NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

ALKALI METAL CATIONS Na+

, K+, Li+ 7405

NaOH, KOH, LiOH MW: 40.00 (NaOH); CAS: 1310-73-2 (NaOH) RTECS: WB4900000 (NaOH)

 56.11 (KOH); 1310-58-3 (KOH); TT2100000 (KOH); 

 23.95 (LiOH) 1310-65-2 (LiOH) OJ6307070 (LiOH)

METHOD: 7405, Issue 1 EVALUATION: FULL Issue 1: 20 March 2018 

OSHA: 2 mg/m3 (NaOH)

NIOSH: C 2 mg/m3 (NaOH, KOH); IDLH 10 mg/m3 (NaOH)

OTHER OELs: Refs. [1,2]

PROPERTIES: basic, hygroscopic, caustic solids and aerosols, 

VP not significant

SYNONYMS: sodium hydroxide; potassium hydroxide; lithium hydroxide; alkali (LiOH, NaOH, KOH); caustic soda (NaOH); caustic 

potash (KOH); lye (NaOH, KOH)

SAMPLING

SAMPLER: FILTER, 37-mm quartz fiber, in 2- or 3-piece 

filter holder

FLOW RATE: 2-4 L/min

VOL-MIN: 30 L

 -MAX: 1000 L

SHIPMENT: routine

SAMPLE

STABILITY: ≥7 days at 25 oC & ≥27 days at 4 oC [3].

BLANKS: 3 field blanks minimum per sample set

ACCURACY

RANGE 

STUDIED: NaOH: 0.08 to 3.7 mg/m3

KOH: 0.07 to 7.4 mg/m3; 

LiOH: 0.16 to 7.2 mg/m3 [3]

BIAS: negligible

OVERALL

PRECISION (SS�rrrr)*: NaOH: 0.023 to 0.066; KOH: 0.018 to

0.043; LiOH: 0.016 to 0.023 [3]

EXPANDED 

UNCERTAINTY*: <22% for all three cations [6] 

*Accuracy calculations were carried out in accordance with 

ISO guidelines [5] rather than NIOSH accuracy criteria.

MEASUREMENT

TECHNIQUE: Ion Chromatography

ANALYTE: Na+, K+, Li+

DISSOLUTION: 10 mL 0.005 M H2SO4, 15 minutes in 

ultrasonic bath

ELUENT: 0.005 M H2SO4

DETECTOR: Conductivity detector

CALIBRATION: ≈0.5 to ≈10 mg/L Na+, K+, Li+ in 0.005 M 

H2SO4

RANGE: <0.01 to >5 mg Na+, K+ per sample; <0.05 

to >2.5 mg Li+ per sample [3,4]

ESTIMATED LOD: 0.003 mg Na+, K+ per sample; 

0.002 mg Li+ per sample [3]

PRECISION (SS�rr): NaOH: 0.009 to 0.030; KOH: 0.008 to 0.019;

LiOH: 0.007 to 0.010 [3,4]

APPLICABILITY: The method is meant for the measurement of alkaline dusts. It is specific for Na+, K+, and Li+ but does not 

differentiate between the hydroxides and their corresponding salts if both are present in the air. If the cations are present only in 

the form of hydroxides, the method is specific for these basic compounds. In other circumstances, the results obtained represent 

the highest air concentration of the hydroxides that could be extant. The method can also be used to measure alkaline earth

hydroxides such as calcium hydroxide [3,4].

INTERFERENCES: Sodium and potassium are ubiquitous in the environment and, if present in the sampled air at high 

concentrations, other soluble salts of Na and K can positively interfere. High concentrations of ammonium can interfere with the 

sodium peak in the chromatographic signal.
ALKALI METAL CATIONS: METHOD 7405, Issue 1, dated 20 March 2018 - Page 2 of 5 

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

OTHER METHODS: NIOSH Method 7401 for alkaline dusts is an acid-base titrimetric procedure that measures hydroxide 

concentration (alkalinity), [OH-] [7]. A harmonized international standard, ISO 17091 [4], has been published.

