HowTo – IC stock solutions and calibration standards
Priority: low
Updating: mature
Change log:
| When | Who | Comment |
|---|---|---|
| This was originally derived from hands-on demonstration by BEE grad students. It is effectively group folklore. | ||
| 2013 08 01 | Sp17 | Added note about drying the crystal solids to place in desiccator. |
| 2016 11 04 | Sp17 | Alternate final dilution to half nitrate and sulfate. |
| 2017 02 27 | Sp17 | Using 50 mL centrifuge tubes instead of 100 mL glass flasks; deleted nitrite. |
| 2018 10 20 | Sp17 | Add a way to spike samples, making 4 mL at +0.5, +1, +2 options (this adds chloride, nitrate-N and sulfate-S using 128/8/16 triple standard.) |
| 2018 10 24 | Sp17 | General editing and formatting. |
| 2019 02 06 | Sp17 | Clarified making test samples using Ricca commercial nitrate and sulfate. |
| 2021 03 12 | Sp17 | Imported to OneNote. Minor touchups. |
| 2022 09 22 | Sp17 | Added KH2PO4 (monobasic) for USDA IC. |
| 2023 06 16 | Sp17 | Converted to Markdown. |
| 2023 06 29 | Sp17 | Major reformatting. |
1. Objectives:
- Create high concentration stock solutions from crystals.
- Create multi-ion calibration standards for ion chromatography.
Maintainer: Steven Pacenka (sp17), Cornell BEE Soil and Water Lab
2. Equipment and supplies
Equipment needed:
- Scale capable of weighing to four decimal places of grams (0.1 milligram)
- Adjustable Eppendorf pipettors 10-100 and 100-1000 uL.
- Sharpie for marking containers.
- Refrigerator to store prepared calibrators and checks.
- Some people use narrow-neck glass containers to make their 1000 ppm singe ion stock solutions. These have scratches on their necks at exactly 100 mL volume.
Supplies needed:
- 15 mL and 50 mL conical bottom centrifuge tubes or other equivalent plastic containers of similar size. It is acceptable to reuse these for the same ion/mixture if they are cleaned thoroughly with deionized water between uses.
- Crystal ion reagents, dried in oven then desiccator.
- Using NaNO3 (as N), K2SO4 (as S), KH2PO4 (as P) and NaCl as the reagents; these should be dried; kept in desiccator in B68. Date the containers in desiccator and discard when “old.”
- Weighing paper or small containers.
- (optional) Commercial anion standard solutions.
- Pipette tips for respective pipettors.
- Deionized water from tap.
3. Advance preparations
- Check for supplies: containers, pipette tips, crystals in desiccator.
- To replenish a dry crystal vial in the desiccator, dry the crystals (in reagent cabinet in stockroom off R-R B68) for at least 1 hr in 80C oven, in their vial without cap. Then cool for 10 minutes with loose cap in the desiccator. Write on the vial what it is, the date prepared, and your initials.[Shree]
- 20150118: Brian Richards said to dry in a steel tray 150C overnight. Better to follow Shree advice.
- Check pipettors for volume accuracy.
- The nitrate stock solution has a limited shelf life, and diluted versions have a shelf life of only a few days, so you should be ready to run the IC shortly after doing this.
4. 1000 ppm stock solutions
Making 1000 ppm stock solutions. Add 0.05g of the target ion to 50 mL of deionized water in three or four single-ion 50 mL conic centrifuge tubes. One ion per tube; use the scale to measure exactly 50 mL of liquid.
NaNO3 as N: 0.05*(Na + N + 3*O)/N = 0.05*(23.0+14.0+3*16.0)/14.0 = 0.3036 g
K2SO4 as S: 0.05*(2*K + S + 4*O)/S = 0.05*(2*39.1 + 32.1 + 4*16.0)/32.1 = 0.2715 g
NaCl as Cl: 0.05*(Na + Cl)/Cl = 0.05*(23.0 + 35.5)/35.5 = 0.0824 g
KH2PO4 as P: = 0.05*(K + 2*H + P + 4*O)/P = 0.05*(39.1+2+30.974+4*16.0)/30.974=0.2197 g
- Alt to NaNO3=KNO3: 0.05*(Na + N + 3*O)/N = 0.05*(39.1+14.0+3*16.0)/14.0 = 0.361 g
These dissolve quickly. Mix well.
Mark the tubes as 1000 ppm of the indicated ion (NO3-N, SO4-S, Cl, PO4-P), date, your initials.
Shelf life in fridge: 4 weeks for nitrate, indefinite for chloride and sulfate, uncertain for phosphorus.
Technique note:
- weigh out cystals using little plastic weighing containers or wax papers;
- per ion:
- zero the scale with empty centrifuge tube without cap
- add tap DIW to exactly 50g using pipettor, or spray bottle;
- add solid crystals, cap tightly, shake.
