Analysis of samples for non volatile and volatile organics

7.1 Introduction

Samples of groundwater were collected from the area surrounding the landfill site that was discussed in Chapter 6. The samples collected were for dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and cations and anions. Samples for the Gas chromatography-mass spectroscopy (GC-MS) analysis of volatile and non-volatile organics were also collected. Protective overalls, organic vapour filter masks, three pairs of surgical gloves and safety spectacles were worn at all times during sampling. Gloves were changed at each site to prevent cross contamination of samples.

Collection methodologies and preservation, and analytical methods are described in the following section.

7.2 Sample containers and preservation

7.2.1 Containers and sample preservation for inorganic carbon

Samples for DIC determination were collected in glass, 40 ml, Shimadzu vials and made 300 mg/1 with respect to mercury (by adding mercury chloride). Mercury is a good preserver for contaminated groundwater samples at concentrations >60 mg/1 (Holum,

1995).

The effect of mercury chloride on DIC determination was investigated by spiking DIC standards and blanks with mercury chloride. No change in the standards and blanks was found.

DIC samples were analysed two weeks after collection, and the samples analysed after a further two weeks, which confirmed that mercury chloride was an effective preservative (Table 7.1).

Groundwater samples can be been preserved by acidification and sparging (see Chapter 3.5), but this method would have removed any inorganic carbon in the sample.

Table 7.1. Results of DIC preservation trials using mercury chloride Sample

point number

DIC (mg/1) in samples stored for 2 weeks

DIC (mg/1) in sample stored for 4 weeks

DIC (mg/1) in unpreserved samples,

stored for 2 weeks

4 59.7 58.3 49.9

5 45.1 46.3 49.4

9 43.9 45.8 42.3

11 39.9 38.5 26.9

7.2.2 Containers and sample preservation for dissolved organic carbon

DOC samples were collected in prepared Shimadzu vials (i.e. cleaned with chromic acid and filled with sodium metabisulphite (see Chapter 3.2)) and preserved by acidification to pH 3 followed by sparging for 15 minutes with nitrogen gas.

Acidification and sparging is an effective method for preserving low concentrations of organic carbon in groundwater samples (see Chapter 3), but it, was not known if this was an effective method of preserving high DOC concentrations. Samples with a range of DOC concentrations were analysed over two weeks to determine whether acidifying and sparging was an effective method of sample preservation (Table 7.2).

Table 7.2. Results o preserving samples with high DOC concentrations. DOC (mg/l) in

preserved samples, stored for 5 days

DOC (mg/l) in preserved samples,

stored for 14 days

% difference between 5 and 14 day storage

DOC (mg/l) in unpreserved samples' 2.44 2.43 +0.5 19.61 4.52 3.79 -17.7 -7.54 8.33 9.43 +12 -6.87 241 249 +0.5 290

= DOC samples from the same sites, taken on the first sampling trip; calculated by subtracting DIC from total dissolved carbon (TDC), measured on the Shimadzu 5000 TOC analyser (see Section 7.4). The negative sign is a result of the DIC concentration being bigger than TDC in the sample.

The preservation trials suggest that bacteria, adapted to live in the extreme environment around the landfill site, do not change the chemistry of samples preserved by acidification and sparging. Microbial communities can acclimatize to chemically stressful environments in time periods as short as several months (Chapelle, 1993), so it is likely that bacterial activity in the groundwaters around the landfill site started very shortly after the disposed wastes entered the groundwater system.

7.2.3 Containers and preservation for volatile and non-volatile organics

The volatility of organics is changed by temperature and pressure effects, so in this work ‘volatile organics’ are any organic compounds extractable, at room temperature and pressure, by the Tekmar 3000 Purge and Trap autosampler (see Chapter 7.4). Non­ volatile organics are any organic compounds that were not extracted, at room temperature and pressure, using purge and trap.

