1

Optimum methods for the analysis of 1,4-dioxane and the potential for false positives

Charles Carter, Ph.D.

Vice President of Quality and Technical Services

September 16, 2014

2

Topics

• Background on 1,4-dioxane as an environmental contaminant• Basic chemistry of 1,4-dioxane• A story• Optimum methods for the analysis of 1,4-dioxane• Field sampling issues that can create false positives for 1,4-

dioxane• Another story• Sample and laboratory conditions that can create false positives for

1,4-dioxane• Achieving standard reporting limits with reduced volume samples• An update

3

Background

• Regulatory levels in between 1 ppb and 3 ppb• EPA clu-in site indicated detection in 73 of 702 sources

sampled in California• Above action limit in 28 of these sources• 67 sites in New Hampshire with concentrations from 2

ppb to 11,000 ppb• Probable human carcinogen• Used as a solvent stabilizer, as a solvent in various

chemical processes, and is present as a by product in a variety of other materials.

4

Chemistry

• Formula and structure~ C4H8O2

• Boiling point 101.1 C• Infinitely water miscible• Miscible with most organic solvents• Boiling point in the range of standard volatiles, e.g

toluene boils at 110 C• Low Henry’s Law constant due to miscibility with water.

Fairly volatile in pure form, not very volatile from water.

5

Story #1

• Site contaminated with trichloroethene• Years of monitoring• Abrupt appearance of 1,4-dioxane at concentrations up to 800 ppb,

field blanks and laboratory blanks clean• Data made no sense, but now 1,4-dioxane was the major risk driver• Please review the data

~ Perfect• Please check for contamination

~ None• Please reanalyze the samples and have a separate analysis done in

a different lab~ Same results

• Now what?

6

Optimum method

• Some criticism from EPA on method choice• 8260 or 8270, SIM or full scan?• Poor purge efficiency, but poor extraction efficiency as

well• Poor purge efficiency accounted for in calculation of

response factor• Is purge efficiency consistent and largely independent of

matrix?• Lots of opinions! Let’s get some data.

7

Results

• Pulled all matrix spike results for a 10 month period

Summary# data points

Avg. Rec.

Avg. RPD

8260 full scan 24565 93.9 19.3

8260 SIM unheated purge 326 98.9 11.3

8260 SIM heated purge 933 103.2 6.2

8270 - 3510 762 39.7 9.1

8270 - 3520 2278 52.4 14.8

8

Test any materials in contact with the sample

• SPLP extracts of well casing, well fittings, gloves, cleaning solutions, and other materials (in Edison)

• Analysis by 8260 SIM with heated purge (in Irvine)• Numerous materials leached 1,4-dioxane including

nylon fittings and the FLUTe well liner• Only those materials that had been either leak checked

or washed prior to use showed contamination• The leak checks were done with Dawn dishwashing

detergent, and the field equipment decontamination was done with an old bottle labeled Alconox.

9

1,4-dioxane in surfactants

• Dawn – 7000 ppb• “Alconox” – 710 ppb• Ethoxylated surfactants – a known issue at FDA• Ajax Dish Lemon Liquid – 1200 ppb• Clairol Herbal Essences Body Envy Volumizing

Shampoo – 24,000 ppb• Era 2X Ultra Laundry Detergent – 14,000 ppb• Tide Laundry Detergent – 55,000 ppb• Healthy Times Baby's Herbal Garden Honeysuckle

Baby Bath – 5300 ppb

10

Field blanks

• If this issue is widespread, one would expect to find an increased frequency of 1,4-dioxane in field blanks.

• Pulled all client sample results where the client sample name included “FB”.

• Results – 1204 field blanks, no hits for 1,4-dioxane above the reporting limit

11

Story #2

• Switched analysis location from one network lab to another

• “Charlie – we have never seen 1,4-dioxane at this site and the location never used 1,4-dioxane, but now we have positive results for 1,4-dioxane. Could you find out if these are false positives or laboratory contamination?”

• Retention time is perfect• Spectrum is perfect• Blank is clean

12

But there are some oddities

13

8 runs later

14

Reanalysis

• Different instrument• Soil mode with purge in VOA vial instead of water purge

with standard sparge chamber• All non-detects• Decided it was a one time anomaly• Happened again in 30 days• Time for a root cause investigation!