REAGENTS:

1. Sodium, potassium and lithium standard

solutions, 1000 ± 10 mg/L; traceable to

national standards.

2. Calibration stock solution: sodium and

potassium, 50 mg/L; lithium, 25 mg/L. Pipet

625 μL Li standard solution and 1250 μL of

each of the Na and K standard solutions into

25-mL volumetric flask. Dilute to volume

with deionized water. This solution can be

stored at 4°C for at least 2 months.

3. Sulfuric acid stock solution, 2.5 M H2SO4.

4. Sulfuric acid extraction / eluent solution,

0.005 M H2SO4. Pipet 2 mL 2.5 M sulfuric acid

into a 1-L volumetric flask containing

deionized water. Fill to volume using

deionized water.

5. Water, deionized, >18.2 MΩ-cm-1 resistivity.

*See SPECIAL PRECAUTIONS.

EQUIPMENT:

1. Samplers: 37-mm diameter quartz fiber filters

in cassette filter holders.

NOTE: Sodium and potassium are ubiquitous

in the environment and their presence 

in filter materials can lead to high 

blanks. Thus it is essential to check 

blank levels of each batch of filters. 

2. Personal sampling pump, 2 to 4 L/min, with

flexible connecting tubing.

3. Flow meter, portable.

4. Ion chromatograph (IC) with autosampler,

cation exchange column (e.g., 250 mm x 4

mm) with guard column (e.g., 50 mm x 4

mm), column oven capable of maintaining

column temperature at 40°C, column

thermostat, suppressor (e.g., cation selfregenerating suppressor) and conductivity

detector.

5. Data analysis unit (e.g., computer).

6. Volumetric flasks, polypropylene, 25-mL, 50-

mL, 1-L.

NOTE: For this method, it is preferable to use

plastic labware rather than glassware.

7. Adjustable pipettors with plastic tips, 10-

10000 μL.

8. Screw-cap polyethylene vessels, 15-20 mL.

9. Autosampler vials, polypropylene, with

screw-caps and siliconpolytetrafluoroethylene (PTFE) septa.

10. Disposable syringes, 5-10 mL.

11. Disposable filters, 0.45 μm pore size PTFE, 25-

mm diameter, suitable for IC.

12. Ultrasonic bath.

13. Ultrapure water system.

14. Tweezers, plastic or plastic-tipped.

SPECIAL PRECAUTIONS: Wear appropriate personal protection during sampling activities and analysis. It 

is essential that suitable gloves, eye protection, laboratory coat, etc., be used when working with the 

chemicals. Perform sample preparation and analysis in a clean, well-ventilated area that is well removed 

from any possible contamination. Any area of skin affected by the stock, dissolution or detection solutions 

must be immediately washed with plenty of water. Avoid exposure by contact with skin or eyes, or by 

inhalation of vapor.

SAMPLING, SAMPLE TRANSPORT AND STORAGE: 

1. Calibrate each personal sampling pump with a representative sampler in line.
ALKALI METAL CATIONS: METHOD 7405, Issue 1, dated 20 March 2018 - Page 3 of 5

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

2. Sample at an accurately known flow rate between 2 and 4 L/min for a sample size of 30 to 1000 L. Do 

not overload the samplers.

3. When sampling is completed, remove the samplers and cap them.

4. Submit at least three blank filters as field blanks from the same lot as sample filters for each set of 

samples, and handle them in the same way as field samples.

5. Transport the samples to the laboratory in a manner that prevents contamination or damage to the 

filters, and in accordance with established chain-of-custody procedures [8].

6. The samples can be stored at room temperature for one week; for longer storage, refrigerate the 

samples at 4 o

C.

NOTE: These storage times relate to the evaluated conditions. Longer storage at room temperature 

may be possible, but was not tested.