Samples for volatile organics were collected in 40 ml vials of the type recommended by the Environmental Protection Agency (EPA) as standard GC^MS purge und trap autosampler vials (see Chapter 7.4). The vials have Teflon Tophat closures containing a Teflon lined septum. Prior to sample collection the vials were washed with detergent, rinsed three times with tap water, rinsed three times with ultra pure water and baked in an oven at 400°C till the vials were dry. Whilst baking may activate glass for the adsorption of organics, the concentrations of organics in the landfill samples was expected to be high in comparison to adsorption effects. As silicon/Teflon septa degrade at 400°C, they were soaked in methanol to remove any organics and dried in an oven at 105°C. This cleaning method for vials and septa met the requirements of the EPA standard cleaning protocol B, and the APHA/AWWA/WEF standard vial cleaning method 6010 B (Greenberg et al., 1992). When analysed using GC-MS, ultra-pure water shaken in the cleaned vials did not contain any peaks that could be separated from background on the gas chromatogram (Fig. 7.3).

Samples for volatile organics were preserved using a 300 mg/l mercury solution (see Chapter 7.2.1). After two weeks of storage, samples that were not preserved with mercury developed slimy, irridescent deposits on the vials, possibly as a result of bacterial activity (see Chapter 2), but samples that had been preserved using mercury did not develop any deposits on the vials, even after two months of storage. Mercury chloride had no affect on the on the GC-MS analysis of volatile organics in laboratory blanks and standards.

Samples for non-volatile organics were collected in 4 ml, brown glass bottles, sealed with a Teflon cap containing a silicon/Teflon septa, and preserved using a 300 mg/l mercury solution. The glass bottles and septa were cleaned as for volatile organics. Mercury chloride had no affect on the on the GC-MS analysis of non-volatile organics in laboratory blanks and standards.

Samples were stored in the dark and insulated against temperature changes. Cold storage was not required as the addition of mercury chloride preserved the samples.

7.3 Sample collection

Sampleswere collected from the wells and piezometers by Watera pump or bailer (Plate 7.1), as determined by the landfill operator policy. The difference in the extraction methods does not make a significant difference to the samples collected (P. Lucas, pers. comm.). Wells were not purged in order to avoid contamination of the ground surface with large quantities of contaminants.

At each site a bucket was rinsed with groundwater three times before the groundwater for sampling was added to the bucket. The sampling points were sampled from the least contaminated first, to the most contaminated last, to limit any possible cross contamination between samples in the bucket.

Plate 7.1. P h o to g rap h sh o w in g the type o f b ailer used for sam p le collection.

S am ples for volatile o rg a n ic s, n o n -v o latile o rg anics and D IC , w ere collected by placing the sam ple vial o r b o ttle Just u n d e r the surface o f the g ro u n d w a te r in the b u ck e t, rem oving the cap, allow ing the vial to fill, and recap p in g w ith the vial still u n d e r the su rfa ce o f the w a te r in th e buck et. T h is en su red that w hen the vial w as full it co n ta in e d no air b u b b les and e n su re d that the d ried m erc u ry ch lo rid e re m a in ed in the vial w ith the sam ple.

D O C sam ples w e re co llec te d by em p ty in g o u t the sodium m etabisulphite in the vial (see C h a p te r 7 .2 .2 ), rinsing the vial several tim es w ith the g ro u n d w a te r from the b u c k e t, and then filling and sealing as before. A lth o u g h air-borne D O C can co n tam in ate D O C sam ples during rin sin g and filling (see C h a p te r 3.6), the co n tam in atio n is insignificant c o m p ared to the D O C in the sam p les.

7.3.1 Well head sampling

Measurements of dissolved oxygen, temperature, pH, electrical conductivity and alkalinity, and samples for cations and anions, major and minor elements, volatile organics and non-volatile organics were taken at each sampling point.

7.4 Sample analysis

7.4.1 Analysis of samples for DOC and DIC

In order to protect analytical equipment and distinguish DOC from particulate organic matter (POC), DIC and DOC samples were filtered before analysis.

Filtering in the field, using glass fibre filters and a glass syringe proved to be impracticably slow. Consequently, samples were filtered in the laboratory using a glass fibre filter and a glass syringe, after dilution of the samples by between 10 and 500. Dilution was found to make filtering times practicable. As filtering may add or remove organics to/from a sample, tests of filtration were undertaken to quantify this effect. Standards and blanks were subject to DOC analysis before and after passage through a glass fibre filter. Results are shown in Table 7.3, and show that filtration adds a variable DOC signal (< 0.086 mg/l DOC) to samples. As this concentration is <1% of the measured DOC in most samples, this contamination is considered as inconsequential.

DOC and DIC, were analysed for using the Shimadzu 5000 TOC analyser, equipped with the Shimadzu ASI-5000 autosampler, in the Wolfson Laboratory (see Chapter 3.8).

