Cross-check for reliability of ion analyses
The ionic composition of inland nicely water can range from appropriate to poisonous to cultured animals. Dependable knowledge on concentrations of main cations (calcium, magnesium, potassium, and sodium) and main anions (bicarbonate, sulfate, and chloride) is subsequently necessary within the administration of waters for inland shrimp farming.
Cation concentrations normally are decided by atomic absorption spectroscopy (AA methodology) or inductively coupled plasma emission spectroscopy (ICP methodology). Bicarbonate focus might be calculated from complete alkalinity focus, which is decided by titration with customary acid. Sulfate focus might be decided by the barium chloride turbidity methodology, and chloride might be measured by titration with customary mercuric nitrate.
In AA and ICP analyses of saline waters, dissolved salts may cause important interference, so it’s at all times a good suggestion to examine analyses for reliability.
Anion-cation stability
One helpful methodology for figuring out the reliability of main ion analyses of freshwater or saline water is measurement of anion-cation stability. This methodology assumes that main ions comprise many of the complete dissolved solids in a water pattern, and requires that every one main ion concentrations are measured.
The precept {of electrical} neutrality requires that the equal weight of positively charged ions (cations) equal that of the negatively charged ions (anions). As a result of main ions normally symbolize many of the dissolved ions in water, equal quantities of main cations and anions are usually discovered. In an correct evaluation, the sum of the milliequivalents of main cations and anions ought to be practically equal.
Milliequivalents
The milliequivalent of an ion is decided by dividing its focus in mg/l by its milliequivalent weight in mg/milliequivalent. Milliequivalent weights for main ions are listed in Desk 1.
Boyd, Milliequivalent weights of main ions. Desk 1
Steadiness calculation – “is calcium a cation or anion”
The anion-cation stability calculation might be illustrated with knowledge on the common concentrations of ions in water from a saline aquifer in Alabama, USA as follows: calcium, 86 mg/l; magnesium, 21 mg/l; potassium, 7.7 mg/l; sodium, 1,392 mg/l; sulfate, 2.0 mg/l; chloride, 2,274 mg/l; complete alkalinity, 105 mg/l.
First, convert complete alkalinity to bicarbonate by the next equation:
The stability calculations are proven in Desk 2. Shut settlement between the milliequivalents of anions and cations signifies the concentrations of main ions within the pattern had been analyzed precisely.
Boyd, Anion-cation stability instance, Desk 2
One other instance
Take into account one other instance from a just lately printed paper on inland shrimp farming. The concentrations of main ions had been reported as follows: calcium, 250 mg/l; magnesium, 22 mg/l; potassium, 14 mg/l; sodium, 820 mg/l; bicarbonate, 248 mg/l; sulfate, 690 mg/l; chloride, 985 mg/l. The anion-cation stability calculation (Desk 3) reveals a higher distinction between complete anions and complete cations than the primary instance. The typical distinction in milliequivalents of anions and cations might be estimated as follows:
If the common distinction exceeds 15 p.c, one ought to have critical reservations in regards to the accuracy of the evaluation.