable particulates, such as surface water and sea water, will match the manual off-line digestion. This should be validated with a typical sample before reporting results. After digestion, nitrate is quantitatively reduced to nitrite by passage of the sample through a copperized cadmium column. The nitrite (reduced nitrate) is then determined by diazotization with sulfanilamide under acidic conditions to form a diazonium ion. The diazonium ion is coupled with N-(1-naphthyl)ethylenediamine dihydrochloride. The resulting dye absorbs at 540 nm and is proportional to the total nitrogen concentration.
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What's the principle of the in-line total phosphorus digestion?
The method is based on the digestion of various phosphorous forms and conversion to phosphate by peroxodisulfate with an in-line UV digestion. Organic phosphorus is converted to orthophosphate by UV catalyzed persulfate digestion. Polyphosphates are converted to orthophosphate by sulfuric acid digestion. The digestion process occurs prior to the sample valve. A portion of the digested sample is then injected and phosphate is determined by FIA.
Wastewater samples are acid-preserved and filtered. When this is the case, in-line digestion results match the manual off-line digestion. If samples are not filtered, in-line results will be 1-15% low compared with off-line digestion. Surface water samples may not require filtration but this should be verified with a sample containing high levels of solids.
After digestion, the orthophosphate ion (PO43-) reacts with ammonium molybdate and antimony potassium tartrate to form a phosphomolybdate complex. This complex is reduced with ascorbic acid to form a blue complex, which absorbs light at 880 nm. The absorbance is proportional to the concentration of orthophosphate in the sample.
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What's the principle of the in-line cyanide distillation?
Using the In-Line Sample Preparation Module, a liquid sample is mixed with KHP, zinc sulfate buffer at 115°C. The HCN(gas) from the sample matrix crosses a gas permeable membrane, and it is trapped into sodium hydroxide. The CN- is then determined colorimetrically using the pyridine-barbituric acid chemistry at 570 nm. Both standards and samples are distilled in-line.
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What's the principle of the in-line total recoverable phenolics?
The sample is fed into a continuously flowing carrier stream, mixed with phosphoric acid and distilled in-line. The distillate, containing steam volatile phenolic compounds, is then mixed with continuously flowing solutions of 4-aminoantipyrine and potassium ferricyanide. Phenolic compounds in the distillate are oxidized by ferricyanide, and resulting quinones react with 4-aminoantipyrine forming yellow condensation products, which are determined by colorimetric detection at 500 nm.
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What's the principle of the in-line surfactants?
Anionic surfactant is associated with the intensely colored methylene blue cation to form a chloroform extractable ion-association complex; the unassociated dye has an extremely small solubility in chloroform. The methylene blue-anionic complex is partitioned into chloroform from an alkaline methylene blue solution to avoid the negative interference of proteinaceous material present in environmental samples. The chloroform phase is then back-extracted with an acidified methylene blue solution in order to remove the positive interference of those materials such as inorganic anions e.g. nitrate, chloride etc, that form methylene blue complexes of low chloroform extractability. The absorbance of the final chloroform phase is measured at 650 nm.
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