Table 7.3. DIC and TDC concentrations in filtered and unfiltered laboratory blanks*.

DIC (m g /l) in lab

blank

DIC (m g /l) in

filtered and diluted lab blank

TDC (m g /l) in lab

blank

TDC in filtered and diluted lab blank

0.005 0.007 0.012 0.040

0.032 0.030 0.007 0.028

0.014 0.029 0.003 0.020

0.024 0.004 0.008 0.022

0.014 0.086 0.009 0.011

M ea n 0.018 ±0.021 M ean 0.031 ±0.066 M ean 0.008 ±0.007 M ean 0.024 ±0.021

= the filter is a Whatman GF/D glass microfibre filter.

7.4.2 Analysis of samples for non-volatile and volatile organics

Non-volatile organics for GC-MS analysis have to extracted from the sample prior to analysis as the GC column is hydrophobic. Traditional methods of extraction, such as solid phase extraction and liquid-liquid extraction require large volumes of sample (the EPA and APHA/AWWA/WEF standard liquid-liquid extraction methods requires T litre of sample), produced large volumes of waste solvents and proved time consuming. Therefore, non-volatile organics were extracted from the groundwater samples using solid phase micro-extraction (SPME), which requires only 5 ml of sample, does not require any solvents and takes only 15 minutes per sample.

SPME is a relatively new technique for the extraction of organics (licensed in 1996), which uses a stationary phase-coated fused silica fibre, contained in a pen sized holder (Plate 7.2), placed into the sample for 15 minutes, during which time any non-volatile organics adsorb onto the fibre. The fibre is withdrawn from the sample and then placed into the heated injection port of the GC-MS, where any organics adsorbed onto the fibre desorb onto the GC column. A polydimethylsiloxane coated fibre was used to extract non-polar semi-volatiles and a poly acrylate coated fibre used to extract polar semi- volatiles

Pin used to expose and withdraw fibre

Fibre

P late 7.2. P h o to g ra p h o f a S P M E fibre and holder.

D uring the ex tra ctio n p ro c ed u re the sam ple vial only has to be o p en for ap p ro x im ately 3 sec o n d s, to place a stirring b ar in the vial, ensu rin g th at no o rg an ics are lost by volatilisation.

S P M E gives g o o d lab o rato ry blanks (Fig. 7.1) and p recision o f 12% (% stan d ard d ev iatio n o f the m ean) on gas ch ro m a to g ra m p eak areas (Fig. 7.1). T h e S P M E fibre b eco m es sa tu ra te d at high c o n c e n tra tio n s o f o rg an ics (Fig. 7 .2 ), b u t the gas c h ro m a to g ra m p ea k areas o f the non-v o latile org an ics in the sam ples te n d e d to be sm aller than the 20 ppb stan d ard , so fibre satu ra tio n did n o t effect the e x tra c tio n o f the n o n -v o latile org an ics from the sam ples.

N o n -v o la tile o rg a n ic s, ex tra c te d from the sam ples using S P M E , w ere an aly sed using a F isons FIRGC 8 0 0 0 series/M D 800 G C -M S system . T his system uses splitless injection, w ith an in jecto r tem p eratu re of 200°C .

NPBLANK2 100 ' %- PPD SPM E3 1 00- %- PPD SPM E2 * 100-1 I % - PPDSPM E1 100-1 0^ 14.000 •J- 16.000 18.000 20.000 22 .0 0 0 2 4 .0 0 0 26.000 Scan EI+ TIC 1.24e7 Scan EI+ TIC 1.24e7 Scan EI+ TIC 1 24 e7 Scan EI+ TIC 1.24e7 28.000

F igure 7.1. G as ch ro m ato g ram s o f org an ics from a sam ple e x tra c te d using S P M E . T he to p ch ro m a to g ra m is an exam ple o f a S P M E blank and th e b o tto m three ch ro m a to g ram s are d u p licates o f S P M E on a m ix ed sam ple.