7. Samples should be analyzed no more than four weeks after sample collection.

SAMPLE PREPARATION:

8. Remove sample cassettes from storage and, if necessary, bring to room temperature.

9. Using tweezers, remove the sample filters from the filter holder (cassette) and place them in 15-20 mL 

plastic (polyethylene) screw-cap vessels.

10. Rinse the inside walls of the cassette with 2-3 mL of extraction / eluent solution (0.005 M H2SO4) and 

direct the rinsate(s) into the plastic vessels that contain the filters. 

11. Bring the final volume of extraction / eluent solution inside the vessels to 10 mL, ensuring that the 

filters are completely immersed.

12. Seal the 15-20 mL plastic vessels and place them in an ultrasonic bath. Sonicate for 15 minutes and 

then allow to stand for at least 30 minutes.

13. For each prepared sample, using a disposable syringe, remove 5 mL of the extraction solution and 

filter into an autosampler vial through a disposable PTFE filter. 

CALIBRATION AND QUALITY CONTROL:

14. Prepare at least five calibration working solution standards to cover the required concentration range, 

e.g., from 0.6 to 20 mg/L for Na+ and K+ and 0.3 to 10 mg/L for Li+

. Accurately pipet appropriate 

volumes of calibration stock solution into individual, labeled volumetric flasks. Dilute to the mark with 

water, close, and mix. 

NOTE: These calibration working solutions can be stored at room temperature for at least 2 weeks. 

Before use, their stability should be confirmed. If stability is inadequate, these solutions should

be prepared fresh daily.

15. Calibrate the ion chromatograph with the above five calibration solutions by preparing a calibration 

graph of peak height (in e.g., μS) vs. concentration (mg/L) for each cation.

16. Analyze calibration working standards together with samples, reagent blanks and field blanks at a 

frequency of at least 1 per 20 samples (3 minimum of each).

17. Check recoveries with at least two media blanks and 3 quality control spikes per 20 samples.

MEASUREMENT:

18. Set the ion chromatograph to the recommended eluent flow rate (e.g., 1.0 mL/min) and system 

pressure (ca. 10 MPa) and other conditions specified by the instrument manufacturer. 

19. Using the autosampler, a 25-μL sample aliquot of the contents of each autosampler vial is injected into 

the ion chromatograph.

20. Measure the peak heights of the lithium, sodium and potassium peaks (at retention times of 

approximately 4, 4.5 and 6 min, respectively) (Figure 1). If the peak height exceeds the linear 

calibration range, dilute with eluent, reanalyze, and apply the appropriate dilution factor in 

calculations.
ALKALI METAL CATIONS: METHOD 7405, Issue 1, dated 20 March 2018 - Page 4 of 5

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

CALCULATIONS:

21. Calculate the mass concentration of each cation, C (mg/m3

), in the air volume sampled, V (m3):

CC = (CCii × VVii × FF) − (CC0 × VV0)

VV ,

where:

C0 = mean concentration, in mg/L, of cation in field blank test solution;

Ci = concentration, in mg/L, of the ith cation (i = Na+

, K+, Li+) in sample test solution;

V = volume of air sample (m3

), where 1 L = 0.001 m3

V0 = volume of field blank test solution (L)

Vi = volume of sample test solution (L) for ith cation (i = Na+

, K+, Li+)

F = dilution factor for each sample test solution

EVALUATION OF METHOD:

The method was evaluated in accordance with an applicable international consensus standard, ISO 20581 

[9]. The component of variation of the method arising from analytical variability, as determined from 

spiked and dried quartz fiber filters, was found to be in the range of 0.9% to 3.0% for NaOH, 0.8% to 1.9% 

for KOH, and 0.7% to 1.0% for LiOH [3,6]. Mean recoveries from these samples were 102 ± 2% for NaOH, 100 

± 2% for KOH and 101 ± 2% for LiOH [3]. The expanded uncertainty of the method, using a coverage factor

