I want to calculate the salinity of my water sample. for that I measure the conductivity in microS/cm I want to change this to TDS (mg/L) and salinity percentage. How do I do that?
TDS mgl-1 =EC(dSm-1) *640, for EC between 0.1 and 5 dSm-1
· 690mgl-1/640 =1.8 dSm-1(EC).
· 1.8dSm-1*640=690mgl-1 or TDS
Hi,
In addition, you have many different on-line calculators to convert your conductivity measurements into TDS or salinity. Here's just an example (there's many more):
https://ponce.sdsu.edu/onlinesalinity.php
You should be aware, however, that this is just a simplification for routine work in the lab. If you require a precise and reliable value, there's different algorithms (some of them rather complex) that may be applied, and which vary depending on your soultion's chemistry (e.g., it is not the same for freshwater than for seawater or wastewater, and it is not the same for NaCl solutions that for CaCO3 or CaSO4 solutions).
Cheers,
I have conductivity readings from a hypersaline lake. How do i calculate TDS and percentage for it?
The field procedure for performing the Water resistivity measurements is simple: once the sampling point (e.g. lake) is identified a water sample is collected.
Afterwards, by using a combo portable resistivity meter (e.g., Hanna HI98130) the readings of water conductivity (s), in mS/cm or microS, and temperature, in °C are taken. Conductivity values, S, in mS/cm or are converted to electrical resistivity values, rw, in Ohm.m by:
Ro(Ohm.m) = 10* (1/S (mS/cm))
Ro (Ohm.m) = 10000* (1/S (microS/cm))
Using a GPS, the UTM coordinates of the sampling point must be taken for graphical representation. Subsequently, the values are corrected at a reference temperature (e.g. 20°C) by the expression (Sorensen and Glass, 1987).
Ro 20°C = Ro(Τ) [1 + α (T - T0)] (2)
Where:
T = water temperature (°C)
α = temperature coefficient equal to 0.0177 1/°C (Beklemishev, 1963)
T0 = reference temperature equal 20°C
Ro = water resistivity measured in field (Ohm.m)
Ro20 = water resistivity corrected at 20°C (Ohm.m)
Taking into account the linear function (logarithmic scale) of water resistivity versus salinity, for a reference temperature equal to 20°C, it is possible, for salinities below 8 gl-1, to estimate the water salinity from water electrical resistivity using the relation:
C = 6 /Ro20
Where C is the salt content (NaCl equivalent) in gl-1.
When the salinity is higher than 8 - 10 g /l there is no linear relationship between both magnitudes, but it is possible to calculate it. I send you table for NaCl salt for a reference temperature of 20°C. I can calculate for any temperature and other salts. I can help you.
Salinity (g/l) Ro (Ohm.m)
---------------------------------
1 0.1000 53.82
2 0.1259 42.75
3 0.1585 33.96
4 0.1995 26.98
5 0.2512 21.44
6 0.3162 17.03
7 0.3981 13.53
8 0.5012 10.75
9 0.6310 8.544
10 0.7943 6.790
11 1.0000 5.397
12 1.2589 4.290
13 1.5849 3.411
14 1.9953 2.713
15 2.5119 2.159
16 3.1623 1.718
17 3.9811 1.368
18 5.0119 1.090
19 6.3096 0.8695
20 7.9433 0.6941
21 10.0000 0.5549
22 12.5893 0.4443
23 15.8489 0.3565
24 19.9526 0.2868
25 25.1189 0.2314
26 31.6228 0.1876
27 39.8107 0.1528
28 50.1188 0.1253
29 63.0958 0.1036
30 79.4329 0.8652E-01
Simply times (x) EC (μS/cm) by .55 to get an approximate mg/L equivalent.
Multiply TDS by 1000 to get ppt salinity.
https://www.naturalresources.sa.gov.au/samurraydarlingbasin/publications/measuring-salinity
Ali Alhayany but isnt the formula conversion you've mentioned is only applicable to NaCl and not other salts like MgSO4 or NH4Cl?