1.4 E + 9 1 .2 E + 9 - 1 .0 E + 9 - D) l.OE+8 - 6 .0 E + 8 4 .0 E + 8 - x: 2 .0 E + 8 - O) O.OE+0 200 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0 c o n c e n t r a t io n of t r ic h lo r o p h e n o l (p b b ) ro 4 .5 E + 8 n 4 .0 E + 8 TO 3 .5 E + 8 3 .0 E + 8 E 2 .5 E + 8 - o 2 .0 E + 8 É 1.5 E + 8 I l.O E + 8 (/> 5 .0 E + 7 - ^ O.OE+0 0 l.O E + 8 9 .0 E + 7 .OE+7 - 7 .0 E + 7 - 6 .0 E + 7 m 5 .0 E + 7 4 .0 E + 7 T 3 .0 E + 7 2 .0 E + 7 - 1 .0 E + 7 -- O.OE+0 200 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 c o n c e n t r a t io n o f p h e n o l (p p b ) 1 6 0 0 1 8 0 0 2 0 0 0 2 0 0 4 0 0 6 0 0 8 0 0 10 0 0 1 2 0 0 1 4 0 0 c o n c e n t r a t io n o f e t h y lb e n z e n e (p p b ) 1 6 0 0 1 8 0 0 2 0 0 0 1 .4E + 9 1 .2E + 9 1 .0 E + 9 ,.0E+8 cn 6 .0 E + 8 4 .0 E + 8 x: 2 .0 E + 8 -- cn _O.OE+0 6 0 0 8 0 0 100 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0 2 0 0 0 concentration of trichloroethene (ppb) 200 4 0 0

F igure 7.2. G raphs o f c o n c en tratio n s versus gas ch ro m a to g ra p h p e a k area; from trials to d eterm in e the satu ratio n point o f the S P M E fibre.

S am p les for volatile organics using the G C -M S do not need any trea tm e n t p rio r to analysis, and w ere analysed using a T e k m a r 3 0 0 0 P urge and T ra p C o n c e n tra to r w ith a T e k m a r P re c e p t 11 A utosam pler, c o n n e c te d to th e F isons H R G C 8 0 0 0 series/M D 800 G C -M S (w ith an E 1+ sou rce), w ith a sam ple size o f 5 ml and p u rg e tim e o f 11 m inutes at a helium flow rate o f 40 ml p e r m inute. P u rg ed v olatiles w e re co llected on a T enax tra p and then d eso rb ed for 4 m inutes at 2 0 0 "C. T his p u rg e and trap m ethod fo r the G C -M S analysis o f volatile organics w as based on the E P A sta n d a rd m eth o d 624, and the A P F IA /A W W A /W E F stan d ard m eth o d 6 2 1 0 A , gives blanks th at did not contain any g as ch ro m a to g ra m peaks that co u ld be se p a ra te d from b a c k g ro u n d , and had a precision on sta n d a rd s o f 6% (% standard d ev iatio n o f the m ean ) (Fig. 7.3).

A L IS T D 10 100- 100 %- e t h y lb e n z e n e t e t r a c h b r o e th y S c a n El* TIC 3 .0 7 e 7 e n e trich lo ro eth en e. 0 4 .0 0 0 6.000 ib e n z e n e te tr a c h lo r o m e th a n e I-! N rt 8 ,0 0 0 1 0 .0 0 0 1 2 .0 0 0 1 4 .0 0 0 1 6 .0 0 0 1 8 .0 0 0 20 0 0 0

F ig u re 7.3. G as ch ro m a to g ram s from p u rg e and trap an a ly se s. T h e top c h ro m a to g ra m is an exam ple o f a volatile organics stan d ard , the b o tto m c h ro m a to g ra m is o f a p urge and trap blank.

The GC column started at 50°C, ramped to 200°C, at 7.5°C per minute. A J&W Standard DB5 capillary column and a J&W Pesticide DB608 capillary column were used in series, to allow the detection of as many compounds as possible in the samples and to increase the retention time separation, making gas chromatogram peak identification easier. The mass spectra of the separated compounds were identified by hand, with the assistance of S.L. Houghton (University College London), and by comparing the mass spectra to previously obtained mass spectra in the NIST and Fison mass spectra libraries.

Anions were diluted between 10 and 100 times prior to analysis. Cation analyses were carried out using a Philips PV8490 Induced Coupled Plasma Optical Emission Spectrometer (ICP-OBS) in the Geology Department at Royal Holloway University of London. Standards were run every 5 samples and all reported cation concentrations are corrected for drift.

Anion analyses were carried out using the Dionex Series 2000 ion chromatograph. Standards were run every 5 samples.