4. Full strength quadruple standard
Make 20 mL of a diluted full-strength quadruple standard: 128 ppm Cl, 16 ppm NO3-N, 32 ppm SO4-S, 16 ppm P, in another 50 mL centrifuge tube (target concentrations may vary based on the application) (best to do this on the lesser scale of B68, using variable pipettor)
20*128/1000 Cl 2.56 mL
+ 20*16/1000 NO3-N 0.32 mL
+ 20*32/1000 SO4-S 0.64 mL
+ 20*31/1000 PO4-P 0.62 mL
bring up to 20 g total with tap deionized water
Alternate 128/8/16 for lower expected nitrate and sulfate: 20mL of full strength 128 ppm Cl, 8 ppm NO3-N, 16 ppm S
20*128/1000 Cl 2.56 mL
+ 20*8/1000 NO3-N 0.16 mL
- 20*16/1000 SO4-S 0.32 mL
bring up to 20 g total with deionized
Shelf life in fridge: 3 days
Alternate 128/4/8 for even lower nitrate and sulfate: 20 mL of full strength 128 ppm Cl, 4 ppm NO3-N. 8 ppm SO4-S
20*128/1000 Cl 2.56 mL
+ 20*4/1000 NO3-N 0.08 mL
- 20*8/1000 SO4-S 0.16 mL
bring up to 20 g total with deionized
5. Serial dilutions of quadruple standard
Make around 5 mL of each dilution from full strength, in 15 mL centrifuge tubes:
- ST5 full strength = 5.0 mL full quadruple-stock (step 2 above)
- ST4 half = 2.5 mL ST5, 2.5 mL deionized
- ST3 quarter = 1.2 mL ST5, 3.6 mL deionized
- ST2 eighth = 0.6 ml ST5, 4.2 mL deionized
- ST1 sixteenth = 0.4 mL ST5, 6.0 mL deionized
All of the deeper dilutions have a minimal shelf life; discard after three more days in fridge. Can reuse tubes if they are marked with element type and washed thoroughly, and dried.
6. Single ion dilutions (optional)
To make a single ion dilution in a 15 mL cent tube, dilute from that ion’s 1000 ppm version in one or two steps.
- For example, to make 4 ppm nitrate-N, start with 0.040 mL of NO3-N 1000 ppm and add DIW to bring final weight to 10g.
7. Spiking (fortifying) samples
To spike (fortify) samples using the 128/4/8 ST5 mixture to +0.5, +1, and +2 nitrate-N (nominally)
+0.5: Start with 0.5 mL of ST5, add 3.5 mL of sample
+1.0: Start with 1.0 mL of ST5, add 3.0 mL of sample
+2.0: Start with 2.0 mL of ST5, add 2.0 mL of sample
It would be better to start with a stronger mixture than ST5, in smaller relative volumes.
8. Known concentrations of nitrate and sulfate using commercial Ricca standards
Starting at 226 ppm N and 1000*32/96=333.3333 ppm S, dilute as follows:
Nitrate alone:
To make 0.5 add 0.063 mL NO3 sol bring to 28.25 mL total Or
(0.0625*10.0/28.25=0.0221) OR
0.0221 Ricca nitrate bring to 10 mL total with deionized water
To make 2.0 add 0.25 mL NO3 sol bring to 28.25 mL total OR
0.085 Ricca nitrate bring to 9.6 mL total
To make 8.0 add 1.0 mL NO3 sol bring to 28.25 mL total OR
0.350 Ricca nitrate bring to 9.9 mL total
Sulfate alone:
To make 0.5 add 0.25 mL SO4 sol bring to 166.5 mL OR
0.125 to 83.25 (0.125*10/83.25=0.015) OR
0.015 Ricca sulfate bring to 10 mL total
To make 2.0 add 1 mL SO4 sol bring to 166.5 mL
1*9.6/166.5=0.0577 =0.06
0.0577 Ricca sulfate bring to 9.6 mL total
To make 8.0 add 4 mL SO4 sol bring to 166.5 mL OR
(4*9.9/166.5=0.2378)
0.2378 Ricca sulfate bring to 9.9 mL total
To make blends of the two at equal concentrations of N and S, combine the indicated amounts of NO3 and SO4 solutions in boldface as above, and bring final volume/weights to 10, 9.6, and 9.9 respectively. Recap:
to make 0.5 mg/L: 22 uL Ricca nitrate + 15 uL Ricca sulfate, bring to 10.0 mL
to make 2.0 mg/L: 85 uL Ricca nitrate + 58 uL Ricca sulfate, bring to 9.6 mL
to make 8.0 mg/L: 350 uL Ricca nitrate + 238 uL Ricca sulfate, bring to 9.9 mL
Shelf life of this dilute mixture is a week. The full strength Ricca containers have expiration dates on them.