As various instruments and other analytical techniques are involved during the chemical analysis of water samples, chances of error is possible. One has to check the results before making any decision for future programs. The following parameters may give valuable information.:

1.Specific conductivity and TDS ratio

2.TDS and sum of total cations and anions.

3 agreement between epm of cations and epm of anions.

4.results of duplicate samples.

5.result of instrument calibration.

Accuracy of the water quality data can be tested by calculating the balance of positive and negative ions. Water fulfills the principle of electroneutrality and is therefore always uncharged. The level of error in the data was calculated using the following formula (Appelo et al., 1996):

Ion Balance Error (IBE)

= [(Sum of cations – Sum of anions)/(Sum of cations + Sum of anions)] *100

An error of up to ±5% is tolerable, while every water sample with a calculated error outside this range should be measured again.

Sajit. Thanks for your interest and appreciate your views.

What do you mean by 'chemical analysis data'?

Major inorganic species, speciation, trace or ultra-trace element concenrtrations, pesticide concentrations, NOM, DOC.....

The answer you will get depends on what the question means.

John thanks for showing interest. Chemical analysis data of water samples includes In particular, pH, specific conductivity, TDS, total hardness, Na,k,Ca,Mg,Cl,HCO3,SO4,F,NO3, SiO2 trace elements and various others..

The subject is too big to be answered here. Some tips have already been given. To risk repetition:

Replicate your analysis. Give the analyst some idea of what he is analysing before he does it - but give him duplicate samples with different numbers known only to you, not the analyst.

Have analysis done by more than one laboratory - results are sometimes frightening.

Plot TDS (calculated) against measured EC; points should cluster tightly to a single trend.

Analyze using well-known protocols - e.g. Standard Methods for the Examination of Water & Wastewater, 22nd Edition.

Does the analysis make sense? For example, if pH is 6.5 and CO3 > HCO3, something is wrong. Again, F> 5 mg/L and Ca 80 mg/L - something is wrong.

Make sure you have plenty of blanks, especially for trace-element analysis and trace organic analysis.

John, Thanks for providing very valuable information in the present context.

Very broad -band question :)

Please specify the target analytes in water, you are interested in.

Elda, Thanks for your interest in this subject. My question is related to chemical analysis of groundwater samples in particular pH, specific conductivity, TH, TDS,cations, anions,NO3,F and various inorganic trace elements.Importance to be given for quality of analysis because most of the future program based on analysis report.

Dear Virendra

The first step is to be sure of the calibration of your analytical instruments, which is confirmed by measuring some standards that you can buy to various companies. Then, if your anions and cations balance is OK, you can go on and be confident on your analyses.

Naghmeh, Thanks for your very useful suggestions.

Olivier, You are very correct, the instrument should be nicely calibrated. Standard from good companies is also necessary for quality data. Appreciate your interest in this context.

Apart from the normal servicing of the analytical instruments, one needs to do daily operational checks whereby a known standard is utilised for the check before an analysis is undertaken. In addition, during analyses, one needs to do replicates of the sample run plus inclusion of internal as well as international standards

Z.Aly. Thanks. convinced with your views. Appreciate for your kind response.

Hello Virendra

I realized you question only now and it is a very important subject, which concerned me all my active time as a geochemist.

At a first glance, the easiest way is to calculate a cation-anion balance (CAB) by multiplying molalities times valencies of cation and anion concentrations (in “normal” waters: Ca2+ / Mg2+ / Na+ / K + / versus Cl- / SO42- / HCO3- (I hope I did not forget one of the “normal” main constituents). The balance has to approximate zero (5 % deviation allowed). In some cases you are obliged to consider also Fe2+, Mn2+, Al3+; in this case the job becomes a touch more difficult because a CAB requires “true” ions in solution. The bulk of these elements occurs as colloids and a CAB becomes impossible. However, filtering the water during sampling

< 0.1 µm takes out colloids (in general) and you could do the calculation (HCO3-:: no filtering).

To be really correct you should consider an additional impediment: to get a real CAB you have to calculate with activities and not only with molalities. I know from experience that very often activities are not factored into the calculations and at low concentrations the simple way will do. At higher concentrations activities are essential to get a reasonable CAB control. In these cases computer programs are a comfortable help (e.g. PHREEQE, WATEQ; public domain).

D. W. Zachmann

Zachmann

You have provided very useful information. Thanks .....

Precision & Accuracy of the chemical data can be checked by the followings-

1. EC/TDS Ratio (0.55-0.70)

2. Cation/Anion Error in %(

Supriya,  Appreciated your answer. Thanks. 

Hope someone can help me with this.

To determine the accuracy of chemical analyses data of groundwater, I am using the electron neutrality equation. However I am struggling with Si, do I use it as an anion or cation?

Please help 

Pieta, you raised a very interesting and useful point in concerned with silica. In some cases we found silica enriched ground water and than confused, for anion and cation balance, regarding to examine the accuracy of chemical analysis. 

Precision & Accuracy of the chemical data can be checked by the followings-

IBE Cation/Anion Error must be in

Sudharshan Reddy, thanks for your interest in this post.

Please refer the APHA (2017) chapter1 Quality control & assurance in water analysis

Supriya, thanks for your participation in this problem.

Mehmet, thanks for your interest in this post.