Cyanide Analysis - Part Two, Interference Discussed Sulfur Analyzer Indonesia

When samples containing 3 parts per million thiocyanate and 5 parts per million nitrate nitrogen were distilled and analyzed by GD-Amperometry 10.9 parts per billion cyanide was detected. When 15 parts per million thiocyanate + 25 parts per million nitrates are distilled, cyanide detects leaps up to ~ 50 - 60 parts per billion.

Real wastewater samples containing 0.1 mg / l thiocyanate and 63.5 ppm NO3 detected cyanide at 100 parts per billion using the distillation-colorimetric method. This same method used in synthetic matrices containing 0.1 ppm thiocyanate and 25 ppm nitrate produces 60 parts per billion of cyanide which is wrongly detected.

As can be seen by the data, distillation produces false positives in samples containing thiocyanates and nitrates. Because thiocyanates and nitrates are almost always present in wastewater, this interference indicates that the distillation method is not suitable for the waste water matrix. Note that nitrates not only react with thiocyanate during distillation, almost all organic compounds can be oxidized during distillation to form cyanide. When examining cyanide from thiocyanate by distillation (or heating), cyanide spike is required in samples containing thiocyanate. For example, samples containing 20 parts per million thiocyanate (without nitrate) and 200 parts per billion
sulfur analyzer indonesia cyanide detected 174 parts per billion cyanide (negative bias). This means thiocyanate causes a positive bias when nitrate is present, and a negative bias when nitrate is absent.

There is a significant negative interference that can occur if the sample is distilled. Oxidized forms of sulfur, such as sulfite, and thiosulfate destroying cyanide during distillation cause low reported results. For example, samples containing 20 ppm SO3 and 200 parts per billion cyanide detected 80 parts per billion of cyanide after distillation, and samples containing 20 ppm thiosulfate and 200 parts per billion cyanide detected 124 parts per billion cyanide after distillation. This interference is significant because thiosulfate and sulfite are often used for dechlorinate samples or for dechlorinate disinfected wastewater. Genuine sulfur causes a negative bias and must be filtered before analysis. Metallic embroidery causes a negative bias and must be filtered before analysis. The loss of cyanide results from sample storage and refining so that the treatment applies to both the flute and non-distilled methods.

Treating sulfides with lead, cadmium, zinc, or bismuth is not recommended. Without on-line sulfide reduction as in ASTM D6888-04, it is recommended that samples containing more than 50 parts per million sulfides (ASTM D6888-04), or more than 20 parts per million sulfides (distillation) be diluted to the sulfide point no longer disturb. All precipitation or volatilization treatment methods produce significant cyanide losses. The preservatives used also have an effect on the recovery of cyanide. We recommend not to use ascorbic acid as determined in most methods because any excess can cause 200 parts per billion of cyanide not to be detected after 72 hours. The use of Arsenite Sodium does not produce a decrease. We also know that the distillation method does not produce accurate results if there are thiocyanates, nitrates, nitrite, sulfite, ozone, peroxide, hypochlorite, metal sulfides, thiosulfates, and organic traces in the sample. This means that if one or all of the parameters mentioned are not available from water, a distillation (or heat destruction) method for cyanide can be used.

The point is that methods that are believed to be accurate for cyanide are not, and cannot reach even 80% recovery of total cyanide in most matrices. We have, on the other hand, a method which even when it does not perform under optimal conditions gets a mid to upper 80% recovery for the iron complex in the sample matrix where cyanide can be detected or very positively biased by distillation. Is there room to improve, yes, but let's consider that even with the disadvantages shown, distillation-free total cyanide is far superior to other methods for determining total cyanide. But even when considering this, it must also specify the purpose of measuring cyanide. When the US first started regulating cyanide in the late 1970s there was no method other than distillation capable of carrying out different forms of cyanide.