Different alpha, but it is possible ti calculate to others salts
Please remember, these results are approximate, as the factors varies in place to place depending on composition of TDS.
TDS(ppm)=EC(dS/m)*640 when EC ranges [0.1 to 5 dS/m]
TDS(ppm)=EC(dS/m)*800 when EC>5 dS/m
Convert your conductivity measurement’s unit from siemens per meter (S/m) to milli-siemens per centimeter (mS/cm). In other words, multiply by 10.
Raise the conductivity (in mS/cm) to the power 1.0878.
Multiply the result by 0.4665. This gives you salinity in grams (of salt) per liter (of solution).
https://sciencing.com/convert-specific-conductivity-salinity-5915328.html
Dear Noor ulhuda... Most physical chemistry book contain data on the relation of ion species (mostly KCl) with the EC values. Even you can standardize your instrument with such data. (micro Siemens versus Molar concentration.
First you convert micro Siemens/cm into “deci Siemens per metre” (dS/m)
Conversion factor is micro Siemens/cm x 0.001 = dS/m
From that you can calculate TDS (total Dissolved Solids) that is in mg/L
TDS (mg/L) = EC (dS/m) x 640
Correlation between EC and TDS depends on type of water.
TDS (mg/L) = k x EC (μS/cm)
and k is defined :
Natural water for irrigation 0.55 - 0.75
Natural water, EC = 500 − 3,000μS⁄cm 0.55 – 0.75
Distillate water, EC = 1 − 10μS⁄cm 0.5
Freshwater, EC = 300 − 800μS⁄cm 0.55
Seawater, EC = 45,000 − 60,000μS⁄cm 0.7
Brine water, EC = 65,000 − 85,000μS⁄cm 0.75
TDS (mg/L or ppm) = EC (dS/m) x 640 (EC from 0.1 to 5 dS/m)
TDS (mg/L or ppm) = EC (dS/m) x 800 (EC > 5 dS/m)
Adel Kadri SVP pouviez vous me donner une référence concernant cette formule
Leyla Benammar :
Une référence : Article Irrigation Water Quality Standards and Salinity Management Strategies
You can use PHREEQ under Diagramme software which will automatically give you the TDS.
It's very simple and easy to use. just import your data from an excel file...
You can refer APHA standards it's good to refer also CPCB guidelines
The EC of brine depends on the salts present. Williams (1986) developed a formula for hypersaline Australian salt lakes up to 100mS/cm. But after that point the magnesium salts suppress the conductivity dramatically. Williams and Sherwood (1994) recommended using direct measures of salinity (density in the field, ionic analysis in the lab) rather than indirect measures like electrical conductivity. But if you have to use EC, there is a good page on this at https://en.wikibooks.org/wiki/Methods_Manual_for_Salt_Lake_Studies/Salinity/measuring_electrical_conductivity
I have attached a well known diagram from Williams and Sherwood 1994
I will repeat, it depends on what ionic composition created tye salinity in your water. Different salts conduct ekectricity differently. In truth electical conduxtivity neasures conductivity, NOT salinity. When tou knos tgd salt conposirion, tou can use the conductivity to estimate salinity. But even then, once a slmition resches a certsin concentration, conductivty does nor continue to increase. It is as conductive as it can be, and adding more salt makes no difference.
Another problem with hyperssline waters is that even if you know what salts were present in the brine at its weakest stage, as the brine concentrates different salts reach their saturation point abd precipitatd out. Then the ratio of the remaining salts is different to tge ratio in the weaker brine.
This is why direct physical measures of density are considered more relliable for estimating salinity. They depend on mass of salts in solution. Archimedes principle. There are sone limitations - yoy need to correct the density for your sample temperature. This can be addressed by recording tempeeature as well as SG. Suspended solids and plankton blooms may impact on density determination. This can be addressed by geneeslly samlling clear brines. Where densd suspended solids or blooms are unavoidable, filtration can help.