15

The known variables

• Desorb temperature~ Old lab 210 C

~ New lab 250 C

• Sparge times and flows~ Identical

• Sparge configuration~ Old lab – water mode

~ New lab – both, but 1,4-dioxane only appears with water mode

• Unusual detail – sulfuric acid is used as the field preservative as opposed to hydrochloric acid

16

The theory

• If H2SO4 somehow got into the purge gas stream and accumulated on the trap, heating could cause a dehydration reaction creating gas phase SO3 during the desorption step

• Methanol is used as the solvent for our internal standards and surrogates, so some methanol is always present

• Plausible reaction mechanism

17

Three step mechanism

• Methanol reacts with sulfur trioxide forming formaldehyde and sulfur dioxide

• CH3OH + SO3 CH20 + SO2 + H2O

• Methanol and formaldehyde have a dehydration reaction with sulfuric acid to form acetaldehyde

• CH3OH + CH2O + SO3 C2H4O + H2SO4

• Acetaldehyde does a cyclic dimerization in the acidic gas phase

18

19

Is there any supporting evidence?

20

How would sulfuric acid get on the trap?

• Bubble ejection~ Bursting bubbles create aerosols~ Could carry raw sample and preservative into purge and trap

system• Water purge versus soil purge

~ Smaller bubbles make smaller ejected droplets~ Same flow through each~ Water sparge vessel had 1 cm ID~ VOA vial > 2 cm ID~ Water sparge vertical velocity more than 4 times greater than

soil vertical velocity~ Droplets created in VOA vial are more likely to settle out.

Larger droplets with a lower vertical velocity

21

We can test this!

• 5% KCl solution• Sparge under different conditions into an impinger• Measure chloride in impinger• Calculate the amount of sample in the purge gas

22

Results

• Coming soon!!

23

Topic #3

Achieving Standard Reporting Limits with Reduced Sample Sizes

•What determines the sensitivity of our methods•Instrument modifications to increase sensitivity•Lower Volume Initiative [LVI]

° SW 846 3510C & 3520C with 250 and 125 ml sample volume° SW 846 3511 with 40 ml sample volume

•QA White Paper•State Certifications•Unanticipated benefit – extraction kinetics

23

24

Method sensitivity

• Key items are the volume of sample which the lab starts with, final volume of the extract and the volume of the extract injected onto the GC column will determine the Reporting Limits the laboratory will provide

• Typical injection volumes are 1 – 2 microliters• Injection port modifications – 4 to 8 microliters• What to do with all this additional sensitivity?

~ Lower reporting limits

~ Increase final extract volume

~ Reduce sample size

24

25

LVI Standard Bottle Sizes

25

40 ml

26

Advantages

• Efficiency: Water samples can be collected at more efficient rates especially from low production groundwater wells

• Easier Field Logistics: Smaller bottles, less bulk to transport to sampling site

• Maximized Shipping Capacity: More samples will fit into a shipping container

• Reduced Shipping Costs: Minimized sample weight due to reduced volume

• Reduced Breakage: Smaller containers are much more durable

26

27

Approvals

• White paper• Verified acceptability with states• Demonstration packages

27

28

• Method 3520• Heavier than water solvent boils

in flask• Vapor condenses in condenser

and drips through sample• Solvent extracts analytes as is

falls through the sample• Condensed solvent

accumulates in bottom of extractor body and flows back into the distillation flask

28

29

Kinetics of extraction

• Change in water concentration is mass removed in solvent divided by the volume of sample

• The volume of solvent is the distillation rate times the elapsed time, so Vs = Q x Δt

• The solvent concentration is the sample concentration times a partition coefficient, so Cs = Cw x k

• Substituting gives

• ΔCw = -(k xCw avg x Q x Δt) / V

• dC = -kCQ/V dt• Rearranging and integrating gives the rate expression

• C/C0 = exp(-kQt/V)

29

ΔCw = -(Vs x Cs_avg)/Vw

30

% Extracted as a function of time at different values of k

30

31

% extracted over time as a function of sample size

• C/C0 = exp(-kQt/V)

31

32

The simple version

• Solvent to water ratio• At a constant distillation rate, the solvent to water ration

will increase by a factor of 4 if the sample size decreases by a factor of 4.

• When the sample size decreases by a factor of 4, the distillation time can decrease by a factor of 4 and we will keep the solvent to water ratio constant.

33

Results

• 81 analytes• 6 replicates at 1000 ml for 18 hours• 6 replicates at 250 ml for 4 hours

33

250 ml, 4 hours 1000 ml, 18 hoursAverage recovery 90.1% 88.6%Maximum recovery 110% 105%Minimum recovery 32% 26%

34

Implementation considerations and advantages

• Precedent for reduced time in 3520 – accepted by EPA and incorporated into the CLP SOW

• Arguably less labor with 3520, definitely better recoveries

• With 36 hours of extraction time, 24 hour turnaround was not possible

• Many laboratories maintained both procedures• With 8 hours of extraction time 24 hour turnaround is

possible

34

35

Conclusions

• 1,4-dioxane chemistry and optimum methods• Potential field contamination that can result in false

positives for 1,4-dioxane• Specific laboratory conditions that can create false

positives for 1,4-dioxane• Reducing sample sizes and unexpected benefits