(k) of 2 [10], was estimated as <22% for all three hydroxides [6]. Method quantitation limits were calculated 

based on the use of low-spike calibration standards [3, 11]. For a sampled air volume of 420 L, the 

quantitation limits were 0.041 mg/m3 for NaOH and LiOH and 0.034 mg/m3 for KOH. Storage stability of 

four weeks was demonstrated by recoveries >95% for quartz fiber filters spiked with NaOH, KOH and LiOH 

and stored at room temperature for 7 days and 4 o

C thereafter [6]. Influence of humidity was investigated 

at a relative humidity (RH) of 70%, established by means of a dynamic test gas apparatus [3]. Amounts of 

0.1 – 0.2 mg of NaOH, KOH and LiOH were spiked onto quartz fiber filters and then dried. Over two hours, 

air with RH=70% was drawn through these filters at 3.5 L/min; humidity was not found to influence the 

analytical recoveries of the three hydroxides. 

REFERENCES:

[1] American Conference of Governmental Industrial Hygienists (ACGIH) [2016]. Threshold Limit Values 

for chemical substances and physical agents & Biological Exposure Indices. Cincinnati, OH: ACGIH; 

updated annually.

[2] Institut für Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung (IFA) [no date]. GESTIS 

international limit values, http://limitvalue.ifa.dguv.de/. Date accessed January 17, 2018.

[3] Breuer D, Heinrich B [2001]. Alkali metal hydroxides and alkaline earth hydroxides, Method no. 1

(lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide); in Air monitoring 

methods, Vol. 8 – The MAK Collection for Occupational Health and Safety. Weinheim, Germany: 

Wiley-VCH.

[4] International Organization for Standardization (ISO) [2013]. ISO 17091, Workplace air –

Determination of lithium hydroxide, sodium hydroxide, potassium hydroxide and calcium 

dihydroxide – Method by measurement of corresponding cations by suppressed ion 

chromatography. Geneva: ISO.

[5] ISO [1995]. ISO Guide 98, Guide to the expression of uncertainty in measurement. Geneva: ISO.
ALKALI METAL CATIONS: METHOD 7405, Issue 1, dated 20 March 2018 - Page 5 of 5 

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

[6] Breuer D [2009]. Hydroxides (LiOH, NaOH, KOH, Ca(OH)2), in BGIA working folder, Sheet no. 7683.

Berlin: Erich-Schmidt Verlag.

[7] NIOSH [1994]. Method 7401, Alkaline dusts. In Schlect PC, O’Connor PF, eds. NIOSH manual of

analytical methods, 4th ed. Cincinnati, OH: U.S. Department of Health and Human Services, Centers

for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS

(NIOSH) Publication No. 94-113.

[8] ASTM International [2010]. ASTM D4840, Standard guide for sampling chain of custody procedures.

West Conshohocken, PA: ASTM International.

[9] ISO [2016]. ISO 20581, Workplace air quality – General requirements for the performance of

procedures for the measurement of chemical agents. Geneva: ISO.

[10] Comité Européen de Normalisacion (CEN) [2009]. EN 13890, Workplace exposure – Procedures for

measuring metals and metalloids in airborne particles – Requirements and test methods. Brussels:

CEN.

[11] NIOSH [1995]. Guidelines for air sampling and analytical method development and evaluation. By

Kennedy ER, Fischbach TJ, Song R, Eller PM, Shulman SA. Cincinnati: U.S. Department of Health and

Human Services, Centers for Disease Control and Prevention, National Institute for Occupational

Safety and Health, DHHS (NIOSH) Publication No. 95-117.

METHOD CONTRIBUTORS: 

Dietmar Breuer, Dr. rer. nat., Petra Heckmann and Krista Gusbeth, IFA, Sankt Augustin, Germany; final 

editing by Kevin Ashley, Ph.D., NIOSH. 

Disclaimer: Mention of any company or product does not constitute endorsement by the National 

Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC). In 

addition, citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring 

organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of 

these websites. All web addresses referenced in this document were accessible as of the publication date.

FIGURE 1. Chromatogram of standard solution containing Li, Na, and K.