TDS(mg/litre or ppm) :- EC ( ds\m ) * 640.
example :- if EC is 4 ds/m then value in ppm :- 640*4= 2560
EC (dS/m) * 640 = SDT (mg/L o ppm)
Example : 542 microSiemens/cm = 0.542 dS/m
0.542 * 640 = 346 mg/L
The relation between ionic conductivity of water and TDS is purely emprical. This emprical relation has been established by taking actual TDS values (experimentally determined) and conductivity values of a large number of water samples collected from different sources. The relation is :
Conductivity (in microS/cm) x 0.64 = TDS (mg/L)
Most researchers propose the formula in which salinity is found by multiplying the electrical conductivity by the factor 0.64 ( S = E.C.*0.64).
Personally, I tried to verify the validity of this empirical relationship and found some limitations that are related either to the conductivity meter used or to the salinity range of the sample.
Not all conductivity meters respond to the same factor (0.64). Some of them use a different factor for each conductivity interval, which reaches 0.74 in some cases.
I therefore recommend that you consult the data sheet for the conductivity meter and use the most appropriate empirical formula.
Note: the formula is only valid with certain restrictions such as the temperature T (in general, this empirical formula is valid at T=25 C), otherwise a temperature correction factor must be used.
In TDS meters (digital tool), a default coefficient (nlf) equal with 0.5 is defined. So When you are using a TDS meter, you are measuring EC. Machine is multiply 0.5 to the number of measured EC in micro Siemens per centimetre. Indeed in environmental - ecologic - limnologic investigations, it is recommended that coefficient (nlf) must calculate by rational numbers of TDS assessments which prepared by gravimeteric standard method. Then in a specific water body such as a river, well, etc. we can make change that 0.5 default nlf to the new nlf which calculated based on specificity and nature of specific water body.
Now by calibration of your TDS meter (actually Which is an EC meter) first by 1413 micro Siemens /cm solution, then by new nlf coefficient, you can measure TDS without longtime laboratory gravimeteric method.
TDS (ppm or mg/L)= ECw (in dS/m or mmhos/cm) x 640
640 should be used when ECw 5 dS/m use 750
You asked a question for which there is no correct answer.
Salinity is the total amount of all salts in grams dissolved in 1 kg of sea water. The main composition of sea water (in ions) is as follows (°/oo): Сl- (18.979); SO42- (2.6486); HCO3 (0.1397); Br- (0.0646); F-(0.0013); H2BO2 (0.0260); Na+ (10.5561); Mg2+ (1.2720); Ca2+ (0.4001); K+ (0.3800); Sr2+ (0.0133). Salinity is measured by measuring the concentration of the chloride ion, assuming a constant salt composition of sea water (Dietmar's law). This law does not apply to river mouths. I regret.
Electrical conductivity does not characterize the total weight of all salts in grams dissolved in 1 kg of sea water. Salt ions with a large weight may have a small electrical charge, and ions with a small weight may have a large electrical charge.
If you need a conversion with an unknown accuracy, use the calculator:
https://planetcalc.ru/9427/
But I guarantee the answer is false.
Dear Nurul-Huda
In most text books of instrumental chemical Analysis you may find correlation of the Molar concentration of KCl with EC values. . For other salts the correlation must be evaluated experimentally.
At ambient conditions, 1 M NaCl (5.54 wt%) and 1 M (6.96 wt%) KCl electrical conductivities are 8.5 and 10.9 S/m respectively (Weiner, 1960).
Good luck......
The relation between electrical conductivity and TDS of water samples is purely empirical. This empirical relation is established by experimentally determining TDS of several water samples collected from different sources and experimentally measuring their conductivity. This I have already mentioned earlier in my answer with respect to this question. Hence if our interest is to know the salinity or TDS of specific water samples the most reliable data will be obtained by determining the salinity or TDS experimentally rather than adopting this empirical relation.
https://iopscience.iop.org/article/10.1088/1755-1315/118/1/012019/pdf